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RADIATION SAFETY

Head and Neck Radiation Doseand Radiation Safety forInterventional Physicians

Kenneth Fetterly, PHD,a Beth Schueler, PHD,b Michael Grams, PHD,c Glenn Sturchio, PHD,d

Malcolm Bell, MD,a Rajiv Gulati, MDa

ABSTRACT

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OBJECTIVES The first aim of this study was to assess the magnitude of radiation dose to tissues of the head and neck of

physicians performing x-ray-guided interventional procedures. The second aim was to assess protection of tissues of

the head offered by select wearable radiation safety devices.

BACKGROUND Radiation dose to tissues of the head and neck is of significant interest to practicing interventional

physicians. However, methods to estimate radiation dose are not generally available, and furthermore, some of the

available research relating to protection of these tissues is misleading.

METHODS Using a single representative geometry, scatter radiation dose to a humanoid phantom was measured using

radiochromic film and normalized by the radiation dose to the left collar of the radioprotective thorax apron.

Radiation protection offered by leaded glasses and by a radioabsorbent surgical cap was measured.

RESULTS In the test geometry, average radiation doses to the unprotected brain, carotid arteries, and ocular lenses

were 8.4%, 17%, and 50% of the dose measured at the left collar, respectively. Two representative types of leaded

glasses reduced dose to the ocular lens on the side of the physician from which the scatter originates by 27% to 62% but

offered no protection to the contralateral eye. The radioabsorbent surgical cap reduced brain dose by only 3.3%.

CONCLUSIONS A method by which interventional physicians can estimate dose to head and neck tissues on

the basis of their personal dosimeter readings is described. Radiation protection of the ocular lenses by leaded

glasses may be incomplete, and protection of the brain by a radioabsorbent surgical cap was minimal.

(J Am Coll Cardiol Intv 2017;10:520–8) © 2017 by the American College of Cardiology Foundation.

T he potential for adverse health effectsfrom occupational radiation exposure is ofconcern for interventional cardiologists,

radiologists, and surgeons who routinely use x-rayfluoroscopy and angiography to diagnose and treatcardiac and vascular disease (1–4). Interventionalphysicians have an appetite for information that can

m the aDepartment of Cardiovascular Diseases, Mayo Clinic, Rochester,

chester, Minnesota; cDepartment of Radiation Oncology, Mayo Clinic, R

stic Radiology, Mayo Clinic, Jacksonville, Florida. The authors have repo

ntents of this paper to disclose.

nuscript received June 27, 2016; revised manuscript received October 4,

help them assess their own health risks associatedwith occupational radiation dose. One aim of thiswork is to provide physicians a simple means to esti-mate radiation dose to tissues of the head, particu-larly the brain, carotid arteries, and ocular lenses.

Methods to minimize radiation dose to tissues ofthe head are also desired by interventional physicians

Minnesota; bDepartment of Radiology, Mayo Clinic,

ochester, Minnesota; and the dDepartment of Diag-

rted that they have no relationships relevant to the

2016, accepted November 17, 2016.

AB BR E V I A T I O N S

AND ACRONYM S

2D = 2-dimensional

ERR = excess relative risk

LCD = left collar dose

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to mitigate risk for radiation injury. Appropriate x-rayshielding remains one of the fundamental ways toprotect physicians from x-ray scatter. The potentialfor a ceiling-mounted upper body shield to protectthe head and neck of physicians is well known (5–8).Other novel shielding devices (9–11) have not beenwidely adopted. The potential for leaded glasses toprotect the eyes and thereby reduce cataract risk haslong been known (12). The remainder of the head andsuperior portion of the neck frequently do not havededicated radiation protection. Radioprotective sur-gical caps have been proposed to reduce dose to thebrain (13–15). The second aim of this work was toassess the potential for select wearable radiationprotection devices to reduce dose to tissues of thehead, particularly the brain and ocular lenses, andprovide interventional physicians practical guidancein the effectiveness of these devices.

