Comparison of Dosimetry Approaches in Interventional Radiology

Author: R. Padovani, E. Quai

Lead Partner: Ospedale S. Maria della Misericordia, Udine, Italy Part 1 Publishable Final Report 1.1 Executive publishable summary Patient dosimetry methods currently used in interventional radiology may be divided in three categories according to dosimetry purposes: (i) dosimetry for stochastic risk evaluation, (ii) dosimetry for quality assurance, (iii) dosimetry to prevent deterministic effects of radiation (i) Dosimetry for stochastic risk evaluation Dosimetry quantities able to measure the stochastic risk from body irradiation are: (a) the organ equivalent dose to selected organs and tissues, (b) effective dose. These quantities represent convenient indicators of overall exposure in the assessment of diagnostic practice and population exposure and they estimate the risks to the health from the stochastic effects of radiation. The quantities are able to compare exposures from different types of procedures, irradiation geometries and radiation type and quality. (ii) Dosimetry for quality assurance Dosimetry for quality assurance is addressed to evaluate the optimization level of the radiological practice, compare performance of equipment and operator skill or compare the practice among different centres. Dose and technical factor quantities are useful indicators for fluoroscopy guided procedures: (a) fluoroscopy time and/or number of acquired images, (b) total dose-area product, dose-area product for image acquisition and dose-area product for the fluoroscopy part of the procedure. (iii) Dosimetry to prevent deterministic effects For intensive image procedures in complex interventions, the knowledge of the localized dose to skin is important to assess the potential of deterministic effects of irradiation on the skin. Such quantity, expressed in term of Maximum Entrance Surface Dose (MESD), can be assessed with different methodologies: (a) by direct calculation, with off or on-line techniques, (b) direct measurements on the patient with point detectors (TLDs or other solid state detectors), (c) direct measurements on the patient with large area detectors (films and TLDs array), and (d) by portal monitoring with area or point/area detectors (DAP, DAP+K). The dosimetric methods for the evaluation of stochastic effects and for the purposes of quality assurance are well defined and, usually, simple to apply. They allow to

obtain comparable results among different institution. In the case of the assessment of localised skin dose, the methods are complex and difficult to apply in the routine practice. Usually they are adopted for research purposes on a reduced sample of patients and procedures. The development of on-line methods, based on calculation of skin dose distribution on the patient’s skin, is in our opinion, the best solution to alert practitioners when the localised skin dose is approaching the threshold for deterministic injuries.

1. Detailed Final Report

2.1 Objective and strategic aspects

Interventional radiology contributes with a significant proportion of the collective effective dose to the population from medical exposures. Its frequency is increasing year on year as knowledge of its benefits becomes more wide spread and more difficult/complicated procedures are technically feasible. Interventional radiology procedures are usually fluoroscopy guided diagnostic and therapeutic interventions; less frequent are the interventions where ultrasound and CT or CTfluoro and MR equipment are used. When complex procedures are performed or procedures are repeated for the same patient high radiation dose levels occur. In particular, reasons for high patient doses are:

- the procedures may be complicated and require even hours of fluoroscopic guidance in some cases

- the procedures may require high-quality, low-noise images - operators may not have sufficient training in radiology imaging, quality

assurance and radiation protection. The most complicated interventional procedures are typically performed for patients who have been diagnosed with severe medical problems. The literature of case reports describing deterministic effects is growing and the potential for deterministic effects on the skin may be of more concern than stochastic long term risks. The Food and Drug Administration (FDA, 1994), World Health Organisation (WHO, 2000) and International Commission on Radiological Protection (ICRP, 2000) have requested attention to the skin dose problems of complicated radiological interventions, giving advices to optimise the techniques. In this context, patient dosimetry approaches are an important issue. Frequently published dose data are expressed in terms of not particularly well defined dose quantities and without clear objective for the measurements performed. This workpackage aims to report and compare dosimetry approaches and propose a classification of the different dosimetry objectives.

2.2 Scientific and technical description of the results

Analysis of different approaches Patient dosimetry methods currently used in interventional radiology, derived from the enclosed literature survey (Annex), may be divided in three categories according to dosimetry purposes:

(i) dosimetry for stochastic risk evaluation (ii) dosimetry for quality assurance (iii) dosimetry to prevent deterministic effects of radiation (skin dose

assessment) Dosimetry for stochastic risk evaluation Models, methods for adult and pediatric patient are well developed and practical tools are available for routine evaluation with an accuracy sufficient for the scope of the evaluation. Assessment of variability of E with patient size in respect to DAP measurements is described in the workpackage WP 5.5.

Dosimetry for quality assurance Methods, technical and dosimetry quantities are defined for the purpose to assess the optimization level of procedures, compare practices performed in different centers or compare operator skill. For such quantities DIMOND has explored the possibility to introduce reference levels in interventional radiology for selected and common procedures.

Dosimetry to prevent deterministic effects of radiation (skin dose assessment) Different approaches to evaluate maximum (localised) entrance surface dose have been developed and experienced but a final conclusion has not been reached. Dosimetry methods for off-line evaluation are developed and they allow the estimation of MESD: methods using area detectors are the choice methodology. Dosimetry methods for on-line evaluation are necessary to prevent deterministic effects in single long and complex procedures, but are not available for routine work.

A two level approach is proposed: 1. A first level able to prevent deterministic effects with an indirect

assessment of MESD: i. A threshold (or trigger) of technical (fluoro time) and/or simple

measurable dosimetry quantities (DAP) is selected for each procedure type and able to alert the operator that a certain value of ESD, corresponding to a threshold for deterministic effects, can be reached

2. A second level with techniques able to assess MESD requires the

development of specific methods: i. Electronic point detectors are useful when procedures are using

almost stationary fileds (e.g. in interventional cardiology: electrophysiology, RF cardiac ablation)

ii. Computational methods able to asses skin dose distribution from technical data on-line supplied by the x-ray equipment (tube output, field sizes, geometry of irradiation, etc.)

