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NCRP DRAFT SC 4-5 REPORT
RADIATION PROTECTION IN DENTISTRY AND ORAL
AND MAXILLOFACIAL IMAGING
March 16, 2016
Note: Copyright permission is being sought for the figures and tables requiring such permission prior to
their use in the final NCRP publication.
National Council on Radiation Protection and Measurements
7910 Woodmont Avenue, Suite 400, Bethesda, Maryland 20814
NCRP SC 4-5 Draft March 16, 2016
2
Preface 1
2
No exposure to x rays can be considered completely free of risk, so the use of radiation by 3
dentists and their assistants implies a responsibility to ensure appropriate protection. The Report 4
provides radiation protection guidance for the use of x rays in dental practice including the use of 5
intraoral imaging, cone beam computed tomography, digital imaging radiation protection 6
devices, and hand held x-ray systems. 7
8
The aim of the Report is to provide a practical radiation protection guide for dentists and 9
their assistants. Information is presented in a clear and comprehensive format focusing on dental 10
radiological practices. 11
12
This Report is dedicated to the memory of S. Julian Gibbs, DDS, PhD, former 13
Professor of Radiology and Radiological Sciences at Vanderbilt University. Dr. 14
Gibbs was the Co-Chair of Scientific Committee 91, that was responsible for NCRP 15
Report No. 145, Radiation Protection in Dentistry, and he served as a member of the Council for 16
many years. His research interests focused on radiation doses from medical and dental radiologic 17
procedures, and he was a pioneer in applying computational techniques to studies of radiation 18
dose distribution to critical organs. He was a true scholar and humanitarian, and was an 19
inspiration and beloved mentor to dentists who pursued careers in the radiation sciences. 20
21
This Report supersedes NCRP Report No. 145, Radiation Protection in Dentistry, which 22
was issued in December 2003. This Report was prepared by Scientific Committee 4-5 on 23
Radiation Protection in Dentistry. Serving on Scientific Committee 4-5 were: 24
25
Co-Chairs 26
27
Alan G. Lurie
University of Connecticut
School of Dental Medicine
Farmington, Connecticut
Mel L. Kantor
University of Wisconsin-Eau Claire
Institute for Health Sciences
Eau Claire, Wisconsin
NCRP SC 4-5 Draft March 16, 2016
3
Members 28
29
Mansur Ahmad
University of Minnesota School of Dentistry
Minneapolis, MN
Veeratrishul Allareddy
University of Iowa College of Dentistry
Iowa City, Iowa
John B. Ludlow
University of North Carolina, School of
Dentistry
Chapel Hill, North Carolina
Edwin T. Parks
Indiana University School of Dentistry
Indianapolis, Indiana
Eleonore D. Paunovich
Veterans Health Administration
San Antonio Texas
Robert J. Pizzutiello
Landauer Medical Physics
Victor, New York
Robert A. Sauer
Food and Drug Administration
Center for Devices and Radiological Health
Silver Spring, Maryland
David C. Spelic
Food and Drug Administration
Center for Devices and Radiological Health
Silver Spring, Maryland
30
31
Consultants 32
33
Edwin M. Leidholdt, Jr.
Veterans Health Administration
Mare Island, California
William Doss McDavid
University of Texas Health Science Center at
San Antonio
San Antonia, Texas
Donald L. Miller
Food and Drug Administration
Center for Devices and Radiological Health
Silver Spring, Maryland
Madan Rehani
Harvard Medical School and
Massachusetts General Hospital
Boston, Massachusetts
34
35
NCRP SC 4-5 Draft March 16, 2016
4
NCRP Secretariat 36
37
Joel E. Gray, Staff Consultant 38
Cindy L. O’Brien, Managing Editor 39
Laura J. Atwell, Office Manager 40
James R. Cassata, Executive Director, 2014 41
David E. Smith, Executive Director, 2014 – 2016 42
43
The Council wishes to express its appreciation to the Committee members for the time and 44
effort devoted to the preparation of this Report, and to the following organizations for providing 45
financial support during its preparation: 46
47
American Academy of Oral and Maxillofacial Radiology 48
American Association of Physicists in Medicine 49
American Board of Radiology Foundation 50
American Dental Education Association 51
Food and Drug Administration, Center for Devices and Radiological Health 52
53
John D. Boice, Jr. 54
President 55
56
NCRP SC 4-5 Draft March 16, 2016
5
Contents 57
58
1. Executive Summary ....................................................................................................................... 13 59
1.1 General ....................................................................................................................................... 13 60
1.1.1 Purpose of the Report ....................................................................................................... 13 61
1.1.2 The Most Significant Methods to Minimize Radiation Dose, and Maximize Image 62
Quality and Diagnostic Efficacy ...................................................................................... 14 63
1.1.3 Quality Assurance of Radiology in the Dental Office ...................................................... 15 64
1.1.4 Education and Training .................................................................................................... 15 65
66
2. Introduction ..................................................................................................................................... 28 67
2.1 Purpose ....................................................................................................................................... 29 68
2.2 Scope .......................................................................................................................................... 29 69
2.3 Radiation Protection Philosophy ................................................................................................ 30 70
71
3. General Considerations .................................................................................................................. 34 72
3.1 Dose Limits ................................................................................................................................ 34 73
3.2 Role of Dental Personnel in Radiation Protection ..................................................................... 39 74
3.2.1The Dentist ....................................................................................................................... 40 75
3.2.2 Auxiliary Personnel .......................................................................................................... 41 76
3.2.3 The Qualified Expert ........................................................................................................ 41 77
3.3 Electronic Image Data Management .......................................................................................... 43 78
79
4. Radiation Protection in Dental Facilities ..................................................................................... 45 80
4.1 General Considerations ............................................................................................................... 45 81
4.1.1 Shielding Design ................................................................................................................. 46 82
4.1.2 Equipment Performance Evaluations and Radiation Protection Surveys ........................... 48 83
4.1.3 Signage ................................................................................................................................ 50 84
4.2 Diagnostic Reference Levels and Achievable Doses .................................................................. 50 85
4.3 Optimization of Image Quality and Patient Dose. General Principles ........................................ 53 86
4.4 Protection of the Patient .............................................................................................................. 55 87
4.4.1 Selection Criteria Examination Type and Frequency ........................................................ 55 88
4.4.1.1 Symptomatic Patients ............................................................................................. 56 89
4.4.1.2 Asymptomatic Patients .......................................................................................... 56 90
NCRP SC 4-5 Draft March 16, 2016
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4.4.1.3 Administrative Radiographs .................................................................................. 57 91
4.4.2 X-Ray Machines ............................................................................................................... 57 92
4.4.3 Examinations and Procedures ........................................................................................... 58 93
4.4.3.1 Intraoral Radiography ........................................................................................... 58 94
4.4.3.2 Panoramic Radiography ........................................................................................ 58 95
4.4.3.3 Cephalometric Radiography ................................................................................. 58 96
4.4.3.4 Fluoroscopy ........................................................................................................... 59 97
4.4.3.5 Cone Beam Computed Tomography ..................................................................... 59 98
4.4.4 Image Viewing Environment ............................................................................................ 60 99
4.4.4.1 Viewing Conditions for Digital Images ................................................................ 61 100
4.4.5 Use of Radiation Protective Aprons .................................................................................. 62 101
4.4.5.1 Use of Thyroid Collars .......................................................................................... 63 102
4.4.5.2 Maintenance of Protective Aprons and Thyroid Shields ...................................... 63 103
4.4.6 Special Considerations for Pediatric Imaging ................................................................... 64 104
4.5 Protection of the Operator .......................................................................................................... 65 105
4.5.1 Shielding Design ............................................................................................................... 65 106
4.5.2 Barriers .............................................................................................................................. 65 107
4.5.3 Distance ............................................................................................................................. 66 108
4.5.4 Position of Operator .......................................................................................................... 66 109
4.5.5 Personal Dosimeters .......................................................................................................... 68 110
4.6 Protection of the Public .............................................................................................................. 69 111
112
5. Quality Assurance and Quality Control ....................................................................................... 71 113
5.1 Image Quality and Patient Dose Optimization ............................................................................ 70 114
5.1.1 Image Quality ..................................................................................................................... 71 115
5.1.2 Patient Dose ....................................................................................................................... 73 116
5.1.3 Technique Charts ............................................................................................................... 73 117
5.2 Quality Control ........................................................................................................................... 74 118
5.2.1 Radiation Measurements of X-Ray Producing Dental Diagnostic Equipment .................. 75 119
5.2.2 Phantoms for Quality Control and Dose Measurements .................................................... 76 120
5.2.3 Quality Control for Film Imaging ...................................................................................... 76 121
5.2.4 Quality Control for Digital Image Receptors ..................................................................... 78 122
5.2.5 Quality Control for CBCT ................................................................................................. 81 123
5.2.6 Quality Control for Image Displays ................................................................................... 84 124
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5.2.7 Quality Control Tests and Frequency for Digital Radiography ......................................... 84 125
5.3 Infection Control ........................................................................................................................ 87 126
127
6. Image Receptors .............................................................................................................................. 88 128
6.1 Direct Exposure X-ray Film ........................................................................................................ 88 129
6.1.1 General Information ........................................................................................................... 88 130
6.1.2 Equipment and Facilities .................................................................................................... 90 131
6.1.2.1 Darkroom Fog ........................................................................................................ 90 132
6.1.2.2 Storage of Radiographic Film ................................................................................ 91 133
6.1.2.3 Film Processors ...................................................................................................... 91 134
6.2 Screen-Film Systems ................................................................................................................. 92 135
6.2.1 General Information .......................................................................................................... 92 136
6.2.2 Equipment and Facilities ................................................................................................... 93 137
6.2.2.1 Care of Screen-Film Systems for Film-Based Cephalometric and Film-Based 138
Panoramic Imaging ............................................................................................... 93 139
6.2.2.2 Screen-Film Speed Recommendation ................................................................... 93 140
6.3 Digital Imaging Systems ............................................................................................................ 94 141
6.3.1 General Information .......................................................................................................... 94 142
6.3.1.1 Proportion of Digital versus Film, Proportion of PSP versus CMOS-CCD ......... 94 143
6.3.1.2 Advantages of Digital Imaging Compared to Film Imaging ................................. 94 144
6.3.1.3 Potential for Dose Reductions for PSP and DR Compared with Film .................. 95 145
6.3.1.4 Disadvantages and Challenges of Digital Imaging ............................................... 98 146
6.3.2 Equipment and Facilities ................................................................................................. 100 147
6.3.2.1 PSP Plates ............................................................................................................ 100 148
6.3.2.2 Solid State Receptors ........................................................................................... 105 149
6.3.2.3 Converting from Film to Digital Imaging—Potential Dose Reduction ............... 107 150
6.3.2.4 Technique Charts ................................................................................................. 107 151
6.3.2.5 Clinical Image Display Monitors for Digital Imaging ......................................... 107 152
153
7. Intraoral Dental Imaging ............................................................................................................. 110 154
7.1 General Considerations ............................................................................................................. 110 155
7.1.1 Beam Energy .................................................................................................................... 110 156
7.1.2 Position-Indicating Devices ............................................................................................. 110 157
7.1.3 Rectangular Collimation .................................................................................................. 111 158
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7.1.4 Patient Restraint ............................................................................................................... 116 159
7.1.5 Diagnostic Reference Levels and Achievable Doses ...................................................... 116 160
7.1.6 Best Practices .................................................................................................................. 117 161
7.1.7 FDA Clearance of Dental Imaging Equipment ............................................................... 117 162
7.2 Conventional X-Ray Systems(Wall Mounted and Portable) .................................................. 119 163
7.2.1 General Information ....................................................................................................... 119 164
7.2.2 Equipment and Facilities ................................................................................................ 119 165
7.2.2.1 Protection of the Operator and Shielding .......................................................... 120 166
7.2.2.2 Tube Head Positional Stability .......................................................................... 120 167
7.2.2.3 Positioning-Indicating Devices ......................................................................... 120 168
7.2.2.4 Rectangular Collimation ................................................................................... 120 169
7.3 Hand-Held X-Ray Systems .................................................................................................... 121 170
7.3.1 General Information ...................................................................................................... 121 171
7.3.1.1 Advantages of Hand-Held X-Ray Units ........................................................... 122 172
7.3.1.2 Disadvantages of Hand-Held X-Ray Units ....................................................... 122 173
7.3.1.3 Safety Issues with Improper Handling of Hand-Held X-Ray Equipment ........ 124 174
7.3.1.4 Exception to “Never Hold the X-Ray Tube” ................................................... 126 175
7.3.2 Equipment ........................................................................................................................ 127 176
7.3.2.1 Backscatter Shield ................................................................................................ 127 177
7.3.2.2 Leakage Radiation ................................................................................................ 128 178
7.3.2.3 Radiation Protective Equipment and Personal Radiation Monitoring ................. 128 179
7.3.2.4 Appropriate Use of Hand-Held X-Ray Machines in Dental Offices 180
Comparison to European Recommendations ....................................................... 131 181
7.3.3 Position-Indicating Devices .............................................................................................. 131 182
7.3.4 Rectangular Collimation ................................................................................................... 131 183
184
8. Extraoral Dental Imaging ............................................................................................................ 133 185
8.1 Panoramic ................................................................................................................................. 133 186
8.1.1 General Information ......................................................................................................... 133 187
8.1.1.1 Diagnostic Reference Levels and Achievable Doses ........................................... 133 188
8.1.1.2 Bitewings from Digital Panoramic Machines ...................................................... 134 189
8.1.2 Equipment and Facilities .................................................................................................. 134 190
8.2 Cephalometric ........................................................................................................................... 136 191
8.2.1 General Information ......................................................................................................... 136 192
NCRP SC 4-5 Draft March 16, 2016
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8.2.1.1 Diagnostic Reference Levels and Achievable Doses ........................................... 136 193
8.2.2 Equipment and Facilities .................................................................................................. 136 194
195
9. Cone-Beam Computed Tomography .......................................................................................... 138 196
9.1 General Information .................................................................................................................. 138 197
9.1.1 Dose Comparisons for CBCT and MDCT Machines ...................................................... 140 198
9.1.2 Use of Simulated Bitewing. Panoramic and Cephalometric Views from 199
CBCT Data ....................................................................................................................... 145 200
9.1.3 Number of CBCTs in the United States and Growth Rate ............................................... 145 201
9.1.4 Efforts Regarding CBCT in Europe—SEDENTEXCT and Evidence-Based 202
Guidelines ........................................................................................................................ 147 203
9.1.5 Patient Selection Criteria for CBCT ................................................................................ 148 204
9.1.5.1 Implants ................................................................................................................ 148 205
9.1.5.2 Oral and Maxillofacial Surgery ............................................................................ 149 206
9.1.5.3 Periodontal Indications ........................................................................................ 150 207
9.1.5.4 Endodontic Indications ........................................................................................ 151 208
9.1.5.5 Temporomandibular Joint Indications ................................................................. 151 209
9.1.5.6 Caries Diagnosis Indications ............................................................................... 151 210
9.1.5.7 Sinonasal Evaluation Indications ........................................................................ 151 211
9.1.5.8 Craniofacial Disorders Indications ...................................................................... 152 212
9.1.5.9 Orthodontics ........................................................................................................ 152 213
9.1.5.10 Obstructive Sleep Apnea ................................................................................... 153 214
9.2 Equipment and Facilities ....................................................................................................... 153 215
9.2.1 Radiation Dose Structured Report Equivalent Needed for CBCT .................................. 155 216
9.2.2 Advantages of Pulsed Systems over Continuous Radiation Exposure Systems ............. 156 217
9.2.3 Advantages of 180 Degree Scan versus 360 Degree Scans ............................................ 157 218
9.2.4 Location of Equipment and Requirements for Shielding ................................................ 157 219
220
10. Administrative and Education ................................................................................................... 158 221
10.1 Administrative and Regulatory Considerations ..................................................................... 158 222
10.1.1 Compliance with FDA Medical Device Regulations and Electronic Product 223
Radiation Control Performance Standards .................................................................. 158 224
10.1.2 General Considerations ............................................................................................... 159 225
10.1.3 Hand-Held X-ray Devices ........................................................................................... 161 226
NCRP SC 4-5 Draft March 16, 2016
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10.1.4 CBCT Units ................................................................................................................ 161 227
10.1.4.1 Advanced Diagnostic Imaging Accreditation ............................................... 163 228
10.2 Education and Training .......................................................................................................... 164 229
10.2.1 Digital Imaging ........................................................................................................... 166 230
10.2.2 Hand-held Imaging Systems ....................................................................................... 166 231
10.2.2.1 Practitioner—Additional Safety Concerns .................................................... 166 232
10.2.2.2 Operator Training .......................................................................................... 166 233
10.2.2.3 Qualified Expert—Required Information ..................................................... 167 234
10.2.3 CBCT Imaging Systems .............................................................................................. 167 235
10.2.3.1 Training for Practitioners .............................................................................. 167 236
10.2.3.2 Training for Operators .................................................................................. 169 237
10.2.3.3 Training for Qualified Experts ...................................................................... 169 238
10.2.3.4 Continuing Education for Practitioners, Operators, and Qualified Experts .. 169 239
240
11. Summary and Conclusions ........................................................................................................ 171 241
242
Appendix A. Quality Control for Film Processing ......................................................................... 173 243
A.1 Five Basic Rules for Film Processing .................................................................................... 173 244
A.2 Quality Control ..................................................................................................................... 174 245
A.2.1 Sensitometry and Densitometry .................................................................................... 174 246
A.2.2 Dental Radiographic Quality Control ........................................................................... 174 247
A.2.3.1 Dental Radiographic Quality Control Device .................................................. 175 248
A.2.3.2 Aluminum Step Wedge .................................................................................... 175 249
A.2.3.3 Lead Foil Step Wedge ...................................................................................... 175 250
A.2.3.4 Reference Film ................................................................................................. 175 251
252
Appendix B. Quality Control for Digital Imaging Systems ........................................................... 177 253
B.1 Quality Control of Digital Intraoral Systems .......................................................................... 177 254
B.1.1 The Display .................................................................................................................... 177 255
B.1.2 Quality Control Phantoms .............................................................................................. 178 256
B.1.3 Baseline Exposure Assessment ...................................................................................... 178 257
B.1.4 Baseline Image ............................................................................................................... 178 258
B.1.5 Follow-up Images ........................................................................................................... 179 259
B.1.6 Record Keeping .............................................................................................................. 179 260
NCRP SC 4-5 Draft March 16, 2016
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261
Appendix C. Historical Aspects of Digital Imaging ...................................................................... 181 262
263
Appendix D. Shielding Design for Dental Facilities ...................................................................... 185 264
D.1 General Shielding Principles ................................................................................................... 186 265
D.2 Shielding for Primary and Secondary Radiation ..................................................................... 188 266
D.3 Shielding Principles ................................................................................................................ 191 267
D.4 Occupancy Factors, Use Factors, and Workloads ................................................................... 191 268
D.4.1 Occupancy Factors ........................................................................................................ 191 269
D.4.2 Use Factors .................................................................................................................... 191 270
D.4.3 Workloads ..................................................................................................................... 191 271
D.5 Summary ................................................................................................................................. 195 272
273
Appendix E. Dosimetry, Intraoral, and Panoramic Imaging ....................................................... 196 274
E.1 Patient Dosimetry .................................................................................................................... 196 275
E.2 Operator Dosimety .................................................................................................................. 200 276
277
Appendix F. Dosimetry for Multidetector-Multislice Imaging of 278
Dentomaxillofacial Areas ........................................................................................................... 202 279
280
Appendix G. Dosimetry for Dental Cone Beam CT Imaging ....................................................... 204 281
282
Appendix H. Dental X-Ray Evaluation by Qualified Expert ........................................................ 220 283
H.1 Radiation Safety ...................................................................................................................... 220 284
H.2 Evaluation of the Image Receptor and Dose ........................................................................... 221 285
H.3 Film Processing Conditions and Quality ................................................................................. 221 286
H.4 Evalutation of the X-Ray Generator and Output ..................................................................... 223 287
H.5 Evaluation of the Beam Collimation ....................................................................................... 223 288
H.6 Occupational Radiation Exposure Assessment ....................................................................... 223 289
290
Appendix I. Radiation Risk Assessment ......................................................................................... 225 291
I.1 Introduction ............................................................................................................................. 225 292
I.2 Definitions ................................................................................................................................. 226 293
I.2.1 Stochastic Effects .............................................................................................................. 226 294
NCRP SC 4-5 Draft March 16, 2016
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I.2.2 Deterministic Effects (Tissue Reactions) .......................................................................... 227 295
I.2.3 Dose Language .................................................................................................................. 227 296
I.3 Studies of Irradiated Human Populations ................................................................................... 228 297
I.3.1 Introductions ....................................................................................................................... 228 298
I.3.2 Atomic Bomb Survivor Lifetime Studies ........................................................................... 230 299
I.3.3 Children Irradiated for Tinea Capitis and Enlarged Thymus.............................................. 230 300
I.3.4 Females Receiving Fluoroscopy for Tuberculosis Treatment Follow-up ........................... 232 301
I.3.5 United Kingdom National Registry of Radiation Workers................................................. 232 302
I.3.6 2013 Australian CT Study of Electronic Medicare Data .................................................... 234 303
I.4 Effects of In Utero Exposure ...................................................................................................... 234 304
I.5 Effects on Children ..................................................................................................................... 234 305
I.5.1 Joint Commission Report (2011) ........................................................................................ 235 306
I.5.2 2012 U.K. Study of Head CT Scans in Children ................................................................ 235 307
I.6 Heritable Genetic Effects ............................................................................................................ 238 308
I.7 Risk from Traditional Oral and Maxillofacial Imaging: Intraoral, Panoramic, and 309
Cephalometric ........................................................................................................................... 238 310
I.8 Risk from CBCT Imaging .......................................................................................................... 239 311
I.9 Other Risks in Daily Living for Comparison.............................................................................. 239 312
313
Appendix J. Radiation Quantities and Units .................................................................................. 244 314
315
Abbreviations, Acronyms and Symbols .......................................................................................... 246 316
317
Glossary ............................................................................................................................................ 247 318
319
References ......................................................................................................................................... 262 320
321
NCRP SC 4-5 Draft March 16, 2016
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1. Executive Summary 322
323
1.1 General 324
325
Radiology in dentistry is omnipresent, as evidenced by the approximately one billion 326
intraoral images produced in the United States in 2014 to 2015 (Farris and Spelic, 2015). In the 327
15 y since the prior NCRP report, NCRP Report No. 145, Radiation Safety in Dentistry, three 328
innovations have found significant application throughout general and specialty dentistry: digital 329
acquisition of images, hand-held intraoral imaging devices, and cone-beam computed 330
tomography (CBCT). 331
332
Dentistry is unique in that most dentists in private practice are not only the treating clinician 333
but also both the radiologist and radiation safety officer in the office. Use of x-ray imaging in 334
dental practice, in particular digital imaging and CBCT, has increased steadily for decades and 335
we anticipate this trend to continue. Conversely, the average radiation exposure for individual 336
intraoral, panoramic and cephalometric images have decreased. However, the addition of CBCT 337
to dentistry, with the potential for use of inappropriate exposure parameters or inappropriate use, 338
along with persistence of round collimation and D-speed film for intraoral imaging, require 339
concerted, focused efforts towards optimization to achieve and maintain diagnostic quality 340
imaging at the lowest possible radiation dose [as low as reasonably achievable (ALARA) 341
principle]. 342
343
1.1.1 Purpose of the Report 344
345
The purpose of this report is to enhance radiation safety in dentistry and to reinforce 346
published, well-known dose-reduction methods that are not yet being widely applied in the day-347
to-day practice of dentistry. The technological advances since NCRP Report No. 145 (NCRP, 348
2003) require changing attitudes and practices of dentists because opportunities are now present 349
for decreasing radiation doses while improving diagnostic efficacy. This report updates the 350
material in NCRP Report No.145, adds new content on digital imaging, hand-held x-ray devices, 351
NCRP SC 4-5 Draft March 16, 2016
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CBCT, and makes recommendations for reducing patient radiation doses and improving image 352
quality, all in the context of the ALARA principle. 353
354
1.1.2 The Most Significant Methods to Minimize Radiation Dose, and Maximize Image Quality 355
and Diagnostic Efficacy 356
357
Many of the recommendations in this report are grounded in the recommendations of NCRP 358
Report No. 145, and are recommendations that could be quickly and inexpensively employed in 359
today’s dental practice environment. They include: 360
361
Use selection criteria for every imaging examination. 362
Use the fastest imaging receptor possible for all intraoral and extraoral imaging. For 363
intraoral imaging use either ANSI F-speed film or digital receptors. Eliminate D-speed 364
film. 365
Use rectangular collimation for all intraoral imaging except where patient anatomy or 366
behavior does not allow its use. 367
Use thyroid collars for all intraoral imaging and extraoral imaging (panoramic and 368
cephalometric) where it does not interfere with the required diagnostic information on the 369
image. 370
Ensure technique factors or imaging protocols are optimized to produce adequate images 371
with the lowest dose to the patient. 372
Follow the film manufacturers’ guidelines for processing film. 373
374
Additionally, new recommendations pertaining to acquisition technical factors and 375
indications for use are provided for digital, hand-held, and CBCT imaging: 376
377
Employ appropriate selection criteria for obtaining CBCT images. 378
Acquire CBCT images using the smallest field of view and acquisition technical factors 379
that deliver the needed diagnostic information at the lowest possible radiation dose. 380
Use only x-ray units which have been cleared by the U.S. Food and Drug Administration 381
(FDA). This is especially true with hand-held, intraoral x-ray devices. 382
NCRP SC 4-5 Draft March 16, 2016
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Embrace the efforts of Image Gently— be mindful of the greater sensitivity to radiation 383
damage in children, conduct imaging exams only when clinically warranted, and 384
downsize radiation doses accordingly, with consideration of the diagnostic requirements 385
of the imaging task. 386
387
1.1.3 Quality Assurance of Radiology in the Dental Office 388
389
The dentist, with the assistance of the qualified expert, must establish and implement 390
protocols and procedures for the safe and effective use of diagnostic radiology in the office. This 391
includes maintenance and optimization of dental imaging equipment and quality control of the 392
components of digital imaging systems. 393
394
1.1.4 Education and Training 395
396
Advances in imaging technology, especially with the rapidly increasing use of CBCT 397
imaging, require more education and training of dentists and staff in the safe and effective use of 398
such technologies. Such training is not within the expertise of salespersons and must be 399
conducted by trained professionals from the manufacturers and by qualified experts. 400
401
The following Table 1.2 lists all of the recommendations made in this report in the order in 402
which they appear in the subsequent chapters. The subsection in which each statement appears 403
and is discussed is noted in the right-hand column. The recommendations should not be read in 404
isolation. The reader should consult the indicated subsection for more complete explanations 405
and further information. 406
407
Two terms used in this Report have a special meaning as indicated by the use of italics. 408
409
1. Shall and shall not are used to indicate that adherence to the recommendation is 410
considered necessary to meet accepted standards of protection. 411
2. Should and should not are used to indicate a prudent practice to which exceptions may 412
occasionally be made in appropriate circumstances. 413
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TABLE 1.2—Recommendations. 414
Number Recommendation Section
1 No individual worker shall receive an occupational effective dose in excess of
50 mSv in any 1 y.
3.1
2 The numerical value of the individual worker’s life-time occupational effective
dose shall be limited to 10 mSv times the value of his or her age in years.
Occupational equivalent doses shall not exceed 0.5 mSv in a month to the
embryo or fetus for pregnant individuals, once pregnancy is known.
3.1
3 Mean nonoccupational effective dose to frequently or continuously exposed
members of the public shall not exceed 1 mSv y-1 (excluding doses from
natural background and medical care); infrequently exposed members of the
public shall not be exposed to effective doses >5 mSv in any year.
3.1
4 The dentist (or, in some facilities, the designated radiation safety officer) shall
establish and periodically review a radiation protection program. The dentist
shall seek guidance of a qualified expert in this activity.
3.2.1
5 The dentist shall employ published. evidence-based selection criteria when
prescribing radiographs.
3.2.1
6 Radiological procedures shall be performed only by dentists or by legally
qualified and credentialed auxiliary personnel.
3.2.2
7 The qualified expert should provide guidance for the dentist or facility
designer in the layout and shielding design of new or renovated dental
facilities and when equipment is installed that will significantly increase the
air kerma incident on walls, floors, and ceilings.
3.2.3
8 The qualified expert shall provide guidance for the dentist regarding
establishment of radiation protection policies and procedures.
3.2.3
NCRP SC 4-5 Draft March 16, 2016
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9 To avoid unnecessary repeat exposures due to lost images or redundant
examinations, the electronic image data management system shall provide for
secure storage, retrieval, and transmission of images.
3.3
10 All digital images acquired shall be retained in the patient’s electronic record. 3.3
11 All digital images should be backed up offsite electronically in a separate,
safe, and secure location at regular intervals.
3.3
12 The qualified expert should perform a pre-installation radiation shielding
design and plan review, to determine the proper location and composition of
barriers used to ensure radiation protection in new or renovated facilities, and
when equipment is installed that will significantly increase the air kerma
incident on walls, floors, and ceilings.
4.1.1
13 The qualified expert shall perform a post-installation radiation protection
survey to assure that radiation exposure levels in nearby public and controlled
areas are ALARA and below the limits established by the state or other local
agency with jurisdiction.
4.1.1
14 The qualified expert should assess each facility individually and document the
recommended shielding design in a written report.
4.1.1
15 The qualified expert should consider the cumulative radiation exposures
resulting from representative workloads in each modality when designing
radiation shielding for rooms in which there are multiple x-ray machines.
4.1.1
16 The facility shall establish administrative controls that assure no more than
one patient is in an x-ray room with multiple x-ray machines during any x-ray
exposure.
4.1.1
17 A qualified expert shall evaluate x-ray equipment to ensure that it is in
compliance with applicable governing laws and regulations.
4.1.2
18 All new dental x-ray installations shall have a radiation protection survey and
equipment performance evaluation carried out by, or under the direction of, a
qualified expert.
4.1.3
NCRP SC 4-5 Draft March 16, 2016
18
19 Equipment performance evaluations shall be performed by a qualified expert
at regular intervals thereafter, preferably at intervals not to exceed 4 y for
facilities only with intraoral, panoramic or cephalometric units. Facilities with
CBCT units shall be evaluated every 1 to 2 y.
4.1.3
20 Diagnostic Reference Levels and Achievable Doses should be developed for
dental CBCT imaging.
4.2
21 Each dental facility should record and track indicators of patient dose, such as
entrance air kerma and associated technique factors.
4.2
22 Each dental facility should compare its doses to DRLs and ADs. In particular,
where established methods exist, the qualified expert shall collect dose data
suitable for comparison with DRLs and ADs. These data and the results shall
be provided in the qualified experts report. For dental imaging systems that
provide dose metrics for patient examinations, the dentist or qualified expert
should periodically compare medians of these data for 10 clinical
examinations appropriate for this purpose with DRLs and ADs.
4.2
23 Organizations such as NCRP, U.S. Food and Drug Administration (FDA),
Conference of Radiation Control Program Directors (CRCPD), American
Academy of Oral and Maxillofacial Radiology (AAOMR), and American
Dental Association (ADA) should strive to provide DRLs and ADs for a
variety of dental examinations.
4.2
24 All radiological examinations shall be performed only on direct prescription of
the dentist, physician, or other individuals authorized by law or regulation.
4.4.1
25 Radiographic examinations shall be performed only when patient history and
physical examination, prior images, or laboratory findings indicate a
reasonable expectation of a health benefit to the patient.
4.4.1
26 For each new or referred patient, the dentist shall make a good faith attempt to
obtain previous, pertinent images prior to acquiring new patient images.
4.4.1
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19
27 For symptomatic patients, the radiological examinations shall be limited to
those images required for diagnosis and treatment of current disease.
4.4.1.1
28 For asymptomatic patients, the extent of radiological examination of new
patients, and the frequency and extent for established patients, shall adhere to
current published, evidence based selection criteria.
4.4.1.2
29 Administrative use of radiation to provide information that is not necessary for
the treatment or diagnosis of the patient shall not be permitted.
4.4.1.3.
30 Students shall not be compelled or permitted to perform radiographic
exposures of humans solely for purposes of education.
4.4.1.3
31 Candidates shall not be compelled or permitted to perform radiographic
exposures of humans solely for purposes of licensure, credentialing or other
certification.
4.4.1.3
32 Personnel responsible for purchase and operation of dental x-ray equipment
shall ensure that such equipment meets or exceeds all applicable U.S. federal
government and state requirements and regulations. In addition, the equipment
should conform to current international standards for basic safety and essential
performance.
4.4.2
33 Fluoroscopy shall not be used for static imaging in dental radiography. If
fluoroscopy is used for dynamic imaging, the practices in NCRP Report No.
168 shall be followed.
4.4.3.4
34 Images shall be viewed in an environment adequate to ensure accurate
interpretation.
4.4.4
35 The use of radiation protective aprons on patients shall not be required if all
other recommendations in this Report are rigorously followed unless required
by state regulation. Otherwise, a radiation protective apron shall be used.
4.4.5
36 Thyroid shielding shall be provided for patients when it will not interfere with
the examination.
4.4.6
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37 Protective aprons and thyroid shields should be hung or laid flat and never
folded, and manufacturer’s instructions should be followed. All protective
shields should be evaluated for damage (e.g., tears, folds, and cracks)
quarterly using visual and manual inspection.
4.4.7
38 Technique factors and selection criteria shall be appropriate to the age and size
of the patient.
4.4.8
39 Adequacy of facility shielding shall be determined by the qualified expert
whenever the average workload increases by a factor of two or more from the
initial design criteria.
4.5.1
40 Shielding designs for new offices with fixed x-ray equipment installations
shall provide protective barriers for the operator. The barriers shall be
constructed so operators can maintain visual contact and audible
communication with patients throughout the procedures.
4.5.2
41 The exposure switch should be mounted behind the protective barrier such
that the operator must remain behind the barrier during the exposure.
4.5.2
42 In the absence of a barrier in an existing facility, the operator shall remain at
least 2 m, but preferably 3 m, from the x-ray tube head during exposure. If the
2 m distance cannot be maintained, then a barrier shall be provided. This
recommendation does not apply to hand-held units with integral shields.
4.5.3
43 Provision of personal dosimeters for external exposure measurement should
be considered for workers who are likely to receive an annual effective dose in
excess of 1 mSv. Personal dosimeters shall be provided for declared pregnant
occupationally-exposed personnel.
4.5.5
44 For new or relocated equipment, the facilities shall provide personal
dosimeters for at least 1 y in order to determine and document the doses to
personnel.
4.5.5
45 The facility shall provide personal dosimeters for all new operators of hand-
held dental x-ray equipment for the first year of use.
4.5.5
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46 In dental facilities using large, multi-patient open bay designs, a patient in
proximity to another patient being radiographed shall be treated as a member
of the public for radiation protection purposes.
4.6
47 When portable or hand-held x-ray machines are used, all individuals in the
area other than the patient and operator shall be protected as members of the
public.
4.6
48 New dental facilities shall be designed such that no individual member of the
public will receive an effective dose in excess of 1 mSv annually.
4.6
49 X-ray machines should provide a range of exposure times suitable for twice
the speed of the fastest available image receptors.
5.1.1
50 A suitable radiographic phantom shall be used to optimize radiation dose and
image quality, and for continuing quality control measurements.
5.2.2
51 Film processing quality shall be evaluated daily, before processing patient
films, for each film processor or manual processing system.
5.2.3
52 There shall be an infection control policy to protect staff and patients that
encompasses imaging equipment and procedures.
5.3
53 Imaging equipment and devices should be designed to facilitate standard
infection control precautions.
5.3
54 Image receptors of speeds slower than ANSI Speed Group E-F film shall not
be used for intraoral radiography, i.e., D-speed film shall not be used.
6.1.1
55 Each darkroom and daylight loader shall be evaluated for fog at initial
installation, and then at least quarterly and following change of room lighting
or darkroom safelight lamp or filter.
6.1.2.1
56 Film, including film in cassettes, shall not be exposed to excessive radiation
during the period it is in storage.
6.1.2.2
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57 Film shall be processed with active, properly replenished chemicals and time-
temperature control, according to manufacturers’ recommendations.
6.1.2.3
58 Screen-film systems of speeds slower than ANSI 400 shall not be used for
panoramic or cephalometric imaging. Rare-earth systems shall be used.
6.2.2.2
59 The dental practice should enlist the assistance from a qualified expert to
ensure each new digital system is properly configured with regard to both
patient dose and image quality.
6.3.1.4
60 When converting from film to digital imaging, the facility shall make proper
exposure technique (time) adjustments, commensurate with the digital imaging
system.
6.3.2.4
61 The operating potentials of intraoral dental x-ray units shall not be <60 kVp
and should not be >80 kVp.
7.1.1
62 Position-indicating devices shall be open-ended devices and should provide
attenuation of scattered radiation arising from the collimator or filter.
7.1.2
63 Source-to-skin distance for intraoral radiography shall be at least 20 cm and
preferably should be at least 30 cm.
7.1.2
64 Rectangular collimation of the x-ray beam shall be used routinely for
periapical and bitewing radiography, and should be used for occlusal
radiography when imaging children with size 2 receptors
7.1.3
65 Occupationally-exposed personnel should not routinely restrain uncooperative
patients and shall not hold the image receptor in place during an x-ray
exposure.
7.1.4
66 Comforters and caregivers who restrain patients or hold image receptors
during exposure shall be provided with shielding, e.g., radiation protective
aprons , and should hold the film holding device. No unshielded body part of
the person restraining the patient shall be in the primary beam.
7.1.4
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67 The stand of a mobile unit shall provide adequate support to the x-ray tube
during travel and when the articulating arm is fully extended, and during x-ray
exposure. The wheels or the casters shall be equipped with a foot brake to
prevent motion of the unit during exposure.
7.2.2
68 Only the patient and operator shall be in the area during an exposure unless
special circumstances do not allow this.
7.2.2
69 The tube head shall achieve a stable position, free of drift and oscillation,
within 1 s after its release at the desired operating position. Drift during that 1
s shall be no greater than 0.5 cm.
7.2.2.2
70 Operators of hand-held x-ray equipment shall have the physical ability to hold
the system in place for multiple exposures.
7.3.1.3
71 Manufacturers should provide a training program for users of hand-held
equipment to emphasize the appropriate safety and positioning aspects of their
unit.
7.3.1.3
72 Operators shall store hand-held x-ray equipment such that it is not accessible
to members of the public when not in use.
7.3.1.3
73 Manufacturers of hand-held x-ray equipment shall incorporate either hardware
or software interlocks on their devices to prevent unauthorized use. Hardware
interlocks may include physical keys or locks necessary for operation while
software interlocks may include password restrictions.
7.3.1.3
74 Instructions supplied with hand-held x-ray equipment shall include
identification of the areas in which it is safe for the operator to stand during
exposures based on the specific protective shielding in the device design.
7.3.1.4
75 Hand-held x-ray devices shall include a clear, external, nonremovable,
radiation protection shield containing a minimum of 0.25 mm lead equivalence
between the operator and the patient to protect the operator from backscatter
radiation.
7.3.2.1
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76 The operator of a hand-held x-ray unit shall not be required to wear a personal
radiation protective garment.
7.3.2.3
77 Rectangular collimation shall be used with hand-held devices whenever
possible.
7.3.4
78 The x-ray beam for rotational panoramic tomography shall be collimated such
that its vertical dimension is no greater than that required to expose the area of
clinical interest and shall not exceed the size of the image receptor.
8.1.2
79 The fastest imaging system consistent with the imaging task (equal to or
greater than ANSI 400 speed, or digital) shall be used for all panoramic
radiographic projections.
8.1.2
80 Panoramic machines shall be on a dedicated electrical circuit. 8.1.2
81 The fastest imaging system consistent with the imaging task (ANSI 400 speed
or greater, or digital) shall be used for all cephalometric radiographic
projections.
8.2.2
82 X-ray equipment for cephalometric radiography shall provide for asymmetric
collimation to limit the beam to the area of clinical interest.
8.2.2
83 Filters for imaging the soft tissues of the facial profile together with the facial
skeleton shall be placed between the patient and at the x-ray source rather than
at the image receptor.
8.2.2
84 CBCT should be used for cross sectional imaging as an alternative to
conventional computed tomography when the radiation dose of CBCT is lower
and the diagnostic yield is at least comparable.
9.1.1
85 CBCT examinations shall use the smallest field of view (FOV) and technique
factors that provide the lowest dose commensurate with the clinical purpose.
9.1.1
86 CBCT examinations shall not be obtained solely for the purpose of producing
simulated bitewing, panoramic, or cephalometric images.
9.1.2
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87 CBCT shall not be used as the primary or initial imaging modality when an
alternative lower dose imaging modality is adequate for the clinical purpose.
9.1.5
88 CBCT examinations shall not be used for routine or serial orthodontic
imaging.
9.1.5.9
89 Manufacturers should develop PKA values for CBCT acquisitions and provide
conversion coefficients or other dose metrics necessary for the calculation of
effective dose in order to allow an estimate of risk for each acquisition.
9.2.1
90 Only hand-held dental x-ray devices cleared by FDA for sale in the United
States shall be used.
10.1.3
91 Regulations preventing the user from holding the x-ray unit should not be
applied to equipment cleared by FDA that is designed to be hand-held.
10.1.3
92 States should develop and apply specific regulations for the dental uses of
CBCT.
10.1.4
93 Radiation safety training shall be provided to all dental staff and other
personnel, including secretaries, receptionists, and laboratory technologists.
This training shall be commensurate with the individual’s risk of exposure
from ionizing radiation.
10.2
94 Every person who operates dental x-ray imaging equipment or supervises the
use of such equipment shall have current training in the safe and efficacious
use of such equipment.
10.2
95 The dentist should regularly participate in continuing education in all aspects
of dental radiology, including radiation protection.
10.2
96 Opportunities should be provided for auxiliary personnel to obtain appropriate
continuing education credits.
10.2
97 The manufacturer shall provide training pertaining to the safe operation of the
hand-held unit.
10.2.2.2
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98 The manufacturer of hand-held dental x-ray units shall provide information
suitable for the qualified expert regarding radiation leakage, backscatter
radiation, and the importance of the integral radiation shield.
10.2.3
99 The predoctoral dental curricula shall include didactic and clinical education
on physics of CBCT image production, artifacts that can lead to image
degradation, indications, and limitations of CBCT in dental practice, and the
effects of acquisition parameters on radiation dose.
10.2.3.1
100 Postdoctoral or clinical residency curricula shall expand upon the predoctoral
education and include discipline-specific indications and limitations of CBCT
imaging and the effects of acquisition parameters on radiation dose.
10.2.3.1
101 Dental practitioners who own CBCT units or use CBCT data sets in their
clinical practice and who have not received CBCT education as part of their
predoctoral or postdoctoral education shall acquire equivalent understanding
of the basic radiation safety aspects of CBCT imaging and sufficient
knowledge in the indications and limitations of CBCT imaging.
10.2.3.1
102 Dental personnel who operate CBCT units shall be adequately trained in the
proper operation and safety of the units. They should demonstrate adequate
knowledge of different protocols affecting the image quality and radiation
dose to the patient.
10.2.3.1
103 Prior to working with CBCT equipment, operators shall receive education on
the basics of CBCT technology, the risks associated with radiological imaging,
and training on the effective operation of CBCT equipment. This education
must include principles of CBCT image formation, equipment settings and
their impact on patient dose, and common artifacts associated with CBCT
images.
10.2.3.2
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104 All operators shall complete training on each individual CBCT system they
will be using, as provided by the manufacturer. This device specific training
must include patient positioning, the range of user selectable exam settings,
and their effect on dose, protocol selection, image processing options, and
periodic maintenance schedules.
10.2.3.2
105 A qualified expert shall have appropriate training and mentored experience in
the evaluation of dental CBCT facilities prior to functioning independently.
10.2.3.3
106 Every person who operates CBCT equipment, supervises the use of CBCT
equipment or tests and evaluates the functions of CBCT equipment shall have
ongoing continuing education in the safe and effective use of that equipment.