METHODS

Primary experimentalmethods used for thisworkweredescribed elsewhere (Fetterly et al. [16]). Therefore,only a brief summary of those methods and relevantenhancements to support this work are included here.Preliminary experiments characterized the energy ofscattered radiation emitting from a patient (phantom)during an x-ray angiographic procedure. Fourdifferent scatter beam qualities were selected tomimicscatter associated with patient sizes ranging from asmall child to a large adult. A standard x-ray tube wastuned to mimic the 4 scatter beam qualities byadjusting the peak tube potential (56, 74, 90, and 106kVp) and half-value layer (3.5, 4.5, 5.5, and 6.5 mm Al)of the beam. The scatter-equivalent beams weredirected upon an anthropomorphic phantom (Alder-son, RANDO phantom, Radiology Support Devices,Long Beach, California) to estimate scatter radiationdose to the head and neck of an interventional physi-cian (Figure 1). The transverse plane slabs of thephantom were assembled on a table to simulate anupright physician. Radiochromic film (XR-QA2, Ash-land, Bridgewater, New Jersey) was placed withintransverse planes of the phantom to measure tissuedose. The scatter-equivalent radiographic x-ray beamand phantom were positioned and oriented to mimicscatter incident upon a physician performing a leftfemoral access cardiac interventional procedure. Thephantom was covered with a 0.5-mm lead-equivalentradioprotective apron, and 3 � 3 cm2 pieces of radio-chromic film were attached to the outside of the leadapron at locations to mimic a personal dosimeterlocated at the left and right collars (Figure 1). Our pre-vious work reported the influence of scatter beam

quality or energy on the percentage of leftcollar dose (LCD) (16). This work reports acomposite or typical dose that is the averagepercentage LCD associated with the variousscatter beam qualities.

A single scatter-equivalent x-ray beam (90

kVp; half-value layer 5.5 mm Al) was used to assessselect radiation safety devices, including 2 types ofradioprotective glasses (Figure 2) (glasses 1: 0.75-mmlead equivalent, Liberty MX30, Phillips Safety Prod-ucts, Middlesex, New Jersey; glasses 2: 0.07-mm leadequivalent, XR-700, Toray Medical, Toray Interna-tional America, Houston, Texas), a commerciallyavailable radiopaque surgical cap (No-Brainer 9100,RadPad Protection, Kansas City, Kansas), and a radi-opaque hood fabricated in our laboratory fromthe material of the radiopaque surgical cap (Figure 3).The surgical cap was positioned on the phantom suchthat the inferior portion of the cap was in contact withthe auricles of the ears and just superior to the loca-tion corresponding to the superciliary arches andeyebrows. Similar to that described by Kuon et al. (7),the hood was fashioned to hang along the side of theface of the phantom, around to the back of the neck,and extend from the surgical cap inferiorly tothe level of the phantom chin (Figure 3). Anatomicregions protected by the wearable shielding deviceswere represented by a region of x-ray shadow recor-ded in the radiochromic film. The reduction in radi-ation dose to tissues protected by the devices wasestimated by comparing radiochromic film dosemeasurements with and without the protectivedevices.

After exposure, the radiochromic films were scan-ned with a flatbed scanner, resulting in 2-dimensional(2D) transverse plane dose distribution maps. The 2Ddose maps were normalized by the dose received bythe LCD, resulting in 2D maps of dose as a percentageof the LCD. Computed tomographic images of thephantom were overlain onto the 2D dose maps toprovide bony landmarks. Dose to select organs andtissues, including the left and right brain, wholebrain, brain stem, ocular lenses, and carotid arteries,was calculated.

RESULTS

Percentage of LCD maps corresponding to the 90-kVpscatter-equivalent beam are shown in Figure 4. Thecolor scale of Figure 4 ranges from 0% LCD (dark blue)through 100% LCD (yellow). The percentage LCDdecreased rapidly from the anterior left (x-ray beamentrance) surface of the phantom and was consistentwith expectations of exponential attenuation of the

FIGURE 1 Experimental Setup Used to Expose the Phantom and Radiochromic Film

Experimental setup used to estimate head and neck tissue dose to an interventional

physician. The x-ray tube was positioned, oriented, and tuned to produce scatter-

equivalent x-ray beams. Anthropomorphic phantom levels a to f correspond to transverse

planes in which the radiochromic films were placed. For explanations of A to F,

see Figure 4.

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x-ray beam by the tissue-equivalent phantom. Also,the highly attenuating cranial and facial bones pro-tect underlying tissues from radiation. The x-rayshadow from the bones of the phantom contributesdetail in the 2D dose maps corresponding to regionsof the otherwise homogenous soft tissue. The steepdose gradient in the posterior region of Figure 4F wasdue to the x-ray shadow cast by the protective apron.Table 1 provides percentage LCD tissue doses to selectorgans and tissues calculated as the average of the4 scatter beam qualities. Tissues that are relativelysuperficial or left sided received greater dose thantissues that are deep and relatively right sided.