1. Dosimetry for stochastic risk evaluation Dosimetry quantities able to estimate the stochastic risk from body irradiation are:

a. organ equivalent dose to each organ and tissue b. effective dose 1, 2, 5, 8, 10, 11, 13, 17, 18, 19, 22, 29, 30, 31

These quantities represent convenient indicators of overall exposure in the assessment of diagnostic practice and population exposure and reflect the risks from the stochastic effects of radiation exposure. These quantities are able to compare exposures from different types of procedures, irradiation geometries and radiation type and quality. ICRP (Report No. 60) recommends that effective dose is not used to estimate detriment (to individuals or population) from medical exposure. This assessment can be inappropriate because of the uncertainties arising from potential demographic differences (status, age, sex, etc.) between population in the study and population for which the risk coefficients have been assessed. For example, when applied to young or pediatric patients, effective dose can underestimate the detriment by a factor of 2 or, in the case of old patient, the detriment can be overestimated by a factor of 5 (NRPB 4, 1993). 2. Dosimetry for quality assurance Dosimetry for quality assurance is addressed to evaluate the optimization level of the practice, to compare performance of equipment and operator skill and to compare radiological practice among different centres. Useful dose quantities, for fluoroscopy guided procedures, are:

a. Dose-area product: the total dose-area product (DAP) for the whole procedure, the dose-area product DAPfluoro for the fluoroscopy part of a procedure and the dose-area product DAPcine for the imaging acquisition part of a proceudre 2,

5, 7, 9, 14, 18, 21 But also technical quantities, characterising the procedure protocol are proposed by different authors:

b. the total fluoroscopy time of a procedure, the total number of acquired images, the number of series of acquired images, the mean number of images per series in a procedure.

3. Dosimetry to prevent deterministic effects (skin dose assessment)

For the intensive image procedures used in interventional radiology, the knowledge of the localized dose to skin is important with respect to the potential for deterministic effects of irradiation.

Such exposure, expressed in term of Maximum Entrance Surface Dose (MESD), can be assessed with different methodologies:

a. calculation (off-line or on-line) 3, 8, 16, 33 b. direct measurements on the patient with point detectors (TLDs or solid state

detectors) 5, 24, 27, 29 c. direct measurements on the patient with area detectors (film and TLD array) 6,

7, 20, 25, 27 d. by portal monitoring (Wagner BJR 1999) with point or area detectors (DAP,

DAP+K) 4, 12, 15, 16, 23, 26, 27

Bibliography 1. Alaei P, Gerbi Bj, Geise Ra. Evaluation of a Model-Based Treatment Planning

System for Dose Computations in the Kilovoltage Energy Range, Med. Phys. (2000); 27(12): 2821-2826

2. Chapple Cl, Broadhead Da, Faulkner K. A Phantom Based Method for Deriving Typical Patient Doses from Measurements of Dose-Area Product on Populations of Patients, Br. J. Radiol. (1995); 68:1083-1086

3. Cotelo E, Pouso J, Reyes W. Radiofrequency Catheter Ablation: Relationship Between Fluoroscopic Time And Skin Doses According to Diagnoses. Basis to Establish a Quality Assurance Programme, Iaea-Cn-85/168 Radiological Protection of Patients in Diagnostic And Interventional Radiology, Nuclear Medicine And Radioterapy

4. Cusma Jt, Bell Mr, Wondrow A Et Al. Real Time Measurement of Radiation Exposure to Patients During Diagnostic Coronary Angiography and Percutaneous Interventional Procedures J. Am. Coll. Cardiol (1999); 33:427-435

5. Garcia-Roman Mj, Prada-Martinez E, Abreu-Luis J, Hernandez-Armas J. Patient Radiation Doses from Neuroradiology Procedures, Iaea-Cn-85/112 Radiological Protection of Patients in Diagnostic and Interventional

6. Geise Ra, Ansel Hj. Radiotherapy Verification Film for Estimating Cumulative Entrance Skin Exposure for Fluoroscopic Examinations Healt Phys. (1990); 59(3):295-298

7. Hernando I, Torres R. Comparison Between Termoluminiscence Dosimetry and Transmission Ionization Chamber Measurements, Iaea-Cn-85/177 Radiological Protection of Patients in Diagnostic and Interventional Radiology, Nuclear Medicine and Radioterapy

8. Huda W, Phadke K, Ogden Km, Roskopf Ml. Patient Doses in Digital Cardiac Imaging Iaea-Cn-85/64 Radiological Protection of Patients in Diagnostic and Interventional Radiology, Nuclear Medicine and Radioterapy

9. Huyskens Cj, Hummel Wa. Data Analysis on Patient Exposures in Cardiac Angiography Rad. Prot. Dosim. (1995); 57(1-4):475-480

10. Le Heron Jc. Estimation of Effective Dose to the Patient During Medical X-Ray Examinations from Measurements of the Dose-Area Product, Phys. Med. Biol. (1992); 37(11):2117-2126

11. Leung Kc, Martin Cj., Effective Doses for Coronary Angiography, Br. J. Radiol. (1996); 69:426-431

12. Marsden Pj, Washington Y, Diskin J. Estimation of Skin Dose in Interventional Neuro and Cardiac Procedures, Iaea-Cn-85/62 Radiological Protection of Patients in Diagnostic and Interventional Radiology, Nuclear Medicine and Radioterapy

13. Marshall Nw, Noble J, Faulkner K. Patient and Staff Dosimetry in Neurological Procedures, Br. J. Radiol. (1995); 68:495-501

14. Mcparland Bj., A Study of Patient Radiation Doses in Interventional Radiological Procedures, Br. J. Radiol. (1998); 71:175-185

15. Mcparland Bj., Entrance Skin Dose Estimates Derived from Dose-Area Product Measurements in Interventional Radiological Procedures, Br. J. Radiol. (1998); 71:1288-1295

16. Mooney Rb, Mckinstry Cs, Kamel Ham., Absorbed Dose and Deterministic Effects to Patients from Interventional Neuroradiology, Br. J. Radiol. (2000); 73:745-751

17. Rodriguez-Romero R, Diaz-Romero F, Hernandez-Armas J., Absorbed Doses to Patients from Angioradiology, Iaea-Cn-85/111 Radiological Protection of Patients in Diagnostic and Interventional Radiology, Nuclear Medicine and Radioterapy

18. Ruiz-Cruces R, Pérez-Martinez M, Martin-Palanca A, Flores A, Cristofol J, Martinez-Morillo M, Diez De Los Rios A., Patient Dose in Radiologically Guided Interventional Vascular Procedures: Conventional Versus Digital Systems, Radiology (1997); 205:385-393

19. Ruiz-Cruces R, Garcìa-Granados J, Diaz-Romero Fj, Hernandez-Armas J., Estimation of Effective Dose in Some Digital Angiographic and Interventional Procedures, Br. J. Radiol. (1998); 71:42-47