10.2.3.4
415
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28
2. Introduction 416
417
Radiology is an essential component of dental diagnosis. While available data clearly show 418
that ionizing radiation at modest to high doses produces biological damage, there is considerable 419
uncertainty and disagreement regarding the existence and nature of biological damage at very 420
low doses such as used in dental diagnosis except for some cone beam computed tomography 421
(CBCT) examinations. Given the billions of dental exposures annually across the population, it is 422
only prudent to address the controversy by assuming that there is a small but real risk of harm, 423
and to promulgate recommendations that foster safe and effective use of diagnostic dental 424
imaging to protect patients, staff and the public from radiogenic harm. Furthermore, the 425
practitioner may reasonably expect that the health benefit to the patient from dental radiographic 426
examination will outweigh any potential risk from radiation exposure provided that the: 427
428
dental radiographic examination is clinically indicated and justified; 429
radiographic technique is optimized to ensure images adequate for diagnosis at the lowest 430
dose consistent with this aim; and 431
principles outlined in this Report are followed to minimize exposure to the patient, staff, 432
and the public. 433
434
Office design, imaging and associated equipment, and procedures that minimize patient 435
exposure will also reduce exposure to the operator, other staff, and the public. Additional 436
measures, however, may be required to ensure that doses to operators and the public are within 437
limits established by regulatory bodies. Doses to all should be kept as low as reasonably 438
achievable (i.e., the ALARA principle) (NCRP, 1990). For operators and the public, the ALARA 439
principle encourages further reduction of doses that are already below regulatory limits. The 440
concept may be extended to patients, for whom dose limits do not apply. In this case, however, 441
we must assure that the imaging chain is optimized such that lower radiation doses are sufficient 442
to produce images of clinically acceptable quality. The process of balancing image quality with 443
radiation dose is known as optimization. 444
445
NCRP SC 4-5 Draft March 16, 2016
29
2.1 Purpose 446
447
The main objective of this Report is to present rationale, methods, and procedures for 448
radiation protection of patients, staff in the dental office and the public. The goals are: 449
450
1. eliminate unnecessary radiation exposure to the patient by assuring that images are 451
obtained only when justified and necessary; 452
2. assure that imaging equipment operates properly; 453
3. assure that images are of diagnostic quality; and 454
4. limit radiation exposure and meet the ALARA principle for staff and for patients. 455
456
This Report makes a number of recommendations to achieve these goals in the dental office. 457
458
2.2 Scope 459
460
This Report provides guidelines for radiation protection regarding the use of x rays in dental 461
practice. It replaces the National Council on Radiation Protection and Measurements Report 462
No. 35 (NCRP, 1970) and Report No. 145 (NCRP, 2003) in their entireties. It presents 463
recommendations regarding the optimization and clinically appropriate use of dental x-ray 464
equipment, as well as recommendations for radiation protection surveys, and monitoring of 465
personnel. Sections are included as specific guidance for dentists, their clinical associates, and 466
qualified experts conducting radiation protection surveys, equipment performance evaluations, 467
and determining facility shielding and layout designs; discussions of administrative and 468
educational considerations are also included. Additionally, there is guidance for equipment 469
designers, manufacturers, and service personnel. Basic guidance for dentists and their office staff 470
are contained in the body; technical details are provided in the appendices. 471
472
The target audience may not have easy access to related documents, therefore this Report is 473
intended to serve as a complete reference, providing sufficient background and guidance for 474
most dental imaging applications. Additional details regarding general medical and related topics 475
NCRP SC 4-5 Draft March 16, 2016
30
may be found in other reports of the NCRP (1976; 1988; 1989a; 1989b; 1990; 1992; 1993a; 476
1993b; 1997; 1998; 2000; 2001; 2004; 2005; 2008; 2009; 2012a; 2012b; 2013). 477
478
This report is to focuses particularly on those imaging procedures commonly performed in 479
dental facilities, including film, digital and hand-held intraoral radiography, and panoramic, 480
cephalometric, and cone beam computed tomography exams, and their associated equipment and 481
techniques. Except as otherwise specified, the recommendations in this Report apply to these 482
equipment and procedures. Other procedures of oral and maxillofacial radiology that are not 483
generally practiced in the dental office and that require more sophisticated equipment are subject 484
to the requirements and recommendations for medical radiology (NCRP, 1989a; 1989b; 2000; 485
2013), and will not be specifically addressed in this report. 486
487
2.3 Radiation Protection Philosophy 488
489
Biological effects of ionizing radiation fall into two classes. Tissue reactions (also known as 490
deterministic effects) and stochastic effects (Appendix I). Tissue reactions occur in all 491
individuals who receive a sufficiently high dose, i.e., exceeding some threshold. Examples of 492
these effects are acute radiation sickness, cataracts, skin burns, and epilation. Their severity 493
increases with increasing dose, and there is a threshold dose below which no clinically-494
significant tissue reactions occur. Stochastic effects, such as cancer, are all-or-nothing effects: 495
either a radiation-induced cancer occurs or it does not, and its severity is not dependent on 496
radiation dose. The probability of its occurrence increases with increasing dose, implying the 497
absence of a threshold. 498
499
The basic goal of radiation protection is to prevent in exposed individuals the occurrence of 500
tissue reactions and to reduce the risk for stochastic effects to an acceptable level when benefits 501
of that exposure are considered (NCRP, 1993a; 2004). 502
503
Achievement of this goal requires two interrelated activities: (1) efforts to ensure that no 504
occupationally exposed individual or member of the public receives doses greater than the limits 505
recommended for occupational and public exposures; and (2) efforts to ensure that patient doses 506
NCRP SC 4-5 Draft March 16, 2016
31
are ALARA . In most applications, ALARA is simply the extension into health care of good 507
radiation protection programs and practices that have traditionally been effective in keeping the 508
average of individual exposures of monitored workers well below the limits. Cost-benefit 509
analysis is applied to measures taken to achieve ALARA goals. For each source or type of 510
radiation exposure, it is determined whether the benefits outweigh the costs. Second, the relation 511
of cost to benefit from the reduction or elimination of that exposure is evaluated. Frequently 512
costs and benefits are stated in disparate units. Costs may be in units such as adverse biological 513
effects or economic expenditure. Benefits may be in units such as disease detected or lives saved. 514
Three principles provide the basis for all actions taken for purposes of radiation protection in 515
diagnostic imaging. These principles are applied differently for patients, occupationally exposed 516
persons, and the public. They are. 517
518
1. Justification: The benefit of radiation exposure outweighs its accompanying risks; 519
2. Optimization of protection: Total exposure remains as low as reasonably achievable 520
(ALARA); 521
3. Application of dose limits: For occupational and public exposure, dose limits are applied 522
to each individual to ensure that no one is exposed to an unacceptably high risk. 523
524
All three of these principles are applied to evaluation of occupational and public exposure. 525
Only the first two apply to exposure of patients. Dose limits do not apply to patients because 526
medical and dental exposures are obtained for diagnostic purposes that benefit the patient. The 527
primary objective of medical and dental imaging is to ensure that the health benefit exceeds the 528
risk to the patient from that exposure. 529
530
NCRP has established recommended dose limits for occupational and public (nonmedical) 531
exposure (Table 2.1) (NCRP, 2004b). Limits have been set below the estimated human threshold 532
doses for tissue reactions. NCRP assumes that for radiation protection purposes, the risk of 533
stochastic effects is proportional to dose without threshold, throughout the range of dose and 534
dose rates of importance in routine radiation protection (NCRP, 1993). This principle was used 535
to set dose limits for occupationally-exposed individuals such that estimated risks of stochastic 536
NCRP SC 4-5 Draft March 16, 2016
32
TABLE 2.1—Recommended dose limits (NCRP, 2004b).a 537
Basis Dose Limit
Occupational
Stochastic effects 50 mSv annual effective dose [10 mSv (x) ・ age (y) = cumulative
effective dose]
Deterministic effects
(tissue reactions)
150 mSv annual equivalent dose to the lens of the eye
500 mSv annual equivalent dose to skin, hands, and feet
Publicb
Stochastic effects 1 mSv annual effective dose for continuous or frequent exposure
5 mSv annual effective dose for infrequent exposure
Tissue reactions 15 mSv annual equivalent dose to the lens of the eye
50 mSv annual equivalent dose to the hands, skin, hands, and feet
Embryo and Fetus
0.5 mSv equivalent dose in a month from occupational exposure of
the mother once pregnancy is declared
aThe appropriate dose limits for adult students (i.e., age 18 y or older) in dental, dental 538
hygiene, and dental assisting educational programs depend on whether the educational entity 539
classifies the student as occupationally exposed or not. Additional guidance for radiation 540
protection practices for educational institutions is given in NCRP (2007). Dose limits for 541
students under 18 y of age correspond to the limits for members of the public (NCRP, 2004b). 542
bThese limits do not apply to exposures for medical or dental diagnosis or treatment. 543
544
NCRP SC 4-5 Draft March 16, 2016
33
effects are no greater than risks of occupational injury in other vocations that are generally 545
regarded as safe. 546
547
Dentists shall use x-ray equipment and procedures in a manner that ensures compliance with 548
both the recommendations in this Report and the requirements of their state or local jurisdictions. 549
When there is conflict between the recommendations in this Report and applicable legal 550
requirements, the more rigorous shall take precedence. 551
552
NCRP SC 4-5 Draft March 16, 2016
34
3. General Considerations 553
554
All persons are exposed to radiation in their daily lives (NCRP, 1987a; 1987b; 1987c; 555
1987d; 1989c; 1989d, 2009). NCRP has estimated the average total annual effective dose per 556
individual in the U.S. population in 2006 from all sources of radiation in the United States as 557
6.2 mSv (Figure 3.1). Approximately 3 mSv of this arises from naturally-occurring sources; 558
these sources have been present since the beginning of the Earth. Medical imaging contributes 559
48 % of the annual effective dose per individual. This represents an increase by a factor of 2.2 560
from the early 1980s to 2006, and is primarily due to increased utilization of the medical 561
modalities of computed tomography, nuclear medicine, and interventional fluoroscopy (NCRP, 562
2009) Dental radiation is a minor contributor to total population burden. However, the increasing 563
use of cone beam CT imaging, increases in conventional dental imaging, and revisions in the 564
ICRP Tissue Weighting Factors (ICRP, 2007) results in a growing contribution of dental imaging 565
to the population effective dose. Thus, appropriate measures are necessary to maintain dental 566
radiation exposures ALARA. 567
568
3.1 Dose Limits 569
570
The Council has recommended annual and cumulative dose limits for individuals from 571
occupational radiation exposure, and separate annual dose limits for members of the public from 572
sources of man-made radiation (Table 2.1) (NCRP, 1993a). The dose limits do not apply to 573
diagnostic or therapeutic exposure of the patient in the healing arts. (Some states may have 574
adopted different occupational limits.) 575
576
The cumulative limit for occupational dose is more restrictive than the annual limit. For 577
example, an individual who begins at 18 y of age to receive annual occupational effective doses 578
of 50 mSv will in 4 y receive 200 mSv, approaching the cumulative limit of 220 mSv at 22 y of 579
age. At that point, occupational exposure to that individual would be constrained by the 580
cumulative, not the annual limit. That is, the individual would then be limited to a cumulative 581
effective dose at the average rate of 10 mSv y-1, with a maximum rate of 50 mSv in any 1 y. The 582
NCRP SC 4-5 Draft March 16, 2016
35
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
Fig. 3.1. Percent contribution of various sources of exposure to the total collective effective 600
dose (1,870,000 person-Sv) and the total effective dose per individual in the U.S. population 601
(6.2 mSv) for 2006. Percent values have been rounded to the nearest 1 %, except for those <1 % 602
(NCRP, 2009). Conventional dental imaging accounts for 0.25 % of the dose from all medical 603
imaging (White and Pharoah, 2014); however, the contribution of cone beam CT imaging to the 604
computed tomography dose (medical) is at present unknown, and likely increasing. 605
606
NCRP SC 4-5 Draft March 16, 2016
36
duties of any individual who approaches the annual or cumulative limit may be changed so the 607
limit is not exceeded. It should be stressed that these are occupational exposures and not 608
exposures from medical diagnosis or treatment. 609
610
Average dental occupational exposures are usually only a small fraction of the limit and are 611
less than most other workers in the healing arts (Table 3.1) (Kumazawa et al., 1984). 612
Occupational exposures have been declining (Figure 3.2) over recent decades in workers in both 613
the healing arts in general and dentistry in particular (HSE, 1998; Kumazawa et al., 1984; 614
UNSCEAR, 2000). It seems reasonable to conclude that no dental personnel will receive 615
occupational exposures exceeding the limit as long as proper facility design, equipment 616
performance, and operating procedures are implemented. 617
618
Facilities are designed, operated, and monitored such that no individual member of the public 619
receives a dose in excess of the recommended limit. Therefore, members of the public are not 620
monitored. 621
622
While there are no recommended dose limits for medically necessary radiation exposure, the 623
ALARA principle of radiation protection optimization can be applied to patients as well. For 624
dental exposures of patients, The NCRP agrees with the statement by ICRP (2007b, paragraph 625
70): “The optimization of radiological protection means keeping the doses ‘as low as reasonably 626
achievable, economic and societal factors being taken into account, and is best described as 627
management of the radiation dose to the patient to be commensurate with the [dental] purpose.” 628
That ICRP publication clarifies the goal of the ALARA principal in medical [dental] imaging 629
(paragraph 47): “In medicine [dentistry] the requirement is to manage the radiation dose to the 630
patient to be commensurate with the medical [dental] purpose. The goal is to use the appropriate 631
dose to obtain the desired image or desired therapy.” 632
633
Facility design, x-ray equipment performance, and operating procedures shall be established 634
to maintain patient, occupational and public exposures as low as reasonably achievable 635
(ALARA). When new equipment is installed or substantially different practices are 636
637
NCRP SC 4-5 Draft March 16, 2016
37
TABLE 3.1—Occupational doses in the healing arts, United States, 1980.a 638
Occupation
Number of Workers Mean Annual Whole-Body Dose
(mSv)
Totalb Exposedc Totalb Exposedc
Hospital 126,000 86,000 1.4 2.0
Medical offices 155,000 87,000 1.0 1.8
Dental (offices) 259,000 82,000 0.2 0.7
Podiatry 8,000 3,000 0.1 0.3
Chiropractic 15,000 6,000 0.3 0.8
Veterinary 21,000 12,000 0.6 1.1
Total 584,000 276,000 0.2 1.5
aKumazawa et al. (1984). 639
bAll workers with potential occupational exposure. 640
cWorkers who received a measurable dose in any monitoring period during the year. 641
642
NCRP SC 4-5 Draft March 16, 2016
38
643
644
645
646
647
648
649
650
651
652
653
654
655
Fig. 3.2. Decline in mean occupational doses over recent decades, for workers in all healing 656
arts combined and dentistry. U.S. data at 5 y intervals from 1960 to 1980 plus that projected for 657
1985 were reported as dosimeter readings (Kumazawa et al., 1984). World estimates from 1975 658
to 1995 were reported as effective doses and are plotted at each 5 y interval (UNSCEAR, 2000). 659
660
NCRP SC 4-5 Draft March 16, 2016
39
implemented, staff shall wear personal radiation badges for 1 y to ascertain the level of typical 661
radiation doses (Section 4.5.5). 662
663
All individuals engaged in dentomaxillofacial imaging shall meet the following radiation 664
protection limits: 665
666
Recommendation 1. No individual worker shall receive an occupational effective dose in 667
excess of 50 mSv in any 1 y. 668
669
Recommendation 2. The numerical value of the individual worker’s life-time 670
occupational effective dose shall be limited to 10 mSv times the value of his or her age in 671
years. Occupational equivalent doses shall not exceed 0.5 mSv in a month to the embryo 672
or fetus for pregnant individuals, once pregnancy is known. 673
674
Recommendation 3. Mean nonoccupational effective dose to frequently or continuously 675
exposed members of the public shall not exceed 1 mSv y-1 excluding doses from natural 676
background and medical care); infrequently exposed members of the public shall not be 677
exposed to effective doses >5 mSv in any year. 678
679
NOTE: NCRP is presently engaged in a major review of NCRP Report No. 116, Radiation 680
Protection Guidance for the United States. NCRP may issue a new report with different 681
occupational and public dose limits that would supersede those specified in Recommendations 1 682
to 3 above. Ultimately, practitioners must comply with applicable federal and state regulations 683
regarding exposure of workers and the public. 684
685
3.2 Role of Dental Personnel in Radiation Protection 686
687
ALARA requires optimizing the practices of all dental personnel who are involved in 688
prescription, exposure, processing, evaluation, and interpretation of dental images. This Section 689
describes the roles of each. 690
691
NCRP SC 4-5 Draft March 16, 2016
40
3.2.1 The Dentist 692
693
In most dental facilities a single dental practitioner is responsible for the design and conduct 694
of the radiation protection program . In large facilities, such as dental educational institutions, the 695
authority and responsibility for design and oversight of the radiation protection program may be 696
delegated to a specific employee with special expertise in the field. This individual is designated 697
the radiation safety officer. The dentist in charge, in consultation with the radiation safety officer 698
(if that person is someone other than the dentist) and with a qualified expert, is responsible for 699
implementing the radiation protection program, which includes (NCRP, 1990; 1998). 700
701
establishing, reviewing, and documenting radiation protection procedures; 702
instructing all dental staff in radiation protection; 703
implementing radiation surveys and recording results and corrective actions; 704
establishing the monitoring of personnel, if required; 705
ensuring that all radiation protection features are functional and the required warning 706
signs are posted; 707
implementing and monitoring the ALARA principle; and 708
implementing and documenting quality assurance (QA) and quality control (QC) 709
procedures. 710
711
Guidance on developing appropriate radiation protection programs for a dental office can be 712
found in most contemporary oral radiology textbooks (White and Pharoah, 2014). 713
714
Recommendation 4. The dentist (or, in some facilities, the designated radiation safety 715
officer) shall establish and periodically review a radiation protection program. The 716
dentist shall seek guidance of a qualified expert in this activity. 717
718
The dentist is qualified by education and licensure to prescribe and perform radiographic 719
examinations and to evaluate and interpret the images produced. 720
721
NCRP SC 4-5 Draft March 16, 2016
41
Recommendation 5. The dentist shall employ published, evidence-based selection 722
criteria when prescribing radiographs. 723
724
Additional details concerning selection criteria are found in Sections 4.4.1 and 9.1.5. 725
726
3.2.2 Auxiliary Personnel 727
728
In most dental facilities the staff involved in radiologic procedures consists of registered 729
dental hygienists and dental assistants who may or may not be certified. Registered hygienists 730
and certified assistants are trained and credentialed to perform radiological examinations, process 731
film, and digital images and evaluate them for quality (NRPB, 2001). In some states noncertified 732
assistants may be credentialed for these procedures upon completion of approved training. 733
734
Recommendation 6. Radiological procedures shall be performed only by dentists or by 735
legally qualified and credentialed auxiliary personnel. 736
737
3.2.3 The Qualified Expert 738
739
This individual is qualified by education and experience to perform advanced or complex 740
procedures in radiation protection that generally are beyond the capabilities of most dental 741
personnel (NRPB, 2001). These procedures include facility design to provide adequate shielding 742
for protection of the occupationally exposed and the public, inspection and evaluation of 743
performance of x-ray equipment, evaluation of and recommendations for radiation protection 744
programs, and to assist in optimizing image quality and patient radiation dose. Usually 745
possessing an advanced degree in medical physics or a similar field, this individual is usually 746
certified by the American Board of Radiology, the American Board of Medical Physics, or 747
equivalent. Care must be taken to ensure that the qualified expert’s credentials include 748
knowledge and familiarity with dental radiologic practices. Some otherwise highly qualified 749
experts may have little experience in dental radiological practices. (Some states credential or 750
license these individuals.) The principal responsibility of this person is to serve as a consultant to 751
the dentist. 752
NCRP SC 4-5 Draft March 16, 2016
42
753
The qualified expert adds essential value to the dental practice by providing expertise in 754
radiation shielding design, radiation safety for the staff and general public, applicable regulatory 755
and accreditation requirements, and establishing the quality control program. Specifically, the 756
qualified expert: 757
758
Performs a pre-installation radiation shielding design and plan review. 759
Performs acceptance testing [equipment performance evaluation (EPE)] and a post-760
installation radiation protection survey. 761
Initiates the quality control program by evaluating the initial characteristics of the x-ray 762
beam, measuring patient exposures, and assessing image quality. 763
Establishes the quality control program by advising on the individual elements of the QC 764
program, procedures to be followed, the qualifications of personnel, expected ranges of 765
results, and actions to be taken when results are beyond the expected ranges. Quality 766
control programs for dental offices are described in oral and maxillofacial radiology 767
textbooks (White and Pharoah, 2014). 768
Compares measured metrics of dose to the patients with published Diagnostic Reference 769
Levels and Achievable Doses. 770
Advises on the x-ray exposure parameters (e.g., exposure time, tube potential, field size 771
or collimation, and other technique factors) to be used to achieve optimum image quality 772
and minimal radiation dose (optimization). 773
774
Recommendation 7. The qualified expert should provide guidance for the dentist or 775
facility designer in the layout and shielding design of new or renovated dental facilities 776
and when equipment is installed that will significantly increase the air kerma incident 777
on walls, floors, and ceilings. 778
779
Recommendation 8. The qualified expert shall provide guidance for the dentist 780
regarding establishment of radiation protection policies and procedures. 781
782
NCRP SC 4-5 Draft March 16, 2016
43
3.3 Electronic Image Data Management 783
784
Secure management of patient image data is an important aspect of quality assurance and 785
overall proper care of patients. Thus, image data must be stored in a way that provides robust 786
security, allows routine access for the practitioner or designee, and enables secure transmission 787
of the image data to other practitioners for consultation or at the request of the patient. 788
789
The electronic health record in a dental office should allow for interaction with a properly 790
configured picture archiving and communication systems (PACS) or should have as a subset a 791
good PACS within its architecture. The PACS is a major component in radiology in dentistry and 792
medicine and is the backbone of digital imaging. It is recommended that images that are stored in 793
the PACS system be in the Digital Imaging and Communications in Medicine (DICOM) 794
standard format. DICOM is the standard for the communication and management of medical 795
imaging information and related data. If a practitioner is using a proprietary storage and 796
communication system that comes with their x-ray equipment, this system should fulfill the basic 797
functions of a PACS system and should store it’s electronic image data in the DICOM format. 798
799
The ability of PACS systems to share imaging data can benefit patients by reducing the 800
likelihood that an x-ray exam is needlessly repeated.. A lack of data sharing in dental imaging is 801
a major problem and often responsible for repeated x-ray exposures because many data systems 802
presently in use do not integrate well with other systems or products, often requiring repeated 803
exposures. 804
805
The benefits of a good PACS system include: 806
807
1. secure storage of images; 808
2. organization of images; 809
3. archiving of current and older images; 810
4. easy workflow organization; 811
5. distribution of images and associated metadata (e.g., image interpretation, photos, 812
histopathologic findings); 813
NCRP SC 4-5 Draft March 16, 2016
44
6. restoration of lost d to prevent downtime and prevent the need to retake images; and 814
7. possible web access to images and data. 815
816
The PACS should allow for: 817
818
1. high quality display of images; 819
2. appropriate adjustment of images (post processing, i.e., window and level adjustment); 820
3. support for multimodality images; 821
4. customizable protocols and display of technical factors; 822
5. the use of templates to create structured reports which include estimated radiation dose to 823
the patient; 824
6. built in quality assurance tools; 825
7. automatic backups; 826
8. retrieval of accessed data; 827
9. easy upgrading; 828
10. compatible with open standards; 829
11. easy integration with electronic health records; and 830
12. easy integration of third party voice transcription software. 831
832
Data management in dentistry and medicine falls under the purview of the Health 833
Insurance Portability and Accountability Act of 1996 (HIPAA), with the primary goal of 834
protecting the confidentiality and security of the electronic health care information of patients. 835
Failure to comply with HIPAA may result in civil and criminal penalties. 836
837
Recommendation 9. To avoid unnecessary repeat exposures due to lost images or 838
redundant examinations, the electronic image data management system shall provide 839
for secure storage, retrieval, and transmission of image data sets 840
841
Recommendation 10. All digital images acquired shall be retained in the patient’s 842
electronic record. 843
844
Recommendation 11. All digital images should be backed up offsite electronically in a 845
separate, safe, and secure location at regular intervals. 846
NCRP SC 4-5 Draft March 16, 2016
45
4. Radiation Protection in Dental Facilities 847
848
Radiation protection recommendations specific to the dental facility are provided in this 849
Section. Technical details are found in the appendices. 850
851
4.1 General Considerations 852
853
Facilities are occupied by patients, dentists, clinical and nonclinical staff, and the public. 854
Therefore, facilities must be designed with the radiation protection and safety of all of these 855
groups. 856
857
From a radiation protection perspective, dental x-ray equipment (both permanently mounted 858
and hand-held equipment) must be installed and utilized so that patient and personnel exposures 859
are maintained ALARA, while simultaneously providing the image quality necessary to meet the 860
clinical needs. An experienced x-ray equipment provider may suggest possible configurations to 861
meet the needs and limitations of each practice environment. However, the qualified expert 862
should review the anticipated workload and proposed installation plan before renovation, 863
construction, and installation begins, to assure that each individual room configuration will meet 864
local regulatory requirements and the ALARA principle. The shielding principles used may be 865
found in NCRP Report No. 147 (NCRP, 2004a). 866
867
Perhaps the most important and often overlooked requirement of an equipment installation 868
plan is that, after positioning the patient and the imaging equipment, the operator must be able to 869
see and hear the patient while initiating the x-ray exposure. This is essential to assure that the 870
patient (or the x-ray equipment) has not moved since positioned by the operator. This may be 871
accomplished by the operator standing in a doorway (if the distance is adequate for radiation 872
protection), viewing the patient through a window designed to meet the radiation protection 873
goals, mirror or video monitoring system, or any other means that assures continuous visual and 874
audible communication between the patient and the operator. 875
876
NCRP SC 4-5 Draft March 16, 2016
46
Depending on the room size, workload, and x-ray modality used, for typical intraoral dental 877
radiography installations, it is common (but not always true) that commercial construction (two 878
layers of 5/8 inch gypsum wallboard, or GWB) provides sufficient radiation protection, since 879
GWB attenuates x-radiation in the dental diagnostic range. High workloads, small rooms and 880
proximity to other persons may increase the shielding requirements. The qualified expert should 881
perform a pre-installation shielding design and a post-installation shielding survey. 882
883
4.1.1 Shielding Design 884
885
Shielding design must be included in facility planning (before floor plans are completed) to 886
ensure that neither occupational nor public doses exceed established limits. The qualified expert 887
may present more than one shielding design for a facility. Each design may include office 888
layouts, equipment locations, doorway positions, construction of partitions, etc. Construction 889
costs vary directly with the magnitude of dose reduction. With innovative design, dose 890
reductions can be achieved at little or no cost and without adverse impact on patient care (i.e., the 891
ALARA principle). 892
893
Recommendation 12. The qualified expert should perform a pre-installation radiation 894
shielding design and plan review, to determine the proper location and composition of 895
barriers used to ensure radiation protection in new or renovated facilities, and when 896
equipment is installed that will significantly increase the air kerma incident on walls, 897
floors, and ceilings. 898
899
Recommendation 13. The qualified expert shall perform a post-installation radiation 900
protection survey to assure that radiation exposure levels in nearby public and 901
controlled areas are ALARA and below the limits established by the state or other local 902
agency with jurisdiction. 903
904
The essential radiation safety requirement of structural shielding is that the exposure to 905
persons near the x-ray equipment shall be maintained ALARA, and within specific requirements 906
NCRP SC 4-5 Draft March 16, 2016
47
set by the state or other jurisdiction. The following general considerations apply to most dental 907
imaging facilities: 908
909
1. Due to the relatively low levels of scattered radiation produced during most intraoral, 910
cephalometric, and panoramic x-ray installations, it is common (though not always true) 911
that the shielding provided by drywall (GWB) used in routine construction will provide 912
sufficient radiation shielding without the need for additional lead or other special 913
shielding materials. The location of walls and doors are an essential component of the 914
room shielding configuration. 915
2. In the design of x-ray shielding, dentists, dental hygienists, and dental assistants are 916
considered to be occupationally exposed personnel. All other persons should be 917
considered members of the general public. 918
3. To minimize unnecessary radiation exposure due to repeated exams, the operator shall 919
maintain visual and audible contact with the patient, or with the care provider of a 920
nonverbal patient, during each x-ray exposure. The qualified expert should keep this in 921
mind and specify the recommended location of the operator during each exposure. 922
4. While it is common to install CBCT systems to replace previously existing panoramic 923
dental radiographic systems, CBCT systems produce substantially more scattered 924
radiation than panoramic dental units (typically by at least a factor of 10). Hence, 925
shielding or location of panoramic rooms will often be insufficient for a CBCT system. 926
5. Some dental facilities equip and utilize a special “x-ray room” for multiple x-ray imaging 927
examinations: intraoral, cephalometric, panoramic, or CBCT imaging. Cumulative 928
radiation exposures resulting from representative weekly workloads in each modality 929
must be considered when designing shielding for such a room. 930
931
Detailed discussions of all aspects of shielding design for dental facilities, including CBCT 932
facilities, are found in Appendix D. 933
934
Recommendation 14. The qualified expert should assess each facility individually and 935
document the recommended shielding design in a written report. 936
NCRP SC 4-5 Draft March 16, 2016
48
937
Recommendation 15. The qualified expert should consider the cumulative radiation 938
exposures resulting from representative workloads in each modality when designing 939
radiation shielding for rooms in which there are multiple x-ray machines. 940
941
Some facilities include rooms with multiple x-ray machines. Shielding design for such rooms 942
assumes that only one patient is imaged at any one time. 943
944
Recommendation 16. The facility shall establish administrative controls that assure no 945
more than one patient is in an x-ray room with multiple x-ray machines during any x-946
ray exposure. 947
948
4.1.2 Equipment Performance Evaluations and Radiation Protection Surveys 949
950
Initial and periodic equipment performance evaluations (EPE) are the responsibility of the 951
qualified expert. This testing is performed to determine compliance with laws and regulations 952
governing the safety and performance of the equipment, assure that patient doses and image 953
quality are optimized, and verify the validity of the technique charts. In addition, this evaluation 954
includes assuring that the equipment is being used in a manner compatible with standards of 955
good radiologic practice. 956
957
Newly installed equipment also must comply with all applicable federal performance 958
standards (FDA, 2015). While this compliance is certified by the equipment installer, the initial 959
performance of new equipment is determined by the qualified expert through acceptance testing. 960
Acceptance testing ensures that the new equipment performs as specified in the agreement 961
between the buyer and seller, and may address equipment performance beyond the scope of the 962
federal performance standard. Any deviations are reported to the dentist, who is responsible for 963
corrective action. 964
965
Recommendation 17. A qualified expert shall evaluate x-ray equipment to ensure that it 966
is in compliance with applicable governing laws and regulations. 967
NCRP SC 4-5 Draft March 16, 2016
49
968
Dental x-ray facilities must have a radiation protection survey before the imaging equipment 969
is used to assure that the radiation protection is sufficient to meet the design goals and regulatory 970
limits. In addition, a survey shall be made after any change in the installation, workload, or 971
operating conditions that might significantly increase occupational, patient, or public exposure 972
(including x-ray machine service or repair that could affect the x-ray machine output or 973
performance). 974
975
These surveys and EPEs are performed by a qualified expert and should be performed at 976
regular intervals. This interval should not exceed 4 y for intraoral, panoramic or cephalometric 977
equipment, and should not to exceed 2 y for CBCT units. 978
979
The essential elements of a survey and EPE performed by a qualified expert should include: 980
981
1. radiation safety survey; 982
2. occupational radiation exposure assessment; 983
3. evaluation of image receptor performance and dose; 984
4. evaluation of the x-ray generator and radiation output characteristics; 985
5. evaluation of beam collimation and filtration; and 986
6. clinical image quality. 987
988
Detailed descriptions of these survey elements and a sample CBCT radiation protection 989
survey can be found in Appendices D and H. 990
991
Recommendation 18. All new dental x-ray installations shall have a radiation protection 992
survey and equipment performance evaluation carried out by, or under the direction of, 993
a qualified expert. 994
995
Constancy testing is a periodic equipment performance evaluation carried out by a qualified 996
expert to determine whether x-ray producing and imaging systems continue to meet performance 997
NCRP SC 4-5 Draft March 16, 2016
50
standards established during acceptance testing. If acceptance testing data is unavailable, the 998
qualified expert uses manufacturer’s specifications as performance criteria. 999
1000
Image quality and dose in dental radiography can be assessed by the use of devices that are 1001
mailed to dental intraoral facilities, exposed, and returned to the vendor for evaluation. These 1002
may be of particular utility for monitoring dental facilities in remote locations and facilities that 1003
are visited by a QMP less often than annually and for regulatory oversight. 1004
1005
Recommendation 19. Equipment performance evaluations shall be performed by a 1006
qualified expert at regular intervals thereafter, preferably at intervals not to exceed 4 y 1007
for facilities only with intraoral, panoramic or cephalometric units. Facilities with 1008
CBCT units shall be evaluated every 1 to 2 y. 1009
1010
4.1.3 Signage 1011
1012
Some states require clearly visible signage in the patient care areas. This may include posted 1013
statements identifying radiation use areas or in imaging rooms instructing patients to notify 1014
dentist and staff if they are or may be pregnant. 1015
1016
4.2 Diagnostic Reference Levels and Achievable Doses 1017
1018
Diagnostic reference levels (DRLs) and achievable doses (AD) can be used as guidance in 1019
optimizing the doses to patients from dental imaging examinations. In particular, DRLs can be 1020
used to help ensure that patient radiation doses are not grossly excessive. 1021
1022
NCRP Report No. 172 (NCRP, 2012) describes DRLs and ADs and their uses, describes the 1023
history of their development, and provides suggested values for the United States for a variety of 1024
imaging modalities and procedures. In particular, it defines a DRL as: 1025
1026
“A radiation dose level serving as an investigational level. When doses exceed the DRL the 1027
reasons for the higher doses should be investigated. A process known as optimization is used 1028
NCRP SC 4-5 Draft March 16, 2016
51
to assure that the image quality is adequate for the clinical task and that the patient doses are 1029
appropriate.” The diagnostic reference level is typically set at the 75th percentile of the 1030
distribution of dose metrics from a representative sample of facilities. 1031
1032
And an achievable dose as: 1033
1034
“A dose which serves as a goal for optimization efforts. This dose is achievable by standard 1035
techniques and technologies in widespread use, while maintaining clinical image quality 1036
adequate for the diagnostic purpose. The achievable dose is typically set at the median value 1037
of the dose distribution.” 1038
1039
Dose metrics used to generate DRLs and ADs may be based upon dose measurements made 1040
by qualified experts or others during simulated examinations without the presence of a patient or 1041
from dose metrics recorded by the x-ray imaging systems from actual patient examinations. To 1042
date, DRLs provided by the NCRP for use in the United States have been based, primarily, upon 1043
data collected by the former method (NCRP, 2012b). There are advantages and disadvantages to 1044
both methods. For patient examination-based DRLs, inaccuracy in the calibration of the dose 1045
measurement system of the imaging device is a potential source of error. Another source of 1046
variability in patient measurements is the variability in the size of the patient. Radiation 1047
exposures can vary substantially for the same examination depending on the thickness of the 1048
patient for the same body part. Alternatively, it takes considerably more effort to measure doses 1049
than to simply record dose metrics from patient examinations. 1050
1051
There are few sources of data today in the United States for use in determining DRLs and 1052
ADs. The U.S. Food and Drug Administration’s (FDA) Center for Devices and Radiological 1053
Health (CDRH), the Conference of Radiation Control Program Directors (CRCPD), and many 1054
states in the United States collaborate in the Nationwide Evaluation of X-ray Trends (NEXT) 1055
program. Data on the radiation exposures for selected diagnostic x-ray exams are collected from 1056
nationally representative samples of clinical facilities in the United States. The initial such 1057
NEXT survey of dental imaging was conducted in 1999; its findings were initially reported in 1058
NCRP SC 4-5 Draft March 16, 2016
52
2007 (Moyal, 2007). At the time of writing, another NEXT survey of dental imaging was 1059
recently completed (Farris and Spelic, 2015). 1060
1061
Another potential source of data for DRLs and ADs is a registry that would automatically 1062
collect dose metrics from dental examinations. The American College of Radiology maintains a 1063
dose registry for diagnostic CT and other examinations. It would be extremely useful to have the 1064
ability to generate DRLs and ADs for CBCT examination in dentistry from a dental dose 1065
registry. 1066
1067
There are disadvantages to this process for creating and using DRLs and ADs in the United 1068
States. In particular, the NEXT process takes time and considerable effort to collect and analyze 1069
the dose data from a large number of institutions. This can limit the number of examinations for 1070
which DRLs and ADs are available and can also cause the DRLs and ADs to be based on data 1071
from many years ago, which may not be fully relevant to current usage and technology. 1072
1073
For examinations for which appropriate and recent DRLs for the United States are not 1074
available, an option is to use DRLs from other countries (e.g., Hart et al., 2012; Holroyd, 2011; 1075
2013). Another option is to compare the doses from a facility’s protocols with dose data 1076
collected by other reputable institutions. In either case, bias can be introduced due to differences 1077
in practice. 1078
1079
Each dental facility should compare its dose metrics against DRLs and ADs. When qualified 1080
experts or state inspectors test dental imaging systems, they should collect dose data in a manner 1081
suitable for comparison with DRLs and ADs. For imaging systems that display dose data, these 1082
data should be compared with DRLs and ADs. 1083
1084
Careful consideration should be given when there are different technologies in use for 1085
imaging. For example, currently, intra-oral radiography is being performed with film, 1086
photostimulable storage phosphor (PSP) plates, and direct digital radiography image receptors. 1087
The currently available DRLs and ADs are largely due to data from facilities using film. 1088
Facilities with direct digital receptors may presume that their doses are optimized if they are less 1089
NCRP SC 4-5 Draft March 16, 2016
53
than these DRLs and similar to the ADs, but in fact their doses may be higher than needed for 1090
clinically-adequate images. 1091
1092
The creation of interim DRLs and ADs, published in the literature from studies involving 1093
small numbers of reputable institutions, is recommended. 1094
1095
Recommendation 20 Diagnostic Reference Levels and Achievable Doses should be 1096
developed for dental CBCT imaging. 1097
1098
Recommendation 21. Each dental facility should record and track indicators of patient 1099
dose, such as entrance air kerma and associated technique factors. 1100
1101
Recommendation 22. Each dental facility should compare its doses to DRLs and ADs. 1102
In particular, where established methods exist, the qualified expert shall collect dose 1103
data suitable for comparison with DRLs and ADs. These data and the results shall be 1104
provided in the qualified experts report. For dental imaging systems that provide dose 1105
metrics for patient examinations, the dentist or qualified expert should periodically 1106
compare medians of these data for 10 clinical examinations appropriate for this purpose 1107
with DRLs and ADs. 1108
1109
Recommendation 23. Organizations such as NCRP, U.S. Food and Drug 1110
Administration (FDA), Conference of Radiation Control Program Directors (CRCPD), 1111
American Academy of Oral and Maxillofacial Radiology (AAOMR), and American 1112
Dental Association (ADA) should strive to provide DRLs and ADs for a variety of 1113
dental examinations. 1114
1115
4.3 Optimization of Image Quality and Patient Dose: General Principles 1116
1117
Clinical image quality and radiation dose to both patients and staff are the two primary 1118
concerns in dental x-ray imaging. The image produced must have sufficient detail and 1119
information to assure the practitioner that subtle pathology can be detected. Optimization is the 1120
NCRP SC 4-5 Draft March 16, 2016
54
balancing of image quality and patient dose. The optimization process is best carried out as a 1121
cooperative effort between dentists and qualified experts. 1122
1123
DRLs and ADs are helpful as part of the optimization process. However, a dose metric found 1124
to be less that the appropriate DRL and near the AD does not necessarily mean that the doses are 1125
optimized and that image quality is acceptable; in some cases a newer technology (e.g., digital 1126
intraoral image receptors) may produce acceptable diagnostic images at doses much lower than 1127
the older technology and, if the DRLs and ADs are largely based upon data from the less dose 1128
efficient technology, an optimized dose may be considerably less that the AD. Furthermore, 1129
optimization can be performed in the absence of DRLs and ADs. 1130
1131
For film radiography the optimization process starts with using EF-speed film, filling the 1132
processor with new developer and fixer, and assuring that the developer is at the temperature 1133
specified by the film manufacturer. The film processor should be performing with a consistent 1134
level of quality. Once the tube current (mA) and potential (kVp) are determined (either selected 1135
by the operator or fixed by the manufacturer), the next step is to optimize the exposure time. 1136
Begin with the film manufacturer’s recommendation for the average adult patient. On subsequent 1137
patients, reduce the exposure time until there is degradation of the image that renders it 1138
nondiagnostic; the baseline exposure time for the average adult patient is then set as one time 1139
station greater than the setting that produced the degraded, nondiagnostic image. As described in 1140
Section 5.1.3, this exposure setting should be incorporated into a technique chart. The chart 1141
should also include adjustments from this baseline exposure for children and for large and small 1142
adults and adolescents. 1143
1144
Having established clinically useful exposure settings, one should expose a stepwedge 1145
phantom with these settings in order to have a phantom-based image for subsequent quality 1146
control checks of film processing and darkroom integrity. 1147
1148
The steps for digital imaging systems are essentially the same as with film, but without the 1149
activities associated with the film processor. A phantom appropriate for the type of digital 1150
NCRP SC 4-5 Draft March 16, 2016
55
imaging should be used to establish the baseline image. CBCT units have special phantoms 1151
which are supplied by the manufacturer (Section 5.2.5). 1152
1153
The primary goal of optimization is to select x-ray techniques, and, consequently, patient 1154
doses, that produce clinically acceptable images at the lowest dose achievable (ALARA) 1155
regardless of whether the image receptor is film or digital. 1156
1157
4.4 Protection of the Patient 1158
1159
Potential health benefits to patients from dental x-ray exposure preclude establishment of 1160
dose limits for patients. Thus the specific goal of optimization of protection of the patient should 1161
be to obtain the necessary clinical information while avoiding unnecessary patient exposure, i.e., 1162
the patient exposure is maintained as low as reasonably achievable (ALARA). 1163
1164
4.4.1 Selection Criteria. Examination Type and Frequency 1165
1166
Elimination of unnecessary radiographic examinations is a very effective method for 1167
avoiding unnecessary patient exposure. Guidance on x-ray imaging appropriateness and selection 1168
criteria have been developed (FDA/ADA, 2015a; 2015b). Procedures are outlined in Sections 1169
4.4.1.1 through 4.4.1.3 for eliminating unnecessary examinations for both symptomatic patients 1170
seeking urgent care and asymptomatic patients scheduled for routine or continuing dental care. 1171
1172
A clear procedure for reducing the extent and frequency of dental radiographic examinations 1173
must be followed when a patient transfers or is referred from one dentist to another. Modern 1174
digital imaging and electronic transfer facilitates exchange of information among dentists and 1175
other health care providers. 1176
1177
Recommendation 24. All radiological examinations shall be performed only on direct 1178
prescription of the dentist, physician, or other individuals authorized by law or 1179
regulation. 1180
1181
NCRP SC 4-5 Draft March 16, 2016
56
Recommendation 25. Radiographic examinations shall be performed only when patient 1182
history and physical examination, prior images, or laboratory findings indicate a 1183
reasonable expectation of a health benefit to the patient. 1184
1185
Recommendation 26. For each new or referred patient, the dentist shall make a good 1186
faith attempt to obtain previous, pertinent images prior to acquiring new patient 1187
images. 1188
1189
4.4.1.1 Symptomatic Patients. When symptomatic patients are seen, the dentist is obligated to 1190
provide care to relieve those symptoms and, when possible, eliminate their cause. Radiographs 1191
required for that treatment are fully justified, but additional, noncontributory radiographs are not 1192
justified. For example, a full-mouth intraoral study is not warranted for emergency treatment of a 1193
single painful tooth. However, if treatment of that painful tooth is the first step in comprehensive 1194