Anatomic regions protected by the radiopaquesurgical cap are demonstrated in Figure 5. The trans-verse planes included in Figure 5 represent the 3 mostsuperior planes of the phantom and correspond toplanes represented in Figures 4A to 4C. Phantom levelsinferior to those shown in Figure 5 (Figures 4D to 4F)were unprotected by the cap. Because the x-ray scatterwas incident upon the phantom head from an inferiorelevation, the x-ray shadow cast by the cap propa-gated tangential to the superior aspect of the headrather than over the brain cavity. Therefore, theradiopaque surgical cap reduced dose to only a smallvolume of tissue within the left anterior-superior re-gion of the cranium. The attenuating material of the

cap reduced radiation to tissues covered by the x-rayshadow that it cast by approximately 65% to 70%.However, because the shadow cast by the cap coveredonly a small volume of the brain and surroundingtissue, the cap provided only 4.9% protection to theleft brain, 1.8% protection to the right brain, and 3.3%protection to the whole brain.

Anatomic regions protected by the hood fabricatedfrom the material of the surgical cap are demon-strated in Figure 6. The x-ray shadow cast by theradiopaque hood covered approximately the poste-rior half of the left brain at the level of the eye brows(Figure 5C) and extended to cover portions of the rightbrain at levels more superior (Figures 5A and 5B).Measurements demonstrated that this hood offered70% protection to the left brain, 49% protection to theright brain, and 55% protection to the whole brain.

Protection of the ocular lenses provided by theglasses is demonstrated in Figure 7. For the single ge-ometry tested, glasses 1 reduced percentage LCD toprotected tissues by 77%. However, the protectiveshadow of glasses 1 provided incomplete coverage ofthe left ocular lens (Figure 7A). Therefore, measuredprotection of the left lens was 27%, and the right eyewas entirely unprotected. Glasses 2 reduced percent-age LCD to protected tissues by 62%. Glasses 2 cast ashadow over the entire left ocular lens (Figure 7B),resulting in a higher protection level compared withglasses 1, despite the lower lead-equivalent thickness(0.07 mm for glasses 2 vs. 0.75 mm for glasses 1).Measured protection of the left lens was 61%, but theright eye was also unprotected by glasses 2.

DISCUSSION

This work describes a straightforward, novel model foraccurate assessment of scatter radiation dose to tis-sues of the head and neck of interventional physicians.By normalizing tissue dose by the dose to the locationof the left collar, this work facilitates individualizedestimates of dose to head and neck tissues of physi-cians on the basis of their personal dosimeter readings.In contrast to other studies (13–15), these findingsdemonstrated that radiation absorbent surgical capsprovide minimal brain protection. Furthermore, thesemeasurements affirm that radiopaque eyeglassesprovide incomplete protection of the ocular lenses.

A primary purpose of this work was to allow theestimation of interventional physicians’ head andneck tissue dose from personal dosimeter readings.Provided that the spatial relationship between thephysician and patient is similar to that used here,tissue dose to a physician may be estimated bymultiplying his or her personal dosimeter reading by

FIGURE 2 Leaded Glasses Tested

Leaded glasses: (A) glasses 1 and (B) glasses 2. Glasses were fixed to the anthropomorphic phantom to assess ocular lens protection.

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the percentage LCD presented in Table 1. Moredetailed results were previously published (16). Thiswork assumes that the personal dosimeter is worn onthe collar of the same side from which the scatteroriginates. If the scatter radiation is incident from thecontralateral side, physician tissue dose can be esti-mated as the product of the personal dosimeterreading times percentage LCD times f, where f ¼ 1.31is the ratio of the LCD to the right collar dose deter-mined by previous experiments (16). The percentageLCD values reported here agree well with similar

FIGURE 3 Radiopaque Surgical Cap and Hood

(A) Radiopaque surgical cap and (B) hood fabricated from the material

measurements reported by Marshall et al. (17),wherein dose to select organs was normalized by doseto the bridge of the nose.

Whereas the spatial relationship between thephysician and patient is variable in practice, a limi-tation of this study is that the protection offered bythe wearable devices was assessed for only a singleexperimental geometry. Therefore, the results pre-sented herein should not be considered absolute butshould rather be considered a guide to the generalmagnitude and distribution of radiation dose to a

of the radiopaque surgical cap.

FIGURE 4 Transverse-Plane Scatter-Equivalent Dose Distributions

Percentage of left collar dose (LCD) for the 90-kVp scatter-equivalent x-ray beam. The color bars represent the percentage LCD range from 0% (dark blue) to 100%

(yellow). Images (A to F) correspond to similarly labeled levels in the phantom shown in Figure 1.