20. Theodorakou C, Butler P, Horrocks Ja., Radiation Doses in Interventional Neuroradiology, Iaea-Cn-85/68 Radiological Protection of Patients in Diagnostic and Interventional Radiology, Nuclear Medicine and Radioterapy

21. Toivonen M., Patient Dosimetry Protocols in Digital and Interventional Radiology, Rad. Prot. Dosim. (2001); 94(1-2):105-108

22. Tort I, Ruiz-Cruces R, Pérez-Martìnez M, Carrera F, Ojeda C, Dìez De Los Rìos A., Organ Doses in Interventional Radiology Procedures: Evaluation of Software, Iaea-Cn-85/226 Radiological Protection of Patients in Diagnostic and Interventional Radiology, Nuclear Medicine and Radioterapy

23. Van De Putte S, Verhaegen F, Taeymans Y., Correlation of Patient Skin Doses in Cardiac Interventional Radiology With Dose-Area Product, Br. J. Radiol. (2000); 73:504-513

24. Vaño E, Gonzalez L, Fernandez Jm, Guibelalde E., Patient Dose Values in Interventional Radiology, Br. J. Radiol. (1995); 68:1215-1220

25. Vano E, Guibelalde E, Fernandez Jm, Ten Ji., Patient Dosimetry in Interventional Radiology Using Slow Films, Br. J. Radiol. (1997); 70:195-200

26. Wagner Lk, Pollock Jj., Real-Time Portal Monitoring to Estimate Dose to Skin of Patients from High Dose Fluoroscopy, Br. J. Radiol. (1999); 72:846-855

27. Waite Jc, Fitzgerald M., An Assessment of Methods for Monitoring Entrance Surface Dose in Fluoroscopically Guided Interventional Procedures, Rad. Prot. Dosim. (2001); 94(1-2):89-92

28. Waite Jc, Fitzgerald M., An Assessment of Methods for Monitoring Entrance Surface Dose in Fluoroscopically Guided Interventional Procedures, Iaea-Cn-85/61 Radiological Protection of Patients in Diagnostic and Interventional Radiology, Nuclear Medicine and Radiotherapy

29. Webster Cm, Hayes D, Horrocks J., Investigation of Radiation Skin Dose in Interventional Cardiology, Iaea-Cn-85/71 Radiological Protection of Patients in Diagnostic and Interventional Radiology, Nuclear Medicine and Radioterapy

30. Wise Kn, Sandborg M, Persliden J, Alm Carlsson G., Sensitivity of Coefficients for Converting Entrance Surface Dose and Kerma-Area Product to Effective

Dose and Energy Imparted to the Patient, Phys. Med. Biol. (1999); 44:1937-1954

31. Zweers D, Geleijns J, Aarts Njm, Hardam Lj, Laméris Js, Schultz Fw, Schultze Kool Lj., Patient and Staff Radiation Dose in Fluoroscopy-Guided Tips Procedures and Dose Reduction, Using Dedicated Fluoroscopy Exposure Settings, Br. J. Radiol. (1998); 71:672-676

32. Recording Information in the Patient's Medical Record that Identifies the Potential for Serious X-Ray-Induced Skin Injuries. Fda. 15th September 1995.

33. Geise Ra, Peters Ne, Dunnigan A, Milstein S. Pacing, Radiation Doses During Pediatric Radiofrequency Catheter Ablation Procedures, Clin Electrophysiol 1996; 19: 1605-11

34. Nawfel Rd, Judy Pf, Silverman Sg, Hooton S, Tuncali K, Adams Df, Patient and Personnel Exposure During CT Fluoroscopy-Guided Interventional Procedures, Radiology 2000; 216: 180-4.

Annex: Literature summary of methods for patient dosimetry in interventional radiology

1. Alaei P, Gerbi BJ, Geise RA. EVALUATION OF A MODEL-BASED TREATMENT PLANNING SYSTEM FOR DOSE COMPUTATIONS IN THE KILOVOLTAGE ENERGY RANGE Med. Phys. (2000); 27(12): 2821-2826

The authors use a commercial treatment planning system (ADAC, Pinnacle) to compute the dose within phantoms from kilovoltage x-rays and to compare the calculation with measurements made using TLD dosimeters placed in several phantoms. The planning system’s capabilities have been extended to lower energies by the addition of energy deposition kernels in the 20-110 keV range and modelling of beams. Phantoms are:

- a cubic solid water phantom; - a solid water phantom with lung-equivalent heterogeneity; - a solid water phantom with bone-equivalent heterogeneity; - an Alderson Rando anthropomorphic phantom.

The comparison between measured and computed values shows that the treatment planning system can be used with reasonable accuracy to determine the dose distribution. The system’s limitations introduce inaccuracies for calculations through moderately high atomic number materials such as bone. These inaccuracies can be greatly reduced by a modification of existing tools to more accurately describe the interactions of radiation for lower-energy photon beams. 2. Chapple CL, Broadhead DA, Faulkner K.

A PHANTOM BASED METHOD FOR DERIVING TYPICAL PATIENT DOSES FROM MEASUREMENTS OF DOSE-AREA PRODUCT ON POPULATIONS OF PATIENTS Br. J. Radiol. (1995); 68:1083-1086

One of the chief sources of uncertainty in the comparison of dosimetry data is the influence of patient size on dose. The purpose of this work is to develop a method for determining size correction factors. Energy imparted correlates better with the ‘equivalent cilindrical diameter’:

de=2(sqrt(W/πH)) than with weight or patient thickness. If an exponential relationship is assumed between dose and size, size correction factor result:

F=ek(deref

– de meas

) The factor k must be determined experimentally.

Measurements were carried out using different thickness of tissue equivalent phantom material. Values of k have been determined and ranged from 0.13 to 0.18 cm-1, all with correlation coefficients greater than 0.997. The use of size correction factor allows the inclusion of all patients within a survey and should improve the accuracy of the results of a small sample size. Data are available for converting DAP to effective dose for reference size man and may be applied to size corrected DAP values.

3. Cotelo E, Pouso J, Reyes W. RADIOFREQUENCY CATHETER ABLATION: RELATIONSHIP BETWEEN FLUOROSCOPIC TIME AND SKIN DOSES ACCORDING TO DIAGNOSES. BASIS TO ESTABLISH A QUALITY ASSURANCE PROGRAMME IAEA-CN-85/168 Radiological Protection of Patients in Diagnostic and Interventional Radiology, Nuclear Medicine and Radioterapy

The authors determinate the fluoroscopy time and skin doses in relation to pathology to treat. Authors evaluate fluoroscopic time and estimate skin doses in 233 procedures. Significant differences among the medians of fluoroscopic time are found in those procedures depending on diagnosis and results. Skin doses were evaluated as:

D(Gy)=BF Output(distance corrected) mA Fluoroscopy Time This method gives dose evaluation affected by significant errors and overestimates skin doses.