dental care, then those radiographs required for that comprehensive care are justified. 1195
1196
Recommendation 27. For symptomatic patients, the radiological examinations shall be 1197
limited to those images required for diagnosis and treatment of current disease. 1198
1199
4.4.1.2 Asymptomatic Patients. Maintenance of oral health in asymptomatic new patients or 1200
those returning for periodic reexamination without clear signs and symptoms of oral disease may 1201
require radiographs. Selection criteria that will aid the dentist in selecting and prescribing 1202
radiographic examination of these patients have been published (FDA/ADA, 2015a; 2015b). 1203
These criteria recommend that dental radiographs be prescribed only when the patient’s history 1204
and physical findings suggest a reasonable expectation that radiographic examination will 1205
produce clinically useful information. 1206
1207
Recommendation 28. For asymptomatic patients, the extent of radiological examination 1208
of new patients, and the frequency and extent for established patients, shall adhere to 1209
current published, evidence based selection criteria. 1210
1211
NCRP SC 4-5 Draft March 16, 2016
57
4.4.1.3 Administrative Radiographs. Radiographs are occasionally requested, usually by outside 1212
agencies, for purposes other than health. Examples include requests from third-party payment 1213
agencies for proof of treatment or from regulatory boards to determine competence of the 1214
practitioner. In some institutions dental or dental auxiliary students have been required to 1215
perform oral radiographic examinations on other students for the sole purpose of learning the 1216
technique. Other methods (such as photographs for treatment documentation or image receptor 1217
and tube-head placement for radiologic technique training) that do not require exposure to x rays 1218
are generally available for providing this information. Dental students can learn to perform x-ray 1219
exams using phantoms. 1220
1221
Recommendation 29. Administrative use of radiation to provide information that is not 1222
necessary for the treatment or diagnosis of the patient shall not be permitted. 1223
1224
Recommendation 30. Students shall not be compelled or permitted to perform 1225
radiographic exposures of humans solely for purposes of education. 1226
1227
Recommendation 31. Candidates shall not be compelled or permitted to perform 1228
radiographic exposures of humans solely for purposes of licensure, credentialing or 1229
other certification. 1230
1231
4.4.2 X-Ray Machines 1232
1233
All x-ray machines should meet the design specifications and all requirements of the 1234
jurisdiction in which they are located. Equipment certified to conform to the federal performance 1235
standard (FDA, 2005) will generally meet these requirements. Equipment of recent manufacture 1236
(especially that manufactured in Europe) may also conform to IEC standards (IEC, 2012) or 1237
regulatory guidance (NRPB, 2001). Specific design considerations are covered in subsequent 1238
chapters that address specific imaging modalities. 1239
1240
Recommendation 32. Personnel responsible for purchase and operation of dental x-ray 1241
equipment shall ensure that such equipment meets or exceeds all applicable U.S. federal 1242
NCRP SC 4-5 Draft March 16, 2016
58
government and state requirements and regulations. In addition, the equipment should 1243
conform to current international standards for basic safety and essential performance. 1244
1245
4.4.3 Examinations and Procedures 1246
1247
The general requirements and recommendations in this Report apply to all dental radiological 1248
examinations and procedures. This Section, however, presents additional recommendations 1249
specific for particular radiographic examinations. 1250
1251
4.4.3.1 Intraoral Radiography. Dental intraoral radiographs and chest radiographs have been the 1252
most common diagnostic x-ray procedures in the United States. A 2005 to 2006 ADA survey 1253
(ADA, 2007), based on practitioner logs, found 308,061,820 periapical images and 423,995,407 1254
bitewing images produced annually in private practices, excluding the military, federal agencies, 1255
hospitals, and academic institutions. It is estimated that 493 million intraoral examinations were 1256
performed in the United States in 2014 (NEXT 2015). In both cases patient dose per image and 1257
resulting radiation detriment are low when compared to other x-ray imaging modalities such as 1258
computed tomography. However, the large number of intraoral x-ray procedures performed 1259
annually delivers a notable collective dose to the exposed population. Consequently, this requires 1260
diligence in optimizing the radiation exposure from these procedures so that unnecessary 1261
exposure is avoided and ensuring that such exams are performed only when there is an 1262
anticipated benefit to the patient. 1263
1264
4.4.3.2 Panoramic Radiography. Panoramic images provide curved-plane tomograms of the 1265
teeth and jaws. This imaging method is widely used in dental practice. A 2005 to 2006 ADA 1266
survey (ADA, 2007), based on practitioner logs, found 29,552,920 panoramic images produced 1267
annually in private practices, excluding the military, federal agencies, hospitals, and academic 1268
institutions. The major advantages are rapid acquisition of a single image encompassing the 1269
entire dental arches and their supporting structures. The zone of sharp focus (“focal trough”) is 1270
limited and varies with manufacturer and model. It is designed to accommodate average adults; a 1271
few machines allow adjustment to patient dimensions. Patient positioning is critical and varies 1272
with manufacturer and model. Some machines allow only limited adjustment of beam technical 1273
NCRP SC 4-5 Draft March 16, 2016
59
factors such as image receptor speed, patient thickness and tube current. Effective dose to the 1274
patient for a single panoramic image is approximately equal to that from two to four intraoral 1275
images, both using state-of-the-art technique (Gibbs, 2000; White and Pharoah, 2014). 1276
1277
4.4.3.3 Cephalometric Radiography. The cephalometric technique provides geometrically 1278
reproducible radiographs of the facial structures. A 2005 to 2006 ADA survey (ADA, 2007), 1279
based on practitioner logs, found 2,733,040 cephalometric images produced annually in private 1280
practices, excluding the military, federal agencies, hospitals, and academic institutions. The 1281
principal application is evaluation of growth and development, as for orthodontic treatment, and 1282
for orthognathic surgery. The equipment provides for standardized positioning of the patient 1283
together with alignment of beam, subject and image receptor. It is frequently useful for the 1284
cephalometric image to show bony anatomy of the cranial base and facial skeleton plus the soft-1285
tissue outline of facial contours. 1286
1287
4.4.3.4 Fluoroscopy. Real-time imaging, or fluoroscopy, is useful only for imaging motion in 1288
structures. Its use should be limited to those tasks requiring real-time imaging, such as the 1289
injection of radiographic contrast fluids for sialography or temporomandibular joint 1290
arthrography. Fluoroscopy requires electronic image intensification and video display to 1291
minimize patient exposure; this equipment is expensive and not usually found in dental facilities. 1292
Furthermore, dental x-ray machines are not generally capable of providing the required 1293
continuous radiation exposure. 1294
1295
Recommendation 33. Fluoroscopy shall not be used for static imaging in dental 1296
radiography. If fluoroscopy is used for dynamic imaging, the practices in NCRP Report 1297
No. 168 shall be followed. 1298
1299
4.4.3.5 Cone Beam Computed Tomography. The CBCT examination is a complementary 1300
modality to, not a replacement for, two-dimensional imaging modalities. Just as for other dental 1301
radiographic examinations, justification for each patient should be based on their imaging history 1302
and the diagnostic yield not achievable with the 2D modalities. The examination is justified if the 1303
anticipated diagnostic yield outweighs the risks associated with radiation (AAOMR, 2008; ADA, 1304
NCRP SC 4-5 Draft March 16, 2016
60
2012; EADMFR, 2009; Farman and Scarfe, 2006; White and Pae, 2009). CBCT should only be 1305
used when the question for which the imaging is required cannot be answered adequately by 1306
conventional, lower dose dental radiography, applying the ALARA principle (NCRP, 2003). 1307
This is especially true for CBCT examinations of children (SPR, 2015). 1308
1309
Prior to the acquisition of a CBCT examination, a dental examination by the ordering 1310
provider should be completed, with a review of the patient’s medical history, as well as the 1311
medical and dental imaging history. Previously acquired dental and medical imaging, which falls 1312
short of yielding the necessary clinical information, may justify the need for the CBCT 1313
examination (ADA, 2012; Farman and Scarfe, 2006). The decision for the clinical indication for 1314
CBCT is the professional determination of the treating clinician. Some of the evidence-based 1315
specific indications for CBCT imaging are provided in Section 9.1.5. 1316
1317
4.4.4 Image Viewing Environment 1318
1319
Poor viewing conditions can suppress the clinician’s ability to perceive important diagnostic 1320
information that is present in the image. This may lead to diagnostic errors or unnecessary repeat 1321
examinations in an attempt to produce an “improved” image to compensate for the poor viewing 1322
conditions. It is essential to assure appropriate viewing conditions to insure optimal 1323
interpretation and to avoid repeating adequate images that appear substandard due to substandard 1324
viewing conditions (Kutcher et al., 2006; Patel, 2000). 1325
1326
For maximum diagnostic yield at minimum exposure, image evaluation and interpretation is 1327
best carried out in a quiet atmosphere, free from distractions. With film radiographs, perception 1328
of image details has been shown to be maximum when the illuminated surface of the view box 1329
that is not covered with films or by the opaque film mounts is masked with opaque material to 1330
eliminate glare. View boxes are available that allow for adjusting the luminance and digital 1331
displays allow for adjusting the image brightness and contrast. These view boxes need to be 1332
maintained by periodic cleaning, visual assessment of uniformity and assessment of luminance. 1333
With digital images, perception of image detail is maximized when the illuminated areas of the 1334
display surrounding the digital image are electronically “masked” to reduce glare. 1335
NCRP SC 4-5 Draft March 16, 2016
61
1336
When viewing either film radiographs or digital images, reduced ambient (room) light is 1337
required to maximize the perception of image details. As a rule of thumb, the lighting in the 1338
reading area should be at a reduced level but with sufficient light that one can read a newspaper 1339
page. 1340
1341
4.4.4.1 Viewing Conditions for Digital Images. In addition to the general considerations covered 1342
above, the information obtained from all digital images (intraoral, panoramic, cephalometric, and 1343
CBCT) that are viewed on a computer display are subject to a number of conditions, including 1344
those of the viewing environment. Some conditions that may affect specifically the appearance 1345
of the digital display include: 1346
1347
ambient room lighting conditions; 1348
viewing display quality, position and location, settings, calibration, and defects; 1349
reflections of light sources (i.e., overhead lights, windows); and 1350
computer graphics capabilities. 1351
1352
A discussion of optimal configurations for computer and display hardware is beyond the 1353
scope of this report. However, an aspect of image viewing that can have a substantial impact on 1354
the perceived image quality is the room environment where clinical images are viewed and 1355
assessed. While most computer displays can be configured to provide a nominal brightness under 1356
well-lit room conditions, a darkened room environment provides an improved viewing 1357
experience and higher clinical benefit. Pakkala et al. (2012) investigated the effect of ambient 1358
viewing conditions and computer display brand on sensitivity and specificity for diagnosis of 1359
caries. Based on their findings Pakkala et al. recommend that darkened ambient room conditions 1360
be employed, noting that their data suggests that simply increasing the display brightness was not 1361
a recommended alternative. The authors further note that in those practices where clinical images 1362
are routinely displayed chair-side near the patient (and presumably under room conditions 1363
providing a high level of ambient light), it is advisable to confirm diagnosis under subdued 1364
viewing conditions, as their data regarding sensitivity suggest. 1365
1366
NCRP SC 4-5 Draft March 16, 2016
62
In the early days of digital imaging, images were presented on cathode ray tube (CRT) 1367
monitors which have largely been replaced by flat-panel displays. A flat panel displays is 1368
composed of a rectangular array of pixels that determine the spatial resolution of the image. 1369
Spatial distortion is not likely, because the pixels are fixed in position, and spatial resolution is 1370
not likely to vary, because the size of the pixels does not change. However, the luminance of the 1371
backlight tends to decrease with time. There are differences between commercial computer 1372
displays and medical grade displays, although some studies have shown comparable diagnostic 1373
efficacy for detecting anatomic sites and common dental pathology (Kallio-Pulkkinen et al., 1374
2014; Tadinada et al., 2015a). 1375
1376
Recommendation 34. Images shall be viewed in an environment adequate to ensure 1377
accurate interpretation. 1378
1379
4.4.5 Use of Radiation Protective Aprons 1380
1381
Radiation protective aprons for patients were first recommended in dentistry many years ago 1382
when dental x-ray equipment was much less sophisticated and image receptors were much 1383
slower than under current standards and when the primary risks were thought to be heritable 1384
effects. They provided protection in an era of poorly collimated and unfiltered dental x-ray 1385
beams. Gonadal (or whole-body) doses from these early full-mouth examinations, reported as 1386
high as 50 mGy (Budowsky et al., 1956), could be reduced substantially by radiation protective 1387
aprons. Gonadal doses from current panoramic or full-mouth intraoral examinations using state-1388
of-the-art technology and procedures do not exceed 5 µGy (White, 1992). A substantial portion 1389
of this gonadal dose results from internal scattered radiation arising within the patient’s head and 1390
body. Technological and procedural improvements have eliminated the requirement for the 1391
radiation protective apron, provided all other recommendations of this Report are rigorously 1392
followed. However, some patients have come to expect the apron and may request that it be 1393
used. Its use remains a prudent but not essential practice. 1394
1395
NCRP SC 4-5 Draft March 16, 2016
63
Recommendation 35. The use of radiation protective aprons on patients shall not be 1396
required if all other recommendations in this Report are rigorously followed unless 1397
required by state regulation Otherwise, a radiation protective apron shall be used. 1398
1399
4.4.5.1 Use of Thyroid Collars. The thyroid gland, especially in children, is among the most 1400
sensitive organs to radiation-induced tumors, both benign and malignant (Appendix I). Even with 1401
optimum techniques, the primary dental x-ray beam may still pass near and occasionally through 1402
the gland. If the x-ray beam is properly collimated to the size of the image receptor or area of 1403
clinical interest, and exposure of the gland is still unavoidable, any attempt to shield the gland 1404
would interfere with the production of a clinically-useful image. However, in those occasional 1405
uncooperative patients for whom rectangular collimation and positive beam-receptor alignment 1406
cannot be achieved for intraoral radiographs, then thyroid shielding may reduce dose to the gland 1407
without interfering with image production. 1408
1409
Recommendation 36. Thyroid shielding shall be provided for patients when it will not 1410
interfere with the examination. 1411
1412
1413
4.4.5.2 Maintenance of Protective Aprons and Thyroid Shields. Minimum acceptable evaluation 1414
of radiation protective aprons and thyroid shields consists of periodic visual inspection for 1415
defects. Fluoroscopic evaluation of lead aprons is not recommended as this exposes the inspector 1416
to substantial scattered radiation (NCRP, 2010). 1417
1418
Recommendation 37. Protective aprons and thyroid shields should be hung or laid flat 1419
and never folded, and manufacturer’s instructions should be followed. All protective 1420
shields should be evaluated for damage (e.g., tears, folds, and cracks) quarterly using 1421
visual and manual inspection. 1422
1423
NCRP SC 4-5 Draft March 16, 2016
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4.4.6 Special Considerations for Pediatric Imaging 1424
1425
Children are not small adults. Some tissues in children, including thyroid and female breast, 1426
are two to ten times more sensitive to radiation carcinogenesis than adults, due to higher levels of 1427
cell proliferation, more cells which are less differentiated, and a much longer proliferative future 1428
(Hall and Giaccia, 2011). Additionally, the thyroid gland in children is higher in the neck than in 1429
adults, thus more thyroid tissue is in the radiation field. It is imperative to child-size all radiation 1430
exposures of children commensurate with the diagnostic need of the examination. 1431
1432
Recent studies have suggested that the lens of the eye may be more susceptible to 1433
cataractogenesis than previously thought (ICRP, 2012). The use of leaded glasses has been 1434
shown to significantly reduce the dose to the lens during cone beam CT examinations (Prins 1435
et al., 2011). Thus, leaded glasses should be considered when the orbital and periorbital regions 1436
are not essential to the image (as they might be for pre-orthognathic surgical treatment planning). 1437
1438
It is essential to assure that pediatric patients are not treated as adult patients with regard to 1439
x-ray techniques. The following guidelines should be observed when imaging pediatric patients 1440
(http://imagegently.org/Procedures/Dental): 1441
1442
select x rays for individual’s needs, not merely as a routine; 1443
use the fastest image receptor possible (E- or F-speed film, or a digital receptor); 1444
collimate beam to area of interest; 1445
always use thyroid collars unless it interferes with imaging the needed anatomy; 1446
child-size the exposure time, i.e., optimize the image quality and patient radiation dose; 1447
and 1448
use cone-beam computed tomography only when clinically necessary. 1449
1450
Further information on imaging pediatric patients can be found on the Image Gently website 1451
(http://imagegently.org/Procedures/Dental.aspx). 1452
1453
NCRP SC 4-5 Draft March 16, 2016
65
Recommendation 38. Technique factors and selection criteria shall be appropriate to 1454
the age and size of the patient. 1455
1456
4.5 Protection of the Operator 1457
1458
Equipment and procedures that reduce patient exposure will also reduce exposure of the 1459
operator and the environment. Additional measures, however, will further reduce occupational 1460
and public exposure without affecting patient dose or image quality. 1461
1462
4.5.1 Shielding Design 1463
1464
Attention to office layout and shielding design provides convenient methods for 1465
implementing the ALARA principle. Shielding does not necessarily require lead-lined x-ray 1466
rooms. Normal building materials may be sufficient in most cases. Expert guidance can provide 1467
effective shielding design at nominal incremental cost with protection by barriers, distance from 1468
x-ray source, and operator position. 1469
1470
Recommendation 39. Adequacy of facility shielding shall be determined by the qualified 1471
expert whenever the average workload increases by a factor of two or more from the 1472
initial design criteria. 1473
1474
It is in the economic best interest of the dentist to obtain shielding design by a qualified 1475
expert at the facility design stage. For a new or remodeled facility, proper shielding design can 1476
usually provide radiation protection to meet shielding design goals at little or no incremental 1477
construction cost. However, if post-construction measurements indicate that these goals are not 1478
met, the cost of retrofitting may be considerable. 1479
1480
4.5.2 Barriers 1481
1482
Fixed barriers, generally walls, provide the most economical, effective and convenient means 1483
of excluding the public and nonoperator office staff from the primary x-ray beam as it exits the 1484
NCRP SC 4-5 Draft March 16, 2016
66
patient or from radiation scattered from the patient or other objects in the primary beam. 1485
Windows (glass, leaded glass or acrylic) in permanent barriers, mirrors, or remote video 1486
monitoring may be helpful. 1487
1488
Barriers are not necessary for protection of the operator of appropriately designed hand-held 1489
x-ray units as these have a nonremovable circular shield built into the device. 1490
1491
Recommendation 40. Shielding designs for new offices with fixed x-ray equipment 1492
installations shall provide protective barriers for the operator. The barriers shall be 1493
constructed so operators can maintain visual contact and audible communication with 1494
patients throughout the procedures. 1495
1496
Recommendation 41. The exposure switch should be mounted behind the protective 1497
barrier such that the operator must remain behind the barrier during the exposure. 1498
1499
4.5.3 Distance 1500
1501
In some existing facilities, design precludes use of a protective barrier. Appropriate distance 1502
and position relative to the position of the x-ray tube and direction of the x-ray beam must be 1503
maintained in these situations. 1504
1505
Recommendation 42. In the absence of a barrier in an existing facility, the operator 1506
shall remain at least 2 m, but preferably 3 m, from the x-ray tube head during 1507
exposure. If the 2 m distance cannot be maintained, then a barrier shall be provided. 1508
This recommendation does not apply to hand-held units with integral shields. 1509
1510
4.5.4 Position of Operator 1511
1512
If the facility design requires that the operator be in the room at the time of exposure, then 1513
the operator should be positioned not only at maximum distance (at least 2 m) from the tube 1514
head, and also in the direction of minimum exposure (Figure 4.1). Maximum exposure will 1515
NCRP SC 4-5 Draft March 16, 2016
67
1516
1517
1518
1519
1520
1521
1522
1523
1524
Fig. 4.1. Recommended positions for operator exposing intraoral images of the central 1525
incisors (left) and molars (right). Operator should stand at least 6 feet from the patient and an 1526
angle of 90 to 135 degrees from the central ray (Richards, 1964; White and Pharoah, 2014). 1527
1528
1529
NCRP SC 4-5 Draft March 16, 2016
68
generally be in line with the primary beam as it exits the patient. Maximum scattered radiation 1530
will be backwards, i.e., 90 to 180 degrees from the primary beam as it enters the patient. 1531
Generally the position of minimum exposure will be at 45 degrees from the primary beam as it 1532
exits the patient, see Appendix E2 (de Haan and van Aken, 1990). In particular, the operator 1533
should not stand on the side of the patient opposite the x-ray tube as this would expose them to 1534
the direct x-ray beam exiting the patient. 1535
1536
4.5.5 Personal Dosimeters 1537
1538
Monitoring of individual occupational exposures is generally required if it can be expected 1539
that any dental staff member will receive a substantial dose. Occupational Safety and Health 1540
Administration (OSHA) regulations state that individuals who are occupationally exposed to x 1541
rays and who may receive >25 % of the quarterly occupational dose limit, are required to wear a 1542
dosimeter [29 CFR 1910.1096(d)(2)(i)]. NCRP (1998) recommends that personal dosimeters be 1543
provided to all personnel who are likely to receive an effective dose >1 mSv y–1. It must be 1544
emphasized that this recommendation concerns effective dose, which is generally much less than 1545
the dose measured by personal dosimeters. The most recent available data (Table 3.1) indicate 1546
that the average annual occupational dose in dentistry in the United States in 1980 was 1547
0.2 mSv y-1 (Kumazawa et al., 1984) and in Canada from 1970 to 1987 was 0.045 mSv y–1 1548
(Zielinski et al., 2005). Few dental workers received >1 mSv and 68 % received exposures below 1549
the threshold of detection. 1550
1551
World data for the period 2000 to 2002 show a mean annual occupational dose of 0.06 mSv 1552
for dental workers (UNSCEAR, 2008). These data suggest that dental personnel are not expected 1553
to receive occupational exposures greater than the recommended threshold for monitoring of 1554
1 mSv y-1. However, the limit applicable to pregnant workers of 0.5 mSv equivalent dose to the 1555
fetus per month once pregnancy is known suggest that personal dosimetry may be a prudent 1556
practice for pregnant workers. Current regulations require that dosimeters be obtained from 1557
services accredited for accuracy and reproducibility. These services distribute dosimeters 1558
regularly; the facility returns the dosimeters to the service after use (generally monthly or 1559
NCRP SC 4-5 Draft March 16, 2016
69
quarterly) for readout and report. The return frequency for personal dosimeters for pregnant staff 1560
should be monthly or more frequent. 1561
1562
Recommendation 43. Provision of personal dosimeters for external exposure 1563
measurement should be considered for workers who are likely to receive an annual 1564
effective dose in excess of 1 mSv. Personal dosimeters shall be provided for declared 1565
pregnant occupationally-exposed personnel. 1566
1567
Recommendation 44. For new or relocated equipment, the facilities shall provide 1568
personal dosimeters for at least 1 y in order to determine and document the doses to 1569
personnel. 1570
1571
Recommendation 45. The facility shall provide personal dosimeters for all new 1572
operators of hand-held dental x-ray equipment for the first year of use. 1573
1574
4.6 Protection of the Public 1575
1576
For shielding design purposes, the public consists of all individuals, including 1577
nonoccupationally exposed staff, who are in uncontrolled areas such as reception rooms, other 1578
treatment rooms, or in adjacent corridors or offices in the building within or outside of the dental 1579
facility (NCRP, 2005). The popular “open design” dental facility, which places two or more 1580
treatment chairs in a single room, may present problems. 1581
1582
Recommendation 46. In dental facilities using large, multi-patient open bay designs, a 1583
patient in proximity to another patient being radiographed shall be treated as a 1584
member of the public for radiation protection purposes. 1585
1586
Recommendation 47. When portable or hand-held x-ray machines are used, all 1587
individuals in the area other than the patient and operator shall be protected as 1588
members of the public. 1589
NCRP SC 4-5 Draft March 16, 2016
70
1590
The annual limit on effective dose to a member of the general public, shielding designs 1591
should limit exposure to all individuals in uncontrolled areas to an effective dose that does not 1592
exceed 1 mSv y–1 (NCRP, 2004a; 2004b). 1593
1594
Recommendation 48. New dental facilities shall be designed such that no individual 1595
member of the public will receive an effective dose in excess of 1 mSv annually. 1596
1597
NCRP SC 4-5 Draft March 16, 2016
71
5. Quality Assurance and Quality Control 1598
1599
Image quality must strike a balance between providing the information necessary for the 1600
diagnosis and the lowest possible radiation dose. Reducing the dose excessively at the expense of 1601
producing a nondiagnostic image is not a good practice. Conversely, exposing a patient to 1602
excessive dose to produce an esthetically pleasing image beyond that needed for diagnosis is not 1603
a good practice either. The goal is to strike the appropriate balance between a diagnostically 1604
acceptable image and the lowest possible radiation dose. Quality assurance is the planned and 1605
systematic activities necessary to provide adequate confidence that a product or service will meet 1606
the given requirements. Quality control is the routine performance of equipment function tests 1607
and tasks, the interpretation of data from the tests, and the corrective actions taken (NCRP, 1608
2010). 1609
1610
5.1 Image Quality and Patient Dose Optimization 1611
1612
5.1.1 Image Quality 1613
1614
Image quality that is appropriate for the specific diagnostic task is essential in 1615
dental radiography. Reduced image quality can result in missed or unobservable pathology and 1616
lead to misdiagnosis or mistreatment. However, image quality should not be maximized without 1617
regard for patient dose. Digital intraoral receptors, for example, can produce exceptional image 1618
quality at doses that well exceed optimal values. It is essential to optimize the balance between 1619
image quality and patient dose (Section 4.3). This means that image quality and patient dose go 1620
hand-in-hand, especially in digital modalities. In particular, facilities operating with median 1621
doses above the DRL should explore ways that they can reduce their doses, keeping in mind that 1622
the images must be clinically acceptable (Section 4.2). However, being below the appropriate 1623
DRL, by itself, does not imply that doses have been fully optimized. 1624
1625
The older technology of film-based imaging provided a built-in means for limiting dose: 1626
excessive exposure to the film would generally result in a film so optically dense, or dark, that it 1627
is virtually useless for diagnostic purposes. Under-development of film (low developer 1628
NCRP SC 4-5 Draft March 16, 2016
72
temperature or improper replenishment of developer solution) will result in excessive patient 1629
doses and poor image quality (low contrast). 1630
1631
Solid state image receptors can offer a reduction in radiation required to produce an image 1632
(Anissi and Geibel, 2014). Patient skin entrance dose per image can be reduced from ~100 µGy 1633
with F-Speed film to ~40 to 80 µGy with a solid state receptor (Table 6.1) while still producing 1634
diagnostically acceptable images. Surveys have shown, however, that many solid state receptors 1635
are using doses similar to or higher than D-speed film (Walker et al., 2014).1 This has been 1636
primarily attributed to the dentists not changing their x-ray techniques when switching from film 1637
to digital solid state receptors. In addition, Farman and Farman (2005) have shown that 1638
practitioners are using 1.5 to 20 times the exposure necessary to produce a diagnostically useful 1639
image. This overexposure is then compensated for by the digital imaging system software, 1640
thereby providing no indication of overexposure to the user. In addition, it is advisable for the 1641
clinical practice to become familiar with the exposure response of the particular digital system 1642
they implement in order for the patient to benefit from the reduced exposures associated with 1643
digital imaging. 1644
1645
An additional problem with the use of solid state receptors is a consequence of their ease and 1646
speed of use, which make retakes easy and fast. This can result in multiple image acquisitions 1647
and total patient doses greater than when film is used (Berkhout, 2003). Therefore, it is critically 1648
important that repeat images be obtained only when absolutely needed for diagnostic purposes. 1649
1650
Give the rapidly advancing technology of image receptors, with increasing receptor speed, it 1651
is important that newly purchased x-ray machines be able to correctly expose such receptors. 1652
1653
Recommendation 49. X-ray machines should provide a range of exposure times suitable 1654
for twice the speed of the fastest available image receptors. 1655
1656
1 Gray, JE (2015). Personal Communication. (DIQUAD, LLC, Steger Illinois)
NCRP SC 4-5 Draft March 16, 2016
73
5.1.2 Patient Dose 1657
1658
Patient doses can be controlled or optimized using many techniques. The speed of the image 1659
receptor is the most important. For example, the use of F-Speed film or digital receptors in place 1660
of D-Speed film can reduce the dose to the patient by ~50 % or more in intraoral imaging. In 1661
panoramic and cephalometric imaging, use of rare-earth screen-film combinations or digital 1662
receptors allows for substantial reduction of patient dose. 1663
1664
Film processing requires careful attention to the concentration and temperature of the 1665
solutions and the time the films spends in each solution. Improper processing can render a 1666
properly exposed image nondiagnostic and useless. It can also lead to an increase in patient 1667
radiation dose—as the developer solution is depleted the x ray exposure time must be increased 1668
to obtain appropriate film density. 1669
1670
In addition to receptor speed, use of rectangular collimation in intraoral imaging reduces the 1671
effective dose to the patient by an additional 80 % (Ludlow, 2008). As an added bonus, 1672
rectangular collimation reduces scatter and improves image quality. 1673
1674
In CBCT imaging, a variety of factors are available to reduce patient dose, including field-of-1675
view, milliampere-seconds, voxel size, and spatial resolution, 360 versus 180 degree movement, 1676
and avoiding the use of machine exam presets such as high definition (HD) only when necessary. 1677
These must be selected judiciously with diagnostic objective and patient dose in mind. 1678
1679
5.1.3 Technique Charts 1680
1681
Regardless of image receptor speed, another method to insure image quality, while reducing 1682
patient dose, is the utilization of size-based technique charts. Technique charts should be 1683
developed for each x-ray unit and image receptor combination. These should include technique 1684
settings for specific anatomical areas in combination with the patient size (small, medium, large) 1685
for adults and children. These should be developed for both intraoral and extraoral imaging, 1686
listing the exam, patient size, along with adult and pediatric settings, and image receptor (film 1687
NCRP SC 4-5 Draft March 16, 2016
74
type, digital image receptor). It is not adequate to use equipment manufacturer technique charts 1688
without validation. Technique charts should be posted conveniently near the control panel where 1689
the technique is adjusted for each x-ray unit. With digital workstations, technique charts may 1690
also be readily placed on the workstation’s desktop. When the x-ray unit is replaced, or an image 1691
receptor is added, the chart must be updated (see Section 6.3.2.4 for further information on 1692
technique charts). 1693
1694
5.2 Quality Control 1695
1696
Quality control (QC) is an integral component of a quality assurance (QA) program. As 1697
noted above QA is the overall program for assuring quality outcomes. QC, on the other hand, is 1698
the part of the QA program that employs regular physical testing designed to detect changes in a 1699
radiographic system before they can interfere with diagnostic performance. Lack of a quality 1700
control program often results in poor quality images, lacking clinically necessary details for 1701
diagnostic purposes, increasing radiation doses to the patient and staff, and repeated images 1702
resulting in increased radiation dose. 1703
1704
The QC program for each facility must be customized to the imaging modalities in use, the 1705
staffing capabilities and equipment available. The QC program should be established in 1706
consultation with the qualified expert, documenting specific QC activities, the personnel 1707
responsible for performing each activity (e.g., dental assistant, qualified expert), procedures to be 1708
followed for each activity, acceptable ranges of results, and actions to be taken when results of 1709
any QC activity are not within the acceptable range. Such a program includes daily, weekly, 1710
monthly, quarterly, and annual tests of the various components of the imaging chain. In general, 1711
QC activities that should be performed frequently do not entail complex equipment or 1712
procedures and can be performed by on-site dental assistants or other technical staff. More 1713
complex tasks or those requiring specialized training or equipment should be performed by the 1714
qualified expert at intervals consistent with the probability of undetected failure, the impact of 1715
failure on patient care, and the availability of the qualified expert. 1716
1717
NCRP SC 4-5 Draft March 16, 2016
75
All dental facilities utilizing x-ray imaging should be evaluated initially (acceptance testing, 1718
also known as initial equipment performance evaluation) and periodically thereafter by a 1719
qualified expert. This will assure that the image quality and the patient radiation dose are 1720
appropriate, persons in the vicinity of the x-ray equipment are safe, regulatory compliance is 1721
maintained, and that the facility staff is maintaining their portion of the quality control program. 1722
1723
No matter what image receptor is used, the QC program should include periodic testing and 1724
calibration of the x-ray system in order to see that tube-head stability, collimation, tube potential, 1725
half-value layer, exposure time, output reproducibility, and other factors are within the 1726
appropriate tolerances. Once it is ascertained that the x-ray unit is functioning properly, the 1727
image receptor can be evaluated using this calibrated x-ray unit for test exposures. 1728
1729
5.2.1 Radiation Measurements of X-Ray Producing Diagnostic Dental Equipment 1730
1731
The qualified expert is the individual who is responsible for, and qualified to measure 1732
radiation dose, interpret the results, and advise on the clinical implications of dose and image 1733
quality in imaging facilities, including dental facilities. While measuring radiation dose may 1734
appear a simple task, the qualified expert must be familiar with many complex technical factors 1735
when measuring and evaluating dose in dental facilities. Different types of radiation detectors are 1736
suited to different types of radiation measurements, and different units of measure are used for 1737
different modalities. For example, a radiation detector that is suitable for measuring entrance 1738
skin exposure in dental radiography may or may not be suitable for measuring dose in a CBCT 1739
system, depending on the units used and the comparisons to be made. Measurements of exposure 1740
to persons in the vicinity of an x-ray producing device must be made with an entirely different 1741
type of radiation detector. Both types of radiation measurement are required for regulatory 1742
compliance in many jurisdictions. 1743
1744
When changing from film to digital imaging, the settings used for film will typically deliver 1745
unnecessarily high radiation to the patient, often by a factor of two or more. Hence, the qualified 1746
expert should be consulted before converting to digital image receptors, so that the exposure 1747
factors may be reduced before commencing patient imaging. The manufacturer may provide 1748
NCRP SC 4-5 Draft March 16, 2016
76
suggestions for technique factors, but only the qualified expert has the knowledge and equipment 1749
needed to accurately measure radiation dose, interpret those data, and to advise the dental 1750
practitioner about the appropriate technique factors to be used with a new digital receptor. 1751
1752
While service engineers can perform radiation measurements in dental imaging facilities, 1753
their results do not replace the testing by a qualified expert. 1754
1755
5.2.2 Phantoms for Quality Control and Dose Measurements 1756
1757
There are a limited number of imaging phantoms that are designed specifically for dental 1758
imaging. When these are not readily available, the qualified expert may adapt conventional 1759
radiography phantoms that are appropriate to the field size and image quality considerations 1760
relevant to dental radiography. 1761
1762
The FDA requires that phantoms be provided by the CBCT manufacturer to assess specified 1763
image quality indicators. Conventional head CT phantoms for image quality and dose 1764
measurements (CTDI) may be used if considered appropriate by the qualified expert. Dose 1765
measurements may also be made in air, without the use of a phantom. Some equipment 1766
manufacturers may provide tabulation of dose-area product for equipment capable of CT-like 1767
imaging. 1768
1769
Recommendation 50. A suitable radiographic phantom shall be used to optimize 1770
radiation dose and image quality, and for continuing quality control measurements. 1771
1772
5.2.3 Quality Control for Film Imaging 1773
1774
For facilities using film-based radiography, the greatest single source of image variability is 1775
film processing. The facility QC program should follow the film processor manufacturer’s 1776
recommendations for quality control. The most critical element of film processing quality control 1777
(whether hand developing or using an automatic film processor) is to assure that the processing 1778
NCRP SC 4-5 Draft March 16, 2016
77
chemistry is maintained at the specified temperature (appropriate for the processing time), 1779
remains fresh (i.e., undiluted and uncontaminated), is replenished daily, and replaced regularly. 1780
1781
Film processing solutions are subject to gradual deterioration. The deterioration may go 1782
unnoticed until it becomes severe enough to degrade image quality and require an increase in 1783
exposure time, thus increasing patient dose. Daily measurements are required to prevent this 1784
degradation. 1785
1786
A baseline radiographic image is first produced using fresh solutions at proper temperatures. 1787
A standardized test object [step wedges are commercially available or can be assembled from 1788
discarded lead foil from film packets (Valachovic et al., 1981; White and Pharoah, 2014)] is 1789
placed on the film, exposed, and processed to produce this baseline image. Subsequent images 1790
are produced daily under identical conditions. The follow-up images are compared to the 1791
baseline images and corrective actions are taken if changes in the image quality are noted. The 1792
images are saved for later reference, and records are maintained of any image technical factors 1793
that are measured and any changes or repairs that are made. 1794
1795
Film processing quality control is essential to maintaining optimum quality radiographic 1796
images and assuring patient doses are as low as reasonably achievable. This is required by some 1797
state radiation protection agencies. 1798
1799
Whether using manual- or automatic-film processing, the specified development time and 1800
temperature must be used. If manually processing films, the films must be agitated during 1801
processing according to the film manufacturer’s instructions. 1802
1803
Developer and fixer solutions must be replenished with eight ounces of appropriate solutions 1804
each day before processing patient films (solutions must be stirred to assure the new solutions 1805
are mixed thoroughly with the older solutions). All solutions should be drained, the tanks 1806
cleaned, and refilled with fresh solutions at least every two weeks. 1807
1808
NCRP SC 4-5 Draft March 16, 2016
78
The water in the wash tank should be changed daily or after every 30 intraoral films that are 1809
processed, whichever occurs first. For higher volumes or larger films, such as panoramic or 1810
cephalometric, the water should be changed more frequently. 1811
1812
Recommendation 51. Film processing quality shall be evaluated daily, before processing 1813
patient films, for each film processor or manual processing system. 1814
1815
Quality control for film processing is an essential part of assuring optimum film quality while 1816
minimizing radiation dose to the patients and staff. The tests and tasks (Table 5.1) are easy to 1817
carry out and take very little time. 1818
1819
5.2.4 Quality Control for Digital Imaging Receptors 1820
1821
It is important to make sure that the quality of the digital images produced with any type of 1822
image receptor is adequate for diagnostic purposes. Often the quality of the images from the 1823
image receptors or storage phosphor plates are evaluated subjectively, thereby leading to the 1824
possibility that there is no consistency in determining when a storage phosphor plate should be 1825
replaced, when a digital image receptor has been damaged, or the image quality has deteriorated. 1826
Studies have shown that objective evaluation of some critical parameters such as spatial 1827
resolution, contrast detail detectability, and dose-response curve over a wide range of exposures 1828
can be used to confirm the quality of the images made from storage phosphor plates or traditional 1829
digital image receptors. A typical QC phantom for dental digital imaging systems is shown in 1830
Figure 5.1. 1831
1832
While there is no clear standard on how often image quality must be tested on different 1833
digital imaging systems it is recommended to test after 40 exposures on storage phosphor plates 1834
and once every three months for digital image receptors using a phantom which is capable of 1835
testing critical characteristics like spatial resolution, contrast, freedom from artifacts and dead 1836
pixels, and dose response over a wide range of exposures. 1837
1838
NCRP SC 4-5 Draft March 16, 2016
79
1839
TABLE 5.1—Frequency of quality control testing for film-based radiography.a 1840
QC Task Frequency Who
Darkroom fog At least annually and when fog is
suspected
Office staff
Developer and fixer replenished with
solution recommended by
manufacturer
Daily Office staff
Change developer and fixer solutions Every two weeks or more frequently
for a busy practice
Office staff
Developer, fixer, wash temperature Check daily before processing films Office staff
Change water in wash tank Daily
If more than 30 films per day, then
after every 30 films
Office staff
X-ray machine performance Not to exceed every 4 y. Annually is
ideal
Qualified expert
1841
aFor more detail, the reader is referred to Appendix A. 1842
1843
NCRP SC 4-5 Draft March 16, 2016
80
1844
1845
1846
Fig. 5.1. A phantom for measuring image quality in intraoral digital radiography, constructed 1847
of tissue-equivalent Lucite with test objects imbedded internally. When the position-indicating 1848
device is placed on the four plastic rest tabs as shown, the geometry of intraoral digital 1849
radiography is simulated. 1850
1851
NCRP SC 4-5 Draft March 16, 2016
81
There are a few activities that can assist in maintaining a quality digital imaging system. For 1852
PSP-based devices, these include cleaning the sensor plate surface and the transport assembly 1853
regularly and when artifacts are observed (using only cleaners recommended by the 1854
manufacturer), and replacing the plates when they become damaged or stained. For many 1855
technical problems the only course of action is a service visit. Some manufacturers also 1856
recommend that certain mechanical parts within the scanner be replaced every 2 to 4 y. Although 1857
not an aspect of routine quality control, a means for ensuring that the PSP plates are exposed on 1858
the correct side is recommended, given the ease with which a PSP image receptor may 1859
accidentally be exposed on the opposite side, leading to the potential for incorrect viewing and 1860
clinical evaluation. Another issue with PSP plates is the propensity for scratching and fraying of 1861
the edges during handling. Damaged plates must be replaced in order to maintain quality 1862
imaging. 1863
1864
A quality control program can reduce patient dose while optimizing diagnostic quality 1865
images. Figure 5.2, which comes from a study examining implementation of a digital QC 1866
program in private dental offices, demonstrates this well. 1867
1868
5.2.5 Quality Control for CBCT 1869
1870
Facilities utilizing CBCT imaging should follow the imaging equipment manufacturer’s specific 1871
instructions for quality control. CBCT manufacturers are required by the Federal Performance 1872
Standard [21 CFR 1020.33(c)(3)(d)] to provide a CBCT QC manual and appropriate phantom 1873
that evaluates specified elements of image quality. If a CBCT system has been installed without 1874
such a quality assurance manual and phantom, the dental practitioner or administrator should 1875
contact the CBCT manufacturer to obtain the required QC manual and phantom. Both the QC 1876
manual and phantom are essential elements of the QC program. A typical QC phantom for dental 1877
CBCT systems is shown in Figure 5.3 (some phantoms are available with software to analyze the 1878
CBCT QC images). 1879
1880
NCRP SC 4-5 Draft March 16, 2016
82
1881
1882
Fig. 5.2. Distribution of skin exposures before and after quality control (adapted from Walker 1883
et al., 2014). The average skin exposure is substantially reduced after a quality control program 1884
is implemented. 1885
1886
For further detail, the reader is referred to Appendix B. 1887
1888
NCRP SC 4-5 Draft March 16, 2016
83
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
Fig. 5.3. A typical dental CBCT phantom for quality measurements, constructed of tissue-1899
equivalent plastic or similar material, and with imaging test objects embedded internally. It is 1900
placed in the machine where the patient’s head would be and then exposed to measure the 1901
various characteristics of the acquired volume. 1902
1903
NCRP SC 4-5 Draft March 16, 2016
84
1904
5.2.6 Quality Control for Image Displays 1905
1906
Since digital radiographs are viewed on a computer display, the display must be calibrated 1907
and evaluated. Digital radiographs should be viewed with the center of the display positioned 1908
slightly below eye level. Subdued lighting should be used and every effort should be made to 1909
eliminate glare and reflections from extraneous sources of light such as room lights, view boxes, 1910
and windows. 1911
1912
It is essential that the computer display used to view digital dental images be properly 1913
calibrated in terms of brightness and contrast. The Society of Motion Picture and Television 1914
Engineers (SMPTE) test pattern (Figure 5.4) is almost universally available in the medical 1915
imaging community for this purpose. This pattern should be available on the digital imaging 1916
system, i.e., stored on the computer hard drive. If not, the vendor or manufacturer should be able 1917
to provide a copy. It is also readily available on the internet. 1918
1919
The brightness and contrast controls are adjusted to obtain a display image similar to those in 1920
Figures 5.2. Of particular importance are the 0 % and 95 % patches which are inset in the 5 % 1921
and 100 % squares of the test pattern. Both of these should be visible when the window width is 1922
set to encompass the maximum pixel range for the computer system, usually 0 to 255. 1923
1924
The SMPTE pattern also provides high contrast (black and white) and low contrast resolution 1925
patterns in the center and four corners. The mid-gray cross hatch pattern can be used to measure 1926
distortion of the display from image processing software and for older cathode ray tube (CRT) 1927
displays. 1928
1929
5.2.7 Quality Control Tests and Frequency for Digital Radiography 1930
1931
Quality control tests must be carried out regularly and the results documented. Most of these 1932
tests (Table 5.2) take very little time but assure the quality of the digital radiographic images. 1933
1934
NCRP SC 4-5 Draft March 16, 2016
85
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
Fig. 5.4. Society of Motion Picture and Television Engineers (SMPTE) test pattern provides 1945
a standard image for calibration and evaluation of computer displays. Left arrow— 0 % patch in 1946
5 % square; right arrow— 95 % patch in 100 % square (Gray, 1985). 1947
1948
NCRP SC 4-5 Draft March 16, 2016
86
TABLE 5.2—Frequency of quality control tests for digital radiography. 1949
QC Task Frequency Who
X-ray machine performance:
Intraoral, panoramic, cephalometric
Not to exceed every 4 y. Annually is
ideal.