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physician’s head and neck from scatter originatingfrom patients. Also, this experiment did not accountfor protection offered by other radiation protectivedevices, including a radioprotective thyroid collar,the upper body shield, or radioabsorbent drapes

TABLE 1 Percentage of Left Collar Dose of Select Tissues

Organ or Tissue

Percentage of Left Collar Dose

Median 5th Percentile 95th Percentile

Brain

Left 14 6.5 24

Right 5.6 2.7 13

Whole 8.4 2.8 21

Brain stem 19 15 23

Ocular lens

Left 25 23 30

Right 9.2 3.7 24

Carotid artery

Left 72 63 81

Right 28 25 32

Summary of percentage of left collar dose for select organs and tissues of the headand neck.

placed on the patient. Finally, only 2 models ofleaded glasses were assessed. Future work to morecompletely describe the influences and de-pendencies of these practical variables is warranted.

There is agreement in the published research andamong these authors that radiation protective glassesshould be worn by operators of x-ray fluoroscopicsystems (18). However, similar to the findings ofGeber et al. (19), the results of this work indicateincomplete protection of the ocular lenses by theglasses. In particular, neither model of glasses pro-tected the ocular lens contralateral to scatter source.This is because dose to the contralateral lens entersthe eye obliquely through the face, whereas theglasses preferentially protect against radiationincident from the front. Further work to assess thereal-world implications of these findings and theinfluence of glasses design on ocular lens protectionis warranted.

This work demonstrates that the radiationabsorbing surgical cap provides essentially no pro-tection to the brain of an interventional physician.This result is readily explained by geometry. Because

FIGURE 5 Protection Offered by Radiopaque Surgical Cap

Percentage of left collar dose (LCD) for phantom wearing the radiopaque surgical cap. The color bars represent the percentage LCD range from 0% (dark blue) to

100% (yellow). The x-ray shadow within the anterior-left portion of the phantom indicates tissue protected by the cap. Arrows indicate the edge of x-ray shadow cast

by the cap. Images (A to C) correspond to similarly labeled levels in the phantom shown in Figure 3. Compare with Figures 4A to 4C.

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the scatter originates from a location inferior to thephysician’s head, the x-ray shadow cast by the cappropagates nominally tangential to the superioraspect of the skull rather than over the cranial cavity.This finding contradicts marketing materials andpublished works suggesting that these or similartypes of caps offer substantial brain protection(13–15). The experimental methods used in theseother works measured attenuation of the surgical caprather than dose to tissues. As demonstrated herein,the optimistic perspective that radiopaque surgicalcaps substantially reduce brain dose is misleading.

Although this work demonstrates limitations ofselected wearable radiation safety devices, there are

FIGURE 6 Protection Offered by Radiopaque Hood

Percentage of left collar dose (LCD) for phantom wearing the radiopaqu

(yellow). The x-ray shadow across the posterior left brain of the phanto

shadow cast by the hood. Images (A to C) correspond to similarly label

several established methods to facilitate head andneck dose reduction in interventional laboratories.Because scatter radiation is directly proportional tothe radiation dose delivered to the patient, methodsto reduce radiation dose to the patient can be ex-pected to have a commensurate effect on physiciandose (20). The x-ray shadow cast by a radiopaquethyroid collar, typically worn in conjunction with alead apron or vest, can be expected to provide sub-stantial protection of the inferior portion of the neck.The merit of a well-positioned ceiling-mounted upperbody shield has been described (5–8). Radiopaquedrapes placed strategically upon the patient havebeen shown to reduce physician dose (21–23). The

e hood. The color bars represent the percentage LCD range from 0% (dark blue) to 100%

m indicates tissue protected by the hood. Arrows indicate the anterior edge of the x-ray

ed levels in the phantom shown in Figure 3. Compare with Figures 4A to 4C.

FIGURE 7 Protection Offered by Glasses

Phantom eye-level percentage of left collar (LCD) dose for (A) glasses 1 and (B) glasses 2. The color bars represent the percentage LCD range

from 0% (dark blue) to 100% (yellow). Arrows indicate x-ray shadow over the left eye. Images (A and B) correspond to level D in Figure 3.

Compare with Figure 4D.

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potential benefit of the drapes is greatest when theupper body shield cannot be used and is dependentupon their design and strategic placement upon thepatient (8,22,23) Marshall et al. (17) reported 81%brain dose reduction associated with a lead-acrylicface mask. The x-ray shadow cast by the face maskcould be expected to provide similar protection to allhead tissues. Kuon et al. (7) described the potentialuse of a lead-equivalent hood. Novel radiationshielding systems that facilitate whole-body protec-tion can be expected to provide good protection ofthe head and neck (8–10) and may offer the user theergonomic benefit of not wearing lead garments.Finally, robotic interventional systems may facilitatesubstantial physician dose reduction for select pro-cedures (24,25).