4. Cusma JT, Bell MR, Wondrow A et al. REAL TIME MEASUREMENT OF RADIATION EXPOSURE TO PATIENTS DURING DIAGNOSTIC CORONARY ANGIOGRAPHY AND PERCUTANEOUS INTERVENTIONAL PROCEDURES J. Am. Coll. Cardiol (1999); 33:427-435

5. Garcia-Roman MJ, Prada-Martinez E, Abreu-Luis J, Hernandez-Armas J. PATIENT RADIATION DOSES FROM NEURORADIOLOGY PROCEDURES IAEA-CN-85/112 Radiological Protection of Patients in Diagnostic and Interventional Radiology, Nuclear Medicine and Radioterapy

The objective of the work is to establish typical values of effective dose and DAP for some neuroradiological procedures. The measurements on patients were:

- DAP measurements both for fluoroscopy and radiography with relative projection;

- Skin dose measurements with TLD placed at the zones thought to be at major exposure.

Some procedures were also performed with a phantom with TLDs into it to measure dose released to organs. Dose released to organs and effective dose were also calculated with Monte Carlo simulation. The comparison between measured and calculated doses gave rise major values to those measured.

6. Geise RA, Ansel HJ. RADIOTHERAPY VERIFICATION FILM FOR ESTIMATING CUMULATIVE ENTRANCE SKIN EXPOSURE FOR FLUOROSCOPIC EXAMINATIONS Healt Phys. (1990); 59(3):295-298

In this study the exposure was measured using an ion chamber system placed in front of pre-packaged film and was corrected for the inverse square distance dependence. The verification film was used to measure patient exposure during air contrast barium enema examinations. TLDs were placed in appropriate locations on several films to check the agreement of film exposures to those determined with the TLDs. The TLDs were calibrated against the same ion chamber system used to perform the sensitometry measurements of the film. TLD reading were converted to exposure for comparing with film exposure values. The average difference between exposures determined by film and exposures determined by TLD was 9%. The maximum difference was 21%. If the TLD happens to be placed near the edge of a field, the dose estimation may be significantly different than that in the centre of the field. The use of an area detector, such as film, allows for locating the centre of each spot film field and correlating the fields with the anatomical regions being examined. 7. Hernando I, Torres R.

COMPARISON BETWEEN TERMOLUMINISCENCE DOSIMETRY AND TRANSMISSION IONIZATION CHAMBER MEASUREMENTS IAEA-CN-85/177 Radiological Protection of Patients in Diagnostic and Interventional Radiology, Nuclear Medicine and Radiotherapy

The authors compare simultaneous measurements of skin dose made with TLDs and with a DAPmeter. TLD are positioned on the patient’s back in an array made by 2x10 chips and 18x2 cm2. DAP-meter: is positioned at the tube exit. The determination of field size at the patient’s skin is made by a radiographic film positioned at the patient’s back. Calculation of skin dose results from:

Dcalc=(F(p,T) Fr Ft L)/S were: F(p,T) = correction factor for pressure and temperature;

Fr = backscattering factor; Ft = transmission factor of operating table; S = field size; L = measurement from DAP-meter.

The calculation does not take into account tube movements, overestimating skin doses. Direct measurements of skin doses with TLDs are more accurate, but do not allow immediate feedback to the operator. On the other hand, the DAP-meter give instantaneous results but all the parameters entering in the dose calculation are affected by significant errors.

8. Huda W, Phadke K, Ogden KM, Roskopf ML. PATIENT DOSES IN DIGITAL CARDIAC IMAGING IAEA-CN-85/64 Radiological Protection of Patients in Diagnostic and Interventional Radiology, Nuclear Medicine and Radiotherapy

The authors estimate entrance skin doses and the corresponding effective doses to patients undergoing digital cardiac imaging procedures. The x-ray output is determined in terms of air kerma per unit of mAs. Data for the x-ray parameters are recorded for each separate projection. From this information maximum skin doses are estimated by taking into account any overlap of the x-ray projection used for each patient.

9. Huyskens CJ, Hummel WA. DATA ANALYSIS ON PATIENT EXPOSURES IN CARDIAC ANGIOGRAPHY Rad. Prot. Dosim. (1995); 57(1-4):475-480

In this study an empirical formula has been derived to estimate the kerma-exposure product as a function of fluoroscopy time and film length, providing an useful method to evaluate exposures in interventional radiology (the variability in film length and fluoroscopy time is generally far more important than variations in technical parameters). The kerma-area product is a direct measure for the patient dose. The kerma-area product can be approximated by the function:

KAP = α FT + β CL

Where: FT = fluoroscopy time (min) CL = film length (m) Using a self-made phantom and instruments calibrated in terms of Gycm2, for all different types of projections and usual image intensifier field sizes, differential values for the kerma-area product per unit fluoroscopy time have been measured as well as the differential values of the kerma-area product per unit film length. For a full interventional procedure, the contribution to the kerma-area product from fluoroscopy and from cinematography were calculated. It is concluded that the kerma-area product per patient (Gy cm2) in the course of an interventional procedure can be approximated by:

KAP = 2.5 FT + 0.7 CL

Uncertainties in the coefficients α and β are estimated to be approximately 40%.

10. Le Heron JC. ESTIMATION OF EFFECTIVE DOSE TO THE PATIENT DURING MEDICAL X-RAY EXAMINATIONS FROM MEASUREMENTS OF THE DOSE-AREA PRODUCT Phys. Med. Biol. (1992); 37(11):2117-2126

Calculation of effective dose requires the evaluation of doses to many organs. In the absence of such data it would be useful to directly estimate effective dose from a quantity that can be easily measured in an x-ray room. Relationship between effective dose and entrance surface dose, entrance air kerma and DAP were studied for common radiographic projections using the organ dose data from Monte Carlo modelling. DAP proved to be the best quantity for estimating effective dose. Groups of projections have similar conversion coefficients and then can be grouped. Within these groupings it is possible to assign a limited number of conversion coefficients to enable an estimate of effective dose from DAP measurements, provided a given level of uncertainty. Use of the conversion coefficients for asymmetrical fields may lead to additional uncertainties. Caution must be exercised with small fields. Finally, the conversion coefficients will provide estimates of effective dose for average patients. 11. Leung KC, Martin CJ.