Qualified expert
X-ray machine performance: CBCT Every 1 – 2 y Qualified expert
Display Performance Quarterly Staff (using SMPTE
Test Pattern)
Evaluate images from PSP plates for
artifacts
Visually inspect CR plates with each
use
Evaluate each image for artifacts
Staff
Evaluate digital sensor images for
artifacts
Evaluate each image for artifacts Staff
Evaluate junction between cable and
sensor
Daily Staff
Phantom test PSP plate performance Every 40 exposures per plate Staff
Phantom test CCD or CMOS sensor Quarterly for each sensor Staff
1950
NCRP SC 4-5 Draft March 16, 2016
87
5.3 Infection Control 1951
1952
Dental radiologic procedures are conducted using universal precautions that prevent transfer 1953
of infectious agents among patients, operator, and office staff. All equipment and procedures 1954
should be compatible with current infection control philosophy and techniques, while still 1955
maintaining the ALARA principles. It is important that a rigorous, written infection control 1956
policy be developed and routinely applied. These practices apply especially to intraoral 1957
radiography, in which multiple projections are commonly used in a single examination. The 1958
image receptors are placed in a contaminated environment. Gloved hands of the operator who is 1959
observing universal precautions can become contaminated when placing image receptors in the 1960
mouth or removing exposed ones from the mouth. This contamination then can be easily spread, 1961
such as to the x-ray machine and to image processing equipment. Universal precautions are 1962
mandated by the Occupational Safety and Health Administration to prevent dissemination of 1963
contamination (OSHA, 2015). Details for dental imaging infection control procedures can be 1964
found in most oral and maxillofacial radiology textbooks (White and Pharoah, 2014). 1965
1966
Recommendation 52. There shall be an infection control policy to protect staff and 1967
patients that encompasses imaging equipment and procedures. 1968
1969
Recommendation 53. Imaging equipment and devices should be designed to facilitate 1970
standard infection control precautions. 1971
1972
NCRP SC 4-5 Draft March 16, 2016
88
6. Image Receptors 1973
1974
6.1 Direct Exposure X-Ray Film 1975
1976
6.1.1 General Information 1977
1978
Patient doses for intraoral film radiography have decreased dramatically since 1920 (Figure 1979
6.1). In fact, the doses today are ~1 % of that used in the early twentieth century (Richards and 1980
Colquitt, 1981). 1981
1982
Since the mid-1950s the most common image receptors for intraoral radiography in the 1983
United States has been direct exposure film of American National Standards Institute (ANSI) 1984
Speed Group D (Goren et al., 1989; Platin et al., 1998). Faster films, ANSI Speed Group E, were 1985
introduced in the early 1980s, with improved versions coming in the mid-1990s. These faster 1986
films have been widely used in Europe (Svenson and Petersson, 1995; Svenson et al., 1996). 1987
Published data show that these faster films provide for patient and staff dose reductions of up to 1988
50 %. However, early E-speed films exhibited decreased contrast and higher sensitivity to 1989
processing conditions than were found with D-speed films (Diehl et al., 1986; Thunthy and 1990
Weinberg, 1982). These problems have been corrected and presently E-speed film can be used 1991
with no degradation of diagnostic information (Conover et al., 1995; Hintze et al., 1994; 1996; 1992
Kitagawa et al., 1995; Ludlow et al., 1997; Nakfoor and Brooks, 1992; Price, 1995; Svenson 1993
et al., 1997a; Tamburus and Lavrador, 1997; Tjelmeland et al., 1998). Digital image receptors 1994
with speeds similar to or faster than E-speed film are available. Intraoral films of speed group F 1995
are commercially available, perform at the same diagnostic levels as both D- and E-speed films 1996
and are suitable for routine use (Farman and Farman, 2000; Ludlow et al., 2001; Thunthy, 2000). 1997
(One manufacturer produces an E-F-speed film. It is E-speed when hand processed and F-speed 1998
when machine processed.) In spite of the fact that use of E and F speed film was a shall 1999
statement in NCRP Report No. 145 (NCRP, 2004), the most recent study of the relative use of D 2000
and F speed films in the United States showed that 78 % of film users continue to use D-speed 2001
film (NEXT, 2015). In fact, D-speed film requires the same exposure to the patient as it did in 2002
2003
NCRP SC 4-5 Draft March 16, 2016
89
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
Fig. 6.1. Approximate relative exposures at skin entry for intraoral radiographs, 1920 to 2016
2000. Arrows indicate introduction of faster films (ANSI speed groups A, B, C, D, E and F, as 2017
indicated). The solid line represents smoothed best fit to the data points, illustrating the 2018
exponential downward trend of exposures over time. The exposure required for F-speed film is 2019
~1 % of that required for the first dental films, and 50 % of that required for D-speed film 2020
(Farman and Farman, 2000). 2021
NCRP SC 4-5 Draft March 16, 2016
90
1955 (red circle, Figure 6.1). Studies in the United Kingdom show that only a very small 2022
minority of facilities using film for intraoral imaging use D-speed film (Holroyd, 2013). 2023
2024
Film users are urged to update their techniques and technique charts as they adopt faster 2025
image receptors. It is incumbent on manufacturers to assist users in establishing new techniques. 2026
2027
Recommendation 54. Image receptors of speeds slower than ANSI Speed Group E-F 2028
film shall not be used for intraoral radiography, i.e., D-speed film shall not be used. 2029
2030
6.1.2 Equipment and Facilities 2031
2032
After exposure, radiographic film must be processed to produce a diagnostic image. The 2033
equipment and facilities which are needed to process intraoral films must be optimized in order 2034
to generate the diagnostic image. A perfectly placed and exposed film can easily be rendered 2035
nondiagnostic by poor processing. 2036
2037
6.1.2.1 Darkroom. Each darkroom should be evaluated for light leaks and safelight performance. 2038
A “coin test” is performed by placing an unexposed, unwrapped intraoral film at a normal 2039
working position and putting a coin upon it. After 2 min, the film is processed. An image of the 2040
coin indicates a problem with either light leaks or the safelight. Repeating the procedure with the 2041
safelights off will determine if the fog is due to the safelights or light from outside the darkroom. 2042
These tests are should be performed at least quarterly, and preferably monthly (White and 2043
Pharoah, 2014) or following a change in the safelight filter or bulb, or other changes to the 2044
darkroom that could affect its integrity. Direct exposure films have different spectral sensitivities 2045
from those used with screens; a safelight filter appropriate for one may not be adequate for the 2046
other. In addition, the film used with screens must be pre-exposed in the cassette to produce a 2047
uniform, mid-gray density when processed in order to carry out this test. 2048
2049
Daylight loaders are commonly used with automatic dental film processors, eliminating the 2050
need for the darkroom. These systems provide light-tight boxes attached to the processor. Each 2051
box contains a port for placing exposed films (still in their wrappers or cassettes) in the box, 2052
NCRP SC 4-5 Draft March 16, 2016
91
ports for inserting the hands so the operator may manipulate films in the box, and a viewing port 2053
through a filter similar to the safelight filter. The processor safelight filter is designed for use in a 2054
room with low-level illumination. It may be necessary to use daylight loaders only in rooms with 2055
reduced illumination. Furthermore, the daylight loader may present difficulties in infection 2056
control with intraoral film wrappers contaminated with oral fluids. Like the darkroom, the 2057
daylight loader may be evaluated for light leaks using the “coin test” (AAPM, 2015). 2058
2059
Recommendation 55. Each darkroom and daylight loader shall be evaluated for fog at 2060
initial installation, and then at least quarterly and following change of room lighting or 2061
darkroom safelight lamp or filter. 2062
2063
6.1.2.2 Storage of Radiographic Film. It is essential to protect radiographic film in storage from 2064
radiation exposure. Radiographic film used in film-screen imaging is less sensitive to direct 2065
radiation exposure today than in the past (Suleiman et al., 1995). 2066
2067
Recommendation 56. Film, including film in cassettes, shall not be exposed to excessive 2068
radiation during the period it is in storage. 2069
2070
6.1.2.3 Film Processors. Film processing is a sequence of chemical reactions that are time and 2071
temperature dependent. Processing solutions must be at the proper concentrations. Solutions that 2072
are either dilute, excessively concentrated, or contaminated will degrade the image quality. Even 2073
with proper solution concentrations and temperatures, film processing depends on a proper 2074
combination of time and temperature. Deviations from proper processing will result in films that 2075
are of reduced contrast, and are either too light or too dark. In addition, poor processing quality 2076
commonly will result in higher radiation doses to the patient as the exposure time will be 2077
increased to obtain a film dark enough to view. 2078
2079
Recommendation 57. Film shall be processed with active, properly replenished 2080
chemicals, and time-temperature control, according to manufacturers’ 2081
recommendations. 2082
2083
NCRP SC 4-5 Draft March 16, 2016
92
6.2 Screen-Film Systems 2084
2085
6.2.1 General Information 2086
2087
Extraoral exposures, such as for panoramic and cephalometric radiography, utilize light-2088
sensitive film in combination with intensifying screens within a cassette. The film sensitivity 2089
must be spectrally matched to the spectrum of light emitted from the intensifying screens. 2090
2091
The intensifying screens consist of thin layers of phosphor crystals that fluoresce when 2092
exposed to x rays. The film is exposed by light emitted by the intensifying screens. Absorption of 2093
light emitted from the intensifying screens is increased by the addition of dyes to the film 2094
emulsion. The spectrum of light most readily absorbed by the film must be matched to the 2095
spectrum of light emitted by the intensifying screens. 2096
2097
Screen-film systems are widely available with varying speed, contrast, and latitude 2098
characteristics, depending on specific imaging needs. Screen-film combinations are more 2099
sensitive to x rays than direct exposure x-ray film, thus reducing the level of exposure to the 2100
patient. Image sharpness, however, is decreased as a result of diffusion of light emitted from the 2101
intensifying screens to expose the film. 2102
2103
Rare-earth intensifying screens, used in conjunction with properly matched film, are the 2104
fastest screen-film combinations available. Rare-earth screens that emit green or blue light are 2105
more efficient at absorbing radiation that exits the patient and converting x-ray energy to light 2106
energy than the blue-emitting calcium tungstate screens. Patient exposure in panoramic and 2107
cephalometric radiography may be reduced by ~50 % using fast rare-earth versus slower calcium 2108
tungstate screen-film combinations with no significant difference in perceived diagnostic quality 2109
(Gratt et al., 1984; Kaugars and Fatouros, 1982). Use of screen-film systems with flat grain 2110
technology results in increased film speed without a loss of image sharpness. Rare-earth imaging 2111
systems using this film have been shown to be 1.3 times faster than a comparable system using 2112
conventional film emulsion technology without compromising diagnostic quality (D’Ambrosio 2113
et al., 1986; Thunthy and Weinberg, 1986; White and Pharaoh, 2014). 2114
NCRP SC 4-5 Draft March 16, 2016
93
2115
6.2.2 Equipment and Facilities 2116
2117
Equipment and facilities for screen-film systems are the same as for direct exposure film 2118
(Section 6.1.2). 2119
2120
6.2.2.1 Care of Screen-Film Systems for Film-Based Cephalometric and Film-Based Panoramic 2121
Imaging. Both cassettes and screens may acquire defects during normal use. Integrity of cassettes 2122
is determined by visual inspection and by processing of an unexposed film that has been in the 2123
cassette for at least 1 h while the cassette is exposed to normal room illumination. Light leaks 2124
from the cassette will appear as dark areas or streaks on the film. Screens are evaluated visually 2125
for surface defects such as scratches or fingerprints. Screens should be cleaned periodically, 2126
following the manufacturer’s instructions. 2127
2128
Poor screen-film contact leads to unsharpness in images. Screen-film contact and uniformity 2129
of response are best evaluated by exposing a film (in its cassette) overlaid with a piece of copper 2130
test screen. Visual inspection of the processed film for sharpness and uniformity of the image can 2131
assess performance of the imaging system. Unsharp areas will appear as darker areas on the 2132
image. This is a test the qualified expert can carry out during the periodic evaluation. 2133
2134
6.2.2.2 Screen-Film Speed Recommendations. It is important to use the fastest possible screen-2135
film combination that provides the necessary diagnostic information when acquiring panoramic 2136
and cephalometric images. 2137
2138
Recommendation 58. Screen-film systems of speeds slower than ANSI 400 shall not be 2139
used for panoramic or cephalometric imaging. Rare-earth systems shall be used. 2140
2141
NCRP SC 4-5 Draft March 16, 2016
94
6.3 Digital Imaging Systems 2142
2143
6.3.1 General Information 2144
2145
Digital radiography involves the acquisition of a digital image consisting of a two-2146
dimensional array of pixels. In direct digital radiography, the latent image is directly recorded by 2147
a suitable sensor. Receptors used in direct digital radiography are photostimulable storage 2148
phosphor plates (PSP) or solid state electronic devices containing either charge-coupled device 2149
(CCD) or complementary metal-oxide semiconductor (CMOS) technology. At times it is 2150
necessary to convert a film image into a digital image—this is referred to as indirect digital 2151
radiography. The resultant electronic image may be presented on a computer display, converted 2152
to a hard copy image, or transmitted electronically. For a historical overview of digital imaging 2153
in dentistry see Appendix C. 2154
2155
6.3.1.1 Proportion of Digital versus Film, Proportion of PSP versus CMOS-CCD. Preliminary 2156
analysis of the data from the 2015 NEXT Dental Survey shows 87 % of the sites surveyed used 2157
digital acquisitions (70 % sensors; 19 % PSP) for intraoral imaging versus 11 % for film. Of 2158
those sites using film, 78 % used D-Speed film and 22 % used F-Speed film. Only 1.2 % of all 2159
sites surveyed used rectangular collimation. 2160
2161
6.3.1.2 Advantages of Digital Imaging Compared to Film Imaging. There are numerous 2162
recognized advantages that digital-based imaging provides over film. Many of the advantages are 2163
very similar to those observed in general radiology such as the elimination of darkroom film 2164
processing, the ability to digitally manipulate images, and the ability to easily store and transmit 2165
copies of patient images. There are also advantages specific to dental radiography. 2166
2167
Recent improvements in the quality of images provided by digital-based image receptors for 2168
dental radiography have permitted the capture of dental x-ray images that provide comparable 2169
clinical value as that for film (Alkurt et al., 2007). From an image quality standpoint the benefits 2170
of digital imaging are numerous. Farman and Farman (2005) published a study of the imaging 2171
characteristics for a number of digital x-ray technologies for dentistry. Their results show a broad 2172
NCRP SC 4-5 Draft March 16, 2016
95
range of values for spatial resolution over wide exposure ranges. The majority of systems (some 2173
with more than one configuration) have spatial resolutions >10 cycles per millimeter (c mm–1). 2174
Huda (2010) reported that the human can resolve ~5 c mm–1 at 25 cm, and ~30 c mm–1 at close 2175
inspection. Therefore while film still retains a lead regarding spatial resolution (~20 c mm–1), the 2176
visualization of clinically relevant image detail using digital technology is likely now 2177
comparable to that for film under typical viewing conditions. 2178
2179
Digital images can be modified by a variety of image processing techniques ranging from 2180
simple enlargement of the image to manipulations of image characteristics such as contrast, 2181
sharpness and ransom noise. 2182
2183
The practice of x-ray imaging should include the optimization of equipment and procedures 2184
to minimize radiation dose to the patient while providing image quality that accomplishes the 2185
clinical task. Digital image receptors can provide acceptable images at patient exposures well 2186
below those for film (Section 5.1). 2187
2188
The following summarizes the advantages of digital imaging in dental radiography compared 2189
with film-based imaging: 2190
2191
acceptable image quality at reduced patient x-ray dose; 2192
post processing image manipulation including contrast, density, and edge sharpness; 2193
the ability to make measurements from the image; 2194
3D reconstruction from CBCT acquisitions; 2195
elimination of the darkroom and film processing; 2196
reduction in time spent making radiographs; 2197
space-efficient storage; 2198
teleradiology; and 2199
environmentally friendly, chemical-free imaging. 2200
2201
6.3.1.3 Potential for Dose Reductions for PSP and DR Compared with Film. Like any x-ray-2202
based imaging modality, the clinical benefits of the modality must be weighed against the 2203
NCRP SC 4-5 Draft March 16, 2016
96
associated risks. The x-ray system should be optimized to provide the required clinical benefit at 2204
the lowest possible radiation dose. Film used for dental intraoral radiography is directly exposed 2205
by the x-ray beam. Consequently, this direct film exposure results in a tenfold or greater 2206
radiation dose to the patient compared with screen-film combinations as used in panoramic and 2207
cephalometric imaging. 2208
2209
Dental film manufacturers have provided film types of several speed classes with differing 2210
image quality and dosimetric properties. A NEXT survey of dental facilities in 1999 found 2211
median patient entrance air kerma for routine bitewing films to be 1.6 mGy (maximum of 2212
5.5 mGy) for D-speed class film, and 1.2 mGy (maximum of 2.9 mGy) for E-speed class film 2213
(Moyal, 2007). Direct digital and PSP-based image receptors can provide useful clinical images 2214
at substantially lower entrance doses (Table 6.1). 2215
2216
Farman and Farman (2005), documented the ability of most tested, commercially available 2217
digital systems to provide images of acceptable image quality at lower entrance air kerma and a 2218
greater exposure latitude compared to film. This improved x-ray efficiency and the ability to 2219
digitally enhance images can allow images that might be otherwise considered to be under-2220
exposed to still provide clinical value. 2221
2222
With digital imaging systems, there is a significant potential for dose reduction compared 2223
with film-based imaging. Corresponding to the decrease in exposure time, the patient dose for 2224
PSP systems is reduced to approximately one-half or less compared to film. The main issues in 2225
digital technology are positioning errors. The size and rigidity of the image receptors, especially 2226
CCD sensors, can make them uncomfortable for the patient and difficult to accurately position 2227
compared with film packets. Combined with the ease of repeating an image, this can lead to 2228
many additional exposures and a concomitant increase in the total radiation dose to the patient, 2229
despite the reduced radiation dose per image. 2230
2231
NCRP SC 4-5 Draft March 16, 2016
97
2232
TABLE 6.1—Typical dental bitewing skin entrance dose ranges. 2233
aGray, J.E. (2015). Personal communication (DIQUAD, LLC, Steger, Illinois) 2234
bBased on 25th and 75th percentile of optimal exposure from Table II from Udupa et al. (2013). 2235
Note—Required exposure for optimal image quality varies with digital image receptor type. Table 6.1 2236
should be considered as a starting point for image quality and dose optimization. 2237
2238
Detector Type Suggested Skin Entrance Dose Ranges
(mGy)
D-speed Film 1.52 – 1.95a
E-F or F-speed Film 0.87 – 1.09a
Digital-PSP 0.52 – 1.04b
Digital- CMOS 0.44 – 0.87b
Digital- CCD 0.35 – 0.52b
NCRP SC 4-5 Draft March 16, 2016
98
Patient radiation doses for intraoral images receptors can vary widely based on several 2239
factors. Table 6.1 provides suggested exposure ranges for various detectors. It should be 2240
emphasized that the image quality and patient dose must be optimized with any detector and that 2241
the exposure ranges in Table 6.1 are merely a starting point. 2242
2243
6.3.1.4 Disadvantages and Challenges of Digital Imaging. In contrast to the advantages outlined 2244
above, digital imaging also has some disadvantages. 2245
2246
Presently, most digital image receptors tend to result in some discomfort for the patient. 2247
While patients will usually agree that no imaging device is comfortable, the flexibility of film 2248
packets compared to the rigid construction of most digital image receptors gives film the 2249
advantage with regard to patient comfort. Many sensors now come in a variety of sizes to 2250
accommodate different size patients. Digital image receptor manufacturers are addressing this 2251
issue with image receptors designed for improved patient comfort. Ergonomic ease is not limited 2252
to patient considerations. Some operators find the new digital imaging receptors challenging to 2253
handle during the x-ray examination (Annisi and Geibel, 2014). PSP digital systems offer 2254
flexible image receptors providing a level of patient comfort similar to film. These systems 2255
include a digital image processing stage prior to viewing the final radiograph. The clinical 2256
challenges of examining a patient with digital-based technology will likely improve in part as 2257
educational institutions better prepare dental students for these new technologies, and as 2258
technologies continue to evolve in response to these types of issues. Collectively, these should 2259
lead to a reduction in the number of repeat images. 2260
2261
Digital dental imaging equipment makes it difficult to see the relationship between x-ray 2262
exposure and overall image quality that is readily evident when using film. The relative broad 2263
exposure latitude provided by digital image receptors, especially PSP plates with their unique 2264
linear detector latitude (Farman and Farman, 2005), and the lack of feedback that film provided 2265
regarding over- and under-exposure can lead to patient exposures that are not optimized. Far 2266
from simple, “plug-n-play,” digital imaging systems require proper set-up at installation as well 2267
as continuous monitoring, much like conventional film-based systems. Failure to properly install 2268
NCRP SC 4-5 Draft March 16, 2016
99
and optimize these systems can lead to lower quality images and higher patient exposure, 2269
potentially higher than that required for D-speed film. 2270
2271
Recommendation 59. The dental practice should enlist the assistance from a qualified 2272
expert to ensure each new digital system is properly configured with regard to both 2273
patient dose and image quality. 2274
2275
The ease with which digital images can be captured and displayed, particularly for all to see, 2276
could motivate dental practices to acquire more images per patient than normally would be taken 2277
with film. Annisi and Geibel (2014), and Berkhout (2003) found that there was a slight but 2278
notable increase in the rate of images acquired per patient, particularly for CCD-based devices. 2279
This was mainly due to the receptor size and positioning of the image receptor. Therefore the 2280
dental practice should implement and adhere to imaging practices that minimize x-ray dose to 2281
patients to levels needed for the clinical task. 2282
2283
Regardless of the technology used to image patients, the dental practice should ensure the 2284
safe and secure storage of patient records including imaging exams. Unlike hardcopy film, 2285
digital images are merely data bits on a computer. Therefore a challenge to the digital-based 2286
dental office is to establish a routine practice for ensuring secure, long-term electronic storage of 2287
patient digital imaging data. This avoids unnecessary radiation resulting from duplicate 2288
examinations to replace images lost due to computer failure. Routine duplicate backup of patient 2289
images, stored off site, is a highly recommended practice to guard against unanticipated 2290
computer storage failure. Finally, the vulnerability of electronic records (medical or otherwise) to 2291
computer hacking mandates the implementation of secure equipment and records-keeping 2292
procedures to minimize this possibility. 2293
2294
In summary, the disadvantages of digital dental imaging include: 2295
2296
high initial cost; 2297
image receptor dimensions and rigidity can cause patient discomfort ; 2298
difficulty in maintaining infection control; 2299
NCRP SC 4-5 Draft March 16, 2016
100
maintaining secure electronic storage of patient records; 2300
ease of repeated images can motivate unnecessary retakes, resulting in increased patient 2301
radiation doses; and 2302
difficulty in identifying excessive doses, especially in the case of PSP, because 2303
unnecessarily high-dose images tend to be clinically acceptable. 2304
2305
6.3.2 Equipment and Facilities 2306
2307
Digital imaging in dentistry requires specific equipment and facilities. These include the 2308
following major components: 2309
2310
image receptors (PSP or solid-state sensor); 2311
image processor for PSP; 2312
computer systems; 2313
image display monitors; and 2314
technique charts. 2315
2316
6.3.2.1 PSP Plates. The migration to digital imaging can eliminate certain routine costs such as 2317
the purchase of film and processing chemicals. However, PSP-based image receptors have a 2318
limited lifetime of useful performance and must be periodically replaced. A limited study by 2319
Ergün et al. (2009) on a sample of PSP image receptors showed that the devices can provide 2320
clinically acceptable images over a lifetime of up to 200 exposures. However, the useful life 2321
depends on the appropriate handling of the PSP plates. Figure 6.2 shows and example of a good 2322
quality image, while Figure 6.3 shows some examples of plates that should be replaced as soon 2323
as possible. The cost of replacing PSP plates is in the range of $25 to $30 per plate. However, 2324
producing a quality image should be the priority over the cost of replacement plates. 2325
NCRP SC 4-5 Draft March 16, 2016
101
2326
2327
2328
2329
2330
2331
2332
2333
2334
Fig. 6.2. Example of good quality image of test phantom. This phantom consists of a Luxel 2335
dosimeter with an extra filter added. It is placed ~5 cm above the film or digital detector. 2336
2337
NCRP SC 4-5 Draft March 16, 2016
102
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
Fig. 6.3. Examples of damaged PSP plates. (Top left) Scratches and frayed edges; (top right) 2351
Scratches or cracked phosphor; (bottom left) Scratches, stains, and low contrast; (bottom right) 2352
Stains of phosphor plate (coffee, soda?). 2353
2354
2355
NCRP SC 4-5 Draft March 16, 2016
103
Photostimulable storage phosphor (PSP) image receptors function similar to conventional 2356
computed radiography (CR) devices in medicine. The receptor consists of a thin imaging plate 2357
encapsulated in a protective, light-proof cover. The receptor is pliable, and, therefore, provides 2358
the patient with a similar experience as with traditional film. Once the x-ray exposure is made, 2359
the plate is read. In this reading process the plate is scanned with a laser and light is emitted in 2360
proportion to the x-ray exposure of the receptor surface, with the amount of light being converted 2361
into pixel intensity values. This image is then stored as a digital image and presented on a 2362
computer display. Unlike direct digital-based technologies where the image is available near-2363
instantly, PSP-based imaging requires a scanning stage before the image can be viewed. 2364
2365
Early PSP devices were capable of spatial resolution of ~6 c mm–1, compared to ~20 c mm–1 2366
for film when exposed and processed properly. One study also found that the latent image on the 2367
PSP plate will degrade if the plate is not processed soon after the exam. Newer PSP-based 2368
systems are capable of resolutions of ~11 c mm–1 or better. Interestingly, even early PSP devices 2369
were shown to have better low-contrast performance than film (Figure 6.4) and to have better 2370
exposure latitude than CMOS based systems (Farman and Farman, 2005) and film (White and 2371
Pharoah, 2014). 2372
2373
There are a number of benefits to PSP-based imaging for dental applications, particularly for 2374
intraoral imaging. The PSP plates are very similar in size and flexibility to film packets and do 2375
not require wires, providing patients an experience similar to film. Although a PSP image reader 2376
is required, the image plates are much less costly to replace than the direct digital image 2377
receptors, and the need for chemicals and film handling facilities (e.g., darkroom) are eliminated, 2378
although a PSP plate scanner and a low light level room are needed for handling the PSP plates. 2379
Sizes of PSP plates available for routine imaging include Size 0 (~35 ・ 22 mm) up to Size 4 2380
(~76 ・ 57 mm). Sizes suitable for cephalometric, panoramic, and temporomandibular joint 2381
(TMJ) imaging are also available. 2382
2383
NCRP SC 4-5 Draft March 16, 2016
104
2384
2385
2386
2387
2388
2389
2390
Fig. 6.4. Images of a test phantom showing differences in contrast between a digital image 2391
(left) and film image (right). Smaller inset darker gray area in circle (upper right) is a low 2392
contrast area which is visible in the digital image but not visible in the film image. Likewise, 2393
light gray linear structures are visible on the left and barely visible on the right. 2394
2395
2396
NCRP SC 4-5 Draft March 16, 2016
105
6.3.2.2 Solid State Receptors. Unlike PSP-based imaging technology where the latent image is 2397
digitized during the storage plate readout process, the direct digital image receptors for dental 2398
radiography are digitized immediately after exposure within the image receptor, and images are 2399
available almost immediately after the exposure is made. The active receptor layer in direct 2400
digital image receptors are CMOS-based (complementary metal oxide semi-conductor) or CCD-2401
based (charge-coupled device). Early receptor devices provided only a wired connection for data 2402
transfer to a computer for processing and eventual display. Newer systems are now capable of 2403
wireless transmission of image data. Direct digital image receptors are rigid; therefore patients 2404
may not tolerate them as readily as they might with conventional film packets or PSP image 2405
receptors. Aside from some potential patient discomfort, a benefit from direct digital imaging is 2406
the near-instant availability of clinical images. Similar to PSP-based systems, direct digital-based 2407
image capture provides all the benefits of electronic image processing and display, archiving, 2408
and communications of images. 2409
2410
There are a number of benefits to CCD- and CMOS-based imaging for dental applications. In 2411
comparison to film, solid state digital receptors have a much wider dynamic range and are 2412
partially decoupled from the characteristics of the entering x-ray beam. Software applications 2413
allow manipulation of the displayed image to rescue nondiagnostic raw images, thus avoiding re-2414
exposure of the patient. An underexposed receptor image can be manipulated to improve contrast 2415
and density; however, such manipulation will lose fine detail. Conversely, an overexposed 2416
receptor image will yield useful information with post-processing, at the expense of 2417
unnecessarily overexposing the patient (in this case, post-processing is comparable to the 2418
overexposure and underdevelopment of film). 2419
2420
Solid state detectors are subject to damage and other issues associated with electronic 2421
imaging. Some examples detectors that should be replaced are shown in Figure 6.5. 2422
2423
2424
NCRP SC 4-5 Draft March 16, 2016
106
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
Fig. 6.5. Examples of solid state detectors with problems degrading image quality. (Top left) 2436
honey-combed background can be eliminated by appropriate subtraction of flat-field image. This 2437
detector also shows a chip on left, a line across the detector, and a light, cone-shaped area. (Top 2438
right) residual latent image from a high density object (step wedge) due to failure to erase or 2439
clear the sensor image before acquiring the next image. (Bottom left) background pattern of 2440
unknown origin. (Bottom right) pattern caused by short in the cord connecting the detector to the 2441
computer (courtesy of W.D. McDavid and J.E. Gray). 2442
2443
NCRP SC 4-5 Draft March 16, 2016
107
2444
6.3.2.3 Converting from Film to Digital Imaging—Potential Dose Reduction. Digital radiography 2445
offers advantages to the dentist and ancillary staff. The image is available almost instantly; there 2446
is no need for a darkroom or film processing; images can be stored and retrieved digitally; and 2447
radiation dose reductions on the order of 40 to 70 %, or more, are possible compared to film 2448
radiography (Table 6.1). However, the ease and speed of acquisition and viewing can lead to 2449
unnecessary re-exposures. In addition, post-processing image manipulation can lead to 2450
inappropriate radiation doses to patients and less than ideal, or even nondiagnostic, images; this 2451
is especially true with PSP plates where inadvertent overexposure is easily done. These two 2452
practice behaviors can lead to systematic overexposures to the patients. 2453
2454
Recommendation 60. When converting from film to digital imaging, the facility shall 2455
make proper exposure technique (time) adjustments, commensurate with the digital 2456
imaging system. 2457
2458
6.3.2.4 Technique Charts. Another method to ensure image quality, while reducing operator 2459
exposure and providing for patient dose optimization is the utilization of size-based technique 2460
charts or protocols. Technique charts should be unique to each x-ray unit and image receptor 2461
combination displaying suggested technique settings for a specific anatomical area along with 2462
the patient size (small, medium, large) for adults and children. These should be developed for 2463
both intraoral and extraoral imaging, listing the exam, patient size, along with adult and pediatric 2464
settings, and image receptor (film type, digital image receptor). Technique charts should be 2465
posted near the control panel where the technique is adjusted for each x-ray unit. With digital 2466
workstations, technique charts may also be readily placed on the workstation’s desktop. When 2467
the x-ray unit is replaced, or an image receptor is added, the chart must be updated. An example 2468
of a technique chart is shown in Figure 6.6. 2469
2470
6.3.2.5 Clinical Image Display Monitors for Digital Imaging. An imaging display is a very 2471
important component in digital radiology. Most image display monitors are liquid crystal 2472
displays (LCD); newer LCD displays have light emitting diode (LED) backlights. Organic light 2473
NCRP SC 4-5 Draft March 16, 2016
108
Sample Technique Chart 2474
Brand X Unit, Room 2 2475
Brand Y Digital Image Receptor, Size 2 2476
70 kVp, 7 mA 2477
Exposure Time, sec
Child Adult
(standard)
Adult
(large)
Maxillary
Incisor or Canine 0.05 0.07 0.09
Premolar 0.06 0.09 0.12
Molar 0.07 0.11 0.14
Mandibular
Incisor or Canine 0.04 0.06 0.08
Premolar 0.04 0.06 0.08
Molar 0.05 0.07 0.09
Bitewing
Anterior 0.04 0.06 0.08
Posterior 0.07 0.07 0.09
Occlusal
0.08 0.12 0.16
2478
Fig. 6.6. Sample technique chart indicating the x-ray unit, image receptor, kilovoltage, 2479
milliampere, and exposure time for various projections for adult patients of two sizes and for a 2480
pediatric patient. 2481
2482
2483
NCRP SC 4-5 Draft March 16, 2016
109
emitting diode (OLED) displays may soon be commercially available.. Image displays may be 2484
monochrome or color. 2485
2486
The amount of ambient light in an interpretation room has a significant impact on image 2487
interpretation; the ambient light levels must be controlled and only indirect lighting allowed. 2488
2489
Medical grade image displays have several advantages over off-the-shelf display monitors, 2490
including the capability of adjusting the brightness to compensate for variations in the intensity 2491
of the back light and ambient room light. If commercial off the shelf displays are used, it is 2492
important that periodic calibration be performed to maintain optimal performance (Section 2493
5.2.6). A poor display quality may lead to inaccurate diagnosis and may result in inappropriate 2494
treatment for a patient. 2495
2496
NCRP SC 4-5 Draft March 16, 2016
110
7. Intraoral Dental Imaging 2497
2498
7.1 General Considerations 2499
2500
7.1.1 Beam Energy 2501
2502
Intraoral dental x-ray machines have been marketed with peak x-ray tube operating 2503
potentials ranging from 40 to >100 kVp. Units operating below 60 kVp result in higher than 2504
necessary radiation doses to the patient (AAPM, 2015). 2505
2506
The operating potentials for intra-oral imaging equipment should be lower than for other 2507
dental imaging because the goal is to deposit x-ray photons into an imaging receptor just behind 2508
the teeth instead of an image receptor on the opposite side of the patient’s head. Published data 2509
show no relationship between peak operating potential and effective dose to the patient with 2510
beam energies ranging from 70 to 90 kVp (Gibbs et al., 1988a). These data apply specifically to 2511
half-wave rectified intraoral dental x-ray machines. Similar beam energy spectra are produced by 2512
modern constant-potential machines operating up to 10 kV below the kilovoltage of full-wave or 2513
half-wave rectified machines. There is little to be gained from operating potentials higher than 2514
80 kVp. In fact, higher kilovoltages decrease the inherent contrast in the images and are, 2515
therefore, detrimental to diagnostic image quality. Most contemporary intraoral x-ray units 2516
operate at a fixed operating potential in the 60 to 70 kV range. 2517
2518
Recommendation 61. The operating potentials of intraoral dental x-ray units shall not 2519
be <60 kVp and should not be >80 kVp. 2520
2521
7.1.2 Position-Indicating Devices 2522
2523
A position-indicating device (PID) provides a visual aid to the operator in aligning the x-ray 2524
beam properly to the structure(s) being imaged. Position-indicating devices are attached to the x-2525
ray tube head, are open-ended, and may be combined with higher atomic number materials that 2526
absorb scattered radiation arising from the patient, collimator, and filter. 2527
NCRP SC 4-5 Draft March 16, 2016
111
2528
Recommendation 62. Position-indicating devices shall be open-ended devices and 2529
should provide attenuation of scattered radiation arising from the patient, collimator or 2530
filter. 2531
2532
The length of the position-indicating device determines the source-to-skin distance. Short 2533
source-to-skin distances (or source-to-image receptor distances) produce unfavorable dose 2534
distributions (van Aken and van der Linden, 1966; White and Pharoah, 2014). They will degrade 2535
the sharpness of the images, and also produce excessive magnification or distortion of the image, 2536
sometimes limiting anatomic coverage. 2537
2538
Recommendation 63. Source-to-skin distance for intraoral radiography shall be at least 2539
20 cm and preferably should be at least 30 cm. 2540
2541
7.1.3 Rectangular Collimation 2542
2543
All medical and dental diagnostic x-ray procedures, except intraoral radiography, must be 2544
performed with the beam collimated to the area of clinical interest; in no case can it be larger 2545
than the image receptor (FDA, 2015). Positive beam-receptor alignment is required to ensure that 2546
all exposed tissue is recorded on the image. However, requirements and recommendations to 2547
date have permitted circular beams for intraoral radiography whose area, measured in the plane 2548
of the receptor, may be up to three times the area of a size 2 receptor, and four to five times the 2549
area of a size 0 receptor. Rectangular collimation of the beam to the size of the image receptor 2550
reduces the tissue volume exposed, especially that of the more sensitive parotid and thyroid 2551
gland tissues. This would reduce the effective dose to the patient by a factor of four to five, while 2552
simultaneously improving image contrast and overall diagnostic quality by reducing the amount 2553
of scattered radiation (Cederberg et al., 1997; Dauer et al., 2014; Freeman and Brand, 1994; 2554
Gibbs, 2000; Gibbs et al., 1988; Underhill et al., 1988; White and Pharoah, 2014). 2555
2556
Due to the close tolerances between the x-ray beam and receptor sizes, it may be necessary to 2557
use a positioning device to assure complete coverage of the image receptor by the x-ray beam. A 2558
NCRP SC 4-5 Draft March 16, 2016
112
variety of types, known as positioning devices, paralleling devices, or film or image receptor 2559
holders, are available. Rectangular collimation is recommended by the American Dental 2560
Association, the Food and Drug Administration, and the National Council on Radiation 2561
Protection and Measurement (FDA/ADA, 2015a; 2015b; NCRP, 2004). 2562
2563
Rectangular collimators may be attached either to the position-indicating device or may be a 2564
part of the receptor-holding device. Receptor-holding devices are used to both stabilize intraoral 2565
image receptors in the mouth, and help align the position-indicating device on the x-ray tube 2566
head. Receptor-holding devices thus reduce artifacts from motion, misalignment, or other 2567
distortions while making radiographs. Receptor-holding devices should be used whenever 2568
possible. 2569
2570
It should be noted that ~50 % of the dental facilities in Great Britain use rectangular 2571
collimation (Holroyd, 2013).2 Most academic institutions in the United States teach this 2572
technique but the proportion of dentists using rectangular collimation is much lower than in 2573
Great Britain, i.e., on the order of only 15 % (Farris and Spelic, 2015). 2574
2575
Anatomy or the inability of occasional specific patients to cooperate, including some 2576
children, may make rectangular collimation and beam-receptor alignment awkward or 2577
impossible for some projections. The rectangular collimation requirement may be relaxed in 2578
these rare cases. 2579
2580
The amount of the patient’s anatomy exposed to radiation with circular collimation is shown 2581
in Figures 7.1, 7.2, and 7.3. Figure 7.2 also shows that a significant amount of radiation exits the 2582
patient’s head on the side opposite the x-ray tube. It should be noted that not all rectangular 2583
collimators produce the same size x-ray field at the skin surface. Collimators which attach to the 2584
end of existing round position indicating devices will provide smaller fields with longer position 2585
indicating device length. Some commercial rectangular collimators produce inherently larger 2586
2587
2 Gray, J.E. (2015). Personal communication (DIQUAD, LLC, Steger, Illinois)
NCRP SC 4-5 Draft March 16, 2016
113
2588
2589
2590
Fig. 7.1. (a) This image shows the entry and exit exposed tissue volumes with round 2591
collimation (above) versus rectangular collimation (below). (b) The area of the primary beam 2592
exiting the round PID is three times greater than the area of a typical size 2 dental film. Thus, 2593
two-thirds of the primary beam without rectangular collimation is not used to create an image 2594
and is an unnecessary radiation exposure to the patient. Thus, the exposed volume is significantly 2595
reduced when rectangular collimation is used (adapted from White and Pharoah, 2014.) 2596
2597
a. b.
NCRP SC 4-5 Draft March 16, 2016
114
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
Fig. 7.2. This image was created by holding a rare-earth screen-film cassette at the exit side 2608
of a patient’s head. The film packet contained a lead foil and one Size 2 intraoral film, shown at 2609
the left. It is clear that the film packet absorbs only a small portion of the x-ray beam and that a 2610
large volume of the patient is exposed to radiation when a rectangular collimator is not used. 2611
This also provides an indication of the unnecessary amount of radiation exiting the patient on the 2612
side opposite the x-ray tube (images courtesy of J.E. Gray) 2613
2614
NCRP SC 4-5 Draft March 16, 2016
115
2615
2616
2617
2618
2619
2620
2621
2622
2623
Fig. 7.3. Radiation fields at entry using round collimation versus rectangular collimation 2624
superimposed over a line drawing of a panoramic image. The exposed tissue area and resulting 2625
scatter are significantly reduced when rectangular collimation is used. 2626
2627
NCRP SC 4-5 Draft March 16, 2016
116
radiation fields leading to less dose reduction in comparison with alternative rectangular 2628
collimators (Johnson et al. 2014). 2629
2630
Recommendation 64. Rectangular collimation of the x-ray beam shall be used routinely 2631
for periapical and bitewing radiography, and should be used for occlusal radiography 2632
when imaging children with size 2 receptors. 2633
2634
7.1.4 Patient Restraint 2635
2636
It may be necessary, in a limited number of cases, that uncooperative patients be restrained 2637
during exposure or that the image receptor be held in place by hand. A member of the patient’s 2638
family (or other caregiver) should provide this restraint or receptor retention. 2639
2640
Recommendation 65. Occupationally-exposed personnel should not routinely restrain 2641
uncooperative patients and shall not hold the image receptor in place during an x-ray 2642
exposure. 2643
2644
Recommendation 66. Comforters and caregivers who restrain patients or hold image 2645
receptors during exposure shall be provided with shielding, e.g., radiation protective 2646
aprons, and should hold the film holding device. No unshielded body part of the person 2647
restraining the patient shall be in the primary beam. 2648
2649
7.1.5 Diagnostic Reference Levels and Achievable Doses 2650
2651
For intraoral radiography, most published DRLs and ADs are based upon entrance air kerma 2652
(Hart et al. 2012; NCRP, 2012b). NCRP Report No. 172 (NCRP, 2012b) recommends for 2653
intraoral bitewing and periapical radiography a DRL of 1.6 mGy entrance air kerma, which was 2654
the 75th percentile value for E-speed film in the 1999 NEXT dental survey (NCRP, 2012). NCRP 2655
Report No. 172 also recommends an AD of 1.2 mGy; this was the median dose for E-F film in a 2656
State of Michigan survey (LARA, 2015). NCRP Report No. 172 notes, “It is recognized, and 2657
intended, that meeting this standard will most likely require dentists in the United States who use 2658
NCRP SC 4-5 Draft March 16, 2016
117
D-speed film to convert to E-F- or F-speed film.” Most digital image receptors should produce 2659
adequate images at entrance air kermas well below these DRLs and Ads, as shown by Table 6.1. 2660
2661
7.1.6 Best Practices 2662
2663
Best practices in intraoral imaging are easily and inexpensively attained with commercially 2664
available equipment with three simple steps: 2665
2666
1. using E-F- or F-speed films reduces the effective dose per image by 50 % or more 2667
compared to D-speed film; 2668
2. using digital image receptors reduces the effective dose per image by 50 to 75 % 2669
compared to D-speed film; 2670
3. using rectangular collimation reduces the effective dose per image by a factor of three to 2671
five, depending on receptor size, compared to round collimation. 2672
2673
Table 7.1 shows the potential for dose reductions by modifying receptor speed and collimation 2674
type. It is clear that simple changes can reduce patient effective dose by as much as 90 %, i.e., 2675
the patient is receiving only 10 % of the effective dose compared to the original technique! 2676
2677
In addition to the significant dose reductions from the use of the fastest receptors and 2678
rectangular collimation, thyroid shielding provides additional protection, especially in children, 2679
where the thyroid is more sensitive to radiation carcinogenesis and is higher in the neck. 2680
2681
7.1.7 FDA Clearance of Dental Imaging Equipment 2682
2683
X-ray units and digital imaging systems used in dental radiography must be cleared by FDA. 2684
The Internet allows purchasing such equipment from suppliers outside of the United States who 2685
may be providing items that have not been cleared by the FDA (Section 10.1). 2686
2687
NCRP SC 4-5 Draft March 16, 2016
118
TABLE 7.1—Effective doses for intraoral dental radiographic views.a 2688
Technique Effective Dose (µSv)
FMXb with D-speed film and round collimation 388
FMX with PSP or F-speed film and round collimation 171
FMX with CCD and round collimation (estimated)c 85
FMX with PSP or F-speed film and rectangular collimation 35
FMX with CCD and rectangular collimation (estimated)c 17
Two BWs with PSP or F-speed film and rectangular collimation 5
2689
a Adapted from Ludlow and Ivanovic (2008). 2690
bFMX = full mouth series = consists of 16 to 20 individual intraoral images 2691
c White and Pharoah (2014). 2692
2693
NCRP SC 4-5 Draft March 16, 2016
119
7.2 Conventional X-Ray Systems (Wall Mounted and Portable) 2694
2695
7.2.1 General Information 2696
2697
Intraoral dental x-ray sources are available in three different configurations. The x-ray source 2698
may be attached to an immovable fixture to the wall or ceiling of the operatory, a mobile unit 2699
supported by a mechanical stand on wheels, or a hand-held device not supported by any 2700
mechanical fixture (Section 7.3). Conventional wall- or ceiling-mounted dental x-ray sources are 2701
the most common type of dental x-ray units. 2702
2703
7.2.2 Equipment and Facilities 2704
2705
The wall- or ceiling-mounted x-ray units should have the following components: a control 2706
timer unit mounted to the wall or connected by a retractable coiled cord and an articulating arm 2707
that connects the x-ray tube to the wall or ceiling fixture. The control unit provides options to 2708
select kilovoltage and milliamperage (if these are not fixed), and exposure time. 2709
2710
The control unit shall provide a visual and audible signal during the emission of x radiation. 2711
The x-ray exposure shall be controlled by a dead man’s switch, i.e., the exposure must be 2712
terminated immediately on release of the switch. If the control unit is for a wall or ceiling 2713
mounted x-ray tube, the switch should be positioned behind a barrier so that the operator must 2714
stay behind the barrier during the exposure, i.e., the exposure switch must be at least 1 m from 2715
any outside edge of the barrier. If the system is a mobile x-ray unit, the control unit must be 2716
connected with a retractable cord and the working length of the cord shall be at least 2 m. 2717
2718
Although a wall- or ceiling-mounted unit is preferred, there may be circumstances where 2719
a mobile x-ray unit may be used. The advantage of such units are use in dental operatories that 2720
do not have x-ray units, operating and emergency rooms, or in temporary clinical facilities. A 2721
mobile unit shall have the same safety features as a wall- or ceiling-mounted unit. 2722
2723
NCRP SC 4-5 Draft March 16, 2016
120
Recommendation 67. The stand of a mobile unit shall provide adequate support to the 2724
x-ray tube during travel and when the articulating arm is fully extended, and during x-2725
ray exposure. The wheels or the casters shall be equipped with a foot brake to prevent 2726
motion of the unit during exposure. 2727
2728
There are circumstances, such as intra-procedure imaging in an operating room or images 2729
acquired on children who have to be seated in their parent’s lap where it is not reasonable to have 2730
all persons cleared from the area during x-ray exposures. In such instances, the distance 2731
recommendations concerning positioning of the operator should be observed. 2732
2733
Recommendation 68. Only the patient and operator shall be in the area during an 2734
exposure unless special circumstances do not allow this. 2735
2736
7.2.2.1 Protection of the Operator and Shielding. Guidance for protection of the operator and 2737
shielding are in Section 4.5 and Appendix D. 2738
2739
7.2.2.2 Tube Head Positional Stability. The articulated arm that supports the x-ray tube head 2740
must be capable of achieving any position and angulation required for intraoral radiography, and 2741
maintaining it until the exposure is complete. 2742
2743
Recommendation 69. The tube head shall achieve a stable position, free of drift and 2744
oscillation, within 1 s after its release at the desired operating position. Drift during that 2745
1 s shall be no greater than 0.5 cm. 2746
2747
7.2.2.3 Position-indicating Devices. The description and recommendations governing 2748
collimation and tube length of position-indicating devices are covered in Section 7.1.2. 2749
2750
7.2.2.4 Rectangular Collimation. The description and recommendations governing rectangular 2751
collimation are covered in Section 7.1.3. 2752
NCRP SC 4-5 Draft March 16, 2016
121
2753
7.3 Hand-Held X-Ray Systems 2754
2755
7.3.1 General Information 2756
2757
Recent developments in x-ray sources for intra-oral dentistry have included systems that are 2758
designed to be held by the operator during use. 2759
2760
Optimal use of hand-held dental x-ray sources in intra-oral imaging requires adherence of 2761
equipment to certain design principles beyond those of wall-mounted systems. Traditional 2762
methods of shielding, including the utilization of fixed barriers and maximizing the source to 2763
operator distance, are not applicable to sources that are designed to be handheld. Indeed, the 2764
requirement that the operator never hold the x-ray source does not apply to devices that are 2765
designed to be hand-held. In these cases, due to the proximity of the operator to the x-ray source, 2766
increased radiation risks require additional design considerations. While the recommendations 2767
below are specific to hand-held equipment, other applicable design considerations such as 2768
Federal performance standards, and international standards (IEC, 2012) must still be observed. In 2769
particular, leakage radiation and backscatter radiation potentially pose a greater risk to the 2770
operator when using a hand-held x-ray source because the operator must be near the device for 2771
operation. In order to mitigate these risks, additional shielding is incorporated into the design. 2772
2773
The first contemporary hand-held dental x-ray units were introduced in 2005 and today there 2774
are over 17,500 in use in the United States (with a growth rate of 15 % y–1). Initially the sale of 2775
these units met resistance from the regulatory community due to an old rule of thumb, sometimes 2776
in regulations and other times not, that one should never hold the x-ray tube. This is a valid rule 2777
for conventional x-ray tubes due to leakage radiation from the tubes. However, properly 2778
designed hand-held dental x-ray units are specially shielded to minimize the dose to the hands 2779
and body of the operator (Gray et al., 2012). Many papers have been published by different 2780
investigators demonstrating the safety and effectiveness of a properly shielded hand-held dental 2781
x-ray unit (Danforth, 2009; Goren, 2008; Gray et al., 2012). 2782
2783
NCRP SC 4-5 Draft March 16, 2016
122
Figure 7.5 (left) shows a hand-held dental x-ray unit, cleared by FDA for sale in the 2784
United States, that has a leaded-acrylic x-ray shield affixed to the front. This shield protects the 2785
operator’s hands and body from backscattered radiation when properly oriented. Figure 7.5 2786
(right) shows the operator using this hand-held unit to make an intraoral dental radiograph. The 2787
zone that is protected by the leaded acrylic shield can be clearly seen (the green area as opposed 2788
to the red area). 2789
2790
7.3.1.1 Advantages of Hand-Held X-Ray Units. Hand-held units can often be used in 2791
environments or circumstances where use of fixed or mobile units is either extremely 2792
cumbersome or impossible, such as operating rooms, emergency rooms, nursing homes, and 2793
remote locations, and intraoperative endodontic and pediatric dental imaging. In addition, they 2794
are quite useful in forensic investigations and in the identification of remains during a major 2795
catastrophe. The following lists some of the other features and advantages: 2796