The magnitude of brain dose from scatter is of in-terest to practicing physicians. Following is anexample of how the percentage LCD values presentedhere can be used to estimate brain dose and thenapplied to facilitate a discussion of associated tumorrisk. An interventional physician who receives the U.S.(European) recommended annual maximum effectivedose of 50 mSv (20 mSv) may have a personal dosim-eter reading of approximately 167 mSv (67 mSv) (26–28). For this example, assume that the annual leftcollar dosimeter reading of an interventional physicianis 50mSv $ year�1 (5,000mrem $year�1). On the basis ofthe measured 8.4% of LCD in the present study, theaverage dose to the whole brain would be 4.2 mSv $

year�1 (50 mSv $ year�1 � 8.4%).

A recent summary of interventional physicianswho developed brain cancer has raised awareness ofthe potential for radiation risk (2). However, studiesdemonstrating a causal effect between radiation ofadults and brain tumor risk are sparse (29). Prestonet al. (30) described a causal relationship betweenbrain dose and neurological tumors in atomic bombsurvivors. Brain dose to the cohort of 80,160 people inthe study ranged from <0.005 to >1 Sv. The naturalincidence rate of fatal neurological tumors (includingmalignant and benign) in that group was about 1 in400, and the excess relative risk (ERR) from acuteexposure to radiation was 1.2 Sv�1 (95% confidenceinterval: 0.6 to 2.1 Sv�1). If the ERR estimate 1.2 Sv�1 isapplied to a group of occupationally exposed personswhose estimated brain dose is 4.2 mSv $ year�1, thenthe annual ERR incurred by the group is 0.005 year�1.If extended over a 25-year interventional career, thelifetime ERR would be 0.13. The predicted fatalneurological brain tumor incidence rate of a group ofpeople so exposed would be about 1 in 350. For agroup of 10,000 interventional physicians soexposed, 25 may be expected to develop fatal braintumors from causes other than occupational expo-sure, and an additional 4 may be expected to developfatal brain tumors from occupational radiation dose.For this hypothetical group, the estimated risk fordeveloping a fatal brain tumor from occupational ra-diation exposure is 0.04%.

Given the many and potentially large uncertaintiesassociated with estimating dose and assessing risk, an

PERSPECTIVES

WHAT IS KNOWN? Practical information regarding radiation

dose to tissues of the head and neck is required to guide radiation

safety practices for interventional physicians.

WHAT IS NEW? This study provides a method by which radi-

ation dose to tissues of the head and neck can be estimated from

radiation dosimeters that are routinely worn by physicians.

Furthermore, this work identifies limitations of radiopaque sur-

gical caps intended to reduce dose to the brain.

WHAT IS NEXT? Future work to incorporate the findings of this

work into radiation safety practices is warranted.

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absolute risk estimate as presented here should beconsidered with healthy skepticism. Practical sourcesof variability in the clinical practice include locationat which the radiation dosimeter is worn, the spatialrelationship of the physician and patient, and theproper use of accessory shielding devices. It has beensuggested that tissue dose estimates such aspresented in this work should be considered toinclude relative uncertainty in the range 0.66� to1.5� to account for this variability (31). Also, with theexception of radiation-induced cataracts, the associ-ation between occupational exposure to radiation andadverse health effects is uncertain (29).

CONCLUSIONS

Radiation safety remains a concern for interventionalcardiologists, radiologists, and surgeons. This workprovides physicians a method to estimate dose tohead and neck organs and tissues from their ownpersonal dosimeter readings and thereby provides ameans to assess the potential for associated healthrisks. Critical assessment of selected wearable radia-tion safety devices demonstrated that radiopaquesurgical caps can be expected to provide only minimalbrain protection because the x-ray shadow they pro-duce is not cast over the brain. Ocular lens protectionoffered by leaded glasses can be expected to depend

on glasses design. This work highlights a need forcontinued development of radiation safety devicesthat are both effective and practical. Furthermore, itprovides a method by which the potential for radia-tion safety devices to protect tissues can be directlyassessed.

ADDRESS FOR CORRESPONDENCE: Dr. KennethFetterly, Mayo Clinic, Cardiovascular Diseases, 200First Street SW, Rochester, Minnesota 55905. E-mail:fetterly.kenneth@mayo.edu.

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KEY WORDS head and neck, interventionalfluoroscopy, occupational radiation dose,radiation protection