EFFECTIVE DOSES FOR CORONARY ANGIOGRAPHY Br. J. Radiol. (1996); 69:426-431

The calculation of dose conversion coefficients for a wide variety of radiographic projections has enabled effective doses to be evaluated for procedures where DAP and exposure factor data were available. Effective doses have been derived for coronary angiography examinations. Data were recorded for 100 coronary angiographies. Data from 10 patients, where fluoroscopy and radiography were similar to the mean for the group, were considered to representative of a standard examination. These procedures were used to derive conversion factors. For every examination the chronological sequence of patient positions and projections was recorded for all periods of radiography and fluoroscopy. A DAP calibration factor was applied to each period related to projection employed and a size correction factor was applied to give the equivalent DAP for a standard man. Because of the similarities in the patterns of exposure, a standard conversion factor between DAP and effective dose was derived for application to data for whole examinations.

12. Marsden PJ, Washington Y, Diskin J. ESTIMATION OF SKIN DOSE IN INTERVENTIONAL NEURO AND CARDIAC PROCEDURES IAEA-CN-85/62 Radiological Protection of Patients in Diagnostic and Interventional Radiology, Nuclear Medicine and Radiotherapy

This paper presents measurements made on antropomorphic phantoms which can be used to link DAP values to skin doses for situations typically encountered in both interventional neuroradiology and cardiac procedures. Skin doses were measured directly using a Skin Dose Monitor placed on the entrance surface at the centre of the field of view. DAP readings were obtained simultaneously from pre-installed DAP-meter. Conversion factors of DAP to Skin Dose Conversion Factors in Cardiac Fluoroscopy for seven projections are reported.

13. Marshall NW, Noble J, Faulkner K. PATIENT AND STAFF DOSIMETRY IN NEUROLOGICAL PROCEDURES Br. J. Radiol. (1995); 68:495-501

The aim of the study was to monitor staff doses and to estimate patient organ doses due to cerebral angiography and evaluate patient effective dose. Examinations were usually performed under automatic exposure-rate control. Patient thyroid doses were measured with TLDs and general patient dosimetry performed using a DAP-meter. Estimation of effective dose, requiring the equivalent dose to 12 organs, was made with TLDs inside a Rando phantom undergoing a typical vessel angiogram. The DAP for the typical angiogram was recorded and from this a DAP to effective dose conversion factor calculated. In order to estimate the contribution to DAP and effective dose from the fluoroscopy component of the examination, this entire procedure was repeated without taking any digital subtraction radiographs. An effective dose/DAP conversion factor for cerebral angiography of 0.087mSvGy-

1cm-2 is reported.

14. McParland BJ. A STUDY OF PATIENT RADIATION DOSES IN INTERVENTIONAL RADIOLOGICAL PROCEDURES Br. J. Radiol. (1998); 71:175-185

A dose survey of interventional radiology procedures performed on a digital angiography unit, its analysis and comparison with other data in the literature, are reported. Owing to the complexity of IR procedures, accurate assessment of patient doses is difficult and averaging over varying beam qualities and anatomical projections is therefore necessary.

DAP values were recorded separately, for fluoroscopy and digital radiography. With knowledge of beam quality, anatomical region imaged and radiographic projection, the effective dose can be estimated from the DAP using factor for converting DAP measurements to effective dose derived from Monte Carlo simulations. The hypothesis that therapeutic procedures have significantly higher DAPs than diagnostic procedures was tested for five sets of pairs of procedures, each in the same anatomical region, so that the DAP to ESD conversion factor for each pair was equal. Even though there may appear to be a large difference in mean DAPs between the two categories, only one pair showed a statistically significant increase in mean DAP for the therapeutic procedure over the diagnostic procedure. There is evidence of a wide variation in patient radiation dose due to clinical technique differences, statistical sampling and type of x-ray equipment used.

15. McParland BJ. ENTRANCE SKIN DOSE ESTIMATES DERIVED FROM DOSE-AREA PRODUCT MEASUREMENTS IN INTERVENTIONAL RADIOLOGICAL PROCEDURES Br. J. Radiol. (1998); 71:1288-1295

A method of estimating ESD from measured DAP data for a number of IR procedures by assuming that each procedure is conducted under a fixed nominal geometry specific to it, is presented. The uncertainties due to the use of a single nominal geometry for a procedure are analysed. Finally, ESD estimates are provided for a number of non-coronary procedures using DAP data accrued for an IR dose survey at the institution. Changes in ESD caused by deviations in the focus-to-skin and focus-to-image intensifier distances from the nominal value are well modelled; the dependence of the dose error upon the image intensifier field-of-view is significant, due to the field area dependence of the denominator in the model. Even for the nominal geometry, there is a difference between the calculated and measured doses due to the measurements performed on an homogeneous phantom. The ESD uncertainty is also due to the additional collimation and image intensifier field-of-view used. The overall uncertainty can be comparable to that of other methods commonly adopted to estimate ESD; moreover, the ease of proposed method allows large numbers of patients to be surveyed. 16. Mooney RB, McKinstry CS, Kamel HAM.

ABSORBED DOSE AND DETERMINISTIC EFFECTS TO PATIENTS FROM INTERVENTIONAL NEURORADIOLOGY Br. J. Radiol. (2000); 73:745-751

Measurements of absorbed dose to the patient skin undergoing interventional neurological procedures, involving long fluoroscopy time, were made. From dose measurements and records of fluoroscopy time and number of digital runs acquired, estimates of the maximum absorbed skin dose and the maximum absorbed dose to the skull were made.

TLD dosimeters were placed over the areas considered most likely to receive the heaviest irradiation. “Effective” fluoroscopy time can be introduced, which is a combination of the actual fluoroscopy time and the number of DSA runs acquired, to give an indication of the procedure length. Early clinical experience with kilovoltage beams suggests that clinically significant bone damage is not likely to occur without accompanying skin effects. 17. Rodriguez-Romero R, Diaz-Romero F, Hernandez-Armas J.

ABSORBED DOSES TO PATIENTS FROM ANGIORADIOLOGY IAEA-CN-85/111 Radiological Protection of Patients in Diagnostic and Interventional Radiology, Nuclear Medicine and Radiotherapy

The aim of the study was to know the patient doses when three different procedures of angioradiology were carried out. DAP measurements and TLDs were used in an anthropomorphic phantom to obtain values of organ doses when the phantom was submitted to the same procedure than the actual patients. The Eff-Dose program was used to estimate the effective doses in the procedures conditions. The organ doses estimated from TLDs measurements were higher than the corresponding values estimated by Monte Carlo simulation.