2797
They are especially helpful in patients with special needs and in surgical operatories 2798
where traditional x-ray machines cannot be easily used during certain procedures. 2799
Hand-held x-ray units provide low radiation exposure to the operator if appropriate 2800
operating instructions are followed. The radiation dose is comparable to wall-mounted x-2801
ray machines. 2802
They are capable of producing sharp images even with mild operator movement. 2803
They are easy to operate and position. 2804
The quality of the radiographs made from hand-held devices is comparable to traditional 2805
wall-mounted devices. 2806
One hand-held unit can be shared between two or more rooms. 2807
2808
7.3.1.2 Disadvantages of Hand-Held X-ray Units. There are disadvantages to hand-held x-ray 2809
units. Some states may impose restrictions on their use. Some can be operated without a 2810
backscatter shield (none is provided or it can be removed), which increases the radiation dose to 2811
the operator. Other potential disadvantages include: 2812
2813
NCRP SC 4-5 Draft March 16, 2016
123
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
Fig. 7.5. A hand-held unit cleared by FDA for sale in the United States. (Left) unit showing 2825
leaded-acrylic shield on front. (Right) leaded-acrylic shield provides protected zone (in green) 2826
for the user compared to no protection (red-to-pink). In an actual patient image acquisition, 2827
rectangular collimation would be used. In order to best illustrate the effect of the acrylic 2828
shielding, rectangular collimation was not included in this illustration. 2829
2830
NCRP SC 4-5 Draft March 16, 2016
124
2831
Misalignment between the unit and the film or receptor, especially if a beam-guiding 2832
device is not used. 2833
The operator must put down the hand-held unit down while positioning film or image 2834
receptor in the patient’s mouth, thus increasing the risk of cross-contamination. 2835
Some are more expensive than traditional x-ray units. 2836
If used incorrectly there can be increased dose to the operator. 2837
Some are heavy and can be awkward and inconvenient to use; using such a machine for a 2838
long time can cause operator fatigue. 2839
Some of the units require connection to a power source which limits their mobility. 2840
While the batteries in the units are capable of powering multiple exposures, they require 2841
an electrical source for recharging and it is possible that there might not be sufficient 2842
power for multiple exposures from a single charge, especially in remote sites. 2843
Infection control is often difficult, especially when a plastic bag is used as the barrier. 2844
Some of the units, especially those available on the Internet, are not cleared by the FDA 2845
for sale in the United States; however, such units are available in the market for purchase 2846
at very low, attractive prices. Such units may exhibit the following problems: 2847
o high leakage radiation; 2848
o no “dead-man switch”; 2849
o actual (measured) kV is far below the indicated value; 2850
o no audible signal of x-ray exposure; 2851
o poor quality components more likely to break down quickly; and 2852
o low image quality due to low x-ray output and resultant long exposure times to 2853
acquire a diagnostic image. 2854
2855
Individuals responsible for the purchase of hand-held x-ray units must be certain that the unit has 2856
been cleared by the FDA. This will be indicated by the label on the device, illustrated in 2857
Figure 10.1. 2858
2859
7.3.1.3 Safety Issues with Improper Handling of Hand-Held X-Ray Equipment. The design of 2860
hand-held x-ray equipment presents different challenges for protecting patients, operators, and 2861
NCRP SC 4-5 Draft March 16, 2016
125
the public from unnecessary radiation exposure. In particular, device positioning, weight, and 2862
security and access controls introduce additional radiation safety issues that must be considered 2863
when using hand-held x-ray equipment. 2864
2865
Many of the assumptions about positioning that are made for wall-mounted systems are not 2866
valid when using a hand-held x-ray system. While permanent installation for a wall-mounted 2867
system allows assumptions to be made about minimum distances between the x-ray equipment 2868
and members of the public, and permanent shielding to be placed between the source and other 2869
patients, these are not always true for hand-held systems. 2870
2871
There is no control for the distance between the source and members of the public for hand-2872
held x-ray systems. The operator must ensure that there is proper distance and shielding between 2873
the source and members of the public. When used in a dental facility to replace a wall-mounted 2874
system, using the hand-held system in the same location as a conventional x-ray machine will 2875
provide sufficient radiation protection for members of the public. More information is needed to 2876
develop guidelines for equipment used outside of the dental office where there is most likely 2877
inadequate shielding design. 2878
2879
The hand-held nature and weight of these systems also introduces risks due to operator 2880
fatigue from holding the device for multiple imaging exams. Operator fatigue can lead to poor 2881
positioning of the system, which can lead to poor quality radiographs and the need for repeated 2882
exposures. Additionally, fatigue could cause the operator to hold the device closer to the chest, 2883
possibly moving the backscatter shield sufficiently back to expose parts of the operators head. 2884
Thus, operators of hand-held x-ray equipment must have the physical ability to hold the system 2885
in place for all exams. This should be taken into consideration while evaluating operator 2886
workloads to minimize the need for repeat exposures to patients. 2887
2888
Recommendation 70. Operators of hand-held x-ray equipment shall have the physical 2889
ability to hold the system in place for multiple exposures. 2890
2891
NCRP SC 4-5 Draft March 16, 2016
126
Additional training is necessary for all operators of hand-held x-ray equipment to introduce 2892
them to the proper operation of these units. This training should include topics such as proper 2893
positioning with the hand-held unit, variations in positioning which improve radiation safety of 2894
staff, and safe areas relative to the leaded-acrylic shield and the necessity for its use. 2895
2896
Recommendation 71. Manufacturers should provide a training program for users of 2897
hand-held equipment to emphasize the appropriate safety and positioning aspects of 2898
their unit. 2899
2900
Many hand-held systems are designed such that the exposure button can be found intuitively 2901
by nontrained users. This benefits operators and reduces the amount of training necessary, but 2902
also increases the risk of use by a nonqualified operator, and even children. Operators and 2903
manufacturers can both take steps to mitigate this risk. 2904
2905
Methods to prevent the unauthorized use of hand-held x-ray units should be implemented, 2906
e.g., a key lock, or a software key that the operator would be required to enter before the device 2907
could be activated. In addition, an exposure counter would provide information about the total 2908
number of exposures and, along with an exposure log, would allow the practitioner to monitor 2909
the use of the equipment. 2910
2911
Recommendation 72. Operators shall store hand-held x-ray equipment such that it is 2912
not accessible to members of the public when not in use. 2913
2914
Recommendation 73. Manufacturers of hand-held x-ray equipment shall incorporate 2915
either hardware or software interlocks on their devices to prevent unauthorized use. 2916
Hardware interlocks may include physical keys or locks necessary for operation while 2917
software interlocks may include password restrictions. 2918
2919
7.3.1.4 Exception to “Never Hold the X-Ray Unit.” Traditional radiation protection 2920
recommendations instruct users to never hold the x-ray unit. The rationale behind this 2921
recommendation is that leakage radiation from the x-ray unit and backscatter radiation expose 2922
NCRP SC 4-5 Draft March 16, 2016
127
the operator to unnecessary radiation. This recommendation is both unnecessary and impractical 2923
for properly designed hand-held x-ray systems that have been FDA-cleared. Properly designed 2924
hand-held x-ray systems include sufficient shielding around the x-ray unit, and backscatter 2925
shielding to protect the operator and mitigate the traditional risks associated with holding the x-2926
ray unit. Properly designed equipment should also include identification of the areas in which it 2927
is safe for the operator to stand during exposures based on the specific protective shielding in the 2928
device design. 2929
2930
Hand-held systems that are not properly designed and not FDA-cleared present the same or 2931
greater risks as traditional x-ray systems and should not be used. More information can be found 2932
in Section 10.1.1 to determine if a particular unit is properly designed and labeled. 2933
2934
Recommendation 74. Instructions supplied with hand-held x-ray equipment shall 2935
include identification of the areas in which it is safe for the operator to stand during 2936
exposures based on the specific protective shielding in the device design. 2937
2938
7.3.2 Equipment 2939
2940
Hand-held x-ray units must include safety interlocks to prevent unauthorized exposures, a 2941
clear shield on the end of the PID to protect the operator from scattered radiation, and additional 2942
shielding to reduce the leakage radiation to the operator. Some states are promulgating specific 2943
hand-held dental radiography regulations; dentists, operators and qualified experts must know 2944
the current regulations in their localities. 2945
2946
7.3.2.1 Backscatter Shield. Since the operator is standing near the patient there is a potential for 2947
increased exposure from back-scattered radiation. 2948
2949
Recommendation 75. Hand-held x-ray devices shall include a clear, external, 2950
nonremovable, radiation protection shield containing a minimum of 0.25 mm lead 2951
equivalence between the operator and the patient to protect the operator from 2952
backscatter radiation. 2953
NCRP SC 4-5 Draft March 16, 2016
128
2954
7.3.2.2 Leakage Radiation. Some hand-held dental x-ray units fail to meet FDA standards. In 2955
February 2012, the FDA issued a Safety Communication regarding units made overseas and 2956
being sold on the Internet without FDA clearance (FDA, 2012). In June 2012, the Health 2957
Protection Agency (HPA) of the United Kingdom issued an alert regarding similar equipment 2958
and published a report of their measurements (HPA, 2012). This device was neither cleared by 2959
the FDA (Figure 10.1) nor does it carry a CE mark. In December, 2014, a similar report was 2960
published in the United States concerning yet another similar system (Mahdian et al., 2014). 2961
2962
The HPA report indicates that the unit they evaluated (Figure 7.6) had several problems 2963
including: 2964
2965
1. substantial radiation leakage from the x-ray source in the front of and behind the unit 2966
(Figure 7.7a and 7.7b); 2967
2. no shielding is provided to protect the operator from backscattered radiation (Figure 7.6); 2968
3. the operator’s hands receive a dose of 7.5 mGy for each x-ray exposure; 2969
4. exposure times were long, e.g., 3 s, which could result in motion and blurred images; and 2970
5. operator annual dose for 100 x-ray exposures per week was estimated at 40 Sv equivalent 2971
dose to the hands and 30 mSv effective dose to the body. 2972
2973
7.3.2.3 Radiation Protective Equipment and Personal Radiation. Hand-held systems with 2974
internal and backscatter shielding have been shown (Danforth, 2009; Goren, 2008; Gray et al., 2975
2012) to be effective in protecting the operator from radiation exposure. Operator exposure when 2976
using these hand-held systems according to the manufacturer’s instructions is generally 2977
comparable to the operator exposure associated with wall mounted systems. Due to the 2978
effectiveness of internal and backscatter shielding of properly designed equipment, personal 2979
protective shielding is not necessary for the operator of hand-held x-ray units. 2980
2981
NCRP SC 4-5 Draft March 16, 2016
129
2982
2983
2984
2985
2986
2987
2988
2989
2990
Fig. 7.6. Example of hand-held dental x-ray system, not cleared by FDA. This device, 2991
manufactured outside the United States, does not carry a CE mark and has not been cleared by 2992
the FDA. It is marketed under several names. (This device was sold in the United States even 2993
though it was not FDA cleared.) 2994
2995
NCRP SC 4-5 Draft March 16, 2016
130
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
Fig. 7.7. (a) Radiographic image showing the radiation from the front of a non-FDA cleared 3007
hand-held x-ray unit. In addition to the primary beam there is a substantial amount of leakage 3008
radiation also exposing the patient. (b) Radiographic image showing the radiation leaking from 3009
the back of this hand-held x-ray unit which would expose the user to unnecessary radiation 3010
(courtesy of the Health Protection Agency of the United Kingdom). 3011
3012
Primary
Leakage
a b
NCRP SC 4-5 Draft March 16, 2016
131
3013
Recommendation 76. The operator of a hand-held x-ray unit shall not be required to 3014
wear a personal radiation protective garment. 3015
3016
Likewise, there is no need for personal radiation monitoring with hand-held x-ray equipment 3017
as long as the whole-body effective dose to the operator is below 1.0 mSv y-1. It is prudent for 3018
operators to use personal monitors when initially using hand-held x-ray units (e.g., for six 3019
months) to confirm their radiation exposure levels. 3020
3021
7.3.2.4 Appropriate Use of Hand-Held X-Ray Machines in Dental Offices. Comparison to 3022
European Recommendations. The Heads of the European Radiological Protection Competent 3023
Authorities (HERCA) June, 2014 position statement on the use of hand-held x-ray equipment 3024
discourages their use except in special circumstances such as nursing homes, residential care 3025
facilities, or homes for persons with disabilities; forensic odontology; and military operations 3026
abroad without dental facilities (HERCA, 2014). The NCRP feels that the HERCA criteria are 3027
overly restrictive and that there are additional circumstances where the use of hand-held x-ray 3028
equipment may be suitable or advantageous (Section 7.3.1.1). The Committee anticipates the 3029
possibility that as hand-held x-ray equipment becomes less expensive, easier to use, and 3030
maintains or improves its safety characteristics, these units may supplant fixed or mobile x-ray 3031
equipment in general dental practice. 3032
3033
7.3.3 Position-Indicating Devices 3034
3035
The description and recommendations governing collimation of position-indicating devices 3036
are covered in Section 7.1.2 Hand-held x-ray units have built-in position indicating devices of 3037
various lengths. 3038
3039
7.3.4 Rectangular Collimation 3040
3041
Rectangular collimators are available as a part of the receptor-holding device on hand-held 3042
x-ray systems. 3043
NCRP SC 4-5 Draft March 16, 2016
132
3044
Recommendation 77. Rectangular collimation shall be used with hand-held devices 3045
whenever possible. 3046
3047
The description and recommendations that apply to rectangular collimation are covered in 3048
Section 7.1.3 3049
3050
NCRP SC 4-5 Draft March 16, 2016
133
8. Extraoral Dental Imaging 3051
3052
8.1 Panoramic 3053
3054
8.1.1 General Information 3055
3056
Panoramic dental units produce a curved-surface tomogram of the oral and maxillofacial 3057
image. The tomographic focal trough follows the curved contours of the jaws, in general 3058
extending from ear to ear and from below the chin to the lower portion of the orbits. 3059
3060
Despite the advantage of imaging the entire dentomaxillofacial anatomy in one sweep, there 3061
are inherent limitations in the anatomical representations due to the very motion necessary to 3062
produce the panoramic image. Vertical image magnification is independent of horizontal 3063
magnification. The degree of magnification varies with position in the dental arch. This image 3064
distortion varies with anatomic area in a given patient and from patient to patient using the same 3065
panoramic x-ray machine. Furthermore, repeat images of the same patient may show differing 3066
distortion because of slight differences in patient positioning. In addition, image resolution is 3067
limited by the imperfect movement of source and image receptor required for the tomographic 3068
technique. Resolution with panoramic imaging (both film and digital) is less than with intraoral 3069
imaging (film and digital, respectively), resulting in diminished diagnostic accuracy of incipient 3070
caries, beginning periapical lesions, or marginal periodontal disease (Farman, 2007; Flint et al., 3071
1998; Rumberg et al., 1996; White and Pharoah, 2014). 3072
3073
Active development of improved projection geometry, digital tomosynthesis and the use of 3074
photon-counting detectors in panoramic imaging are likely to appear soon and should improve 3075
the quality and utility of panoramic imaging in dentistry. 3076
3077
8.1.1.1 Diagnostic Reference Levels and Achievable Doses. For panoramic imaging, NCRP 3078
Report No. 172 uses the air kerma-area product as the dose metric for its recommended DRL and 3079
AD. NCRP Report No. 172 recommends a DRL of 100 mGy cm2 and an achievable dose-area 3080
product of 76 mGy cm2 (NCRP, 2012b). Both are based upon European surveys. 3081
NCRP SC 4-5 Draft March 16, 2016
134
3082
8.1.1.2 Bitewings from Digital Panoramic Machines. Numerous manufacturers of panoramic 3083
equipment have devised imaging techniques that produce an image similar to a bitewing 3084
projection. The use of these images may be indicated for patients that cannot tolerate an intraoral 3085
bitewing radiograph. Situations such as hyperactive gag reflex, trismus, or large tori are 3086
suggested as indications for the use of these “extraoral bitewings.” Currently, there is only one 3087
study comparing the diagnostic efficacy of specific panoramic bitewing technique images with 3088
intraoral images and claimed that the intraoral bitewings were superior in caries detection. The 3089
data analysis was not robust, and, therefore, the conclusions are suggestive but equivocal 3090
(Kamburog-lu et al., 2012). Further studies are needed in order to make specific 3091
recommendations on the use of panoramic bitewing programs for caries detection, and likely 3092
periodontal evaluations. 3093
3094
8.1.2 Equipment and Facilities 3095
3096
Panoramic dental units employ a stationary anode radiographic x-ray tube operating at tube 3097
peak potentials in the 70 to 100 kVp range. These systems utilize a narrow vertical collimator to 3098
produce a correspondingly narrow x-ray beam that passes through the patient. During a 3099
panoramic x-ray exposure the moving x-ray beam paints the image on the image receptor as the 3100
x-ray tube rotates around the patient. In the case of film-screen imaging, the screen-film cassette 3101
shifts during panoramic motion, resulting in exposure of the entire film. This produces a curved-3102
surface tomogram of the dentomaxillofacial structures. Panoramic x- ray beams must be no 3103
larger than the area of receptor exposed to the beam at any point in time. This area is defined by 3104
the slit collimator at the tube head. 3105
3106
Digital panoramic images can be produced by replacing the screen-film cassette with a 3107
cassette containing a photostimulable phosphor plate. Direct digital panoramic x-ray units utilize 3108
a narrow CCD or CMOS receptor array to create the familiar panoramic image. As with any 3109
digital imaging modality, digital panoramic x-ray unit displays allow the user to vary the 3110
brightness and contrast appearance of the image by adjusting window and level settings. Some 3111
NCRP SC 4-5 Draft March 16, 2016
135
direct digital panoramic units allow adjustment of the position of the image layer after the image 3112
has been acquired reducing the impact of patient positioning on image quality. 3113
3114
Recommendation 78. The x-ray beam for rotational panoramic tomography shall be 3115
collimated such that its vertical dimension is no greater than that required to expose the 3116
area of clinical interest and shall not exceed the size of the image receptor. 3117
3118
Older machines were designed for use with medium-speed calcium tungstate screen-film 3119
systems. In some cases the required reduction in x-ray output for use with high-speed rare-earth 3120
screen-film systems may only be accomplished by electronic modifications or addition of 3121
filtration at the x-ray tube head. Electronic modifications are permitted by the manufacturer if the 3122
modified device is cleared by the FDA through the 510(k) process. A manufacturer can modify 3123
an installed device in this manner. Added filtration, unless compensated by lower kilovoltage, 3124
hardens the beam spectrum, resulting in decreased image contrast. The dentist must be aware of 3125
these limitations in selecting and maintaining panoramic equipment or prescribing panoramic 3126
examinations. Otherwise, the limited diagnostic information obtained from the panoramic image 3127
may necessitate additional imaging. Periapical views alone may be adequate. 3128
3129
Recommendation 79. The fastest imaging system consistent with the imaging task 3130
(equal to or greater than ANSI 400 speed, or digital) shall be used for all panoramic 3131
radiographic projections. 3132
3133
Power for panoramic units may be an important factor. Panoramic units should not be on the 3134
same power supply as high power devices, e.g., elevators and air conditioners. Operation of other 3135
high power consuming devices can cause a fluctuation in the voltage to the panoramic unit and, 3136
hence, a fluctuation in the kilovoltage output. 3137
3138
Recommendation 80. Panoramic machines shall be on a dedicated electrical circuit. 3139
3140
NCRP SC 4-5 Draft March 16, 2016
136
8.2 Cephalometric 3141
3142
8.2.1 General Information 3143
3144
Cephalometric equipment provides for positioning (and repositioning) of the patient together 3145
with alignment of beam, subject and image receptor. The source-to-skin distance is on the order 3146
of 150 cm or more, minimizing geometric distortion (magnification) in the image. It is frequently 3147
useful for the cephalometric image to show bony anatomy of the cranial base and facial skeleton 3148
plus the soft-tissue outline of facial contours, requiring image receptors of wide latitude. 3149
Additional filtration can further enhance soft tissue contours on the same image as the bone 3150
details (Section 8.2.2). 3151
3152
8.2.1.1 Diagnostic Reference Levels and Achievable Doses. For cephalometric radiography, 3153
NCRP Report No. 172 provides DRLs and ADs for entrance air kerma and air-kerma area 3154
product, both for the lateral projection. For the DRL, the report recommends, for the entrance air 3155
kerma, 0.14 mGy and for the air-kerma area product, 26.4 mGy cm2 for children and 32.6 mGy 3156
cm2 for adults. For ADs, the report recommends for the entrance air kerma 0.09 mGy and for the 3157
air-kerma area product 14 mGy cm2 for children and 17 mGy cm2 for adults. 3158
3159
8.2.2 Equipment and Facilities 3160
3161
The area of clinical interest in cephalometric radiography is usually significantly smaller than 3162
the image receptor. Thus, collimation to the size of the image receptor does not meet the intent of 3163
restricting the beam to image only those structures of clinical interest (FDA/ADA, 2015a). The 3164
central axis of the beam is usually aligned through external auditory canals, which are positioned 3165
by the ear rods of the cephalostat. Imaging of structures superior to the superior orbital rim, 3166
posterior to occipital condyles, and inferior to the hyoid bone is clinically unnecessary. 3167
Therefore, the beam should be collimated such that these areas are shielded from exposure. Thus, 3168
the desired collimation is asymmetric, and the central axis of the beam is not centered on the 3169
image receptor. Further, it is usually desirable to image the soft-tissue facial profile along with 3170
the osseous structures of the face; this is accomplished by reducing exposure to the anterior soft 3171
NCRP SC 4-5 Draft March 16, 2016
137
tissues using filters that are placed between the x-ray source and the patient (Freedman and 3172
Matteson, 1976; Tanimoto, 1989). Placement of filters at the image receptor instead of at the x-3173
ray source does not reduce the dose to the patient and is inappropriate. 3174
3175
Recommendation 81. The fastest imaging system consistent with the imaging task 3176
(ANSI 400 speed or greater, or digital) shall be used for all cephalometric radiographic 3177
projections. 3178
3179
Recommendation 82. X-ray equipment for cephalometric radiography shall provide for 3180
asymmetric collimation to limit the beam to the area of clinical interest. 3181
3182
Recommendation 83. Filters for imaging the soft tissues of the facial profile together 3183
with the facial skeleton shall be placed between the patient and at the x-ray source 3184
rather than at the image receptor. 3185
3186
NCRP SC 4-5 Draft March 16, 2016
138
9. Cone-Beam Computed Tomography 3187
3188
3189
9.1 General Information 3190
3191
Dental cone-beam computed tomography (CBCT) has expanded the field of oral and 3192
maxillofacial imaging enhancing diagnostic information for the dental clinician through three-3193
dimensional volumetric image data of dental and maxillofacial structures (ADA 2012; Tyndall 3194
et al 2012). Since its introduction in 1997, CBCT has gained an increasing role in dentistry, 3195
transitioning from two- to three-dimensional imaging. By providing diagnostic images without 3196
magnification, distortion, superimposition, and misrepresentation of structures, CBCT imaging 3197
provides increased diagnostic accuracy, enhancing treatment outcomes. CBCT is also used by 3198
head and neck radiologists and ear-nose-throat, or otolaryngologist, physicians to assess midface, 3199
and middle and inner ear, throat, and other skull base structures (Cakli et al., 2012; Miracle and 3200
Mukherji, 2009a; 2009b). 3201
3202
The value of CBCT image data may be augmented with sophisticated software applications 3203
which enhance images and permit merging of images with complementary data sets. An example 3204
of this is the combination of CBCT images with photographic images of the teeth and soft tissues 3205
acquired with intraoral cameras. Merging of these data sets provides an accurate representation 3206
of the hard and soft tissues and their relationship to each other, enabling visualization of not only 3207
implant position, but also the final restoration. In addition, CBCT scans through computer aided 3208
design and manufacturing (CAD-CAM) technology can provide surgical guides for implant 3209
placement. Several CBCT equipment manufacturers and software vendors provide the capability 3210
of integrating 3D scans with CAD-CAM technology by CBCT impression scanning of 3211
conventional dental impressions so that crowns can be designed and milled chairside. 3212
3213
Many CBCT systems present an appearance that is similar to panoramic dental units. Indeed 3214
there are many similarities, including patient positioning, approximate imaging time, kilovoltage 3215
and milliamperage. From an imaging perspective, the most substantive difference is the 3216
availability of reconstructed images of various slice thicknesses, viewable in many planes, 3217
NCRP SC 4-5 Draft March 16, 2016
139
orientations or 3-dimensional renderings . From a safety perspective, substantial differences in 3218
the size and shape of the x-ray beam affect the dose to the patient, dose to the operator, and 3219
people who may be nearby. Median effective dose imparted by a standard CBCT examination 3220
with a medium field of view is ~107 µSv. Typical conventional panoramic doses are 20 % of this 3221
value (Ludlow et al., 2015). 3222
3223
CBCT scanners differ from conventional CT scanners [multi-detector CT (MDCT)] primarily 3224
in image data acquisition. In a conventional CT scanner, the x-ray beam emerges from the x-ray 3225
source as a flat fan beam. Data is acquired as a series of consecutive slices of the patient’s head 3226
acquired from multiple rotations of the x-ray source around the patient. In some MDCT scanners 3227
the width of the beam can be as large as 160 mm, enabling acquisition of individual organs in a 3228
single sweep. In contrast, the x-ray beam in a dental CBCT scanner diverges from the x-ray 3229
source as a cone or pyramid. Data is acquired as a series of area projections made with small 3230
angular differences as the beam rotates around the patient’s head. Scanners acquire image data 3231
(termed basis images) through a single rotation of at least 180 degrees and up to 360 degrees 3232
around the patient’s head. Images are reconstructed through algorithms, producing three-3233
dimensional images. Due to hardware differences CBCT scan acquisition times may range from 3234
10 to 70 s. Similar volume sizes may be acquired with MDCT, while decreasing acquisition 3235
times to as little as 1 s or less. The radiation dose to the patient from CBCT may be up to 10 3236
times less than that from a similar MDCT examination; however, some CBCT units and 3237
examination protocols produce doses comparable to MDCT scans (Ludlow and Ivanovic. 2008) 3238
and, in some cases, doses which may exceed those of MDCT scans (Ludlow et al., 2014). 3239
3240
Most CBCT systems employ fixed anode x-ray tubes similar to those in panoramic x-ray 3241
machines, operating in the 70 to 100 kVp range. Instead of a narrow vertical aperture, CBCT 3242
systems employ collimation that permits larger area exposures. These beam limiting devices 3243
have varying degrees of adjustment selectable by the operator. Several manufacturers provide 3244
systems with a choice of several beam sizes, allowing the operator to select both beam height 3245
and width appropriate for few teeth or the full maxillofacial region. 3246
3247
NCRP SC 4-5 Draft March 16, 2016
140
CBCT image receptors are essentially direct digital radiography receptors that employ flat 3248
panels. The larger image receptors are generally capable of collecting smaller x-ray fields of 3249
view. 3250
3251
9.1.1 Dose Comparisons for CBCT and MDCT Machines 3252
3253
Although CBCT radiation doses are usually less than those produced during MDCT, the 3254
radiation doses to tissue are usually higher than those of conventional dental radiographic 3255
modalities. The effective dose of an optimized CBCT examination is 2 to 5 % of a conventional 3256
CT of the same region, but approximately seven times greater than that from a panoramic image 3257
(Ludlow and Ivanovic, 2008). 3258
3259
Table 9.1 shows approximate effective doses from CBCT and MDCT units, operating with 3260
different fields of view. The values are averaged from wide ranges of exposures, depending on 3261
the specific units measured and the acquisition parameters. 3262
3263
Recommendation 84. CBCT should be used for cross sectional imaging as an alternative to 3264
conventional computed tomography when the radiation dose of CBCT is lower and the 3265
diagnostic yield is at least comparable. 3266
3267
Doses for CBCT devices vary widely, but median, typical protocol adult doses are ~60 µSv 3268
for small FOVs, 107 µSv for medium FOVs and 151 µSv for large FOVs (Figure 9.1). Similar 3269
patterns of increased dose with increased FOV size are seen for child phantom exposures (Figure 3270
9.2). 3271
3272
In summary, Figures 9.1 to 9.3 show that the effective dose varies by FOV size for both 3273
adults and children. Furthermore, these also show the relative contributions of bone marrow, 3274
brain, and thyroid decrease with decreasing FOV size. However, the relative contributions of 3275
salivary gland and remainder tissues increase with decreasing FOV size. 3276
3277
3278
NCRP SC 4-5 Draft March 16, 2016
141
3279
TABLE 9.1—Approximate effective doses from CBCT and MDCT examinations. 3280
Examinationa Effective Dose
(µSv)
CBCT small FOV 60
CBCT medium FOV 107
CBCT large FOV 151
MDCT mandible (isotropic voxels) 427
MDCT jaws 697
MDCT head 1,088
3281
aCBCT doses are from Ludlow et al., 2015. MDCT doses are from Tables F1 and F2 in Appendix F 3282
NCRP SC 4-5 Draft March 16, 2016
142
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
Fig. 9.1. Effective doses of typical CBCT examinations by field of view size for adult 3293
phantom exposures. Median and inter-quartile spread are shown (Ludlow et al., 2015). 3294
3295
NCRP SC 4-5 Draft March 16, 2016
143
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
Fig. 9.2. Effective doses of typical CBCT examinations by field of view size for child 3306
phantom exposures. Median and inter-quartile spread are shown (Ludlow et al., 2015). 3307
3308
3309
NCRP SC 4-5 Draft March 16, 2016
144
3310
3311
3312
3313
3314
3315
3316
3317
3318
3319
3320
Fig. 9.3. Relative organ contributions to effective dose by FOV size (Ludlow et al., 2015). 3321
3322
NCRP SC 4-5 Draft March 16, 2016
145
3323
Recommendation 85. CBCT examinations shall use the smallest field of view (FOV) and 3324
technique factors that provide the lowest dose commensurate with the clinical purpose. 3325
3326
9.1.2 Use of Simulated Bitewing, Panoramic, and Cephalometric Views from CBCT Data 3327
3328
Cephalometric images produced with conventional x-ray equipment using rare earth screens 3329
and matched film or digital technologies produce typical adult effective doses around 5 µSv. 3330
Standard panoramic doses vary for different devices, but typical adult doses are between 15 and 3331
25 µSv. 3332
3333
While bitewing projections, panoramic image layers, and cephalometric projections can be 3334
reconstructed from a CBCT image volume, low resolution and artifact from nearby metal 3335
restorations limit the usefulness of these reconstructions for diagnosis of dental caries. In 3336
addition, radiation doses are substantially greater than needed to produce conventional 3337
panoramic and cephalometric images (Table 9.2). As such, they cannot replace the use of 3338
conventional bitewing, panoramic, and cephalometric images in dental practice. 3339
3340
Table 9.2 presents patient effective doses reported in the literature for CBCT, compared with 3341
other common x-ray imaging exams. 3342
3343
Recommendation 86. CBCT examinations shall not be obtained solely for the purpose 3344
of producing simulated bitewing, panoramic, or cephalometric images. 3345
3346
9.1.3 Number of CBCTs in the United States and Growth Rate 3347
3348
The just-completed 2015 Nationwide Evaluation of X-Ray Trends (NEXT) survey examined 3349
the use of x-ray diagnostics in dentistry (Farris and Spelic, 2015). Preliminary analysis estimates 3350
there are 5,500 dental CBCT units in the United States. It also estimates 300,000 pediatric CBCT 3351
examinations annually and 3,876,000 adult and adolescent CBCT examinations annually. 3352
3353
NCRP SC 4-5 Draft March 16, 2016
146
3354
TABLE 9.2—Comparison of effective doses for CBCT. MDCT, and conventional radiographic 3355
examinations (EC, 2012). 3356
3357
3358
3359
3360
3361
3362
3363
3364
3365
3366
3367
Modality Median (µSv) Range (µSv)
CBCT, dento-alveolar 61 11 – 674
CBCT, craniofacial 87 30 – 1,073
Intraoral radiograph — <1.5
Panoramic radiograph — 2.7 – 24.3
Cephalometric radiograph — <6.0
MDCT maxillo-mandibular — 280 – 1,140
NCRP SC 4-5 Draft March 16, 2016
147
3368
CBCT in dentistry has grown rapidly over the past decade through its features of short 3369
scanning times, increased diagnostic yield relative to radiation exposure, high resolution, and 3370
geometric accuracy. A 2011 study found 15 different manufacturers offer 24 CBCT models in 3371
the United States and many more worldwide (Ludlow, 2011). This suggests an impressive 3372
continuing demand for this technology. With its increasing application in dentistry, there has 3373
been a focus to develop guidelines for its safe and effective use, along with the development of 3374
selection criteria, quality assurance programs and clinical optimization in through evidence based 3375
research. National and international groups have provided basic principles (White and Pharoah, 3376
2014), selection criteria and professional guidelines (EC, 2012) for CBCT in dentistry. Position 3377
statements (AAE/AAOMR, 2011; AAOMR, 2013; Tyndall et al., 2012) and CBCT guidance 3378
documents (EC, 2012) have been developed by dental specialty organizations. 3379
3380
9.1.4 Efforts Regarding CBCT in Europe—SEDENTEXCT and Evidence-Based Guidelines 3381
3382
The SEDENTEXCT project of the European Commission (2008 to 2011) was a widespread 3383
effort by stakeholders throughout the European Union (partnership from the United Kingdom, 3384
Greece, Romania, Belgium, Sweden, and Lithuania) to develop guidelines for the safe and 3385
effective use of cone beam CT in maxillofacial imaging. The final report, entitled Radiation 3386
Protection No 172. Cone Beam CT for Dental and Maxillofacial Radiology. Evidence-Based 3387
Guidelines was published in 2012 (EC, 2012) and contains exhaustive data and discussion on all 3388
aspects of CBCT imaging, including radiation dose and risk, basic principles of CBCT imaging, 3389
selection criteria, quality assurance, and protection and training of staff. Additionally, a CBCT 3390
quality assurance protocol and phantom were developed. The reader is referred to this robust 3391
document for further details as well as the SEDENTEXCT website www.sedentexct.eu. A 3392
comprehensive review of CBCT indications and use has been published recently (Horner et al., 3393
2015). 3394
3395
NCRP SC 4-5 Draft March 16, 2016
148
9.1.5 Patient Selection Criteria for CBCT 3396
3397
The CBCT examination is a complementary examination to, not a replacement for, two-3398
dimensional imaging modalities. Just as for other dental radiographic examinations, justification 3399
for each patient should be based on their imaging history and the diagnostic yield not achievable 3400
with the 2D modalities. The examination is justified if the anticipated diagnostic yield outweighs 3401
the risks associated with radiation (AAOMR, 2008; ADA, 2012; EADMFR, 2009; Farman and 3402
Scarfe, 2006; White, 2009). CBCT should only be used when the question for which the imaging 3403
is required cannot be answered adequately by conventional, lower dose dental radiography, 3404
applying the ALARA principle (NCRP, 2003). 3405
3406
Prior to the acquisition of a CBCT examination, a dental examination by the ordering 3407
provider should be completed, with a review of the patient’s medical history, as well as the 3408
medical and dental imaging history. Previously acquired dental and medical imaging, which falls 3409
short of yielding the necessary clinical information, may justify the need for the CBCT 3410
examination (ADA, 2012; Farman and Scarfe, 2006). The decision about the clinical indication 3411
for CBCT is the professional determination of the treating clinician. 3412
3413
Recommendation 87. CBCT shall not be used as the primary or initial imaging 3414
modality when an alternative lower dose imaging modality is adequate for the clinical 3415
purpose. 3416
3417
Some of the evidence-based specific indications for CBCT imaging follow. 3418
3419
9.1.5.1 Implants. The initial overall evaluation of a potential dental implant patient should be 3420
completed using panoramic imaging. CBCT is widely considered as the imaging modality of 3421
choice for preoperative, cross-sectional imaging of potential implant sites (Tyndall et al., 2012). 3422
CBCT demonstrates bone volume, quality or topography, and relationships to vital anatomical 3423
structures such as nerves, vessels, nasal floor, and sinus floors. Implant planning using CBCT 3424
must take into consideration the restorative process for which implants are being planned. For 3425
this reason, when treatment of multiple implant sites is being planned, radiographic guides 3426
NCRP SC 4-5 Draft March 16, 2016
149
should be considered prior to any CBCT for implant planning. This also insures that patient 3427
radiation dose is optimized when planning multiple sites. 3428
3429
CBCT may also be considered when clinical conditions suggest a need for augmentation or 3430
site development before placement of implants. CBCT should be considered if bone 3431
reconstruction and augmentation procedures have been performed. In the absence of clinical 3432
signs or symptoms, intraoral periapical imaging should be used for the postoperative assessment 3433
of implants. Panoramic radiographs may be indicated for more extensive implant therapy cases. 3434
CBCT should be considered if implant retrieval is anticipated (ADA, 2012; Almog et al., 1999; 3435
Benavides et al., 2012; Ebrahim et al., 2009; Harris et al., 2012; Tyndall and Rathore, 2008; 3436
Tyndall et al., 2012; Wang et al., 2011). 3437
3438
Use of CBCT immediately post-operatively may be indicated if the patient presents with 3439
implant mobility or altered sensation, particularly if the fixture is in the posterior mandible 3440
(Harris et al., 2012; Tyndall et al., 2012). CBCT imaging is not indicated for the periodic review 3441
of clinically asymptomatic implants. 3442
3443
9.1.5.2 Oral and Maxillofacial Surgery. Many surgical procedures involving bony components 3444
of the jaws and maxillofacial structures may benefit from CBCT. CBCT images often provide 3445
valuable information for surgical planning and follow-up. Before ordering CBCT imaging, the 3446
clinician should evaluate other imaging modalities requiring less radiation that may provide 3447
sufficient diagnostic information. Where soft tissue evaluation is essential to diagnosis and 3448
treatment planning, CBCT is inappropriate because of poor soft tissue resolution. In such 3449
circumstances, MDCT, MRI, or ultrasound are likely to be more appropriate and efficacious. 3450
3451
In treatment planning the surgical removal of third molars or other impacted teeth, 3452
conventional imaging may suggest a direct inter-relationship between the teeth and surrounding 3453
key anatomic areas such as the maxillary sinus, adjacent teeth, and mandibular nerve. Limited 3454
CBCT may be indicated for pre-surgical assessment of an impacted or unerupted tooth as an 3455
adjunct to conventional imaging (Becker et al., 2010; Neugebauer et al., 2008; Suomalainen 3456
et al., 2010; White, 2008). 3457
NCRP SC 4-5 Draft March 16, 2016
150
3458
Limited-volume, high-resolution CBCT may also be indicated for evaluation of intraosseous 3459
pathological entities when the initial imaging modality used for diagnosis and staging does not 3460
provide satisfactory three-dimensional information (Rosenberg et al., 2010; Simon et al., 2006; 3461
White, 2008). In evaluating lesions in the maxilla and mandible, intraoral or panoramic 3462
radiographs show only two dimensions of the lesion. CBCT imaging may provide additional 3463
information on the extent of the lesion, cortical expansion, internal or external calcifications, and 3464
proximity to teeth as well as other vital anatomy. In surgical planning, a lesion must be measured 3465
from different angles. CBCT measurements, when compared to the gold standard dry skull have 3466
been shown to be acceptably accurate with <1 % error (Ludlow et al., 2007; Stratemann et al., 3467
2008). 3468
3469
Initial assessment of a simple dental or jaw fracture, and in some cases complex jaw fracture, 3470
may also be achieved with periapical or panoramic radiographs. However, vertical root fracture 3471
(Wang et al., 2011) or multiple jaw fractures (Palomo and Palomo, 2009; Shintaku et al., 2009) 3472
may be better visualized with CBCT images. In such cases, CBCT may be a valid alternative 3473
imaging modality to MDCT, considering image quality and radiation dose (Tyndall, 2008; 3474
White, 2008). 3475
3476
CBCT may be utilized for pre-operative orthognathic surgical planning (Farman and Scarfe, 3477
2006). DICOM data from CBCT can be used to fabricate physical stereolithographic models or 3478
to generate virtual 3D models (O’Neil et al., 2012), which have been useful for orthognathic 3479
assessment of morphology, spatial relationship, and growth and developmental anomalies. The 3480
3D reconstructions from CBCT are useful in the diagnosing and treatment planning of facial 3481
asymmetry cases. Follow-up CBCT imaging is useful in evaluating the success of orthognathic 3482
surgery, as well as to measure the displacement of the surgical segments in all three orientations 3483
(Cevidanes et al., 2007). 3484
3485
9.1.5.3 Periodontal Indications. CBCT is not indicated for routine evaluation of the 3486
periodontium. When clinical examination and conventional imaging studies do not provide the 3487
information needed for the management of infra-bony defects and furcation lesions, limited 3488
NCRP SC 4-5 Draft March 16, 2016
151
volume, high resolution CBCT may be indicated (Tyndall et al., 2008; Vandenberghe et al., 3489
2008; Walter et al., 2010; White, 2008). In CBCT fields of view that include images of teeth, 3490
periodontal bone should be evaluated for periodontal disease. 3491
3492
9.1.5.4 Endodontic Indications. CBCT is not indicated as a standard method for demonstration of 3493
root canal anatomy. Limited volume, high resolution CBCT may be indicated when conventional 3494
intraoral imaging provides inadequate information, contradictory clinical signs and symptoms 3495
are present, evidence of inflammatory root resorption, internal resorption, suspected root 3496
fracture, combined periodontal-endodontic lesions, perforations or atypical pulp anatomy 3497
(AAE/AAOMR, 2011; 2015; Tyndall et al., 2008). In CBCT fields of view that include images 3498
of teeth, periradicular bone should be evaluated for periapical disease. 3499
3500
9.1.5.5 Temporomandibular Joint Indications. The high spatial resolution of CBCT makes it 3501
ideal for detailed evaluation of osseous changes in the temporomandibular joint. While 3502
panoramic imaging often gives a limited overview of the status of these bone components, 3503
CBCT is indicated when a more detailed examination is needed. This would be most often 3504
indicated for severity assessment of arthritides, evaluation of erosive or proliferative bone 3505
lesions, or intracapsular condylar trauma (Alexiou et al., 2009; dos Anjos Pontual et al., 2012; 3506
Librizzi et al., 2011; Palomo and Palomo, 2009). 3507
3508
CBCT is not appropriate for evaluation of internal derangements due to its poor contrast 3509
resolution and inability to demonstrate the soft tissue structures (Marques et al., 2010). 3510
3511
9.1.5.6 Caries Diagnosis Indications. CBCT is not an acceptable diagnostic examination for 3512
occlusal (Rathore et al., 2012) or proximal (Wenzel et al., 2014) carious lesions (Section 9.1.2). 3513
3514
9.1.5.7 Sinonasal Evaluation Indications. Spatial and contrast resolution of CBCT is acceptable 3515
for evaluating osseous and gross soft tissue changes of the sinusonasal complex (Tadinada, 3516
2015b; Xu et al., 2012). In particular, details of the integrity and configuration of the borders of 3517
these structures are clearly shown on CBCT images. Compared to current gold standard of 3518
sinonasal imaging by MDCT, CBCT provides substantial dose reduction (Guldner et al., 2013) . 3519
NCRP SC 4-5 Draft March 16, 2016
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3520
Compared to panoramic radiographs, CBCT provides better information about the 3521
relationship of the sinus floor to the roots of molars (Jung and Cho, 2012; Shahbazian et al., 3522
2014). Inflammatory diseases of the sinus can be evaluated with CBCT (Ritter et al., 2011). 3523
Sinusitis related to apical periodontitis can be identified with CBCT (Lu et al., 2012; Maillet 3524
et al., 2011; Shanbhag et al., 2013). However, soft tissue tumors, fluid or blood cannot be 3525
differentiated based solely on CBCT (Ritter et al., 2011). 3526
3527
9.1.5.8 Craniofacial Disorders Indications. Compared to traditional dental imaging, CBCT can 3528
provide additional information for the treatment planning and complex management of 3529
craniofacial disorders and syndromes. CBCT volume renderings allow complete representation 3530
of the altered three-dimensional anatomy that is the hallmark of most craniofacial disorders. 3531
Additionally, CBCT is useful for evaluating positions and orientations of impacted teeth, extent 3532
and involvement of bony structures with palatal or alveolar cleft, and variations of normal bony 3533
structures (Kuijpers et al., 2014). 3534
3535
9.1.5.9 Orthodontics. Children and young adolescents, who comprise the substantial majority of 3536
patients receiving orthodontic treatment, have increased sensitivity to cancer induction by 3537
radiation. Estimates range from at least two times greater sensitivity (NA/NRC, 2006; 3538
UNSCEAR, 2013) to 10 times greater than adults (NA/NRC, 2006), depending on the tissue 3539
irradiated and the age of the patient. Additionally, most orthodontic CBCT imaging, excluding 3540
small volume acquisitions for localizing impacted teeth, involves large fields of view, including 3541
structures in the skull base and neck. Thus, it is incumbent on professionals using CBCT to 3542
image children and young adolescents to be especially judicious in their use of this imaging 3543
modality. 3544
3545
The recent position paper of the AAOMR presented the following evidence-based guidelines 3546
for CBCT use in orthodontics (AAOMR, 2013): 3547
3548
1. image appropriately according to clinical condition; 3549
2. assess the radiation dose risk; 3550
NCRP SC 4-5 Draft March 16, 2016
153
3. minimize patient radiation exposure; and 3551
4. maintain professional competency in performing and interpreting CBCT studies . 3552
3553
These AAOMR guidelines are consistent with the 2012 American Dental Association (ADA) 3554
advisory statement regarding the use of CBCT in dentistry and the general principles 3555
promulgated in the joint ADA-FDA guidelines (ADA, 2015a; 2015b). However, they are less 3556
explicit than the recommendations found in the European SEDENTEXCT report (EC, 2012). 3557
The SEDENTEXCT guidelines clearly state that “CBCT examinations should not be repeated 3558
‘routinely’ on a patient without a new risk-benefit assessment having been performed, and that 3559
using CBCT for routine or screening imaging is unacceptable practice. 3560
3561
Recommendation 88. CBCT examinations shall not be used for routine or serial 3562
orthodontic imaging. 3563
3564
9.1.5.10 Obstructive Sleep Apnea. CBCT can be useful in the management of obstructive sleep 3565
apnea. CBCT volumes have been used to assess dimensional and morphologic changes in the 3566
upper airway, as well as to assess changes in these parameters after appliance or surgical therapy. 3567
While current studies suggest such efficacy of CBCT imaging, further evidence is needed to 3568
document its impact on patient outcomes (Alsufyani et al., 2013). 3569
3570
9.2 Equipment and Facilities 3571
3572
The amount of scattered radiation produced when a radiation beam is incident on the human 3573
head at a given distance depends on the kilovoltage, milliampere-seconds, and the volume of 3574
tissue irradiated. Panoramic dental radiographic units produce relatively little scatter because the 3575
beam is only ~3 ・ 100 mm at the patient's head. In CBCT systems, the x-ray beam may entirely 3576
cover the maxillofacial region and is commonly as large as 80 ・ 80 mm at the patient's head. 3577
Scattered radiation exposure at a fixed distance (e.g., 1 m) will be approximately 300 times 3578
higher for a CBCT system, compared with a panoramic x-ray system. 3579
3580
NCRP SC 4-5 Draft March 16, 2016
154
Scattered radiation will increase linearly with the workload, i.e., the total milliampere-3581
seconds used per week. Panoramic dental radiography is a well-established imaging modality, 3582
and workloads may be reliably estimated from the literature (MacDonald et al., 1983; Reid and 3583
MacDonald, 1984; Reid et al., 1993) CBCT, however, is a relatively new imaging modality and 3584
its clinical indications continue to expand. It is likely that increased efficacy of CBCT will result 3585
in continued increases in its clinical utility. As new indications for appropriate use of CBCT are 3586
added, the CBCT workload in dental clinics will increase proportionally. 3587
3588
Preliminary assessment of the data from the 2015 NEXT Survey (Farris and Spelic, 2015) 3589
show proportionately lower exposures for children compared with adults: average milliamperage 3590
for children, 6.8 mA, and for adults, 8.3 mA; scan time for children, 7.7 s, and for adults, 12.1 s. 3591
The substantial majority of examinations were performed on adults: 11.6 per week versus 1.3 per 3592
week for children. 3593
3594
Although it may be tempting to physically replace a panoramic radiographic device with a 3595
CBCT system by simply removing the old unit and installing the CBCT gantry, this method 3596
creates the potential for substantial radiation exposure to people in the vicinity of the CBCT 3597
system. Some panoramic x-ray units have been installed in dedicated, shielded dental x-ray 3598
rooms. It is not uncommon, however, to find panoramic radiographic units installed on an open 3599
space within the dental suite, often a remote corner or alcove. The small field size and resultant 3600
minimal scatter from panoramic units may permit such installations while maintaining radiation 3601
exposures to persons in the vicinity well below permissible levels. 3602
3603
However, CBCT systems placed in the location formerly occupied by a panoramic dental 3604
unit will generate substantially more scattered radiation per exam, and may not result in 3605
exposures that are ALARA. The combination of substantially greater volume of tissue irradiated 3606
and potentially much higher workload must be considered when assessing radiation safety 3607
requirements for a CBCT installation. It is preferable to install a CBCT unit in a dedicated room 3608
that meets these safety requirements. 3609
3610
NCRP SC 4-5 Draft March 16, 2016
155
Using the NEXT data of 11.6 adult CBCT examinations per week and 1.3 pediatric CBCT 3611
examinations per week, and assuming a very heavy workload and tripling these exam 3612
frequencies, the resulting number of exams would be 45 per week. Even with this estimated 3613
weekly workload, the occupational exposure would be well below the regulatory limits for a 3614
well-designed CBCT facility. However, for a poorly designed CBCT installation, exposures to 3615
the general public, office staff, and occupationally exposed personnel could potentially exceed 3616
the respective regulatory maximums. Hence, we recommend an initial radiation shielding design 3617
be performed by a qualified expert before installation of a CBCT, and that the qualified expert 3618
annually assess the radiation safety of the installation by validating the workload assumptions 3619
and recalculating exposures when indicated. 3620
3621
9.2.1 Radiation Dose Structured Report Equivalent Needed for CBCT 3622
3623
Modern medical CT units provide a DICOM radiation dose structured report that allows 3624
determination of the patient dose from individual examinations. Differences in acquisition 3625
physics and data structures between CBCT and MDCT prevent the same method of 3626
determination and require development of a new method of determination for CBCT. 3627
3628
In addition, there is presently much discussion among medical and health physicists, and 3629
radiation biologists, regarding effective dose versus dose area product as a metric for expressing 3630
dose and risk to the patient from a particular examination (NCRP, 2012b). In this report, we have 3631
elected to use effective dose because it provides units in terms of risk and because the 3632
presentation of dose and risk in the dental literature is entirely in terms of effective dose. 3633
3634
While the use of dose area product (DAP), also known as the Kerma Area Product (PKA) has 3635
been advocated as a measure of dose for CBCT units, their accuracy as a measure of risk for the 3636
small volumes acquired for dental diagnostic imaging is debatable (EC, 2012; HPA, 2010). In 3637
relating DAP to effective dose, a conversion coefficient must be used. Illustrating this problem, 3638
one study using a single CBCT unit calculated conversion coefficients for DAP to effective dose 3639
for large to small FOVs and found that a 3.8-fold range of values was required for different field 3640
sizes and anatomic locations (Kim et al., 2014). A 7.5-fold range of DAP to effective dose ratios 3641
NCRP SC 4-5 Draft March 16, 2016
156
were calculated from the adult phantom data in a recent study encompassing a large number of 3642
measurements on CBCT devices of varying beam energies (Ludlow et al., 2014). The use of 3643
volume height in the place of projection area in this study resulted in statistically improved 3644
accuracy in the estimation of effective dose but still led to a range in the conversion coefficient 3645
of 2.4-fold for adult phantom imaging. This improvement is intriguing as beam height may be 3646