18. Ruiz-Cruces R, Pérez-Martinez M, Martin-Palanca A, Flores A, Cristofol J, Martinez-Morillo M, Diez de los Rios A.

PATIENT DOSE IN RADIOLOGICALLY GUIDED INTERVENTIONAL VASCULAR PROCEDURES: CONVENTIONAL VERSUS DIGITAL SYSTEMS Radiology (1997); 205:385-393

The work includes: evaluations of DAP value differences between conventional and digital systems and, evaluation of organ and effective dose in procedures performed with digital systems. For interventional vascular procedures, which involve considerably long fluoroscopy time and variation in beam direction and size, the entrance dose cannot be conveniently measured with TLD dosimeters. The dose measured in five organs whit the Padovani’s method with TLDs placed on the surface of the patient’s skin was compared with the organ dose calculated with Eff-Dose. In addition Eff-Dose was used to calculate the effective equivalent dose. It is reported that, DAP was higher with the digital system in 13 of the 15 groups analysed.

19. Ruiz-Cruces R, Garcìa-Granados J, Diaz-Romero FJ, Hernandez-Armas J. ESTIMATION OF EFFECTIVE DOSE IN SOME DIGITAL ANGIOGRAPHIC AND INTERVENTIONAL PROCEDURES Br. J. Radiol. (1998); 71:42-47

Effective dose is an indicator of radiological risk, but its magnitude cannot be measured directly, conversion factors from measurable quantities, like DAP, and effective dose are necessary. In this study, who objective is to provide dose data for

some digital angiographic and interventional procedures, effective dose has been estimated using Monte Carlo method. For each procedure, technical parameters for both fluoroscopy and radiography, field size, fluoroscopy time and number of radiographic films were acquired. DAP values were corrected for the attenuation of the patient table. Effective dose, calculated independently for radiography and fluoroscopy, was estimated by comparing the actual procedure with simple radiographic projections published. The fluoroscopy component makes a large contribution to the total DAP values and a similar influence is observed on the average values of the effective dose. Effective dose values per minute of fluoroscopy and per radiographic film for the five types of procedure analysed can be adopted as conversion factors to estimate the patient effective dose.

20. Theodorakou C, Butler P, Horrocks JA. RADIATION DOSES IN INTERVENTIONAL NEURORADIOLOGY IAEA-CN-85/68 Radiological Protection of Patients in Diagnostic and Interventional Radiology, Nuclear Medicine and Radiotherapy

A preliminary study, performed on 13 patients that underwent to celebral embolization, is reported. Images are taken after injection of contrast medium with two imaging modalities: fluoroscopy and Digital Subtraction Angiography (DSA). The study investigates: Entrance Skin Dose TLDs Radiotherapy verification films System calculated values. DAP Organ Dose Operators dose TLD100 chips array 15x15cm2 (6x6 chips) were used. The chips were placed on the radiographic films: one under the patient’s head and one on the right side of the head. For doses above 1Gy, correction factors have been applied to TLD readings in order to account for supralinearity. Radiotherapy verification films has been used to visualise the radiation field. Software calculated doses from DAP-meter measurements, for each plane and for each mode separately and from technical parameters of radiation beam. Isodose curves are obtained superimposing TLD measurements and images taken from the films. Comparing the ESDcalc and the ESDmes for both planes, it may be seen that the ESDcalc in most cases are higher than ESDmes, overestimating the actual dose. Comparing the dose rates for fluoroscopy and DSA it may be seen that the doses from DSA are much higher than that from fluoroscopy.

21. Toivonen M. PATIENT DOSIMETRY PROTOCOLS IN DIGITAL AND INTERVENTIONAL RADIOLOGY Rad. Prot. Dosim. (2001); 94(1-2):105-108

In this paper the quantities proposed to express reference values for IR are reviewed, and methods to collect data required for estimation of their values are compared. Exposure indicators are manufacturer-specific and depend on several technical factors. The indicators must be calibrated to a particular air kerma at the image receptor periodically. Both the ESD and the DAP, multiplied by their related conversion factors E/ESD or E/DAP, provide an evaluation of the effective dose. The accuracy of the factors E/DAP is better than those of E/ESD.

22. Tort I, Ruiz-Cruces R, Pérez-Martìnez M, Carrera F, Ojeda C, Dìez de los

Rìos A. ORGAN DOSES IN INTERVENTIONAL RADIOLOGY PROCEDURES: EVALUATION OF SOFTWARE IAEA-CN-85/226 Radiological Protection of Patients in Diagnostic and Interventional Radiology, Nuclear Medicine and Radiotherapy

The objective is to estimate organ doses and to make a comparison between the results given by different software available to carry out the calculation of organ doses in complex interventional radiology procedures. Organ doses and effective dose have been calculated, for each projection used in the procedures, with different commercially available software based on Monte Carlo simulation: Eff-dose, PCXMC and DiaSoft. Eff-dose and DiaSoft provide results practically equal; on the other hand, PCXMC gives very different results. The latter gives the advantage to adjust beam geometry and patient size.

23. Van de Putte S, Verhaegen F, Taeymans Y. CORRELATION OF PATIENT SKIN DOSES IN CARDIAC INTERVENTIONAL RADIOLOGY WITH DOSE-AREA PRODUCT Br. J. Radiol. (2000); 73:504-513

For a standardized coronary catheterization procedure and a left ventricle angiography investigation, an average skin dose distribution was calculated from the measured DAP of the different x-ray projections used in the procedure, using Monte Carlo derived conversion factors. Attempts have been made to calculate individual skin dose distributions, based on individual DAP measurements. Skin dose measurements were made using eight TLDs attached to the patient’s skin. To determine the optimal TLD position, an antrophomorphic phantom was covered with radiographic film and irradiated using the geometries and irradiation times used

in a standard procedure. The densitometric information obtained was used to calculate skin dose distribution and the area of the skin receiving the highest dose. Using Monte Carlo derived conversion factors, skin dose distributions were calculated for two average procedures. The study investigates whether DAP is representative of the skin dose in interventional cardiology and whether the DAP can be used as an indicator for local overexposure. Based on the average DAP values, the skin dose distribution, typical for a standard procedure, was calculated. Good agreement was observed between the calculated values and the TLD measurements. When applying the conversion factors to calculate the individual skin doses, the agreement between the calculated skin dose and the measured dose was rather poor. The study shows that the total DAP per procedure can give only an approximate indication of the skin dose, and support the view that total DAP cannot be used as an indicator of local overexposure.

24. Vaño E, Gonzalez L, Fernandez JM, Guibelalde E. PATIENT DOSE VALUES IN INTERVENTIONAL RADIOLOGY Br. J. Radiol. (1995); 68:1215-1220

Dose-area product can be used for patient stochastic risk evaluations, where the surface dose provides an indication of possible deterministic effects. In this study:

- DAP was measured using a transmission ionization chamber - surface dose was measured using four TLDs placed over, under and on both

sides of the perimeter of the most irradiated patient region; the sum of the four values is used as a Surface Dose Indicator (SDI) for comparative purposes.

The suitability of this method has been checked by comparing the results with those obtained using TLD arrays based on larger chip numbers. No noticeable loss of information was observed when using four dosimeters. The transmission ionization chamber and TLD measurements were periodically checked. SDI values in cardiology are lower than for the rest of IR in nearly all instances, despite the higher DAP values.

25. Vano E, Guibelalde E, Fernandez JM, Ten JI. PATIENT DOSIMETRY IN INTERVENTIONAL RADIOLOGY USING SLOW FILMS Br. J. Radiol. (1997); 70:195-200

Patient dosimetry in IR and IC is extremely complex, due to the irradiation of different anatomical areas, with the x-ray beam changing to various projections, field sizes, radiation qualities, focus-to-skin distances and focus-to-image intensifier distances. Typical measurement systems will not provide enough information for body areas receiving higher doses.

The method proposed allows the simultaneous estimation of DAP, skin dose and distribution of the irradiated fields, together with their corresponding dose levels. Kodak X-Omat V film has been used to visualize and estimate doses from the different irradiation fields. X-ray sensitometry was carried out to calibrate the film for the x-ray spectrum and filtration employed in IR and IC. Doses and reproduction of technical parameters were checked by using a calibrated chamber. Doses were also measured with TLD placed in contact with the film. The main source of error is due to the propagation of the error when the characteristic function is reversed to calculate doses.

26. Wagner LK, Pollock JJ.

REAL-TIME PORTAL MONITORING TO ESTIMATE DOSE TO SKIN OF PATIENTS FROM HIGH DOSE FLUOROSCOPY Br. J. Radiol. (1999); 72:846-855

The author investigates advantages and disadvantages of a scintillation dosimeter (SD) as a portal monitor used to estimate skin dose during fluoroscopically-guided procedures. Uncertainties associated with the use of a portal monitor are discussed. Several methods have been proposed to perform real-time monitoring of skin dose:

- direct monitoring: conceptually the simplest method, but the dosimeter, prior the procedure, must be placed at the site on the skin that will receive the highest dose;

- indirect monitoring: infer skin doses from measurements made remotely from the skin; will overestimate the maximum dose because it cannot distinguish which area of the skin is being exposed at any time.

In portal monitoring the detector is attached to the x-ray collimator beam at the position of the central axis. A calibration factor was generated to convert the portal monitor reading into tissue dose. Errors in the real time measurements of absorbed dose to the skin have several sources here categorized as those related to the monitor and those related to the monitoring technique. SD has a reasonably accurate response over the range of energies, doses and operating conditions encountered in interventional work.

27. Waite JC, Fitzgerald M. AN ASSESSMENT OF METHODS FOR MONITORING ENTRANCE SURFACE DOSE IN FLUOROSCOPICALLY GUIDED INTERVENTIONAL PROCEDURES Rad. Prot. Dosim. (2001); 94(1-2):89-92

28. Waite JC, Fitzgerald M. AN ASSESSMENT OF METHODS FOR MONITORING ENTRANCE SURFACE DOSE IN FLUOROSCOPICALLY GUIDED INTERVENTIONAL PROCEDURES IAEA-CN-85/61 Radiological Protection of Patients in Diagnostic and Interventional Radiology, Nuclear Medicine and Radiotherapy

The authors compare three methods of monitoring Entrance Surface Dose (ESD) in fluoroscopically guided interventional procedures:

- array of 35 TLDs - Skin Dose Monitor (SDM): a small detector in a reflecting plastic housing,

linked by a fibre optic to a meter - DAPmeter+K

TLD arrays are the most accurate means of measuring ESD but suffer from the substantial drawback of requiring post-exposure processing. A more simple method of monitoring ESD would be to establish a relationship between ESD and DAP reading, but no correlation between the two sets of measurements for cardiac procedures was obtained due, maybe, to great irradiation geometry variation. The SDM compared favourably with a calibrated ionisation chamber in the laboratory, is easy to use and gives a real time running total of the ESD, but:

- the sensor has a small surface area, monitoring a limited area of the skin, that may not be the more irradiated

- the system is too bulky - the optic cables are fragile and should be often replaced.

29. Webster CM, Hayes D, Horrocks J. INVESTIGATION OF RADIATION SKIN DOSE IN INTERVENTIONAL CARDIOLOGY IAEA-CN-85/71 Radiological Protection of Patients in Diagnostic and Interventional Radiology, Nuclear Medicine and Radiotherapy

In the study, for 56 patients randomly selected (23 undergoing Radiofrequency Catheter Ablation (RFCA); 33 undergoing Percutaneous Transluminal Coronary Angioplasty (PTCA)), skin doses have been investigated:

- radiation skin doses DAP-meter - TLD - possible skin damages resulting from the procedure (follow-up for a three

month period). Measurements:

- TLD gives point value of skin dose; the chips are placed directly on the patient’s back in 7 standard positions

- DAPmeter gives an average value of dose, does not take into account dose distribution due to x-ray tube movements.

Skin dose for each projection is achieved by dividing the DAP by the field size at the patient’s skin and by multiplying for the backscatter factor. Results: RFCA: not significant correlation between calculated and TLD measured skin doses (Correlation=0.76; p=0.08ns); PTCA: no correlation between calculated and TLD measured skin doses (Correlation=0.15).