easily substituted for beam area in dose calculations. While use of volume height in place of area 3647
in dose calculation warrants further investigation, it is apparent that development of universal 3648
conversion coefficients to translate simple measures of exposure to patient dose with the goal of 3649
risk estimation is problematic. In addition to Kerma Area Product or dose area product or dose 3650
height product (DHP) for different scan parameters, it would be useful for manufacturers to 3651
provide machine specific coefficients for the conversion of PKA, DAP or DHP into effective dose 3652
so that an estimate of risk associated with an examination would be available for the clinician 3653
and patient. 3654
3655
Recommendation 89. Manufacturers should develop PKA values for CBCT acquisitions 3656
and provide conversion coefficients or other dose metrics necessary for the calculation 3657
of effective dose in order to allow an estimate of risk for each acquisition. 3658
3659
9.2.2 Advantages of Pulsed Systems over Continuous Radiation Exposure Systems 3660
3661
Dental radiographic x-ray generators use transformers and other circuits to step-up the 120 3662
volts AC source provided by the utility to the kilovoltage range needed for x-ray imaging. In 3663
recent decades, dental radiographic x-ray generators have most often been designed to produce 3664
relatively continuous waveforms at a fixed milliamperage. Varying the exposure time is typically 3665
used to change the amount of radiation used to expose the patient and create the image. For ease 3666
of use and consistency, many generators display different patient sizes (pediatric, small, medium 3667
and large adult) so that the operator may select the most appropriate technique. 3668
3669
Most image receptors used in CBCT applications are unable to record x-ray exposure during 3670
the period when the image detector integrates (processes) the x-ray energy absorbed in individual 3671
receptor pixels and transfers this signal to the computer. Continued x-ray exposure during signal 3672
integration contributes to patient dose but adds nothing to image formation. To eliminate this 3673
NCRP SC 4-5 Draft March 16, 2016
157
unnecessary patient exposure, many CBCT units utilize a pulsed x-ray source, where x-ray 3674
emission is intermittently turned off during the image acquisition process. This feature can 3675
significantly reduce patient exposure when appropriately applied and is explicitly engineered 3676
into CBCT equipment. For example, a pulsed generator operating at 7 mA for 20 s may deliver 3677
substantially <140 mAs. This methodology for pulsing the x-ray beam in sequence with active 3678
pixel measurement should not be confused with half-wave rectification found in some older 3679
dental x-ray machines. Whether an x-ray generator produces continuous or pulsed x-ray beams, 3680
it is critical that the total dose be measured by the qualified expert and compared with published 3681
benchmarks to assure that patient image quality is optimized and the dose ALARA. The 3682
qualified expert should ensure that his/her measuring instrumentation is capable of capturing data 3683
from both continuous and pulsed x-ray systems. 3684
3685
9.2.3 Advantages of 180 Degree Scan versus 360 Degree Scan 3686
3687
Some newer CBCT machines have an optional acquisition mode that rotates the x-ray source 3688
and detector through a 180 degree arc rather than a 360 degree arc. This reduces the radiation 3689
dose by close to 50 % at the expense of a somewhat noisier image. However, an in vitro study on 3690
detection of artificially created TMJ bone defects (Yadav et al., 2015) showed no differences in 3691
detection efficacy between the two rotational acquisition modalities. If the results of this study 3692
are confirmed and are shown to apply to other diagnostic tasks, such as implant site dimensional 3693
measurements and precise relationships between mandibular third molar roots and mandibular 3694
canals, this could become the technique of choice in some well-defined situations to substantially 3695
reduce radiation dose while maintaining diagnostic efficacy. 3696
3697
9.2.4 Location of Equipment and Requirements for Shielding 3698
3699
Requirements for equipment location and shielding for CBCT facilities are based upon CT 3700
requirements as promulgated in NCRP Report No. 147 (NCRP, 2004a). There are special 3701
considerations for CBCT operation, based on machine location, machine settings, imaging 3702
geometry, position of the patient, and workload. These issues are dealt with in general terms in 3703
Sections 4.1.1 and 4.5.1, and are given in greater detail in Appendix D. 3704
NCRP SC 4-5 Draft March 16, 2016
158
10. Administration and Education 3705
3706
10.1 Administrative and Regulatory Considerations 3707
3708
Regulatory, accreditation, and professional organizations provide the oversight and guidance 3709
needed to meet accepted image quality standards, safety standards, and standards of care. The 3710
requirements of such bodies are accomplished through the practitioner’s or facility’s quality 3711
control program (NCRP, 2010). Operators of radiation-emitting devices such as dental x-ray 3712
machines must be familiar with and comply with applicable federal, state, and local regulations. 3713
3714
10.1.1 Compliance with FDA Medical Device Regulations and Electronic Product Radiation 3715
Control Performance Standards 3716
3717
The FDA Center for Devices and Radiological Health “is responsible for regulating firms 3718
who manufacture, repackage, relabel, and-or import medical devices sold in the United States,” 3719
including dental x-ray unit (http//www.fda.gov/MedicalDevices/DeviceRegulationandGuidance/ 3720
Overview/default.htm). 3721
3722
Legally marketed dental x-ray devices comply with federal regulations for medical devices 3723
and radiological health. Under the medical device regulations (21 CFR Subchapter H), dental x-3724
ray devices must be cleared by the FDA before being offered for sale in the United States. These 3725
regulations are intended to provide reasonable assurance of safety and effectiveness for medical 3726
devices marketed in the United States. To verify that a particular device has been reviewed by 3727
the FDA, practitioners can search the FDA’s online searchable database for Medical Device 3728
Premarket Notifications at http//www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfPMN/pmn.cfm. 3729
3730
The radiological health regulations (21 CFR Subchapter J) are intended to protect the public 3731
from hazardous or unnecessary radiation exposure from radiation emitting-electronic products. 3732
These regulations require that manufacturers of radiation emitting electronic products adhere to 3733
specific reporting, recordkeeping, and labeling requirements as well as comply with applicable 3734
performance standards in 21 CFR 1020.30 through 1020.33. Diagnostic x-ray devices that 3735
NCRP SC 4-5 Draft March 16, 2016
159
comply with the radiological health regulations will include certification, identification, and 3736
warning labels. These labels will be permanently affixed, legible, and readily accessible to view 3737
when the device is fully assembled for use [21 CFR 1010.2(b) and 1010.3(a)]. Figure 10.1 shows 3738
identification and certification labels. 3739
3740
A radiation-emitting device that meets the FDA requirements will be deemed “cleared by the 3741
FDA.” It is worth noting that the appropriate terminology uses the word “cleared”. The FDA 3742
does not “approve” radiation-emitting devices. An FDA cleared device meets the stringent 3743
design requirements necessary to minimize the dose to the operator with proper use of the 3744
equipment. 3745
3746
When new technology is introduced, especially in the current global marketplace, it is 3747
critical that buyers and operators be certain that the devices they are purchasing and using are 3748
cleared by the FDA. 3749
3750
10.1.2 General Considerations 3751
3752
The following are good imaging practices in a dental setting: 3753
3754
1. Clear policies and procedures governing safe and effective use of radiation in the dental 3755
practice. For example, quality assurance and quality control (Section 5.2), and radiation 3756
safety of the patient and operators (Sections 4.4 and 4.5). 3757
2. Selection criteria for all imaging procedures (see Sections 4.4.1 for general radiology and 3758
9.1.5 for CBCT). 3759
3. Recording of the date, number, types, retakes, and operator for each examination. 3760
4. Maintenance of all records at least as long as required by the administrative authority, 3761
e.g., state dental or medical board, or other government agencies. 3762
3763
NCRP SC 4-5 Draft March 16, 2016
160
3764
3765
3766
3767
3768
3769
3770
3771
3772
3773
3774
3775
3776
3777
3778
3779
3780
3781
3782
Fig. 10.1. FDA required identification and certification x-ray equipment labels. Top and 3783
middle photos show the two labels required for FDA-cleared equipment (indicated by 3784
compliance with DHHS Rules 21CFR, subchapter J). Bottom photo shows placement of the two 3785
labels on an x-ray tube. 3786
3787
NCRP SC 4-5 Draft March 16, 2016
161
10.1.3 Hand-Held X-Ray Devices 3788
3789
There are several handheld x-ray units for sale in the United States. The design of the internal 3790
components of these machines varies tremendously, as do the dose levels and exposure times. 3791
FDA’s performance standards for intra-oral imaging devices, including hand-held systems are 3792
included in sections 21 CFR 1020.30 and 1020.31. These performance standards address 3793
requirements such as control and indication of technique factors, reproducibility, and source-to-3794
skin distance. Some units offered for sale, primarily through the Internet, have not been cleared 3795
by the FDA and present radiation hazards to the operator and the patient (Sections 7.3.2.3 and 3796
10.1.1). 3797
3798
Recommendation 90. Only hand-held dental x-ray devices cleared by FDA for sale in 3799
the United States shall be used. 3800
3801
Some regulatory organizations have implemented rules and regulations preventing the user 3802
from holding the x-ray tube. These rules and regulations are unnecessary and impractical for 3803
FDA-cleared hand-held x-ray systems. The risks associated with holding the x-ray tube are 3804
mitigated by properly designed and labeled hand-held x-ray systems. Because properly designed 3805
and labeled hand-held systems can offer a cost-effective, flexible, and safe alternative to wall-3806
mounted systems, these rules and regulations should be relaxed for equipment that is designed to 3807
be hand-held. 3808
3809
Recommendation 91. Regulations preventing the user from holding the x-ray unit 3810
should not apply to equipment cleared by FDA that is designed to be hand-held. 3811
3812
10.1.4 CBCT Units 3813
3814
FDA’s performance standards specific to CT systems are included in 21 CFR 1020.33. Of 3815
particular importance to CBCT systems is the requirement to include quality assurance and 3816
control information (21 CFR 1020.33d). CT manufacturers are required to provide an image 3817
quality phantom, instructions for using the phantom, and a schedule for its use. 3818
NCRP SC 4-5 Draft March 16, 2016
162
3819
Considerable variability exists in the way state radiation control programs address CBCT 3820
systems, if at all. At the time of this writing, most states do not have specific requirements for 3821
dental CBCT systems and consider CBCT to be a form of dental radiography or panoramic 3822
radiography, although some states view CBCT to be a form of medical CT. The FDA classifies 3823
CBCT systems the same as conventional CT systems. The committee thinks that dental CBCT 3824
occupies a unique niche in the imaging world; CBCT should be considered neither a traditional 3825
dental equipment (intraoral, cephalometric or panoramic equipment) nor a conventional medical 3826
CT system. 3827
3828
The CRCPD Suggested State Regulations (SSR), Part F (Diagnostic and Interventional X-3829
Ray & Imaging Systems; http://crcpd.org/SSRCRs/default.aspx.), were revised in 2015 and 3830
include specific recommendations for CBCT units. At the time of writing, four states have 3831
adopted the SSR and others are considering it. 3832
3833
Recommendation 92. States shall develop and apply specific regulations for the dental 3834
uses of CBCT. 3835
3836
The radiation safety officer (RSO), which in a typical dental practice is the dentist, is 3837
responsible for remaining aware of current and potentially evolving changes in regulatory 3838
requirements for CBCT. The qualified expert may provide valuable help in this ongoing process. 3839
3840
Even in the complete absence of any specific state requirements for CBCT use, the RSO 3841
remains responsible for the safe use of radiation at the facility. Hence, it is prudent for the RSO 3842
to remain aware of the evolving state of the practice regarding state and local CBCT regulations 3843
as well as CBCT quality and safety practices, and to establish procedures in the dental clinic with 3844
these in mind. An experienced qualified expert can be a valuable resource in this important 3845
ongoing activity and may serve as the RSO. 3846
3847
NCRP SC 4-5 Draft March 16, 2016
163
Independent of any federal or state regulations, each dental practice employing CBCT 3848
should establish and maintain policies and procedures that address at least the following: 3849
3850
1. qualifications (including training and continuing education requirements) of individuals 3851
who may perform or read CBCT exams; 3852
2. personnel monitoring of occupational exposure, including periodic review by the 3853
radiation safety officer (RSO) or qualified expert; 3854
3. a CBCT quality assurance program, including both equipment related QC and clinically 3855
related QA activities; 3856
4. radiation safety and regulatory compliance program; 3857
5. standard CBCT protocols for common clinical indications; and 3858
6. periodic review of CBCT protocols by the dental practitioner and the qualified expert. 3859
3860
10.1.4.1 Advanced Diagnostic Imaging Accreditation. The Medicare Improvements for Patients 3861
and Providers Act of 2008 requires the accreditation of suppliers of the technical component of 3862
advanced diagnostic imaging services in order to obtain payment from the Centers for Medicare 3863
and Medicaid Services (CMS). For more information go to the CMS website (www.cms.gov) 3864
and search for “advanced diagnostic imaging accreditation.” 3865
3866
This provision of the act went into effect January 1, 2012, and includes dentists who obtain 3867
and bill Medicare for the technical component of CBCT examinations. The accreditation 3868
standard applies only to the suppliers of the images themselves, and not to the clinician’s 3869
interpretation of the images. The purpose of the accreditation is to ensure that quality images are 3870
produced in a safe and effective manner that benefits the patient. 3871
3872
Some states and private payers have adopted similar regulations. Clinicians and imaging 3873
facilities that utilized CBCT are advised to consult with local officials or representatives of the 3874
individual insurance company or payer for details specific to their location or situation. 3875
3876
NCRP SC 4-5 Draft March 16, 2016
164
10.2 Education and Training 3877
3878
NCRP Report No. 127 and Report No.134 (NCRP, 1998; 2000;) and ICRP Publication 3879
113 (ICRP, 2009) recommend that all dental personnel be appropriately trained in radiation 3880
protection. Basic familiarity with radiation protection can be expected in those who by education 3881
and certification are credentialed to expose radiographs, i.e., dentists, registered dental 3882
hygienists, certified dental assistants, and radiologic (or dental radiologic) technologists. 3883
Curricula for their education are subject to recommendations by various professional 3884
organizations and requirements of accrediting and credentialing agencies (IAC, 2015; ICRP, 3885
2009). These recommendations included credentialing of faculty and adequacy of resources and 3886
curricula for predoctoral and postdoctoral education, and required frequency of continuing 3887
education. Others have shown that dentists who are better informed in radiation science are more 3888
likely to adopt modern dose-optimization technology (Svenson et al., 1997b; 1998). 3889
3890
The ability of office personnel to understand and implement all of the recommendations 3891
in this Report cannot be assumed. Other personnel, e.g., secretaries, receptionists, laboratory 3892
technologists, who are not credentialed for performing radiographic procedures may be subjected 3893
to incidental exposure to radiation. These personnel are likely to have received little or no 3894
training or experience in radiation protection. 3895
3896
The required training may be provided by any combination of self-instruction (including 3897
reading), group instruction, online instruction, mentoring, or on-the-job training. Periodic 3898
evaluation of staff practices will determine the need, if any, for retraining. Essential topics to be 3899
covered in the training program include: 3900
3901
the ALARA principle; 3902
risks related to exposure to radiation and to other hazards in the workplace; 3903
dose limits; 3904
sources of exposure; 3905
basic protective measures; 3906
secure access to radiation equipment; 3907
NCRP SC 4-5 Draft March 16, 2016
165
warning signs, postings, labeling, and alarms; 3908
responsibility of each person; 3909
overall safety in the workplace; 3910
specific facility hazards; 3911
special requirements for women of reproductive age; 3912
regulatory and licensure requirements; and 3913
infection control. 3914
3915
This training may be expedited by the development and maintenance of a site-specific 3916
radiation protection manual. 3917
3918
Recommendation 93. Radiation safety training shall be provided to all dental staff and 3919
other personnel, including secretaries, receptionists, and laboratory technologists. This 3920
training shall be commensurate with the individual’s risk of exposure from ionizing 3921
radiation. 3922
3923
Recommendation 94. Every person who operates dental x-ray imaging equipment or 3924
supervises the use of such equipment shall have current training in the safe and 3925
efficacious use of such equipment. 3926
3927
When new imaging technology is introduced into a dental practice it is essential that the 3928
dentist and all operators be properly trained so as to be thoroughly familiar with the safe and 3929
efficient operation of the equipment. Continuing education resources are generally available to 3930
keep the dentist apprised of new developments. 3931
3932
Recommendation 95. The dentist should regularly participate in continuing education 3933
in all aspects of dental radiology, including radiation protection. 3934
3935
Recommendation 96. Opportunities should be provided for auxiliary personnel to 3936
obtain appropriate continuing education credits. 3937
NCRP SC 4-5 Draft March 16, 2016
166
3938
10.2.1 Digital Imaging 3939
3940
In addition to the basic education and training required for film-based imaging, the operator 3941
should be trained in the use of the radiographic imaging software that is used to acquire and 3942
manipulate the images. This training should be provided by the manufacturer or vendor of the 3943
equipment. 3944
3945
Furthermore, the operator should be educated and trained in the appropriate quality assurance 3946
and quality control protocols to assure the optimal performance of the film or digital imaging 3947
equipment components (Sections 5.2.4 and 5.2.6). 3948
3949
10.2.2 Hand-held Imaging Systems 3950
3951
Hand-held dental x-ray units are relatively new to the marketplace and require specific 3952
additional education for their safe and efficient operation. 3953
3954
10.2.2.1 Practitioner—Additional Safety Concerns. Practitioners should be aware of the potential 3955
for misuse of hand-held x-ray equipment and assure that the appropriate safeguards are in place. 3956
In addition, there is a potential for increased operator radiation exposure if the device is not used 3957
properly. 3958
3959
10.2.2.2 Operator Training. The hand-held x-ray equipment manufacturer must provide training 3960
materials for the operator. A DVD or online source could be used for operator training. 3961
3962
Operator training materials should include the basics of x-ray production and scatter (some 3963
operators such as dental assistants may not have had formal radiation safety training) and 3964
information on proper positioning. The positioning information should include the position of the 3965
patient, operator, location, and orientation of the hand-held device, and operator’s hand 3966
positioning on the device. This training should emphasize that the operator be positioned in a 3967
way that minimizes their exposure to backscattered radiation. In addition, the value of the x-ray 3968
NCRP SC 4-5 Draft March 16, 2016
167
shield which is an integral part of the unit should be emphasized, i.e., the shield must always be 3969
in place. 3970
3971
It is critical that operators follow the positioning instructions. Failure to follow proper 3972
positioning techniques can result in an increased exposure to backscattered radiation to the 3973
operator. 3974
3975
Recommendation 97. The manufacturer shall provide training pertaining to the safe 3976
operation of the hand held unit. 3977
3978
10.2.2.3 Qualified Expert—Required Information. The primary training issue for the qualified 3979
expert is the radiation safety of the hand-held x-ray unit. 3980
3981
Recommendation 98. The manufacturer of hand-held dental x-ray units shall provide 3982
information suitable for the qualified expert regarding radiation leakage, backscatter 3983
radiation, and the importance of the integral radiation shield. 3984
3985
10.2.3 CBCT Imaging Systems 3986
3987
CBCT units are an order of magnitude more sophisticated than any of the other dental 3988
imaging modalities and they require specific additional education for their safe and efficient 3989
operation. 3990
3991
In addition, the operator should be educated and trained in the appropriate quality control 3992
protocols to assure the optimal performance of the digital imaging equipment components 3993
(Sections 5.2.5). 3994
3995
10.2.3.1 Training for Practitioners 3996
3997
The complexity of CBCT image acquisition, and the subsequent multiplanar demonstration 3998
of patient anatomy, are far more complex than any imaging previously employed in dentistry. 3999
NCRP SC 4-5 Draft March 16, 2016
168
Thus, it is incumbent on practitioners to ensure that they receive proper training in the safe and 4000
effective use of this modality and provide opportunity for appropriate levels of training for the 4001
staff. 4002
4003
Recommendation 99. The predoctoral dental curricula shall include didactic and 4004
clinical education on physics of CBCT image production, artifacts that can lead to 4005
image degradation, indications, and limitations of CBCT in dental practice, and the 4006
effects of acquisition parameters on radiation dose. 4007
4008
Recommendation 100. Postdoctoral or clinical residency curricula shall expand upon 4009
the predoctoral education and include discipline-specific indications and limitations of 4010
CBCT imaging and the effects of acquisition parameters on radiation dose. 4011
4012
Recommendation 101. Dental practitioners who own CBCT units or use CBCT data 4013
sets in their clinical practice and who have not received CBCT education as part of 4014
their predoctoral, postdoctoral, or equivalent to predoctoral education shall acquire 4015
equivalent understanding of the basic radiation safety aspects of CBCT imaging and 4016
sufficient knowledge in the indications and limitations of CBCT imaging. 4017
4018
Recommendation 102. Dental personnel who operate CBCT units shall be adequately 4019
trained in the proper operation and safety of the units. They should demonstrate 4020
adequate knowledge of different protocols affecting the image quality and radiation 4021
dose to the patient. 4022
4023
Inadequate knowledge of the anatomy or not providing a proper interpretation of the image 4024
data set would negate and render moot any radiation protection benefits gained from safe and 4025
effective image acquisition. Thus, it is critical that the practitioner receive appropriate education 4026
and training in the interpretation of the anatomy as displayed on multiplanar and post-processed 4027
three-dimensional images. 4028
4029
NCRP SC 4-5 Draft March 16, 2016
169
10.2.3.2 Training for Operators. The operators of CBCT equipment are those licensed by the 4030
state in which they practice to operate dental radiographic equipment. Operators often select the 4031
equipment settings and perform image acquisition. In most states, operators of CBCT equipment 4032
are usually dental hygienists or dental assistants. 4033
4034
Recommendation 103. Prior to working with CBCT equipment, operators shall receive 4035
education on the basics of CBCT technology, the risks associated with radiological 4036
imaging, and training on the effective operation of CBCT equipment. This education 4037
must include principles of CBCT image formation, equipment settings and their impact 4038
on patient dose, and common artifacts associated with CBCT images. 4039
4040
Recommendation 104. All operators shall complete training on each individual CBCT 4041
system they will be using, as provided by the manufacturer. This device specific 4042
training must include patient positioning, the range of user selectable exam settings, 4043
and their effect on dose, protocol selection, image processing options, and periodic 4044
maintenance schedules. 4045
4046
10.2.3.3 Training for Qualified Experts. To be qualified for evaluation of CBCT equipment an 4047
individual must be a qualified expert with a minimum of 3 h CBCT training (available as online 4048
training) and have evaluated at least three CBCTs under the supervision of an experienced 4049
qualified expert. 4050
4051
Recommendation 105. A qualified expert shall have appropriate training and mentored 4052
experience in the evaluation of dental CBCT facilities prior to functioning 4053
independently. 4054
4055
10.2.3.4 Continuing Education for Practitioners, Operators, and Qualified Experts. CBCT 4056
technology is continually improving and practitioners, operators, and qualified experts must stay 4057
up-to-date. Manufacturers may provide software updates that substantially change the operation 4058
of the CBCT unit, which may require re-education and re-training of all parties. Similarly, 4059
hardware updates, while occurring less frequently, will also require additional education and 4060
NCRP SC 4-5 Draft March 16, 2016
170
training. It is the responsibility of the dentist to ensure that all office personnel are properly 4061
educated and trained in the safe and efficient operation of the equipment. 4062
4063
Recommendation 106. Every person who operates CBCT equipment, supervises the use 4064
of CBCT equipment or tests and evaluates the functions of CBCT equipment shall have 4065
ongoing continuing education in the safe and effective use of that equipment. 4066
4067
NCRP SC 4-5 Draft March 16, 2016
171
11. Summary and Conclusions 4068
4069
Oral and maxillofacial radiology encompasses a wide variety of techniques, ranging from 4070
traditional intraoral, panoramic and cephalometric imaging to more recently introduced digital, 4071
hand-held, and CBCT imaging. 4072
4073
While significant advances have been made in radiation dose reduction to patients and the 4074
public, there are still many examples of the utilization of equipment, supplies, and applications 4075
that are outdated and inappropriate. 4076
4077
Attention must be paid not only to how a radiographic image is captured but also to when the 4078
image should be captured. The dental clinician can minimize the exposure to the patient while 4079
maintaining diagnostic yield by utilizing the following: 4080
4081
1. selection criteria – have a good reason for acquiring any image; 4082
2. fastest available image receptor; 4083
3. optimized exposure technical factors; 4084
4. rectangular collimation with intraoral imaging; 4085
5. thyroid shielding for all intraoral images, and for other examinations as appropriate; 4086
6. smallest FOV and lowest dose acquisition parameters commensurate with the diagnostic 4087
task in CBCT; 4088
7. continuous quality control programs for equipment, techniques, film processing, and 4089
image receptors; and 4090
8. up-to-date training for all personnel. 4091
4092
Dentists who conduct their radiology practices in accordance with the requirements and 4093
suggestions in this Report can obtain maximum benefit to the oral health of their patients and 4094
minimum radiation exposure to patients, operators, and the public. All of the factors addressed in 4095
this Report are important and interrelated; quality practice dictates that no shall statement be 4096
neglected and that should statements be incorporated whenever possible. The technical factors, 4097
including office design and shielding, equipment design, clinical techniques, image receptors, 4098
NCRP SC 4-5 Draft March 16, 2016
172
darkroom procedures, quality control, and quality assurance are essential. However, the 4099
professional skill and judgment of the dentist in prescribing radiologic examinations and 4100
interpreting the results are paramount. 4101
4102
While radiogenic harm due to most very low-dose dental x-ray examinations may not be 4103
unequivocally demonstrable, recent epidemiological studies have shown an association between 4104
low-dose exposures associated with CBCT (doses on the order of those found with MDCT) and 4105
increased cancer risk across the population (Appendix I). 4106
4107
Given the uncertainty regarding the estimated risk from low-doses such as those found in 4108
diagnostic imaging (NCRP, 2010b; UNSCEAR, 2012), there is disagreement about the 4109
application of the risk estimates to policy development and radiation protection issues (AAPM, 4110
2012; HPS, 2016). However, given the large number of dental images taken annually, the 4111
possibility that the risks are real, especially for CBCT imaging, demands that they be taken 4112
seriously in the interest of patient, staff, and public safety. 4113
4114
NCRP SC 4-5 Draft March 16, 2016
173
Appendix A 4115
4116
Quality Control for Film Processing 4117
4118
Radiation exposure to the patient, operator, and public can be reduced by minimizing the 4119
need for repeat exposures because of inadequate image quality (NRPB, 2001). In addition, the 4120
chemical solutions must be maintained at the proper activity level. As the chemicals are depleted 4121
or oxidized, the films will be lighter resulting in an increased exposure times and higher doses to 4122
the patients and staff. Film processing chemistry and procedures, image receptor performance 4123
characteristics, and darkroom integrity must be evaluated at appropriate intervals. These routine 4124
quality control procedures can be performed by dental office staff. 4125
4126
A.1 Five Basic Rules for Film Processing 4127
4128
1. Films should be processed at the time and temperature specified by the film 4129
manufacturer. 4130
Film processing is a chemical reaction requiring accurate control of the processing time 4131
and temperature. 4132
An important part of processor quality control is maintaining the appropriate 4133
developer and fixer activity. This is accomplished through replenishing of the solutions in 4134
the developer and fixer tanks. 4135
2. The developer and fixer must be replenished regularly to maintain diagnostic image 4136
quality, and minimize patient dose. 4137
Eight ounces of replenisher should be added every day, assuming 30 intraoral or five 4138
panoramic films. An additional eight ounces of replenisher should be added per day for 4139
each additional 30 intraoral or five panoramic films processed (White and Pharoah, 4140
2014). Manufacturer’s instructions should be followed where applicable. 4141
3. Never top off the chemical tanks with water. 4142
This dilutes the chemicals, reduces image quality, and could lead to an increase in patient 4143
radiation dose. 4144
4145
NCRP SC 4-5 Draft March 16, 2016
174
4. Developer and fixer solutions should be changed every two weeks. 4146
Over time the solutions tend to collect bits of debris from the film, become depleted, and 4147
oxidize. Consequently, it is necessary to drain the solutions, clean the tanks, and fill the 4148
tanks with fresh chemicals. 4149
5. The water in the wash tank should be changed daily for up to 30 films developed per 4150
day. For higher volumes, the water should be changed after every 30 films. (Some 4151
processors have water flowing through the wash tanks—the water in these processors 4152
does not have to be changed due to the continuous flow of fresh water.) 4153
Improper washing of films will result in premature fading and staining of the images.3 4154
4155
A.2 Quality Control 4156
4157
A.2.1 Sensitometry and Densitometry 4158
4159
The most sensitive and rigorous method of quality control requires the use of a sensitometer, 4160
a precise optical device to expose a film to produce a defined pattern of optical densities in the 4161
processed film. These densities are then measured with a densitometer, and compared to the 4162
densities of a similarly exposed film previously processed in fresh solutions under ideal 4163
conditions. These values are placed on a control chart. Any change beyond pre-specified limits 4164
indicates a problem with processing which could be a result of changes in development time or 4165
temperature, or due to depleted or contaminated solutions. This method requires additional 4166
equipment but only a few minutes of operator time to execute. It is highly recommended for the 4167
busy facility, but simpler, less costly methods may be adequate for average dental offices. 4168
4169
A.2.2 Dental Radiographic Quality Control 4170
4171
Two devices are available from most dental supply companies for simple quality control of 4172
film processors—a dental radiographic quality control device (DRQCD) and an aluminum step 4173
wedge. In addition to daily QC, the DRQCD assists in selecting appropriate exposure time to 4174
3 Gray, JE (2015). Personal Communication. (DIQUAD, LLC, Steger Illinois)
NCRP SC 4-5 Draft March 16, 2016
175
assure that patients are receiving an appropriate radiation dose. A third test device can be 4175
constructed from the leaf foils in dental film packets. 4176
4177
A.2.3.1 Dental Radiographic Quality Control Device. This device consists of a small sheet of 4178
copper and a comparison optical density step wedge. For quality control, an exposure is made 4179
with a film packet under the copper, the film is processed, and then compared to the step wedge. 4180
If the film density changes by more than one step then a change in photographic processing has 4181
occurred and it will be necessary to determine and correct the cause. 4182
4183
This device is also useful in establishing the appropriate exposure time for dental 4184
radiographs. In this case, a film packet is exposed under the copper plate and compared to the 4185
optical density step wedge. The appropriate exposure time results in the film density matching 4186
the middle step of the step wedge. 4187
4188
A.2.3.2 Aluminum Step Wedge. An aluminum step wedge with 1 mm steps can be used for film 4189
processor quality control. A film packet is exposure under the aluminum step wedge and the film 4190
is processed with fresh film processing chemistry. This film becomes the comparison or baseline 4191
film. For daily quality control purposes, the procedure is repeated with the resultant film being 4192
compared to the baseline film. If the steps of the baseline film and the recently exposed film are 4193
not similar then it will be necessary to determine and correct the cause. 4194
4195
A.2.3.3 Lead Foil Step Wedge. A step wedge can be made of multiple layers of the lead foil from 4196
dental film packets (Valachovic et al., 1981). Overall size of the stepwedge should be similar to 4197
that of a standard intraoral film. It is made to resemble stairs. There should be at least six steps. 4198
4199
The lead foil step wedge is used in the same manner as the aluminum step wedge. 4200
4201
A.2.3.4 Reference Film. Use of a properly exposed and processed intraoral film as a reference 4202
has been proposed as another method of quality assurance (Valachovic et al., 1981). When using 4203
this method, a high-quality film is attached to a corner of the view box. Subsequent clinical films 4204
can then be compared with this reference film. This method is not as sensitive or reliable as the 4205
NCRP SC 4-5 Draft March 16, 2016
176
use of the DRQCD device, or a stepwedge, and is not recommended for routine use. In rare 4206
circumstances it may be used as a stopgap measure, usually in facilities with very low 4207
radiographic workload (fewer than 10 intraoral films per week). 4208
4209
NCRP SC 4-5 Draft March 16, 2016
177
Appendix B 4210
4211
Quality Control for Digital Imaging Systems 4212
4213
B.1 Quality Control of Digital Intraoral Systems 4214
4215
Quality control testing of digital systems requires: 4216
4217
1. computer display adjusted to display a high-quality radiographic image and viewed under 4218
optimal conditions; 4219
2. suitable phantom or test object to be used for the assessment of image quality; 4220
3. procedure providing verification that the radiographic technique being used yields the 4221
maximum diagnostic information at an acceptable level of dose (optimization); 4222
4. exposure of a baseline image to serve as a reference for subsequent images; 4223
5. exposure of follow-up radiographs at regular intervals; and 4224
6. system of record keeping for purposes of documentation. 4225
4226
B.1.1 The Display 4227
4228
Since digital radiographs are viewed on a computer display, it should be verified that the 4229
display is viewed under optimal conditions. The display should be tested to verify that it is 4230
functioning optimally and the brightness and contrast are properly adjusted. 4231
4232
Digital radiographs should be viewed with the center of the display positioned slightly below 4233
eye level. Subdued lighting should be used and every effort should be made to eliminate 4234
reflections from extraneous sources of light such as room lights or view boxes. 4235
4236
The display should be checked periodically using the Society for Motion Picture and 4237
Television Engineers (SMPTE) Medical Diagnostic Imaging Test Pattern or the equivalent. The 4238
overall image should be inspected to insure the absence of gross artifacts such as blurring or 4239
bleeding of bright display areas into dark areas. All the provided gray levels should be visible 4240
NCRP SC 4-5 Draft March 16, 2016
178
and both the 5 % and the 95 % areas should be seen as distinct from the surrounding 0 % and 4241
100 % areas. Brightness and contrast should be adjusted until these conditions are met (Gray, 4242
1992; Gray et al., 1985). 4243
4244
B.1.2 Quality Control Phantoms 4245
4246
A thorough evaluation of image quality requires a phantom containing suitable test objects 4247
for assessing low-contrast detectability and spatial resolution as well as a step wedge or some 4248
other suitable object covering the relevant range of radiographic attenuation (Mah, 2011; Udupa, 4249
2013). The phantom should be exposed using the source-to-image distance used clinically and 4250
the test objects should be positioned at the same distance from the x-ray source and image 4251
receptor as the relevant anatomy. 4252
4253
B.1.3 Baseline Exposure Assessment 4254
4255
The object of the original baseline assessment is to evaluate the technique being used for 4256
routine exposures and to improve on it, if possible. The objective is to determine the lowest 4257
exposure at which the greatest number of low-contrast details are visualized and the highest 4258
resolution is obtained while continuing to display the full range of clinically relevant gray levels. 4259
Established guidelines for Diagnostic Reference Level and Achievable Dose set limits on the 4260
exposures that should be used, even when the image receptor is capable of producing high 4261
quality images at levels of radiation exposure exceeding these guidelines. NCRP 172 establishes 4262
the DRL and AD for intraoral imaging at 1.6 and 1.2 mGy, respectively (NCRP, 2012b). 4263
4264
A starting point for baseline exposure assessment can be obtained from Table 6.1 of this 4265
report. This phase is a process of trial and error but it is a necessary step before quality control 4266
monitoring begins. 4267
4268
NCRP SC 4-5 Draft March 16, 2016
179
B.1.4 Baseline Image 4269
4270
Once the baseline exposure time is established, the test image should be saved for future 4271
reference. Any information extracted from the image, as well as the geometry and exposure 4272
factors should be recorded. 4273
4274
A new baseline exposure assessment should be performed and a new baseline image acquired 4275
if any components of the x-ray equipment are altered, repaired, or adjusted, or if any changes are 4276
made to the hardware or software used for image capture. 4277
4278
B.1.5 Follow-up Images 4279
4280
Following the baseline assessment, the phantom should be radiographed at regular intervals 4281
using the standard exposure geometry and baseline exposure factors. The image should be 4282
compared to the baseline image. A significant deviation from the baseline indicates that a change 4283
has occurred that should be investigated. Corrective action should be taken as needed. The test 4284
should also be performed if damage to the image receptor is suspected after an event such as 4285
dropping the image receptor, biting the image receptor, running over the cord with chairs or 4286
equipment, snagging the electrical cord, etc. 4287
4288
B.1.6 Record Keeping 4289
4290
A permanent record should be kept of baseline and follow-up data. The date of the test and 4291
the name of the person performing the test procedure should be included. The nominal 4292
kilovoltage and milliamperage as well as the baseline exposure time should be noted as well as 4293
the technical factors that are measured. A separate log should be maintained for every x-ray unit 4294
and image receptor combination and, in the case of a practice using PSP plates, every x-ray unit 4295
and scanner combination. The following is a quality control record containing the essential 4296
elements discussed above: 4297
4298
NCRP SC 4-5 Draft March 16, 2016
180
Quality Control Record 4299
4300
Image receptor (Manufacturer, Model, Serial #) ________________________________ 4301
4302
X-ray Machine (Manufacturer, Model, Serial #) _________________________ 4303
4304
kVp ___________ 4305
4306
mA ___________ 4307
4308
Baseline Quality Control Exposure. ________ sec 4309
4310
Baseline
Date
Name Steps Line-Pairs Top Row
of Contrast
Holes
Second Row
of Contrast
Holes
4311
4312
Date Name Steps Line-Pairs Top Row
Of Contrast
Holes
Second Row
of Contrast
Holes
4313
4314
NCRP SC 4-5 Draft March 16, 2016
181
Appendix C 4315
4316
Historical Aspects of Digital Imaging 4317
4318
The benefits to the practice of dentistry from capturing “skiagrams”, as x-ray images were 4319
called at the time, were realized soon after the discovery of x rays. During the following 100 y 4320
substantial technological improvements advanced most aspects of radiological imaging; 4321
however, the film based format of radiographic image capture, display, and archiving remained 4322
largely unchanged throughout most of the 20th century. Xeroradiography, with its capture of 4323
image detail, was a somewhat viable alternative to film based methods; however, initial 4324
investment cost, unique equipment requirements, and perhaps a reluctance of radiologists to 4325
interpret a blue radiographic image on dull white paper likely played a role in the mainstay of 4326
radiographic film into the 21st century. Digital imaging has been a facet of general radiological 4327
practice since the 1980s, first with computed radiography (using PSP technology) and later with 4328
direct digital radiography in various forms (although one can argue that computed tomography 4329
was actually the first digital oriented radiological imaging procedure based on the digital 4330
acquisition and computational nature of this modality). Recent technological advances have 4331
allowed x-ray imaging in the dental practice to quickly embrace digital technology. 4332
4333
Digital based x-ray imaging for dental applications has been a part of clinical practice since 4334
the early 1990s. There are likely a number of reasons for the increase in the number of dental 4335
practices that have switched to digital imaging for intraoral and extraoral modalities. A recent 4336
study found that 87 % (n = 81) of facilities in the United States are now using digital imaging for 4337
intraoral examinations (Farris and Spelic, 2015). A second study in the United States found that 4338
85.8 % (n = 1,312) for facilities are using digital intraoral imaging.4 This same study found that 4339
the percentage of facilities using digital intraoral imaging in the United States was increasing by 4340
~8 % y–1 from 2010 through 2015. Another study conducted recently of dental practices in New 4341
Zealand found that the majority of dental practices had implemented digital x-ray imaging, and 4342
not surprisingly, younger practitioners were more likely to be using digital imaging. Among the 4343
4 Gray, J.E. (2015) Personal communication (DIQUAD, LLC, Steger, Illinois).
NCRP SC 4-5 Draft March 16, 2016
182
reasons that dental practices preferred digital imaging were the chemical free imaging process, 4344
lower dose that digital imaging could offer, the rapid availability of the image, and the ability to 4345
digitally archive patient imaging records. Practices surveyed that were still using film tended to 4346
be satisfied with the modality and felt that switching to digital imaging would be costly. One 4347
survey finding that supports the assumption that digital imaging is a more timely modality than 4348
film was the finding that practices using digital imaging tended on average to acquire more 4349
images per day. 4350
4351
Digital imaging first became available for dentistry in the late 1980s when technology was 4352
sufficient to allow the digital image capture devices to be packaged suitably for dental 4353
applications. In 1987 the French company Trophy introduced their product, RadioVisioGraphy, 4354
as a digital based tool for dental x-ray imaging. Although early digital technologies were not 4355
capable of the high spatial detail that traditional film provides, these technologies continued to 4356
mature, and some device manufacturers now offer a wireless means of image capture. One study 4357
demonstrated that 2D imaging with digital technology for bone lesions provided better clinical 4358
performance than traditional film imaging. Today the digital technologies for oral radiography 4359
fall into two broad categories of image receptors: solid state (predominantly CCD or CMOS 4360
based) devices and photostimulable storage phosphor (PSP) technology. 4361
4362
Although the spatial resolution of digital systems may be inferior to film, the contrast 4363
resolution, i.e., the ability to see small density differences, is better for digital imaging (Figure 4364
C.1). 4365
4366
Similar to imaging equipment available for general radiological imaging, digital based x-ray 4367
equipment generally is either PSP based or solid state receptor based. While the fundamental 4368
technologies of these two equipment types are different, there are a number of common benefits 4369
that these two systems offer. 4370
4371
NCRP SC 4-5 Draft March 16, 2016
183
4372
4373
4374
4375
4376
4377
4378
Fig. C.1. (Left) film image; (right) digital image. Low contrast area on the digital image (red 4379
arrow) is not visible on the film image. Low contrast area consists of 1 mm aluminum disk with 4380
a circular hole in two layers of tape. 4381
4382
NCRP SC 4-5 Draft March 16, 2016
184
4383
One benefit to embracing digital imaging in clinical practice is the elimination of chemical 4384
film processing. Film processing can be a time consuming and laborious aspect of x-ray imaging 4385
to maintain at an acceptable level of quality. A survey of dental facilities in 2014 4386
(http://imagegently.org/) showed broad ranges for clinical image quality including film 4387
background optical density, film contrast, and the quality of film processing. Poor film 4388
processing (generally considered to be the under-development of film) can affect clinical image 4389
quality and also leads to higher patient doses to compensate. The same 2014 survey found that 4390
even for those surveyed sites using D-speed film, patient exposures varied broadly, with the first 4391
and third quartiles for patient exposure differing by a factor of 2.3 and 45 % failed an acceptance 4392
criteria of 2.6 mGy, i.e., exceeded this radiation exposure level. (The range of exposures for D-4393
speed film was from 50 to 800 mR.) Although arguably PSP based systems still require digital 4394
image “processing”, the general need to provide a darkroom environment for handling film and 4395
maintaining a chemical based processing environment are eliminated. Digital images can be 4396
easily and quickly transferred to other clinical practices as DICOM standard formatted images 4397
using the Internet. 4398
4399
Likely one of the most substantial benefits of capturing radiographs using digital technology 4400
is the ability to conduct digital image processing. Although (intraoral) dental film offers 4401
tremendous spatial resolution of 20 c mm–1 or greater, digital image processing can provide a 4402
system of tools that offer the clinician the ability to manipulate the image to suit the clinical task 4403
at hand. In general the near instant availability of digital images provides a level of convenience 4404
for both the dental practitioner and the patient. However, when considering a migration to digital 4405
based imaging, clinical considerations are helpful in determining the particular system 4406
requirements that are suitable for the practice, such as the routine imaging of challenging 4407
anatomical presentations, and the workload for pediatric exams. 4408
4409
NCRP SC 4-5 Draft March 16, 2016
185
Appendix D 4410
4411
Shielding Design for Dental Facilities 4412
4413
NCRP Report No. 147 entitled, Structural Shielding Design for Medical X-Ray Imaging 4414
Facilities (NCRP, 2004), discusses shielding design for x-ray sources with operating potentials in 4415
the range from 25 to 150 kVp. Techniques used for calculating shielding barriers for diagnostic 4416
medical x-rays also have been discussed in the literature (Dixon and Simpkin, 1998; Simpkin 4417
and Dixon, 1998). Since dental radiography uses equipment similar in radiation quality to that 4418
used in diagnostic medical x-ray facilities, this appendix will provide information regarding the 4419
unique features of dental radiography equipment so that the qualified expert will be able to 4420
design shielding using the methodology described in NCRP Report No. 147 (NCRP, 2004). 4421
4422
Conventional building materials in partitions, floors, and ceilings may provide adequate 4423
radiation shielding for dental installations. However, assuming that conventional or pre-existing 4424
barriers provide sufficient shielding without a qualified expert performing a careful review of the 4425
required shielding based on current equipment, current workloads, and occupancy of surrounding 4426
areas can lead to exceeding permissible levels of radiation exposure in public and controlled 4427
areas, and therefore is ill advised. 4428
4429
Implementing several of the recommendations of this report (e.g., eliminating the use of D-4430
speed film, using digital imaging, and using rectangular collimators for intraoral imaging) may 4431
decrease the total amount of amount scattered radiation produced for each intraoral radiographic 4432
image. Diagnostic quality images may be produced using a lower radiation exposure for each 4433
image with photostimulable phosphor or direct digital imaging receptors instead of film for 4434
intraoral imaging. Whether converting to F-speed film or digital image receptors, where such 4435
technique factor reductions are implemented clinically, the attenuation requirements for 4436
structural shielding will be proportionally reduced if the total number of exams remains 4437
unchanged. 4438
4439
NCRP SC 4-5 Draft March 16, 2016
186
Despite the common misconception that CBCT systems are “nothing more than fancy 4440
panoramic x-ray systems and no shielding is needed,” scattered radiation from CBCT is 4441
substantially higher than from panoramic x-ray systems, typically by approximately a factor of 4442
10 times or more. Compared with panoramic x-ray installations, the substantially higher 4443
scattered radiation levels in CBCT installations require significantly greater shielding to maintain 4444
radiation exposures to nearby persons ALARA. Because CBCT systems are often replace 4445
existing panoramic systems, it is especially critical to have a qualified expert assess the adequacy 4446
of shielding prior to the CBCT installation. While some panoramic x-ray systems can be 4447
operated in a corridor or alcove without exceeding permissible radiation levels to nearby 4448
individuals, CBCT systems installed in a corridor or alcove will often expose nearby persons to 4449
doses that exceed permissible levels. Typically, CBCT systems should be installed in an enclosed 4450
room, with the thickness of shielding materials determined by a qualified expert. Figure D.1 4451
depicts typical configurations for CBCT systems 4452
4453
D.1 General Shielding Principles 4454
4455
In dental radiology, the beam energy is determined by the demands of radiographic contrast, 4456
but typically ranges from 60 to 70 kVp for intraoral dental radiography. Recently manufactured 4457
dental intraoral radiography units do not exceed 80 kVp. [Most intraoral dental units utilize fixed 4458
kilovoltage (70 kVp) and fixed milliamperage.] Panoramic x-ray units operate from 70 to 4459
100 kVp. Cephalometric systems are similar to standard radiographic systems and operate from 4460
60 to 90 kVp. Cone beam computed tomography (CBCT) systems generate significant higher 4461
levels of scattered radiation since the entire image receptor is irradiated continuously during the 4462
exposure, as opposed to irradiation from a small slit aperture in panoramic imaging. CBCT 4463
systems operate from 70 to 120 kVp. 4464
4465
4466
NCRP SC 4-5 Draft March 16, 2016
187
4467
4468
4469
4470
4471
4472
4473
4474
4475
Fig. D.1. Diagram illustrating primary barrier B, protecting person at C from useful beam at 4476
a distance dP from dental x-ray source A. 4477
4478
NCRP SC 4-5 Draft March 16, 2016
188
D.2 Shielding for Primary and Secondary Radiation 4479
4480
The primary beam is the intense, collimated radiation field that emanates from the x-ray tube 4481
focal spot and tube port, and is incident upon the patient. Figure D.1 illustrates a primary 4482
protective barrier B in the useful beam that attenuates the beam before it reaches a person located 4483
at C. In most situations, the primary beam also is attenuated by the patient before impinging on 4484
the primary barrier. The theory of shielding primary radiation from diagnostic x-ray facilities has 4485
been discussed by Dixon and Simpkin (1998) and in NCRP Report No. 147 (NCRP, 2004a). 4486
4487
Experimental evidence using the Rando phantom (de Haan and van Aken,1990) suggests that 4488
the intensity of the primary beam exiting the patient may be approximately twice that of the 4489
scattered radiation (Figure D.2). However, additional attenuation from the image receptor and 4490
bony anatomy of the human head, coupled with the relatively small beam size and logistical 4491
aspects of intraoral imaging5 serve to mitigate the primary beam effect. In addition, Figure 7.2 4492
indicates that the radiation exposure exiting the patient is ~0.5 to 1.0 mR for D-speed intraoral x-4493
ray film. (The image in Figure 7.2 was produced using a 400-speed screen-film system which 4494
requires ~0.5 mR to produce an optical density of 1.00 on the film.) Entrance exposures are even 4495
lower for digital imaging systems so the exit exposure from the patient would be approximately 4496
one-quarter to one-half of that with D-speed film. [The recent NEXT survey found that 87 % of 4497
facilities in the United States are now using digital imaging (Farris and Spelic, 2015)]. 4498
4499
Neglecting the primary beam in shielding calculations for dental facilities will not affect the 4500
calculated barrier thicknesses or resultant exposures to persons who occupy areas nearby the 4501
intraoral radiographic installation. 4502
4503
Consequently, the NCRP recommends that primary radiation can be neglected in dental 4504
imaging. Only scattered radiation must be considered in shielding design for dental facilities. 4505
4506
5 Unlike conventional radiology, the primary beam in dental imaging is placed at different locations and angles for intraoral radiography for each image. This results in the radiation being at projected at multiple locations on barrier B in Figure D.1.