30. Wise KN, Sandborg M, Persliden J, Alm Carlsson G. SENSITIVITY OF COEFFICIENTS FOR CONVERTING ENTRANCE SURFACE DOSE AND KERMA-AREA PRODUCT TO EFFECTIVE DOSE AND ENERGY IMPARTED TO THE PATIENT Phys. Med. Biol. (1999); 44:1937-1954

The estimation of the conversion coefficients from ESD or KAP to effective dose E requires computer-intensive Monte Carlo methods. Tables are available for a wide range of tube potentials and filtrations but, field size, film-focus distance and position of the centre of the field are fixed for each combination of phantom age and examination. Again, there is limited information on the sensitivity of the conversion coefficients to a number of variations seen in clinical work. The authors investigate the effect on E/DAP and E/ESD for variations of up to five factors of: tube potential, field size, field position, phantom size and sex. The method adopted a factorial analysis procedure in which each factor being studied is varied over all combinations of two values, one low and the other high, chosen from observed variations in a single x-ray room. The question to be addressed is: which of the conversion coefficients is the least sensitive to variations which naturally occur within a given practice? The work confirms that substantial variations in the conversion coefficients can occur due to variation in field size, field position, patient size and sex. Whether effective dose or energy imparted to the patient is best estimated using ESD or KAP? The study shows no strong preference for KAP over ESD for estimation of E when all parameters are varied. A practical argument for the use of KAP over ESD can be based on the observation that use of KAP automatically allows for variations in field size. In general KAP provides a good measure of energy imparted and is to be preferred for its determination.

31. Zweers D, Geleijns J, Aarts NJM, Hardam LJ, Laméris JS, Schultz FW, Schultze Kool LJ.

PATIENT AND STAFF RADIATION DOSE IN FLUOROSCOPY-GUIDED TIPS PROCEDURES AND DOSE REDUCTION, USING DEDICATED FLUOROSCOPY EXPOSURE SETTINGS Br. J. Radiol. (1998); 71:672-676

The DAP from fluoroscopy and imaging, displayed separately on the operator’s viewing console, were recorded after each procedure. DAP figures were calculated from technical parameters by software. Comparison of calculated DAP to measurements by means of calibrated flat ionization chamber showed consistent deviations throughout a range of different beam sizes with low, medium and high air kerma rates. Patient entrance doses were calculated by the measured DAP, average entrance beam diameters and application of appropriate backscatter factor.

32. RECORDING INFORMATION IN THE PATIENT'S MEDICAL RECORD THAT IDENTIFIES THE POTENTIAL FOR SERIOUS X-RAY-INDUCED SKIN INJURIES. FDA. 15th September 1995.

The agency has been requested to clarify the recommendations given in the FDA Public Health Advisory document of 9th September 1994 regarding ‘which patients should have such information recorded’ and ‘what information should be recorded’. The document presents the Agency's advice on these questions. Medical facilities are encouraged to implement these or similar procedures in order to reduce the likelihood of radiation-related complications. (WP3.7)

33. Geise RA, Peters NE, Dunnigan A, Milstein S. Pacing RADIATION DOSES DURING PEDIATRIC RADIOFREQUENCY CATHETER ABLATION PROCEDURES Clin Electrophysiol 1996; 19: 1605-11

Radiofrequency catheter ablation procedures may be lengthy and are commonly performed in young patients and therefore, concern has arisen about radiation dose in this group of patients. The authors investigate radiation doses in pediatric patients undergoing RF catheter ablation. Standard fluoroscopic equipment used for diagnostic electrophysiological catheterization studies is technologically capable of dose rates as high as 90 mGy/min to skin and adjacent lung and 260 mGy/min to vertebral bone. Dose rates of this magnitude when used for extended periods of time have been known to cause erythema, pneumonitis, and retardation of bone growth. Skin dose rates of nine paediatric patients undergoing RF catheter ablation for tachycardia and calculated doses to the skin using standard dosimetric methods (from exposure factors, gantry angle, X-ray field size and SSD) are reported. Fluoroscopic techniques and equipment were studied using a patient simulating phantom. Overlap of fluoroscopic fields was checked using radiotherapy portal verification film, and regions in which doses overlapped from multiple angle exposures were verified using a treatment planning computer. Patient skin dose rates ranged from 6.2-49 mGy/min for patients ranging in age from 2-20 years. Maximum skin doses ranged from 0.09-2.35 Gy. Actual skin dose rates may exceed 400 mGy/min. Some bone could receive a dose 2 or 3 times the threshold set up for dry desquamation of the skin and so there is a potential for serious immediate effects (retardation of bone grow or even complete cessation of growth occurs in young people at 30 Gy). The paper also highlights that TLD measurements of other authors do not account the fact that TLD readings do not reflect the maximum skin dose if the dosimeter is not in the exact position of the fluoroscopic beam (see reference 12: Radiation exposure to patients undergoing percutaneous transluminal coronary angioplasty. Cascade PN ; Peterson LE ; Wajszczuk WJ ; Mantel J. Am J Cardiol, 59(9):996-7 1987 Apr 15). On average, the patient’s skin is getting about 1 thousand times the dose a person would receive from secondary radiation at a distance of 1 m without wearing

protective lead apparel. Data demonstrate the need to directly measure dose rates for individual fluoroscopic equipment and procedural techniques in order to determine whether limitations need to be set for procedural times. (WP 3.7)

34. Nawfel RD, Judy PF, Silverman SG, Hooton S, Tuncali K, Adams DF PATIENT AND PERSONNEL EXPOSURE DURING CT FLUOROSCOPY-GUIDED INTERVENTIONAL PROCEDURES Radiology 2000; 216: 180-4.

Surface dose was estimated on a CT dosimetric phantom by using thermoluminescent dosimetric (TLD) and CT pencil chamber measurements. Scatter exposure was estimated from scattered radiation measured at distances of 10 cm to 1 m from the phantom. Scatter exposures measured with and without placement of a lead drape on the phantom surface adjacent to the scanning plane were compared. Phantom surface dose rates ranged from 2.3 to 10.4 mGy/sec. Scattered exposure rates for a commonly used CT fluoroscopic technique (120 kVp, 50 mA, 10-mm section thickness) were 27 and 1.2 µGy/sec at 10 cm and 1 m, respectively, from the phantom. Lead drapes reduced the scattered exposure by approximately 71% and 14% at distances of 10 and 60 cm from the scanning plane, respectively. As a conclusion, high exposures to patients and personnel may occur during CT fluoroscopy–guided interventions. Radiation exposure to patients and personnel may be reduced by modifying CT scanning techniques and by limiting fluoroscopic time. In addition, scatter exposure to personnel may be substantially reduced by placing a lead drape adjacent to the scanning plane. (Vano 3.7)