NCRP SC 4-5 Draft March 16, 2016
189
Proposed CBCT
4507
4508
a. 4509
4510
4511
4512
4513
4514
4515
4516
4517
4518
4519
4520
4521
4522
4523
4524
4525
4526
4527
b. 4528
4529
Proposed CBCT
NCRP SC 4-5 Draft March 16, 2016
190
4530
4531
c. 4532
4533
4534
4535
4536
4537
4538
4539
4540
4541
4542
4543
Fig. D.2. (a) Initially proposed installation of CBCT system, to replace existing panoramic 4544
unit. This installation provides suboptimal radiation protection and would require administrative 4545
occupancy restrictions in the hallway during x-ray exposure. (b, c) Options for preferred 4546
installation of CBCT system in a different area of the suite, providing significant improvement in 4547
radiation protection and eliminating the need for administrative controls on hallway occupancy 4548
during x-ray exposure needed for the initially proposed installation. 4549
4550
NCRP SC 4-5 Draft March 16, 2016
191
4551
D.3 Shielding Principles 4552
4553
Shielding design goals for dental x-ray sources are practical values that result in the 4554
respective limits for effective dose in a year to workers and the public not being exceeded, when 4555
combined with conservatively safe assumptions in the structural shielding design calculations 4556
(NCRP, 2004). The shielding design goal is expressed as a weekly value, consistent with 4557
workload and occupancy factor data 4558
4559
D.4 Occupancy Factors, Use Factors, and Workloads 4560
4561
D.4.1 Occupancy Factors 4562
4563
Suggested occupancy factors are provided in Table D.1. 4564
4565
D.4.2 Use Factors 4566
4567
Since one need consider only scattered radiation for shielding design in dental radiography, 4568
the use factor is not applicable. 4569
4570
D.4.3 Workloads 4571
4572
Suggested workloads for intraoral (IO) imaging are provided in Table D.2. 4573
4574
Suggest workloads for panoramic, cephalometric, and CBCT imaging are given in Table D.3 4575
(see also MacDonald et al., 1983; Reid and MacDonald, 1984; Reid et al., 1993). 4576
4577
4578
NCRP SC 4-5 Draft March 16, 2016
192
TABLE D.1—Suggested occupancy factorsa (for use as a guide in planning shielding where 4579
other occupancy data are not available) (NCRP, 2004). 4580
4581
Location Occupancy
Factor (T)
Administrative or clerical offices; laboratories, pharmacies and other work areas
fully occupied by an individual; receptionist area, attended waiting rooms,
children’s indoor play areas, adjacent x-ray rooms, reading area, nurse’s stations, x-
ray control rooms
1
Patient examination and treatment rooms 1/2
Corridors, patient rooms, employee lounges, staff toilets 1/5
Public toilets, unattended vending areas, storage rooms, outer areas with seating,
unattended waiting rooms, patient holding areas 1/20
Outdoor areas with only transient pedestrian or vehicular traffic, unattended parking
lots, vehicular drop off areas (unattended), attics, stairways, unattended elevators,
janitor’s closets
1/40
aWhen using a low occupancy factor for a room immediately adjacent to an x-ray room, care should
be taken to also consider the areas further removed from the x-ray room that may have significantly higher
occupancy factors and may, therefore, be more important in shielding design despite the larger distances
involved.
NCRP SC 4-5 Draft March 16, 2016
193
TABLE D.2—Suggested workloads for intraoral (IO) units. 4582
Type of Unit Images w-1 kVp mAs per
Image
Film or Image Receptor
Speed
Low Volume IO 25 70 4.5 F or Digital
Medium Volume IO 100 70 4.5 F or Digital
High Volume IO 200 70 4.5 F or Digital
4583
4584
NCRP SC 4-5 Draft March 16, 2016
194
TABLE D.3—Suggested workloads and technique factors for cephalometric, panoramic, and 4585
CBCT examinations. 4586
Panoramic Cephalometric CBCT
Low volume facility
(exams w-1) <15 <10 <10
Medium volume facility
(exams w-1) 15 – 30 10 – 20 10 – 20
High volume facility
(exams w-1) >30 >20 >20
kVp 85 – 100 80 – 90 90 – 120
mAs per image for 400-speed
film or digital image receptor 50 – 1006 7 – 25 60 – 1607
4587
6 Slot beam. Depends on pulsed or nonpulsed beam, pulse width, and patient size. 7 Depends on pulsed or nonpulsed beam, pulse width, field of view, resolution, and patient size.
NCRP SC 4-5 Draft March 16, 2016
195
D.5 Summary 4588
4589
Shielding in dental radiography facilities is not as complex as for medical facilities. 4590
However, sufficient consideration must be given to future workloads to assure that 4591
shielding is adequate. Particularly for new construction and typical circumstances, 4592
appropriate shielding adds little to the cost of construction. Prior to facility operation, a 4593
performance assessment by a qualified expert is necessary to confirm that occupational and 4594
public effective dose limits will not be exceeded. The recommendations in this Report are 4595
to be applied to upgraded or new shielding designs, but not necessarily to existing barriers 4596
that otherwise met prior requirements. 4597
4598
NCRP SC 4-5 Draft March 16, 2016
196
Appendix E 4599
4600
Dosimetry, Intraoral and Panoramic Imaging 4601
4602
E.1 Patient Dosimetry 4603
4604
Dental radiographic procedures are very common but the associated x-ray doses are 4605
quite low. Application of the ALARA principle to reduction of these doses is justified. For 4606
intraoral radiography, changing from D- to E-F-speed film or to digital image receptors 4607
results in dose reduction by factors of at least two. Introduction of rectangular collimation 4608
to replace the 7-cm round beam reduces dose by factors of four to five. Both of these are 4609
accomplished at little or no cost, and together may result in ten-fold reductions in effective 4610
doses. 4611
4612
This Section provides the dentist with data, e.g., Tables E.1 and E.2, on the magnitude 4613
of effective doses from typical dental x-ray procedures. General statements are given in 4614
this Section that can be used to inform the patient about the radiation doses from dental x-4615
ray procedures and the nature of risk associated with these doses. Additional background 4616
on radiation risk assessment is found in Appendix I. Dentists are encouraged to use this 4617
information to educate their patients as opportunity provides. 4618
4619
Tables E.1 and E.2 are taken from literature reporting 2007 ICRP calculations of 4620
effective dose. 4621
4622
Figure E.1 shows the distribution of absorbed radiation doses throughout structures in 4623
the maxillofacial region following a full mouth series (Gibbs et al., 1987). While this is an 4624
old figure using D-speed film, it is the only such figure in the literature. The doses for 4625
E-F-speed film or digital imaging would be approximately one-half of the printed values. 4626
4627
4628
NCRP SC 4-5 Draft March 16, 2016
197
TABLE E.1— Effective dose of dental panoramic radiography units. 4629
Unit Manufacturer kVp mA Time
(s)
Effective
Dose
(µSv)
Reference
Veraviewepocs 3De Morita 78 10 7.4 11 Al-Okshi (2013)
ProMax 3D Planmeca 66 9 16 8 Al-Okshi (2013)
ProMax Planmeca 74 12 16 14 Al-Okshi (2013)
OP200 Instrumentarium 66 10 17.6 11 Han (2013)
Orthophos CD Sirona 71 15 13.9 14 Han (2013)
Orthophos XG plus Sirona 69 15 14.1 19 Han (2013)
ProMax Planmeca 66 12 16 26 Grünheid T (2012)
OP100 Instrumentarium 73 12 17.6 22 Ludlow (2011)
Orthophos XG Sirona 64 8 14.1 14 Ludlow (2011)
ProMax Planmeca 68 13 16 24 Ludlow (2011)
Kodak - 9000 Carestream 70 10 14.3 15 Ludlow (2011)
SCANORA 3D Soredex 73 6.3 15 13 Ludlow (2011)
OP 200 VT Instrumentarium 66 8.9 16.8 15 Ludlow (2011)
Average 70 11 15 16
Standard deviation 4.1 2.6 2.7 5.4
NCRP SC 4-5 Draft March 16, 2016
198
TABLE E.2— Effective Doses for plain dental radiographic views. 4630
Technique Effective Dose
(µSv)
FMX with D Speed film and Round Cone† 388
FMX with PSP or F-Speed film and Round Cone 171
FMX with PSP or F-Speed film and Rectangular Collimation 35
BWs with PSP or F-Speed film and Rectangular Collimation 5
PA Cephalometric - PSP 5.1
Lateral Cephalometric - PSP 5.6
4631
4632
NCRP SC 4-5 Draft March 16, 2016
199
4633
4634
4635
4636
4637
4638
4639
4640
4641
4642
4643
4644
4645
Fig. E.1. Isodose curves calculated for full-mouth intraoral examinations obtained at 4646
80 kVp using optimum exposures for D-speed film. Lines without numeric annotations 4647
indicate skin surface and internal hard tissue surfaces. Numeric annotations indicate 4648
absorbed dose in microgray (1,000 µGy = 1 mGy). For example, the tissues contained 4649
within the contour labeled 5,000 receive an absorbed dose of at least 5 mGy (5,000 µGy). 4650
(A) Transverse section through the occlusal plane, 7 cm round beams. Note that the teeth 4651
receive absorbed doses of at least 12 mGy, and all tissues anterior to the cervical spine 4652
receive at least 5 mGy. (B) Same plane with rectangular collimation. Areas contained 4653
within each isodose contour are smaller than in A. Absorbed dose is generally confined to 4654
the facial area, with posterior regions receiving absorbed doses no >1 mGy (Gibbs et al., 4655
1987). 4656
4657
NCRP SC 4-5 Draft March 16, 2016
200
E.2 Operator Dosimetry 4658
4659
Figure E.2 provides the supporting evidence for recommendation that the operator 4660
exposing intraoral images should stand at an angle of 90 to 135 degrees from the central 4661
ray (Figure 4.1). 4662
4663
NCRP SC 4-5 Draft March 16, 2016
201
4664
4665
4666
4667
4668
4669
4670
4671
4672
4673
4674
4675
4676
Fig. E.2. Operator exposure as a function of position in a room relative to patient and 4677
primary beam for intraoral imaging. View from above for a left molar bitewing. The heavy 4678
line in the polar coordinate plot indicates dose by its distance from the center of the plot. 4679
Maximum dose is in the exit beam on the side of the patient opposite the x-ray tube. The 4680
recommended positions for minimum exposures (crosses) are at 45 degrees from the exit 4681
beam. Note that most scattered radiation is backward toward the x-ray tube (de Haan and 4682
van Aken, 1990). 4683
4684
NCRP SC 4-5 Draft March 16, 2016
202
Appendix F 4685
4686
Dosimetry for Multidetector-Multislice Imaging of Dentomaxillofacial Areas 4687
4688
TABLE F.1— Effective dose from MDCT scanning of dental and maxillofacial areas. 4689
Unit Exam kVp mA Time
(s)
Voxel
(mm)
Height
(cm)
Effective
Dose
(µSv)
Somatom Emotion 6 - low
dose (Jeong, 2012) Mandible 110 3.1 16 0.6 5 199
Somatom Sensation 10
(Jeong, 2012) Mandible 120 23.8 8.4 0.6 5 426
Somatom VolumeZoom 4
(Loubele, 2009) Mandible 120 90 15 0.75 7 494
Somatom Sensation 16
(Loubele, 2009) Mandible 120 90 8 0.75 6 474
Mx8000 IDT
(Loubele, 2009) Mandible 120 140 8 0.75 6 541
Somatom 64 - low dose
(Ludlow, 2008) Jaws 120 48 – 64 1 0.6 12 534
Somatom 64
(Ludlow, 2008) Jaws 120 90 1 0.6 12 860
Somatom VolumeZoom 4
(Loubele, 2009) Head 120 90 44 0.75 23 1,110
Somatom Sensation 16
(Loubele, 2009) Head 120 90 29 0.75 23 995
Mx8000 IDT
(Loubele, 2009) Head 120 140 30 0.75 23 1,160
4690
4691
NCRP SC 4-5 Draft March 16, 2016
203
TABLE F.2—Summary of effective doses from MDCT scanning of dental and maxillofacial 4692
areas. 4693
MDCT - Isotropic Voxels
Average
Effective Dose
(µSv)
Low
(µSv)
High
(µSv)
Mandible 427 199 541
Jaws 697 534 860
Head 1,088 995 1,160
4694
NCRP SC 4-5 Draft March 16, 2016
204
Appendix G 4695
4696
Dosimetry for Dental Cone Beam CT Imaging 4697
4698
The effective dose data in Tables G1 through G6 as well as the salivary gland, thyroid 4699
gland, and brain components of effective dose (recorded without weighting as equivalent dose) 4700
were assessed using one-way ANOVA (Tables G7 to G11), followed by pairwise comparisons 4701
when appropriate (Tukey HSD). 4702
4703
4704
NCRP SC 4-5 Draft March 16, 2016
205
TABLE G.1— Effective doses for standard or default exposures for large FOV CBCT units 4705
(>15 cm height). 4706
Unit Name (reference)
Manufacturer
FOV Size
H ・ Wa
(cm)
kVp mAs Effective
Dose (µSv)
3D eXam (Rottke, 2013)
Imaging Sciences 17 ・ 23 120 18.5 78
3D eXam (Schilling, 2013)
Imaging Sciences 17 ・ 23 120 18.5 72
CB Mercuray (Librizzi, 2011; Jadu, 2010)
Hitachi 19 ・ 19b 120 150 924c
CB Mercuray (Ludlow, 2008; Jadu 2010)
Hitachi 19 ・ 19b 100 100 518c
CS 9500 (Ludlow, 2011; Pauwels, 2012; Rottke, 2013)
Carestream 18 ・ 20 90 108 150c
DCT PRO (Qu, 2012a)
VATECH 19 ・ 20 90 105 254
i-CAT FLX (Ludlow, 2013)
Imaging Sciences 17 ・ 23 120 18.5 69
i-CAT NG (Davies, 2012. Grunheid, 2012; Ludlow, 2008; Morant, 2013; Roberts, 2009)
Imaging Sciences 17 ・ 23 120 18.5 71c
Iluma Elite (Ludlow, 2008)
Imtec 19 ・ 19 120 152 498
NewTom 3G (Ludlow, 2008)
Cefla 19 ・ 19b 110 8.1 68
NewTom 9000 (Qu, 2012b)
Cefla 19 ・ 19b 110 automatic 95
SkyView (Pauwels, 2012)
Cefla 17 ・ 17b 90 51.5 87
ProMax Mid – stitched (Ludlow, 2015)
Planmeca 16 ・ 16 90 325 283
4707
a H ・ W = height x width. 4708
b Spherical field of view. 4709
c Extrapolated or averaged dose. 4710
NCRP SC 4-5 Draft March 16, 2016
206
4711
TABLE G.2— Effective doses for standard or default exposures for medium FOV CBCT 4712
units (10 to 15 cm height). 4713
Unit Name (reference)
Manufacturer
FOV Size
H ・ Wa
(cm)
kVp mAs Effective
Dose (µSv)
3D Accuitomo 170 (Theodorakou, 2012; Ludlow, 2015)
J Morita 10 ・ 14 90 87.5 229
3D Accuitomo 170 (Theodorakou, 2012; Ludlow, 2015)
J Morita 12 ・ 17 90 87.5 271
3D Accuitomo 170 (Ludlow, 2015)
J Morita 10 ・ 10 90 87.5 257
3D eXam (Schilling, 2014)
Imaging Sciences 13 ・ 16 120 18.5 107
CB Mercuray (Jadu, 2010; Ludlow, 2008; Librizzi, 2011)
Hitachi 15 ・ 15b 120 150 514†
CB Mercuray (Lukat, 2013)
Hitachi 15 ・ 15 b 100 96 227
CS 9300 (Ludlow, 2015)
Carestream 13.5 ・ 17 90 45.2 184
CS 9300 (Ludlow, 2015)
Carestream 11 ・ 17 90 51.5 204
CS 9300 (Ludlow, 2015)
Carestream 10 ・ 10 90 25 76
CS 9500 (Ludlow, 2011)
Carestream 9 ・ 15 85 108 98
DCT PRO (Qu, 2012a)
VATECH 10 ・ 16 90 105 249
Galileos Comfort (Ludlow, 2008; Pauwels, 2012)
Sirona 15 ・ 15 b 85 21 67c
i-CAT Classic (Ludlow, 2008)
Imaging Sciences 13 ・ 16 120 18.5 69
i-CAT FLX Imaging Sciences 11 ・ 16 120 18.5 79
NCRP SC 4-5 Draft March 16, 2016
207
(Ludlow, 2013)
i-CAT FLX (Ludlow, 2013)
Imaging Sciences 13 ・ 16 120 18.5 85
i-CAT NG (Morant, 2013)
Imaging Sciences 10 ・ 16 120 18.5 53
i-CAT NG (Morant, 2013)
Imaging Sciences 11 ・ 16 120 18.5 58
i-CAT NG (Davies, 2012; Ludlow, 2008; Morant, 2013; Pauwels, 2012; Roberts, 2009; Theodorakou, 2012)
Imaging Sciences 13 ・ 16 120 18.5 84
Iluma Elite (Pauwels, 2012)
Imtec 14 ・ 21 120 76 368
NewTom VG (Pauwels, 2012)
QR, Verona 10 ・ 15 110 10.4 83
NewTom VG (Theodorakou, 2012)
Cefla 11 ・ 15 110 auto 81
NewTom VGi (Pauwels, 2012; Ludlow, 2012)
QR, Verona 15 ・ 15 110 8.8 147 c
OP300 Maxio Instumentarium 13 ・ 15 90 45 102
Scanora 3D (Pauwels, 2012)
Soredex 13.5 ・ 14.5 85 48 68
4714
a H ・ W = height ・ width. 4715
b Spherical field of view. 4716
c Extrapolated or averaged dose. 4717
4718
NCRP SC 4-5 Draft March 16, 2016
208
TABLE G.3— Effective doses for standard or default exposures for dento-alveolar centered small FOV CBCT units (<10 cm height). 4719
Unit Name Manufacturer
FOV Size
H ・ Wa
(cm)
kVp mAs Effective
Dose (µSv) Reference
3D eXam Kavo 8 ・ 16 120 18.5 88b Schilling (2013)
3D eXam Kavo 8 ・ 8 120 18.5 62 Schilling (2013)
i-CAT FLX Imaging Sciences 8 ・ 16 120 18.5 70 Ludlow (2013)
i-CAT FLX Imaging Sciences 8 ・ 16 120 18.5 70 Ludlow (2013)
i-CAT FLX Imaging Sciences 8 ・ 8 120 18.5 44 Ludlow (2013)
i-CAT NG Imaging Sciences 8 ・ 16 120 18.5 65 Grunheid (2012)
i-CAT NG Imaging Sciences 8 ・ 8 120 18.5 29 Morant (2013)
Kodak 9500 Carestream 8 ・ 15 90 108 92 Pauwels (2012)
NewTom VGi QR, Verona 8 ・ 12 110 6.14 42b Pauwels (2012)
Prexion 3D TeraRecon 8 ・ 8 90 76 189 Ludlow (2008)
ProMax 3D Planmeca 8 ・ 8 84 72 581b Suomalainen (2009); Ludlow (2008)
Promax 3D-upgraded filtration
Planmeca 8 ・ 8 84 169 138b Pauwels (2012); Theodorakou (2012)
4720
NCRP SC 4-5 Draft March 16, 2016
209
a H ・ W = height ・ width. 4721
b Extrapolated or averaged dose. 4722
4723
NCRP SC 4-5 Draft March 16, 2016
210
4724
TABLE G.4— Effective doses for standard or default exposures for small FOV CBCT units (<10 cm height) maxillary views. 4725
Unit Name Mfg.
FOV Size
H ・ Wa
(cm)
Region of Interest
kVp mAs Effective
Dose (µSv) Reference
3D Accuitomo 170 J Morita 5 ・ 10 Maxilla 90 87.5 54 Pauwels (2012)
3D Accuitomo 170 J Morita 5 ・ 14 Maxilla 90 87.5 70 Theodorakou (2012)
3D eXam Kavo 4 ・ 16 Maxilla 120 18.5 33 Schilling (2013)
CB Mercuray Hitachi 10b Maxilla 120 150 125 Jadu (2010)
i-CAT FLX Imaging Sciences 6 ・ 16 Maxilla 120 18.5 32 Ludlow (2013)
i-CAT NG Imaging Sciences 6 ・ 16 Maxilla 120 18.5 36.8c Davies (2012; Morant (2013); Pauwels (2012); Roberts (2009); Theodorakou (2012)
Pan eXam Plus 3D Kavo 6 ・ 4 Maxilla 90 23 40 Schilling (2013)
Pan eXam Plus 3D Kavo 6 ・ 8 Maxilla 90 47 79 Schilling (2013)
Promax 3D-upgraded filtration
Planmeca 5 ・ 8 Maxilla 84 192 115c Qu (2010)
Scanora 3D Soredex 7.5 ・ 10 Maxilla 85 30 46 Pauwels (2012)
3D Accuitomo 170 J Morita 4 ・ 4 Maxillary anterior
90 87.5 32 Theodorakou (2012)
NCRP SC 4-5 Draft March 16, 2016
211
CS 9000 Carestream 4 ・ 5 Maxillary anterior
70 107 19 Pauwels (2012)
PaX-Uni3D VATECH 5 ・ 5 Maxillary anterior
85 120 44 Pauwels (2012)
Promax 3D-upgraded filtration
Planmeca 4 ・ 5 Maxillary anterior
84 120 10 Al-Okshi (2013)
Veravieweposcs 3D J Morita 4 ・ 4 Maxillary anterior
80 47.5 21 Al-Okshi (2013)
4726
a H ・ W = height ・ width. 4727
b Spherical field of view. 4728
c Extrapolated or averaged dose. 4729
4730
NCRP SC 4-5 Draft March 16, 2016
212
TABLE G.5— Effective doses for standard or default exposures for small FOV CBCT units (<10 cm height) mandibular views. 4731
Unit Name Manufacturer
FOV Size
H ・ Wa
(cm)
Region of Interest
kVp mAs Effective
Dose (µSv) Reference
3D eXam Kavo 4 ・ 16 Mandible 120 18.5 38 Schilling (2013)
3D eXam Kavo 5 ・ 10 Mandible 120 18.5 56b Jeong (2012)
AZ3000CT Asahi 7 ・ 7 Mandible 85 102 332 Jeong (2012)
CB Mercuray Hitachi 10 Mandible 120 150 414b Jadu (2010); Ludlow (2008)
DCT PRO VATECH 7 ・ 16 Mandible 90 105 180 Qu (2012a)
i-CAT FLX Imaging Sciences 6 ・ 16 Mandible 120 18.5 61 Ludlow (2013)
i-CAT NG Imaging Sciences 6 ・ 16 Mandible 120 18.5 53b Davies (2012); Morant (2013); Pauwels (2012); Roberts (2009); Theodorakou (2012)
Implagrapy VATECH 5 ・ 8 Mandible 80 66.5 83 Jeong (2012)
Pan exam Plus 3D Kavo 6 ・ 4 Mandible 90 23 49 Schilling (2013)
Pan exam Plus 3D Kavo 6 ・ 8 Mandible 90 47 110 Schilling (2013)
Picasso Trio VATECH 7 ・ 12 Mandible 85 91 81 Pauwels (2012)
Promax 3D-upgraded filtration
Planmeca 5 ・ 8 Mandible 84 192 150b Qu (2010)
NCRP SC 4-5 Draft March 16, 2016
213
Scanora 3D Soredex 7.5 ・ 10 Mandible 85 30 47 Pauwels (2012)
3D Accuitomo 170 J Morita 4 ・ 4 Mandibular posterior
90 87.5 43 Pauwels (2012)
CS 9000 Carestream 4 ・ 5 Mandibular posterior
70 107 40 Pauwels (2012)
Veravieweposcs 3D J Morita 4 ・ 4 Mandibular posterior
80 47 22 Al-Okshi (2013)
4732
a H ・ W = height ・ width. 4733
bExtrapolated or averaged dose. 4734
NCRP SC 4-5 Draft March 16, 2016
214
TABLE G.6— Effective doses for standard or default exposures for small FOV CBCT Units (<10 cm height) mandibular views. 4735
Unit Name Manufacturer FOV Size
H ・ Wa (cm) Region of Interest
kVp mAs Effective
Dose (µSv) Reference
3D eXam Kavo 4 ・ 16 Mandible 120 18.5 38 Schilling (2013)
3D eXam Kavo 5 ・ 10 Mandible 120 18.5 56 b Jeong (2012)
AZ3000CT Asahi 7 ・ 7 Mandible 85 102 332 Jeong (2012)
CB Mercuray Hitachi 10 Mandible 120 150 414 b Jadu (2010); Ludlow, 2008)
DCT PRO VATECH 7 ・ 16 Mandible 90 105 180 Qu (2012a)
i-CAT FLX Imaging Sciences 6 ・ 16 Mandible 120 18.5 61 Ludlow (2013)
i-CAT NG Imaging Sciences 6 ・ 16 Mandible 120 18.5 53 b Davies (2012); Morant (2013); Pauwels (2012); Roberts (2009); Theodorakou (2012)
Implagrapy VATECH 5 ・ 8 Mandible 80 66.5 83 Jeong (2012)
Pan eXam Plus 3D Kavo 6 ・ 4 Mandible 90 23 49 Schilling (2013)
Pan eXam Plus 3D Kavo 6 ・ 8 Mandible 90 47 110 Schilling (2013)
Picasso Trio VATECH 7 ・ 12 Mandible 85 91 81 Pauwels (2012)
Promax 3D-upgraded filtration
Planmeca 5 ・ 8
Mandible 84 192 150 b Qu (2010)
NCRP SC 4-5 Draft March 16, 2016
215
Scanora 3D Soredex 7.5 ・ 10 Mandible 85 30 47 Pauwels (2012)
3D Accuitomo 170 J Morita 4 ・ 4
Mandibular posterior
90 87.5 43 Pauwels (2012)
CS 9000 Carestream 4 ・ 5
Mandibular posterior
70 107 40 Pauwels (2012)
Veravieweposcs 3D J Morita 4 ・ 4 Mandibular posterior
80 47 22 Al-Okshi (2013)
4736
a H ・ W = height ・ width. 4737
b Extrapolated or averaged dose. 4738
NCRP SC 4-5 Draft March 16, 2016
216
TABLE G.7— Effective dose was statistically associated with FOV size (p = 0.0109) Tukey HSD 4739
demonstrated substantial differences between large and small FOVs. 4740
Level Least Sq Mean (µSv)
Large A 240
Medium A B 149
Small B 92
4741
NCRP SC 4-5 Draft March 16, 2016
217
TABLE G.8— Salivary gland dose was not associated with FOV size (p = 0.8701). 4742
Level Least Sq Mean (µGy)
Large A 3,336
Medium A 2,779
Small A 2,754
4743
NCRP SC 4-5 Draft March 16, 2016
218
TABLE G.9—Thyroid dose (µGy) was statistically associated with FOV size (p = 0.0299). 4744
Tukey HSD demonstrated substantial differences between large and small FOVs. 4745
Level Least Sq Mean (µGy)
Large A 1,450
Medium A B 645
Small B 475
4746
NCRP SC 4-5 Draft March 16, 2016
219
TABLE G.10—Brain dose (µGy) was statistically associated with FOV size (p = 0.0047). Tukey 4747
HSD demonstrated substantial differences between large and small FOVs. 4748
Level Least Sq Mean (µGy)
Large A 2,159
Medium A B 1,101
Small B 211
4749
NCRP SC 4-5 Draft March 16, 2016
220
TABLE G.11—Small FOV maxillary versus mandibular doses were not statistically different by 4750
effective dose (p = 0.0566), brain (p = 0.3696), or salivary glands (p = 0.1987). Substantial 4751
differences in thyroid dose are present (p = 0.0407). 4752
Level Least Sq Mean (µGy)
Mandible 616
Maxilla 121
4753
NCRP SC 4-5 Draft March 16, 2016
221
Appendix H 4754
4755
Dental X-Ray Evaluation by Qualified Expert 4756
4757
H.1 Radiation Safety 4758
4759
Radiation Safety should be evaluated based on integrated exposure measurements using a 4760
dosimeter, taken at various locations within and near the x-ray source. It may be necessary to 4761
increase the milliamperage-seconds to obtain a reading on your survey instrument. Inquire about 4762
workload with the staff, controlled or noncontrolled occupancy of areas near x-ray sources, and 4763
verify by reviewing representative patient logs. These should be readily available on digital 4764
systems. The qualified expert should document that radiation exposures to occupationally 4765
exposed persons and the general public are in compliance with the applicable regulations. 4766
4767
CBCT systems are often located where panoramic units were previously installed. However, 4768
the scattered radiation dose from CBCT is substantially higher than for panoramic units (about 4769
an order of magnitude), due to the significantly larger field of view exposed in CBCT systems. 4770
Calculate the exposure to persons in the vicinity of the x-ray source following the principles of 4771
NCRP Report No. 147 and information provided in this report. While exposures and workloads 4772
may remain consistent from year-to-year for intraoral x-ray units, increased utilization of CBCT 4773
systems in recent years make it essential for the qualified expert to evaluate personnel exposure 4774
during each annual survey. At the very least, the qualified expert should recalculate estimated 4775
weekly exposures using initial area survey measurements and recent workload data. Results 4776
should be compared with requirements from the local jurisdiction. Pay particular attention to 4777
personnel who may be working within line of sight of a CBCT unit or in an adjacent room, and 4778
make appropriate recommendations to assure ALARA. 4779
NCRP SC 4-5 Draft March 16, 2016
222
4780
H.2 Evaluation of the Image Receptor and Dose 4781
4782
If the facility is using dental film, determine whether they are using D-speed film, E-speed 4783
film, F-speed film , or what is referred to as “E-F-speed” film. This may require some detective 4784
work, if the film is purchased by mail in bulk. While many facilities have converted to digital 4785
image receptors, recent data shows that among those still using film 78 % continue to use D 4786
speed film (Farris and Spelic, 2015). The image quality for E-, F-, and E-F-speed films is similar 4787
to that obtained with D-speed film (Bernstein, 2003; FDA, 2014; Ludlow, 2001; Syriopoulos, 4788
2001) at approximately one-half of the radiation dose (Table H.1). More information on the 4789
different speed films and image quality can be found at http://diquad.com/Tips.html. 4790
4791
Table H.1 provides other helpful information.. The average exposure for D-speed film is 4792
~2.3 mGy. This is much higher than necessary. D-speed film should be on the order of 1.50 to 4793
1.95 mGy (Table 6.1). In other words, there is no justifiable reason for dental doses to routinely 4794
exceed 1.95 mGy for D-speed film. Facilities that are using ‘D’ speed film should be advised of 4795
the lower doses possible with the use of ‘E’ or ‘F’ speed films. They should also be advised of 4796
the potential for low doses with digital-based equipment as shown in the table. 4797
4798
H.3 Film Processing Conditions and Quality 4799
4800
Processing conditions and quality have been found to vary considerably in the dental imaging 4801
community. Verify that proper time-temperature developing is being used. Film processing tips 4802
are included in http://diquad.com/Tips.html. Film processing is usually the weakest link in the 4803
imaging chain, with under-processing resulting in low contrast radiographs and increased 4804
patient doses. The histograms from the recent NEXT survey (Farris and Spelic, 2015) clearly 4805
demonstrate the broad range of patient doses and suboptimal film processing (approximately 4806
one-third of the facilities produce films with inferior contrast). To assist with testing processing 4807
conditions, consider an inexpensive step wedge or dental radiographic quality control device for 4808
4809
4810
NCRP SC 4-5 Draft March 16, 2016
223
TABLE H.1— Dental bitewing x-ray exposures (mR) for 2001, 2005, 2009.a 4811
Dental Bitewing for 2009 (n = 7,205)
Speed Total % of Total Average SD Highest
D 3,483 55 % 256 99 2,150
E 1,001 16 % 162 72 1,320
F 774 12 % 148 63 520
Digital 1,947 31 % 105 59 693
4812
Dental Bitewing for 2005 (n = 6,325)
Type Total % of Total Average SD Highest
D 3,084 49 % 258 93 860
E 1,118 18 % 162 70 786
F 500 8 % 140 67 952
Digital 1,623 26 % 106 58 712
Dental Bitewing for 2001 (n = 8,600)
Type Total % of Total Average SD Highest
D 5,127 81 % 262 106 3,308
E 1,674 26 % 161 68 675
F 510 8 % 148 58 650
Digital 1,289 20 % 110 64 560
4813
aCourtesy New York State Department of Health. 4814
4815
NCRP SC 4-5 Draft March 16, 2016
224
dental film processing quality. The dental radiographic quality control device is also helpful in 4816
assuring appropriate initial film exposure technique selection and processing conditions 4817
(Valachovic, 1981). 4818
4819
H.4. Evaluation of the X-Ray Generator and Output 4820
4821
The x-ray generator can be evaluation using standard techniques. Be sure that the radiation 4822
detector is properly positioned, and sized appropriately to include the complete x-ray beam. 4823
Modern units typically operate at only a single kilovoltage, 60 to 70 kVp, and a single 4824
milliamperage, 6 to 10 mA. Be sure to account for any effect of very short radiographic 4825
exposure times, i.e., overshoot of output for the first few milliseconds.. 4826
4827
H.5 Evaluation of the Beam Collimation 4828
4829
For intraoral radiographic units, consider recommending rectangular collimation, which has 4830
been shown to reduce effective dose four to five times by providing an x-ray beam that more 4831
closely approximates the rectangular image receptor (White and Pharoah, 2014). The qualified 4832
expert’s experience with the benefits (image quality and radiation safety) derived from 4833
collimating the x-ray beam to the image receptor in body radiography and fluoroscopy (for 4834
example), will be directly applicable here. 4835
4836
Evaluating collimation for panoramic or CBCT systems requires some pre-planning, and 4837
may be accomplished using GAF Chromic Film and the equipment manufacturer’s 4838
specifications for geometry. Figure H.1 shows how this may be accomplished. 4839
4840
H.6 Occupational Radiation Exposure Assessment 4841
4842
While many dental offices are not required to use personal dosimetry, increased utilization 4843
of digital and CBCT imaging may warrant a renewed assessment of occupational exposure with 4844
personnel dosimetry. The qualified expert should advise the facility management whether 4845
occupational dosimetry is appropriate or is required by state or local regulations. 4846
4847
NCRP SC 4-5 Draft March 16, 2016
225
4848
4849
4850
4851
4852
4853
4854
4855
4856
Fig. H.1. The photo on the left shows the self-developing x-ray film taped to the surface of 4857
the x-ray tube cover. The images at the right show two strips, following exposure (photos 4858
courtesy R. Pizzutiello). 4859
4860
NCRP SC 4-5 Draft March 16, 2016
226
Appendix I 4861
4862
Radiation Risk Assessment 4863
4864
I.1 Introduction 4865
4866
The assignment of risk of biological damage from radiation has long been an arena of 4867
considerable controversy. Damage from moderate to high doses are well documented and the 4868
risk well quantified. However, risks from small and very small doses are inferred from data for 4869
moderate to high doses based on one of several risk models. While there is growing new 4870
evidence, and strengthening of existing evidence, for damage from very low doses of radiation, 4871
there is considerable controversy over the methodology and conclusions in many of these 4872
studies, and the application of these population risks to individuals HPS, 2016; NCRP, 2010b; 4873
UNSCEAR, 2012). This is especially true in oral and maxillofacial imaging, where radiation 4874
doses (except for high resolution moderate-to-large field-of-view cone-beam CT imaging) are 4875
considerably smaller than in other fields of medical imaging. Nonetheless, dentistry as a 4876
profession has a responsibility for the radiation safety of the population-at-large as well as for 4877
the individual seeking care. 4878
4879
In the time since NCRP-145, Radiation Safety in Dentistry, there have been significant 4880
advances in the understanding of radiogenic DNA damage and repair, based on considerable 4881
laboratory research in genetics and molecular biology. Solidification of long-term studies of 4882
Japanese atomic bomb survivors, have increased confidence in risk estimates at low radiation 4883
doses. The understanding of genetic instability has given us a better understanding of the long 4884
latent periods associated with radiation carcinogenesis and heritable defects. Substantial 4885
publications elucidating the uncertainties in risk estimation have recently been published 4886
(NA/NRC, 2006; UNSCEAR, 2015b). Recent retrospective studies on large populations of 4887
head-irradiated children in the UNITED KINGDOM and in Australia, while eliciting some 4888
controversy over their epidemiologic methodology, have supported the existing risk modeling 4889
for radiogenic brain, thyroid, salivary gland and leukemia neoplasms (Brenner and Hall, 2007; 4890
NCRP SC 4-5 Draft March 16, 2016
227
Mathews et al., 2013). A recent publication provides a clear and comprehensive review of 4891
cancer risks from diagnostic imaging (Linet et al., 2012). 4892
4893
There must always be a balance between the benefit to the patient and the risk of damage to 4894
the patient when diagnostic x-radiation is used for imaging. There are many steps, 4895
recommended in this report, to maintain, or improve, the diagnostic quality of the images while 4896
minimizing the radiation dose to the patient – a patient care application of the ALARA 4897
principle. The goal is always to maximize diagnostic efficacy while minimizing radiation dose. 4898
4899
I.2 Definitions 4900
4901
I.2.1 Stochastic Effects 4902
4903
These low-dose effects consist almost entirely of cancer and mutation. They are generally 4904
rare events, occurring only after a latent period of years to decades for cancer and generations 4905
for genetic effects. Thus, they present practical problems in the design of studies for their 4906
investigation. In the cohort of 87,000 Japanese atomic-bomb survivors, there were 9335 deaths 4907
from solid cancers between 1950 and 1997 attributable to radiation exposure (Preston et al., 4908
2003). Recent analyses have confirmed and reinforced the risk estimates from the atomic-bomb 4909
survivor studies (Douple et al., 2011; Preston et al., 2007). 4910
4911
Risks from low doses have been estimated by extrapolation from high dose data (ICRP, 4912
1991; NA/NRC, 1990; 2006; NCRP, 1993b; UNSCEAR, 2000; 2015a). There has been 4913
considerable disagreement in the literature concerning the model used for such extrapolation to 4914
dose levels used in diagnostic imaging (AAPM, 2012). For radiation protection purposes, 4915
NCRP and most regulatory agencies worldwide use the most conservative, patient- and 4916
population-oriented modeling, and recommend use of the linear nonthreshold dose-response 4917
model for estimating the nominal risk of low doses (Douple et al., 2011; NA/NRC, 2006; 4918
NCRP, 1993b, 2009; Puskin, 2009; UNSCEAR, 2015a). 4919
4920
NCRP SC 4-5 Draft March 16, 2016
228
I.2.2 Deterministic Effects (Tissue Reactions) 4921
4922
Deterministic effects (also referred to as tissue reactions) result from structural or functional 4923
damage to tissue caused by irradiation. The type and amount of tissue damage increases with 4924
dose once a threshold is passed. When sufficient numbers of functional parenchymal cells in a 4925
given organ or tissue are killed, then the function of that organ or tissue may be impaired or 4926
destroyed. If that function is vital, then the injury may be life threatening to the organism. 4927
Classic examples of tissue reactions are the acute radiation syndromes (Rubin and Casarett, 4928
1968), non-melanotic skin carcinogenesis and cataractogenesis. The dose thresholds for tissue 4929
reactions are sufficiently large that it is highly unlikely that a dental worker or a patient would 4930
suffer a tissue reaction, provided that common radiation safety precautions are followed. 4931
4932
I.2.3 Dose Language 4933
4934
In this document, and throughout radiation biology and radiation health physics literature, 4935
the terms high, moderate, low and very low radiation doses or exposures are used. In this 4936
document, the terms are defined in effective dose units as follows (UNSCEAR, 2015a): 4937
4938
average annual background radiation dose in the United States = 6.2 mSv; 4939
high = greater than ~1 Sv; 4940
moderate = ~100 mSv to ~1 Sv; 4941
low = ~10 to ~100 mSv (dose to an individual from multiple whole-body CT scans 4942
and from multiple large field-of-view, high resolution CBCT scans); and 4943
very low = less than ~10 mSv [dose to an individual from conventional radiology (i.e., 4944
without CT or fluoroscopy)]. 4945
4946
NCRP SC 4-5 Draft March 16, 2016
229
I.3 Studies of Irradiated Human Populations 4947
4948
I.3.1 Introduction 4949
4950
The nature of the risk of carcinogenesis at low radiation doses has long been the subject of 4951
controversy. Major publications during recent years have focused on uncertainties in risk 4952
estimation at low doses (NCRP, 2012; UNSCEAR, 2015b). Several models have been 4953
developed to explain low dose risk, and these are shown in the graph below. 4954
4955
The committee finds the linear nonthreshold (LNT) model to be a computationally 4956
convenient starting point. Actual risk estimates improve upon this simplified model by using a 4957
dose and dose-rate effectiveness factor (DDREF), which is a multiplicative adjustment that 4958
results in downward estimation of risk and is roughly equivalent to using the line labeled 4959
“Linear Nonthreshold” (low dose rate). The latter is the zero-dose tangent of the linear-4960
quadratic model. While it would be possible to use the linear-quadratic model directly, the 4961
DDREF adjustment to the linear model is used to conform with historical precedent dictated in 4962
part by simplicity of calculations. In the low-dose range of interest, there is essentially no 4963
difference between the two (adapted from Brenner and Elliston, 2004). 4964
4965
A meta-analysis of data from cohorts with prolonged occupational exposure has indicated 4966
that risks per unit dose are consistent with those derived from the Life Span Study (LSS) cohort 4967
of the atomic bombing survivors (Jacob et al., 2009; UNSCEAR, 2015b). Recent evidence from 4968
continued analysis of cancer in Japanese survivors of the atomic bombings, radiation workers in 4969
the UNITED KINGDOM, Canada and the United States, and children exposed to diagnostic 4970
head CT exposures in Australia have provided substantial direct evidence that solid 4971
tumorigenesis follows the linear model and that leukemogenesis follows the linear-quadratic 4972
model. 4973
4974
Most of the information on radiation risks therefore still comes from studies of populations 4975
with medium to high doses, with the notable exceptions of childhood cancer risk following in 4976
utero exposures and thyroid cancer risk following childhood exposures, for which significant 4977
increases have been shown consistently in the low- to medium-dose range (NA/NRC, 2006). 4978
4979
4980
NCRP SC 4-5 Draft March 16, 2016
230
4981 Fig. I.1. Models of low dose radiogenic cancer risk (NA/NRC, 2006). 4982
4983
4984
NCRP SC 4-5 Draft March 16, 2016
231
Brenner et al. (2007), estimate that from 1.5 to 2 % of all cancers in the United States may 4985
be attributable to the radiation from CT studies. An annual growth rate of >10 % y–1 for CT 4986
procedures in the United States (NCRP, 2009) appears to be mirrored in the growth rate of 4987
CBCT since its introduction (Farris and Spelic, 2015). 4988
4989
I.3.2 Atomic Bomb Survivor Lifetime Studies 4990
4991
Survivors of the atomic bombings of Hiroshima and Nagasaki and their offspring comprise 4992
the single largest cohort exposed to ionizing radiation that is currently being followed, and are 4993
the major source of lifetime studies of radiation-induced cancers, other diseases, and life 4994
shortening. A major reevaluation of the dosimetry at Hiroshima and Nagasaki has recently been 4995
completed that lends more certainty to dose estimates and provides increased confidence in the 4996
relationship between radiation exposure and the health effects observed in this population. 4997
4998
Solid tumors that are well described by the linear model include female breast and thyroid, 4999
while leukemias appear to fit the linear-quadratic model best. This is shown in the graph below. 5000
5001
Additional new information is also available from radiation worker studies, medical 5002
radiation exposures, and populations with environmental exposures. Although the cancer risk 5003
estimates have not changed greatly since the 1990 BEIR V report (NA/NRC, 1990), confidence 5004
in the estimates has risen because of the increase in epidemiologic and biological data available 5005
to the committee (Douple et al., 2011; NA/NRC, 2006). 5006
5007
I.3.3 Children Irradiated for Tinea Capitis and Enlarged Thymus 5008
5009
Studies on the risk of thyroid cancer following irradiation of the head for tinea capitis has 5010
been extensively followed, from post-WW2 through 1986. These studies have shown a clear 5011
risk when radiation occurred in childhood – especially before 10 y of age. There was a fourfold 5012
increase in the incidence of thyroid cancer and a twofold increased incidence in benign thyroid 5013
tumors (Ron et al., 1989). Additionally, there was a 4.5-fold increase in the incidence of 5014
5015
NCRP SC 4-5 Draft March 16, 2016
232
5016
5017
5018
5019
5020
5021
5022
5023
5024
5025
5026
5027
5028
5029
Fig. I.2. Excess relative risks of solid cancer for Japanese atomic bomb survivors. Plotted 5030
points are estimated excess relative risks of solid cancer incidence (averaged over sex and 5031
standardized to represent individuals exposed at age 30 y who have attained age 60 y) for 5032
atomic bomb survivors, with doses in each of 10 dose intervals, plotted above the midpoints of 5033
the dose intervals. Vertical lines represent approximate 95 % confidence intervals. Solid and 5034
dotted lines are estimated linear and linear-quadratic models for excess relative risk, estimated 5035
from all subjects with doses in the range 0 to 1.5 Sv. A linear-quadratic model will always fit 5036
the data better than a linear model, since the linear model is a restricted special case with the 5037
quadratic coefficient equal to zero. For solid cancer incidence however, there is no statistically 5038
significant improvement in fit due to the quadratic term. It should also be noted that in the low-5039
dose range of interest, the difference between the estimated linear and linear-quadratic models 5040
is small relative to the 95 % confidence intervals. The insert shows the fit of a linear-quadratic 5041
model for leukemia to illustrate the greater degree of curvature observed for that cancer 5042
(NA/NRC, 2006) (adopted from NA/NRC, 2006, Figure ES-1). 5043
5044
NCRP SC 4-5 Draft March 16, 2016
233
malignant salivary gland tumors and a 2.6-fold increase in benign salivary gland tumors in the 5045
same population (Modan et al., 1998). 5046
5047
Children in Rochester, NY who received X-ray treatment for enlarged thymus glands 5048
between 1926 and 1957 prior to six months of age showed statistically significant increases of 5049
both benign and malignant thyroid tumors (Shore et al., 1985), as well as tumors of bone, 5050
nervous system, salivary glands, skin and female breast (Hildreth et al., 1985). The most recent 5051
study (Shore et al., 1993) again showed increased risk of thyroid cancer, even at low doses. 5052
5053
These data all fit well with a LNT model for thyroid carcinogenesis in children. 5054
5055
I.3.4 Females Receiving Fluoroscopy for Tuberculosis Treatment Follow-up 5056
5057
Significant increases in breast cancer was found in a cohort study of 64,172 tuberculosis 5058
patients of whom 25,007 received highly fractionated radiation from repeated fluoroscopy for 5059
lung collapse treatment of tuberculosis. There was a significant increase in risk of breast cancer 5060
in a dose dependent manner, commensurate with the LNT model (Boice et al., 1991). The 5061
excess cancer risk did not occur until 15 y after exposure, and held for over 50 y (Boice et al., 5062
1991a; Davis et al., 1989; Howe and McLaughlin, 1996; Miller et al., 1989; NA/NRC, 2006) 5063
5064
I.3.5 United Kingdom National Registry of Radiation Workers 5065
5066
This study has provided the most recent, direct estimates of long-term, low-dose, low-LET 5067
radiation effects on occupationally exposed populations, and has provided estimates of 5068
leukemia and all solid cancer risks. Risks, comparable to those in the atomic bomb survivors, 5069
range from slightly below to twice above those estimated using the current linear, nonthreshold 5070
model. The ERR/Gy calculated from the Nuclear Industry Workers study was comparable with 5071
risk estimates for atomic bomb survivors for both solid tumors and leukemias (Muirhead et al., 5072
2009). 5073
5074
5075
NCRP SC 4-5 Draft March 16, 2016
234
5076
5077
Fig. I.3. Incidence rate ratio (IRR) for all types of cancer in exposed versus unexposed 5078
individuals, by number of CT scans (Matthews et al., 2013). 5079
5080
NCRP SC 4-5 Draft March 16, 2016
235
I.3.6 2013 Australian CT Study of Electronic Medicare Data 5081
5082
This study examined 680,000 children receiving CT scans from 1985 to 2005 versus 5083
10.9 million controls. Overall cancer incidence was 24 % higher in those receiving CT scans, 5084
and the incidence increased with increasing numbers of scans, and was greater for children 5085
<5 y. These results confirmed U.K. Radiation Workers study of increased incidence of 5086
leukemia and brain cancer, and added other solid tumors (Mathews et al., 2013). 5087
5088
I.4 Effects of In Utero Exposure 5089
5090
In the case of in utero exposure (exposure of the fetus during pregnancy) during diagnostic 5091
radiography, it was reported that excess cancers could be detected at doses as low as 10 mSv 5092
(Doll and Wakeford, 1997). 5093
5094
In the domain of conventional diagnostic dental radiology, the in utero radiation dose is so 5095
small as to be essentially negligible. The measured dose in utero from a full-mouth series of 5096
intraoral images is 0.25mSv (White and Pharoah, 2014). Thus, we project that the risk to a 5097
developing embryo/fetus from conventional dental imaging is negligible. Risk from CBCT 5098
examinations can range from very small when small FOV and low dose parameters are used, to 5099
comparable to MDCT when large FOV and high dose parameters are used. 5100
5101
Recent reports based on atomic bomb survivors compared the risk estimates for those 5102
exposed in utero to those exposed during childhood as to the incidence of solid cancer at ages 5103
12. These studies suggest that in utero exposure does not confer greater adult cancer risk than 5104
childhood exposure. However, better understanding of cancer risks from in utero exposures and 5105
further follow-up of those exposed in utero and as children to older ages is needed” (Douple 5106
et al., 2011; Linet, 2012). 5107
5108
I.5 Effects on Children 5109
5110
Children have sensitivity anywhere from 2x to 10x greater than adults, depending on the 5111
cancer being considered. This is largely a function of their tissues, composed of cells with 5112
NCRP SC 4-5 Draft March 16, 2016
236
higher proliferative rates, less differentiation and longer mitotic future. The risk is greater the 5113
younger the child, and diminishes rapidly after 10 to 15 y of age. 5114
5115
Figure I.4 shows the risk differences due to age (Brenner and Hall, 2007). 5116
5117
I.5.1 Joint Commission Report (2011) 5118
5119
In August, 2011, The Joint Commission published a Sentinel Event Alert (TJC, 2011). They 5120
cited the near doubling of the U.S. population’s total exposure to ionizing radiation, specifying 5121
the significant increases in CT imaging, and used dose and risk estimates to emphasize the 5122
importance of ALARA and Image Gently guidelines when imaging adult and pediatric patients. 5123
This report estimated that 72 million CT scans in United States in 2007 could lead to 29,000 5124
future cancers – this would be 2 % higher than the normal frequency in the general population. 5125
This calculation assumed 2007 ICRP tissue weighting factors and LNT model for low dose 5126
carcinogenesis (UNSCEAR, 2015a). Cone-beam CT scans of children and adolescents were not 5127
specifically considered in this report, but the doses delivered in high-resolution, large field-of-5128
view CBCT examinations are of the same order of magnitude as the CT scans evaluated in this 5129
report. 5130
5131
I.5.2 2012 U.K. Study of Head CT Scans in Children 5132
5133
A recent study published Pearce et al. (2012) retrospectively examined a large cohort of 5134
patients receiving CT examinations during childhood for subsequent development of brain 5135
cancer and leukemia. This study showed that “use of CT scans in children [which] deliver 5136
cumulative doses of ~50 mGy might almost triple the risk of leukemia and doses of ~60 mGy 5137
might triple the risk of brain cancer” 5138
5139
These estimates agree reasonably with the 2001 estimates based on the atomic bomb 5140
survivor data (Preston et al., 1994; Ron et al.,1988). 5141
5142
NCRP SC 4-5 Draft March 16, 2016
237
5143
5144
Fig. I.4. Lifetime risks of radiogenic cancer versus age at time of a single head CT study. 5145
The risk of brain cancer and other solid cancers is considerably greater in children under the 5146
age of 15 y. A similar trend, but with substantially lower risk, applies to leukemia. 5147
5148
NCRP SC 4-5 Draft March 16, 2016
238
5149
TABLE I.1—U.K. CT study: Absolute risks versus atomic-bomb based estimates for a pediatric 5150
head CT scan, circa 1995.a 5151
U.K. CT study
(10 y follow-up)
U.K. CT study
(corrected to lifetime
follow-up)
Atomic-Bomb Estimates
(corrected to lifetime
follow-up)
Leukemia 1 in 10,000 1 in 7,500 1 in 10,000
Brain tumor 1 in 10,000 12 in 10,000 5 in 10,000
Pearce et al. (2012) Brenner and Hall (2007)
5152
aHall, E. (2012). Presentation at the American Academy of Oral and Maxillofacial Radiology 5153
Annual Session (Columbia University, New York). 5154
5155
NCRP SC 4-5 Draft March 16, 2016
239
I. Heritable Genetic Effects 5156
5157
Genetic instability is a molecular hallmark of radiogenic DNA damage. The transmission of 5158
such genetic instability across human generations is unknown at the present time. There is 5159
evidence for heritable genetic effects of radiation from animal experiments; however, these 5160
results to not apply directly to human beings. The risk estimates in animals are very small 5161
relative to the baseline rate of genetic diseases in the population, and are ~0.4 to 0.6 % of 5162
baseline risk per gray (NA/NRC, 2006). 5163
5164
In the atomic bomb survivor LSS, children from exposed parents (8,322) and unexposed 5165
parents (7,976) have been followed extensively in a long-term study initiated by Neel and 5166
Schull in the 1950s (Neel and Schull, 1956). Thus far, the level of mutagenesis, if present, is not 5167
detectable with the sensitivity of current methods. Additionally, there is no evidence of an 5168
increase of multifactorial diseases (e.g. hypertension, type-2 diabetes mellitus, 5169
hypercholesterolemia, ischemic heart disease, stroke) in this cohort. 5170
5171
The radiation doses for dentomaxillofacial imaging are in the microgray to milligray range 5172
Tissues not included in maxillofacial imaging effective dose calculations account for <2 % of 5173
the effective dose, and <0.1 % with use of a lap apron. Thus, heritable genetic effects from 5174
conventional dental imaging are essentially negligible. 5175
5176
5177
I.7 Risk from Traditional Oral and Maxillofacial Imaging: Intraoral, 5178
Panoramic, and Cephalometric 5179
5180
Doses from traditional dentomaxillofacial imaging are given in Appendix E and in Sections 5181
7.1.6, 8.1.1.1, and 8.2.1.1 of this report. These doses are in the microgray and milligray ranges. 5182
While the contribution of tissues in the maxillofacial area to the effective dose have been 5183
significantly increased by the revised ICRP (2007) tissue weighting factors, the doses from 5184
properly acquired intraoral, panoramic and cephalometric images are extremely small. 5185
Nevertheless, prudent practice and ALARA principles demand that the dentist use the dose 5186
NCRP SC 4-5 Draft March 16, 2016
240
reduction techniques, stated in this report, to minimize the dose to the patient, staff and public. 5187
These techniques also result in high quality diagnostic images. 5188
5189
I.8 Risk from CBCT Imaging 5190
5191
In children, the principle carcinogenesis risks from dentomaxillofacial imaging involve 5192
brain, thyroid and salivary glands. In adults, the risk primarily involves salivary glands as the 5193
risk of thyroid and brain tumors is very small. A comprehensive and detailed demonstration of 5194
the variety of doses that can result from CBCT examinations are shown in Appendix G and 5195
Section 9.1.1 of this report. 5196
5197
The revision of the tissue weighting factors by ICRP in 2007 have resulted in a 10 % 5198
increase in the weight of tissues located in the maxillofacial area, and a 28 % increase in the 5199
weight adjusted for distribution of these tissues. 5200
5201
Comparison of doses with MDCT show that CBCT doses can equal or exceed MDCT 5202
doses, especially when large FOV and/or high resolution presets are used. Using high resolution 5203
presets on small, medium and large field-of-view CBCT acquisitions can result in radiation 5204
doses that are greater than multi-detector CT scans of the head and neck. 5205
5206
Thus, risks for dental CBCT imaging are greater than previously thought and the risks for 5207
head CT exams as promulgated in the above studies can apply to dental CBCT imaging. 5208
5209
I.9 Other Risks in Daily Living for Comparison 5210
5211
There are many tables showing various risks from activities of daily living, ranging from 5212
where you live, what type of building you live in, your work, travel, and other habits. These can 5213
be effectively related to risks from diagnostic dental imaging. Background equivalents in one 5214
case and one-in-a-million risks in the other are shown in Tables I.3 and I.4. Most conventional 5215
dentomaxillofacial imaging, excluding CBCT, is considered to be approximately a one-in-a-5216
million risk of death during one’s lifetime from cancer. 5217
5218
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241
TABLE I.2—Summary of published data for CT and CBCT effective doses (2007 ICRP tissue 5219
weighting factors) adult phantoms – all protocols. 5220
5221
5222
5223
5224
5225
5226
5227
5228
5229
Scan Type Effective Dose Range (µSv)
Large FOV CBCT 46 – 1,073
Medium FOV CBCT 9 – 560
Small FOV CBCT 5 – 652
Medium FOV MDCT 534 – 860
NCRP SC 4-5 Draft March 16, 2016
242
TABLE I.3—Effective dose from radiographic examinations and equivalent background 5230
exposure (White and Pharoah, 2014). 5231
Examination Effective Dose (µSv) Equivalent Background
Exposure (d)
INTRAORAL a
RECTANGULAR COLLIMATION
Posterior bitewings: PSP or F-speed film 5 0.6
Full-mouth: PSP or F-speed film 35 4
Full-mouth: CCD sensor (estimated) 17 2
ROUND COLLIMATION
Full-mouth: D-speed film 388 46
Full-mouth: PSP or F-speed film 171 20
Full-mouth: CCD sensor (estimated) 85 10
EXTRAORAL
Panoramic a,b,c 9 – 24 1 – 3
Cephalometric a,b,d 2 – 6 0.3 – 0.7
CONE BEAM CT e,f
Large field of view 68 – 1,073 8 – 126
Medium field of view 45 – 860 5 – 101
Small field of view 19 – 652 2 – 77
MULTISLICE CT
Head: Conventional protocol f,g,h,i 860 – 1,500 101 – 177
Head: Low-dose protocol f,h 180 – 534 21 – 63
Abdomen g 5,300 624
Chest g 5,800 682
NCRP SC 4-5 Draft March 16, 2016
243
Plain films j
Skull 70 8
Chest 20 2
Barium enema 7,200 847
5232
CCD = charge-coupled device 5233
PSP = photostimulable phosphor 5234
5235
aData from Ludlow JB, Davies-Ludlow LE, White SC: Patient risk related to common dental radiographic examinations: 5236
The impact of 2007 International Commission on Radiological Protection Recommendation Regarding dose calculation, J 5237
Am Dent Assoc 139:1237·1243, 2008. 5238
bData from Lecomber AR, Yoneyama Y, Lovelock DJ et al: Comparison of patient dose from imaging protocols for dental 5239
implant planning using conventional radiography and computed tomography, Dentomaxillofac Radio 30:255·259, 2001. 5240
cData from Ludlow JB, Davies-Ludlow LE, Brooks SL: Dosimetry of two extraoral direct digital imaging devices: 5241
NewTom cone beam CT and Orthophos Plus OS panoramic unit, Dentomaxillofac Radio 32:229–234, 2003. 5242
dData from Gijbels F, Sanderink G, Wyatt J et al: Radiation doses of indirect and direct digital cephalometric radiography, 5243
Br Dent1 197:149·152, 2004. 5244
eData from Pauwels R, Beinsberger J, Callaert B et al: Effective dose range for dental cone beam computed tomography 5245
scanners, EurJ Radio 81 :267·271, 2012. 5246
fData from Ludlow JB, lvanovic M: Comparative dosimetry of dental CBCT devices and 64-slice CT for oral and 5247
maxillofacial radiology, Oral Surg Oral Med Oral Pathol Oral Radio Endod 106:1 06·114, 2008. 5248
gData from Shrimpton PC, Hillier MC, Lewis MA et al: National survey of doses from CT in the UK: 2003, Br J Radio 5249
79:968·980, 2006. 5250
hData from Loubele M, Jacobs R, Maes F et al: Radiation dose vs. image qualily for low-dose CT protocols of the head for 5251
maxillofacial surgery and oral implant planning, Radial Prot Dosimetry 117:211 -216, 05. 5252
iData from Loubele M, Bogaerts R, Van Dijck E et al: Comparison between effective radiation dose of CBCT and MSCT 5253
scanners for dentomaxillofacial applications, EurJ Radio 71:461·468, 2009. 5254
jData from European Commission: Referral guidelines for imaging, Radiation Protection 118, 2007. 5255
5256
NCRP SC 4-5 Draft March 16, 2016
244
TABLE I.4—Comparable risk table—risks that increase probability of death by one in a million 5257
(Wilson, 1979). 5258
Activity Cause of Death
Smoking 1.4 cigarettes Cancer, heart disease
Drinking 1/2 liter of wine Cirrhosis of the liver
Traveling 10 miles by bicycle Accident
Traveling 300 miles by car Accident
Flying 1,000 miles by jet Accident
Traveling 6,000 miles by jet Cancer caused by cosmic radiation
Living 2 months in average brick building Cancer caused by natural stone or radioactivity
1 chest x-ray taken in a good hospital Cancer caused by radiation
Living 2 months with a cigarette smoker Cancer, heart disease
Eating 40 tablespoons of peanut butter Liver cancer caused by aflatoxin B
Eating 100 charcoal broiled steaks Cancer from benzopyrene
Drinking 30 12 oz. cans of diet soda Cancer caused by saccharin (no longer classified as a carcinogen)
Living 5 y at site boundary of a typical nuclear power plant in the open
Cancer caused by radiation
Living 20 y near PVC plant Cancer caused by vinyl chloride (1976 standard)
Living 150 y within 20 miles of a nuclear power plant
Cancer caused by radiation
Risk of accident by living within 5 miles of a nuclear reactor for 50 y
Cancer caused by radiation
5259
5260
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245
Appendix J 5261
5262
Radiation Quantities and Units 5263
5264
NCRP presently expresses the values of radiation quantities in the International System of 5265
Units (SI units). These units have replaced the previously used units (Table J.1) in most of the 5266
scientific literature. The quantity exposure, previously expressed in roentgens (R), has been 5267
largely replaced by the quantity air kerma (K) (an acronym for kinetic energy released per unit 5268
mass), which is expressed in the same units as absorbed dose. However, some older instruments 5269
may provide readout only in roentgens while with others either SI or the legacy units may be 5270
selected. Absorbed dose, the energy imparted by ionizing radiation to matter per unit mass, is 5271
expressed in gray (Gy) (the previous name was the rad). Equivalent dose, expressed in sievert 5272
(Sv) (the previous name was the rem), is used extensively in radiation protection. Equivalent 5273
dose is the mean absorbed dose in an organ or tissue modified by the radiation weighting factors 5274
for different types of radiation (e.g., photons, neutrons, heavy charged particles). For diagnostic 5275
x rays (including dental), the radiation weighting factor is assigned the value of one, and 5276
absorbed dose in gray is numerically equal to equivalent dose in sievert. 5277
5278
Another quantity, effective dose, is useful in comparing different dose distributions in the 5279
body. It takes into account the equivalent doses in radiosensitive organs or tissues, each 5280
modified by a tissue weighting factor that represents the relative contribution of risk of 5281
stochastic effect to that organ or tissue to total stochastic risk. The tissues receiving the higher 5282
doses in patients from dental radiography are portions of the active bone marrow, thyroid, bone 5283
surface of the skull, brain, and salivary glands. 5284
5285
Conversion factors from the previous units to SI units are given in Table J.1. Detailed 5286
discussions of these concepts are given elsewhere (Bushberg et al., 2012; Johns, 1983). 5287
5288
NCRP SC 4-5 Draft March 16, 2016
246
TABLE J.1—Radiation quantities and units. 5289
Quantity
SI Unitsa Previous Unitsa
Conversion
Unit Special Name Unit Special Name
Exposure C kg–1 none C kg–1 roentgen (R) 1 R = 2.58 × 10–4 C kg–1
Kerma; absorbed
dose J kg–1
gray (Gy)
1 Gy = 1 J kg–1 erg g–1
rad
1 rad = 100 erg g–1 1 Gy = 100 rad
Equivalent dose;
effective dose J kg–1
sievert (Sv)
1 Sv = 1 J kg–1 erg g–1
rem
1 rem = 100 erg g–1 1 Sv = 100 rem
5290
aC = coulomb 5291
J = joule 5292
g = gram 5293
kg = kilogram5294
NCRP SC 4-5 Draft March 16, 2016
247
Abbreviations, Acronyms and Symbols 5295
5296
ALARA as low as reasonably achievable 5297
ANSI American National Standards Institute College 5298
CDRH Center for Devices and Radiological Health, U.S. Food and Drug 5299
Administration 5300
CTDI computed tomography dose index used for comparing radiation outputs 5301
from CT scanners under varying conditions 5302
d distance 5303
D absorbed dose 5304
DRL diagnostic reference level 5305
ESE entrance skin exposure 5306
HERCA Heads of European Radiological Protection Competent Authorities 5307
HIPAA Health Insurance Portability and Accountability Act 5308
HT equivalent dose 5309
K kerma or air kerma 5310
kerma kinetic energy released in a mass 5311
MDCT Multi-detector computed tomography 5312
NEXT Nationwide Evaluation of X-Ray Trends 5313
NRPB National Radiological Protection Board (now known as Health 5314
Protection Agency) 5315
T occupancy factor 5316
wR radiation weighting factor 5317
wT tissue weighting factor 5318
5319
NCRP SC 4-5 Draft March 16, 2016
248
Glossary 5320
5321
absorbed dose (D): The energy imparted by ionizing radiation to matter per unit mass of 5322
irradiated material at the point of interest. In the System Internationale (SI), the unit is J kg–1, 5323
given the special name gray (Gy). 1 Gy = 1 J kg–1. 5324
achievable dose: A dose which serves as a goal for optimization efforts. This dose is achievable 5325
by standard techniques and technologies in widespread use, while maintaining clinical image 5326
quality adequate for the diagnostic purpose. The achievable dose is typically set at the 5327
median value of the dose distribution. 5328
air kerma (K): (see kerma). Kerma in air. In this Report, the symbol K always refers to the 5329
quantity air kerma (in place of the usual symbol Ka), followed by an appropriate subscript to 5330
further describe the quantity (e.g., KP, air kerma from primary radiation). 5331
ALARA. As low as reasonably achievable. The principle of reducing the radiation dose of 5332
exposed persons to levels as low as is reasonably achievable. 5333
alveolar bone: The bone of the maxilla (upper jaw) or mandible (lower jaw) that supports the 5334
teeth. 5335
ampere: Unit of electric current. One ampere is produced by one volt acting through a resistance 5336
of 1 ohm. 5337
anode: The positive terminal of an x-ray tube. A tungsten block embedded in a copper stem and 5338
set at an angle to the cathode (the negative terminal of an x-ray tube, from which electrons 5339
are emitted). The anode emits x rays from the point of impact of the electron stream from the 5340
cathode. 5341
area (or facility) dosimeter: A device used to estimate the absorbed dose or effective dose 5342
received by personnel, but not worn by an individual. 5343
arthrography: Radiographic evaluation of a joint after injection of radiopaque contrast material 5344
into the joint space(s). 5345
attenuation: Loss of energy from a beam of ionizing radiation by scatter and absorption. 5346
background: Ionizing radiation present in the region of interest and coming from sources other 5347
than that of primary concern (see also natural background radiation). 5348
bisecting angle technique (bisect angle geometry): A technique for the radiographic exposure 5349
of intraoral image receptors whereby the central axis of the x-ray beam is directed at right 5350
angles to a plane determined by bisecting the angle formed by (1) the long axis of the tooth 5351
NCRP SC 4-5 Draft March 16, 2016
249
or teeth being imaged, and (2) the plane in which the image receptor is positioned behind the 5352
teeth. 5353
bitewing radiograph: A radiographic view that shows the crown of both the upper and lower 5354
teeth in a region on the same image. This view is used to detect interproximal tooth decay or 5355
alveolar bone loss associated with periodontal disease. So named because the patient bites 5356
upon a tab or “wing” projecting from the center of the image-receptor packet. 5357
cathode: (see anode). 5358
cephalometer: A device used in obtaining cephalometric images. It consists of a source 5359
assembly, a connector arm, a head holder, and an image-receptor holder. 5360
cephalometric radiography: Images of the head, primarily the dentofacial structures, usually 5361
obtained in lateral and posteroanterior orientation. Reproducible geometry is maintained by 5362
use of a cephalometer. The images are used to measure and study maxillofacial growth and 5363
maxilla-mandible relationships. 5364
collimator (or beam-limiting device): A device that provides a means to restrict the dimensions 5365
of the useful beam. 5366
computed tomography (CT): An imaging procedure that uses multiple x-ray transmission 5367
measurements and a computer program to generate tomographic images of the patient. 5368
computed radiography (CR): A radiographic imaging technique in which an image is captured 5369
by a photostimulable phosphor and converted into a digital image. This term is generally 5370
used in medical imaging. In dental imaging, the term PSP or storage phosphor imaging is 5371
generally used (see photostimulable storage phosphor). 5372
cone: (see position indicating device). 5373
constant potential: The electrical potential formed by a constant-voltage generator 5374
contrast: 5375
subject contrast: The difference between two anatomic structures in attenuation of an x-ray 5376
beam or, where C is subject contrast, and IA and IB are beam intensities after traversing 5377
structures A and B. 5378
image contrast: The ability of a film (or other image receptor) to translate subject contrast to 5379
differences in the resulting image. Image contrast depends on both image receptor 5380
characteristics and film or computer processing. 5381
NCRP SC 4-5 Draft March 16, 2016
250
cycles per millimeter (c mm–1): The SI unit for spatial frequency often used to specify 5382
resolution of an imaging system. Each cycle consists of a light bar and a dark bar. Similar to 5383
line pairs per millimeter (lp mm–1) in both definition and numeric value. 5384
craniofacial: Of or involving both the cranium and the face. 5385
CT dose index (CTDI): A standardized measure of radiation dose output of a CT scanner which 5386
allows the user to compare radiation output of different CT scanners. CTDI is not a dose but 5387
rather a dose index. 5388
dental assistant: A member of the dental office staff whose principal duty is chair-side 5389
assistance of the dentist in delivery of care. The assistant, properly trained, may be 5390
credentialed for exposure of dental radiographs. 5391
dental caries: Technical term for tooth decay, sometimes referred to as “caries”. 5392
dental hygienist: A member of the dental office staff whose principal duty is performing oral 5393
prophylaxis and related procedures; in the United States, a graduate of an accredited 5394
educational program in dental hygiene and registered in the state or political jurisdiction in 5395
which the practice is located. The dental hygiene curriculum includes training in radiography 5396
and the hygienist is credentialed to expose dental radiographs. 5397
dental radiographic technologist: An individual who is trained and skilled in, and credentialed 5398
for, performing both routine and specialized radiographic examinations of the dentofacial 5399
region. 5400
dentist: A graduate of an accredited dental institution with a degree of Doctor of Dental Surgery 5401
(D.D.S.) or Doctor of Dental Medicine (D.M.D.), or equivalent. 5402
deterministic effect (tissue reaction): Effects that occur in all individuals who receive greater 5403
than the threshold dose and for which the severity of the effect varies with the dose. 5404
detriment: The overall risk of radiation-induced health outcomes, including fatal and nonfatal 5405
cancer, genetic effects, and loss of life span from cancer and hereditary disease, weighted for 5406
severity and time of expression of the harmful effect, and averaged over both sexes and all 5407
ages in the population of interest (i.e., general or working population). 5408
diagnostic source assembly: A diagnostic source housing (x-ray tube housing) assembly with a 5409
beam-limiting device attached. 5410
diagnostic reference level: A radiation dose level that, when consistently exceeded, elicits 5411
investigation of the reasons for the higher doses and subsequent efforts to improve dose 5412
NCRP SC 4-5 Draft March 16, 2016
251
management. A process known as optimization is used to assure that the clinical image 5413
quality is adequate for the clinical task and that the patient doses are appropriate. 5414
digital radiography: A diagnostic procedure using an appropriate radiation source and imaging 5415
system that collects, processes, stores, recalls and presents image information in a digital 5416
array rather than on film. 5417
direct digital radiography (DR): A radiographic technique in which an image is captured by a 5418
solid-state receptor and converted into a digital image. 5419
direct exposure film: Film which is exposed directly by x rays without the use of intensifying 5420
screens to produce a radiographic film image. 5421
display: An electronic device for viewing digital images. 5422
dose: (see absorbed dose). Often used generically in place of a specific quantity, such as 5423
equivalent dose. 5424
dose-area product (DAP): The product of the entrance skin dose and the cross-sectional area of 5425
the x-ray beam. DAP is also known as kerma area product (PKA). 5426
dose and dose rate effectiveness factor (DDREF): A judged factor by which the radiation 5427
effect, per unit of dose, caused by a given high or moderate dose of radiation received at high 5428
dose rates is modified when doses are low or are received at low dose rates. 5429
dose limit (annual): The maximum effective dose an individual may be permitted in any year 5430
from a given category of sources (e.g., the occupational dose limit). 5431
dosimetry: The science or technique of determining radiation dose. 5432
dosimeter: Dose measuring device (see also personal dosimeter and area dosimeter). 5433
E-F-speed film: A direct exposure dental imaging film that is an E-speed film when hand 5434
processed and an F-speed film when machine processed. The designation of E/F-speed film 5435
is also used. 5436
effective dose (E): The sum over specified organs and tissues of the products of the equivalent 5437
dose in an organ or tissue (HT) and the tissue weighting factor for that organ or tissue (wT): 5438
5439
(G.1) 5440
5441
E wTHTT=
NCRP SC 4-5 Draft March 16, 2016
252
entrance air kerma (or entrance skin exposure): Air kerma (or exposure) measured free-in-air 5442
at the location of the entry surface of an irradiated person or phantom in the absence of the 5443
person or phantom. 5444
equipment performance evaluation: This evaluation is carried out by the qualified expert 5445
initially to assure equipment meets purchase specifications and then on a periodic basis to 5446
assure that the image quality and patient radiation doses remain at the same level. 5447
equivalent dose (HT): The mean absorbed dose in a tissue or organ modified by the radiation 5448
weighting factor (wR) for the type and energy of radiation. The equivalent dose in tissue T is 5449
given by the expression. 5450
5451
(G.2) 5452
5453
where DT,R is the mean absorbed dose in the tissue or organ T due to radiation type R. The SI 5454
unit of equivalent dose is the J kg–1 with the special name sievert (Sv). 1 Sv = 1 J kg–1 5455
exposure: A measure of the ionization produced in air by x or gamma radiation. The unit of 5456
exposure is coulomb per kilogram (C kg–1) with the special name roentgen (R). Air kerma is 5457
often used in place of exposure. An exposure of 1 R corresponds to an air kerma of 5458
8.76 mGy (see kerma, gray, roentgen). 5459
field size: The geometrical projection of the x-ray beam on a plane perpendicular to the central 5460
ray of the distal end of the limiting diaphragm, as seen from the center of the front surface of 5461
the source. 5462
film: A thin, transparent sheet of polyester or similar material coated on one or both sides with 5463
an emulsion sensitive to radiation and light. 5464
direct exposure film: Film that is highly sensitive to the direct action of x rays rather than in 5465
combination with an intensifying screen. 5466
screen-film system: Film whose light spectral absorption characteristics are matched to the light 5467
emission characteristics of the intensifying screens; film for screen-film imaging is not 5468
designed for use as direct exposure film as it absorbs only a limited amount of x rays. 5469
film speed: For intraoral films, film speed is expressed as the reciprocal of the exposure (i.e., 5470
R–1) necessary to produce a density of one above base plus fog. 5471
D-Speed film: Direct exposure film with a speed range of 12 to 24 R–1. 5472
H wRDT,RR=
NCRP SC 4-5 Draft March 16, 2016
253
E-speed film: Direct exposure film with a speed range of 24 to 48 R–1. 5473
F-speed film: Direct exposure film with a speed range of 48 to 96 R–1. Faster films need less 5474
exposure (i.e., a larger value of R–1) to produce the same film density (e.g., F-speed film 5475
is faster than E-speed film). For screen-film systems, film speed is expressed in 5476
combination with an intensifying screen. 5477
filter; filtration: Material in the useful beam that absorbs, preferentially, the less penetrating 5478
radiation, i.e., the radiation that will be absorbed by the body and not contribute to forming 5479
the image. The total filtration consists of inherent and added filters. 5480
inherent filtration: The filtration permanently in the useful beam; it includes the window of the 5481
x-ray tube and any permanent enclosure for the tube or source. 5482
added filtration: Filter in addition to the inherent filtration. 5483
fluoroscopy: The process of producing a real-time image using x rays. The machine used for 5484
visualization, in which the dynamic image appears in real time on a display screen (usually 5485
video) is a fluoroscope. The fluoroscope can also produce a static record of an image formed 5486
on the output phosphor of an image intensifier. The image intensifier is an x-ray image 5487
receptor that increases the brightness of a fluoroscopic image by electronic amplification and 5488
image minification. 5489
focal spot, effective: The apparent size of the radiation source region in a source assembly when 5490
viewed from the central axis of the useful radiation beam. 5491
fog: A darkening of the whole or part of a radiograph by sources other than the radiation of the 5492
primary beam to which the film was exposed. This can be due to chemicals in the processing 5493
solutions, light, or nonprimary beam (scattered) radiation. 5494
geometric distortion: Distortion of the recorded image due to the combined optical effect of 5495
finite size of the focal spot and geometric separation of the anatomic area of interest from the 5496
image receptor and the focal spot. 5497
genetic effects: Changes in reproductive cells that may result in detriment to offspring. 5498
gray (Gy): The special name given to the SI unit of absorbed dose and kerma. 1 Gy = 1 J kg–1. 5499
grid: A device used to reduce scattered radiation reaching an image receptor during the making 5500
of a radiograph. It consists of a series of narrow (usually lead) strips closely spaced on their 5501
edges, separated by spacers of low density material. 5502
half-value layer: Thickness of a specified substance that, when introduced into the path of a 5503
given beam of radiation, reduces the air-kerma rate (or exposure rate) by one-half. 5504
NCRP SC 4-5 Draft March 16, 2016
254
hazardous chemical: Any chemical that is a physical hazard or a health hazard as defined by 5505
the Occupational Safety and Health Administration (OSHA, 1994a). 5506
HERCA: The Heads of European Radiological Protection Competent Authorities is a voluntary 5507
association of radiation protection program representatives. The association addresses 5508
common issues and proposes practical solutions for these issues. Similar to the CRCPD in 5509
the United States. 5510
image receptor: A system for deriving a diagnostically usable image from the x rays transmitted 5511
through the patient. Examples include direct exposure x-ray film, screen-film system, 5512
photostimulable storage phosphor, and solid state receptor. 5513
inherent filtration: (see filter). 5514
intraoral radiograph: Radiograph produced on an image receptor placed intraorally and 5515
lingually or palatally to the teeth. 5516
in utero. In the uterus; refers to a fetus or embryo. 5517
inverse square law: A physical law stating that in the absence of intervening absorbers, the 5518
intensity of radiation from a point source is inversely proportional to the square of the 5519
distance from the source. As an example, a point source that produces 10 Gy h–1 at 1 m will 5520
produce 2.5 Gy h–1 at 2 m. 5521
ionization chamber: A device for detection of ionizing radiation or for measurement of 5522
radiation exposure and exposure rate. 5523
ionizing radiation: Any electromagnetic or particulate radiation capable of producing ions, 5524
directly or indirectly, by interaction with matter. Examples are x-ray photons, charged atomic 5525
particles, and other ions, and neutrons. 5526
kerma (K) (kinetic energy released per unit mass): The sum of the initial kinetic energies of 5527
all the charged particles liberated by uncharged particles per unit mass of a specified 5528
material. The SI unit for kerma is J kg–1 with the special name gray (Gy). 1 Gy = 1 J kg–1. 5529
Kerma can be quoted for any specified material at a point in free space or in an absorbing 5530
medium (see air kerma). 5531
kerma area product (KAP): See dose area product. 5532
kilovolt (kV): A unit of electrical potential difference equal to 1,000 volts. 5533
kilovolt peak (kVp): (also see operating potential). The peak-to-peak value in kilovolts of the 5534
potential difference of a pulsating potential generator. When only one-half of the waveform 5535
is used, the value refers to the useful half of the cycle. In this Report, the potential formed by 5536
NCRP SC 4-5 Draft March 16, 2016
255
a constant-potential generator is also expressed as kilovoltage. The operating potential of x-5537
ray equipment is expressed in terms of kilovoltage peak (kVp). 5538
latent image: The invisible change produced in an x-ray or photographic film emulsion by the 5539
action of x radiation or light, from which the visible image is subsequently developed and 5540
fixed chemically; or the change produced in a photostimulable storage phosphor and 5541
recovered by scanning with a laser. 5542
latitude: The range between the minimum and maximum radiation exposures to an image 5543
receptor that yield diagnostic images of structures. 5544
lead apron: An apron made with lead or other radiation absorbing material used to reduce 5545
radiation exposure. 5546
leakage radiation: (see radiation). 5547
linear nonthreshold (LNT): The hypothesis for radiation induction of cancer that states that no 5548
dose is completely without risk of such detriment, and that the relationship between 5549
increasing dose and increasing cancer incidence is linear through zero dose. 5550
luminance: A photometric measure of the luminous intensity per unit area of light travelling in a 5551
given direction. The SI unit for luminance is the candela m–2, sometimes referred to as a nit. 5552
magnification (in medical x-ray imaging): An imaging procedure carried out with 5553
magnification usually produced by purposeful introduction of distance between the subject 5554
and the image receptor. 5555
milliampere (mA): Electrically, 1 × 10–3 ampere. In radiography, the current flow from the 5556
cathode to the anode of the x-ray tube that, in turn, regulates the intensity of radiation 5557
emitted by the x-ray tube, thus directly influencing radiographic exposure. 5558
milliampere-minutes (mA min): The product of the x-ray tube operating current and exposure 5559
time, in minutes. 5560
milliampere-seconds (mAs): The product of the x-ray tube operating current and exposure time, 5561
in seconds. 5562
monitor: To determine the level of ionizing radiation or radioactive contamination in a given 5563
region or a device used for this purpose. Also, a device used for viewing x-ray images for 5564
diagnostic purposes. 5565
natural background radiation: Radiation originating in natural sources. e.g., cosmic rays, 5566
naturally occurring radioactive minerals, naturally occurring radioactive 14C and 40K in the 5567
body. 5568
NCRP SC 4-5 Draft March 16, 2016
256
noise: The presence of random fluctuations in image intensity that do not relate to the subject 5569
being imaged. Noise is related to both speed and resolution pf the image receptor. Generally, 5570
faster systems have greater noise. Noise can also be caused by physical factors in the 5571
imaging system, e.g., contact with rollers in film processing or interference with image 5572
capture by intervening materials. 5573
occlusal radiograph: An intraoral radiograph made with the image receptor placed between the 5574
occlusal surfaces of the teeth, parallel to the occlusal plane, with the x-ray beam directed 5575
caudad or cephalad. 5576
occupancy factor (T): The factor by which the workload should be multiplied to correct for the 5577
degree of occupancy (by any one person) of the area in question while the source is in the 5578
“ON” condition and emitting radiation. This multiplication is carried out for radiation 5579
protection purposes to determine compliance with shielding design goals. 5580
occupational exposure: Exposures to individuals that are incurred in the workplace as a result 5581
of situations that can reasonably be regarded as being the responsibility of management. 5582
Exposures associated with medical diagnosis or treatment for the individual are excluded. 5583
operating potential: (also see kilovolt peak). The potential difference between the anode and 5584
cathode of an x-ray tube. 5585
operator: Any individual who personally utilizes or manipulates a source of radiation. 5586
optimization. A process through which image quality and patient radiation exposure are 5587
balanced. The goal is to assure image quality sufficient for diagnostic purposes while 5588
minimizing the radiation dose to the patient. 5589
oral and maxillofacial radiology: The dental specialty that deals with the production and 5590
interpretation of images of dentomaxillofacial structures, practiced by a dental specialist who 5591
has undergone additional training in the use of imaging procedures for diagnosis and 5592
treatment of diseases, injuries, and abnormalities of the orofacial structures. In general, the 5593
individual should be credentialed by either the American Board of Oral and Maxillofacial 5594
Radiology or a comparable specialty board, or be eligible to sit for credentialing by such a 5595
board. 5596
orofacial: Relating to the mouth and face. 5597
orthodontic treatment: Dental treatment that corrects misalignment of the teeth and jaws. 5598
NCRP SC 4-5 Draft March 16, 2016
257
panoramic radiography (pantomography): A method of radiography by which continuous 5599
curved surface tomograms of the maxillary and mandibular dental arches and their associated 5600
structures may be obtained. 5601
periapical radiograph: An intraoral radiograph that demonstrates crowns and roots of teeth and 5602
the surrounding alveolar bone structures. 5603
periodontal disease: An inflammatory process of the hard and soft tissues of the marginal 5604
periodontal structures that may destroy alveolar bone and result in tooth loss. 5605
personal dosimeter: A small radiation receptor that is worn by an individual and measures their 5606
exposure to radiation. Common personal dosimeters contain film, thermoluminescent or 5607
optically-stimulated luminescent materials, or an electronic sensor as the radiation detection 5608
device. 5609
phantom: An object used to simulate the absorption and scatter characteristics of the patient’s 5610
body for radiation or image quality measurement purposes. 5611
photon: A quantum of electromagnetic radiation. 5612
photostimulable storage phosphor (PSP) plate: The PSP plate is an image receptor which 5613
consists of a thin imaging plate encapsulated in a protective, light-proof cover. The receptor 5614
is pliable. Once the x-ray exposure is made, the plate is scanned (or read) with a laser. 5615
During this scanning light is emitted in proportion to the x-ray exposure of the receptor 5616
surface. The amount of light is converted into pixel intensity values. This image is then 5617
stored as a digital image for diagnostic purposes. 5618
pixel: A two-dimensional picture element in a digital image. 5619
position-indicating device (PID) (cone): An open-ended device on a dental x-ray machine (in 5620
the shape of a cylinder) designed to indicate the direction of the central ray and to serve as a 5621
guide in establishing a desired source-to-image receptor distance. Provision for beam 5622
collimation and added filtration can be incorporated into the construction of the device. 5623
short cone: An open ended cylinder that establishes a source-to-image receptor distance of ~20 5624
cm. 5625
long cone. An open ended cylinder that establishes a source-to-image receptor distance of ~40 5626
cm. 5627
protective apron: An apron made of radiation absorbing material(s), used to reduce radiation 5628
exposure. 5629
NCRP SC 4-5 Draft March 16, 2016
258
protective barrier: A barrier of radiation absorbing material(s) used to reduce radiation 5630
exposure. 5631
primary protective barrier: A protective barrier used to attenuate the useful beam for radiation 5632
protection purposes. 5633
secondary protective barrier: A barrier sufficient to attenuate scattered and leakage radiation 5634
for radiation protection purposes. 5635
qualified expert: As used in this Report, a medical physicist or medical health physicist, with 5636
experience in dental imaging, who is competent to design radiation shielding in dental x-ray 5637
facilities, and to advise the staff regarding other radiation protection needs of dental x-ray 5638
installations. The qualified expert is also competent to evaluate image quality and measure 5639
patient radiation doses. The qualified expert is a person who is certified by the American 5640
Board of Radiology, American Board of Medical Physicists, American Board of Health 5641
Physics, or Canadian College of Physicists in Medicine. 5642
quality assurance (QA): The mechanisms to ensure continuously optimal functioning of both 5643
technical and operational aspects of radiologic procedures to produce maximal diagnostic 5644
information while minimizing patient radiation exposure. A quality assurance program also 5645
sets the qualifications and continuing education of staff. 5646
quality control (QC). The technical part of the quality assurance program which provides 5647
physical measurements of imaging functions, e.g., film processor QC to monitor chemical 5648
activity or periodic checks of the quality of digital images by the qualified expert. 5649
rad: The previous name for the unit of absorbed dose. 1 rad = J kg–1. In the SI system of units, it 5650
is replaced by the gray (Gy). 1 Gy = 100 rad. 5651
radiation (ionizing): Electromagnetic radiation (x or gamma rays) or particulate radiation (alpha 5652
particles, beta particles, electrons, positrons, protons, neutrons, and heavy charged particles) 5653
capable of producing ions by direct or secondary processes in passage through matter. 5654
leakage radiation: All radiation coming from within the source assembly except for the useful 5655
beam. It includes the portion of the radiation coming directly from the source and not 5656
absorbed by the source assembly, as well as the scattered radiation produced within the 5657
source assembly. 5658
scattered radiation: Radiation that, during interaction with matter, is changed in direction. The 5659
change is usually accompanied by a decrease in energy. For purposes of radiation protection, 5660
NCRP SC 4-5 Draft March 16, 2016
259
scattered radiation is assumed to come primarily from interactions of primary radiation with 5661
tissues of the patient. 5662
useful beam: The radiation that passes through the opening in the beam-limiting device that is 5663
used for imaging. 5664
radiation biology: That branch of science dealing with radiation effects on biological systems. 5665
radiation protection survey: An evaluation of the radiation protection in and around an 5666
installation that includes radiation measurements, inspections, evaluations and 5667
recommendations. 5668
radiation weighting factor (wR): The factor by which the absorbed dose in a tissue or organ is 5669
modified to account for the type and energy of radiation in determining the probability of 5670
stochastic effects. For diagnostic x rays the radiation weighting factor is assigned the value 5671
of one. 5672
radiograph: A film or other record produced by the action of x rays on a sensitized surface. 5673
radiography: The production of images on film or other record by the action of x rays 5674
transmitted through the patient. 5675
radiology: That branch of healing arts and sciences that deals with the use of images in the 5676
diagnosis and treatment of disease. 5677
rare earth: Commonly used to refer to intensifying screens that contain one or more of the rare-5678
earth elements and that make use of the absorption and conversion features of these elements 5679
in x-ray imaging. 5680
receptor: Any device that absorbs a portion of the incident radiation energy 5681
and converts that portion into another form of energy which can be more easily used to produce 5682
desired results (e.g., production of an image) (also see image receptor). 5683
receptor holding device: A device containing intraoral and extraoral components that allows for 5684
the positioning and stabilization of the image receptor within the mouth and which extends 5685
outside of the mouth to aid in the alignment of the position-indicating device of the x-ray 5686
tube head. 5687
relative risk: The ratio of the risk of a given disease in those exposed to the risk of that disease 5688
in those not exposed. 5689
excess relative risk: Relative risk minus one (i.e., the fractional increase in incidence in the 5690
irradiated population). 5691
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260
rem: The previous name for the unit numerically equal to the absorbed dose (D) in rad, modified 5692
by a quality factor (Q). 1 rem =0.01 J kg–1. In the SI system of units, it is replaced by the 5693
sievert (Sv), which is numerically equal to the absorbed dose (D) in gray modified by a 5694
radiation weighting factor (wR). 1 Sv = 100 rem. 5695
resolution: In the context of an image system, the output of which is finally viewed by the eye, 5696
it refers to the smallest size or highest spatial frequency of an object of given contrast that is 5697
just perceptible. The intrinsic resolution of an imaging system is measured in cycles per 5698
millimeter (c mm–1) the SI unit. Previously, line pairs per millimeter (lp mm–1) The 5699
resolution actually achieved when imaging lower contrast objects is normally much less, and 5700
depends upon many variables such as subject contrast levels and noise of the overall imaging 5701
system. 5702
roentgen (R): The previous name for exposure, which is a specific quantity of ionization 5703
(electrons) produced by the absorption of x- or gamma-radiation energy in a specified mass 5704
of air under standard conditions. 1 R = 2.58 × 10–4 coulombs per kilogram 5705
(C kg–1). 5706
safelight: Special lighting used in a darkroom that permits film to be transferred from cassette to 5707
processor without fogging. 5708
scatter: Deflection of radiation interacting with matter, causing change of direction of subatomic 5709
particles or photons, attenuation of the radiation beam, and usually some absorption of 5710
energy. 5711
scattered radiation: (see radiation). 5712
screen-film system. (see entry under film) 5713
secondary protective barrier: (see protective barrier). 5714
sharpness (image): (see resolution). 5715
shielding design goals (P): Practical radiation levels, measured at a reference point beyond a 5716
protective barrier, that result in the respective annual effective dose limit for workers or the 5717
general public not being exceeded, when combined with conservatively safe assumptions in 5718
the structural shielding design calculations. For low-LET radiation, the quantity air kerma is 5719
used. P can be expressed as an annual or weekly value (e.g., mGy week–1 or mGy y–1 air 5720
kerma). 5721
sievert (Sv): The name for the SI unit of dose equivalent (H), equivalent dose (HT) and effective 5722
dose (E). 1 Sv = 1 J kg–1. 5723
NCRP SC 4-5 Draft March 16, 2016
261
source assembly: (see diagnostic source assembly). 5724
source-to-image receptor distance. The distance, measured along the central ray, from the 5725
center of the x-ray focal spot to the surface of the image receptor. 5726
source-to-skin distance. The distance, measured along the central ray, from the center of the x-5727
ray focal spot to the skin of the patient. 5728
spatial resolution (see resolution). 5729
speed: (also see film speed). As applied to an image receptor, an index of the relative exposure 5730
required to produce an image of acceptable quality; faster image receptors need less 5731
exposure. 5732
stepwede: A device consisting of increments of an absorber through which a radiographic 5733
exposure is made on film to permit determination of the amounts of radiation reaching the 5734
film by measurements of film density. 5735
stochastic effects: Effects, the probability of which, rather than their severity, is a function of 5736
radiation dose, implying the absence of a threshold. (More generally, stochastic means 5737
random in nature). 5738
structured display: A display of digital images following a predefined template placing the 5739
images on a computer monitor in a standardized format. There are structured displays for 5740
different studies, e.g., full mouth series, or cephalometric series. 5741
tissue reactions: (see deterministic effects). 5742
tissue weighting factor (wT): The factor by which the equivalent dose in tissue or organ T is 5743
weighted, and which represents the relative contribution of that organ or tissue to the total 5744
detriment due to stochastic effects resulting from uniform irradiation of the whole body. 5745
tomography: A special technique to show in detail images of structures lying in a 5746
predetermined plane of tissue, while blurring or eliminating detail in images of structures in 5747
other planes. 5748
use factor (U): Fraction of the workload during which the useful beam is directed at the barrier 5749
under consideration. 5750
useful beam: (see radiation). 5751
user: Dentists, physicians, and others responsible for the radiation exposure of patients. 5752
waveform: An expression of the temporal variation of the operating potential applied to the x-5753
ray tube in the course of an exposure. 5754
single-phase: Produced by conventional alternating current line current. 5755
NCRP SC 4-5 Draft March 16, 2016
262
half-wave rectified: Producing a single 1/120 s pulse of x rays during each 1/60 s alternating 5756
current cycle. 5757
full-wave rectified: Producing two 1/120 s pulses of x rays during each 1/60 s alternating 5758
current cycle. 5759
three-phase: Produced by three-phase, full-wave rectified current, providing 12 overlapping 5760
1/120 s pulses during each 1/60 s alternating current cycle. 5761
constant potential: Produced by electronic manipulation of alternating line current to provide 5762
constant tube voltage and a beam energy spectrum that varies little or not at all during 5763
exposure. 5764
workload (W): The degree of use of a radiation source. For the dental x-ray machines covered 5765
in this Report, the workload is expressed in milliampere-minutes per week (mA min week–1). 5766
x rays: Electromagnetic radiation that is produced by high-energy electrons passing close to a 5767
nucleus of a high atomic number element such as when impinging on a metal target in an x-5768
ray machine. 5769
5770
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263
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