Special Topics
Occupational Radiation Exposure to Interventional Radiologists: A Prospective Study1 M . Victoria Marx, M D Loren Niklason, PhD ElizabethA. Mauger, MS Index terms: Fluoroscopy Interventional procedures * Radiology and radiologists Radiations, exposure to patients and personnel Radiations, measurement
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JVIR 1992; 3:597-606 Abbreviations: CRCPD = Conference of Radiation Control Program Directors, ED = effective dose, EDE = effective dose equivalent, ICRP = International Commission on Radiological Protection, NCRP = National Council on Radiation Protection and Measurements, PYD = projected yearly dose, TLD = thermoluminescent dosimetry
From the Departments of Radiology (M.V.M., L.N.) and Biostatistics (E.A.M.), University of Michigan Hospitals, 1500 E Medical Center Dr, Ann Arbor, MI 481090030. From the 1991 SCVIR annual meeting. Received March 17, 1992; revision requested May 7; revision received August 6; accepted August 7. Address reprint requests to M.V.M.
" SCVIR, 1992
This study investigates the occupational radiation dose to interventional radiologists and the operator-controlled factors that may affect dose. Thirty interventional radiologists wore radiation badges over and under lead aprons for 2 months and answered a questionnaire. The relationships between dose and caseload, case mix, experience, optional fluoroscopy features, lead apron type, and additional lead shielding were evaluated. Mean projected yearly dose (PYD)over lead was 49.1 mSv (1mSv = 100 mrem) but was 66.6 mSv for persons performing 1,000 or more cases per year and 31.0 mSv for those performing fewer than 1,000 cases per year (P= .027). Mean PYD under lead was 0.9 mSv but was 1.3 mSv for persons with 0.5-mm lead coverage and 0.4 mSv for those with 1.0-mm lead coverage (P= .002). No other significant correlation was found. Conclusions are that caseload and apron thickness are the primary determinants of total body dose, that over-lead dose is high enough to warrant additional lead shielding for the head and neck, and that a double-thicknessapron lowers under-lead dose by two-thirds. The large difference between under-lead and over-leaddoses suggests that use of a collar badge alone for monitoring purposes is not predictive of total-body effective dose for this group of radiation workers. lNTERVENT10NAL radiologists specialize in the performance of invasive diagnostic and therapeutic procedures with use of fluoroscopic guidance. While occupational radiation exposure is something that all interventional radiologists accept, most have a vague feeling that their exposure levels are "high." Daily use of C-arm or U-arm fluoroscopy (1,2), manual injection of contrast material during digital subtraction angiography (3), and frequent performance of lengthy procedures with the operator in close proximity to the patient (4,5) are among the factors that contribute to elevated exposure. Previous investieations have documented Droce" dure-specific and body part-specific exposures (1-9), but few (10-12) have looked a t exposure levels over time for physicians performing a wide range of fluoroscopically guided interventions. To our knowledge,
none have studied operator-controlled factors that might affect occupational radiation absorbed dose. The time has come to evaluate critically the occupational radiation exposure received by interventional radiologists for several reasons. First, the radiation dose received by individual interventional radiologists is likely to be rising because fluoroscopically guided interventional procedures are becoming more common, complex, and lengthy. Second, the specialty of interventional radiology is growing, and this population may be an increasingly significant segment of the medical worker population. In addition, in the relatively near future, it may be necessary for the specialty of interventional radiology to respond to changes in government regulations concerning permissible occupational radiation exposure. Finally, and perhaps most important,
598
Journal of Vascular and Interventional Radiology
November 1992
the population of physicians performing fluoroscopically guided interventional procedures includes not only interventional radiologists (who have formal training in radiation physics and radiation safety) but cardiologists, vascular surgeons, urologists, orthopedic surgeons, and gastroenterologists. Evaluation of the occupational radiation exposure to interventional radiologists may, therefore, have relevance to a much broader segment of health care workers. The goal of this investigation is to calculate, as accurately as possible, the projected yearly over-lead and under-lead radiation doses to a population of interventional radiologists and to identify what operator-controlled factors contribute to dose.
MATERIALS AND METHODS In March 1990,35 interventional radiologists were invited to participate in a prospective evaluation of their occupational radiation exposures. Thirty of the initial 35 subjects (86%)completed the project and comprise the final study group. The group included 22 men and eight women from 17 institutions. There were 18 faculty members and nine fellows-in-training from 14 teaching hospitals, and three interventionalists from three non-teaching institutions. Each member of the study group completed three phases of the project, including completing a lengthy preliminary questionnaire, wearing dosimetry badges for a predetermined time period, and completing a short final questionnaire. The preliminary questionnaire was used to acquire basic demographic data, as well as information about practice patterns, fluoroscopy equipment and habits, radiation protection practices, and compliance with standard departmental monitoring procedures. With respect to practice patterns, project participants were asked how many interventional procedures they perform per year, what percentage of their practices are spent doing
interventional procedures, what percentage ', of their interventional work is diagnostic and what percentage is therapeutic, how much of their work involves fluoroscopy (rather than computed tomographic [CT] or ultrasonographic [US] guidance), how many years after residency have they been practicing primarily interventional radiology, and what are their future plans with regard to practice pattern. They were also asked how many weeks per year they spend away from clinical duties (ie, meeting and vacation time). On the topic of fluoroscopy, participants were asked what types of x-ray equipment they use, including the diameter of the image intensifier of each unit. They were also asked how often (always, frequently, sometimes, rarely, or never) they employ each of the following fluoroscopy features: lead collimators, high-dose fluoroscopy, magnification fluoroscopy, pulsed fluoroscopy, and last-image hold. In addition, they were asked how often they manually inject contrast material during acquisition of digital angiographic images and how often they stand behind an extra lead shield while doing so. Radiation protection questions included what style (front coverage or wrap-around) and thickness (millimeters lead equivalent) lead aprons participants wear and how often they check their aprons for defects. The group members were asked how often (always, frequently, sometimes, rarely, or never) they use the following additional types of shielding: thyroid shield, leaded glasses, leaded gloves, or a movable leaded-glass barrier. With regard to monitoring procedures, the participants were asked how many departmental dosimetry badges they are normally assigned, and where and how often they wear their dosimeters. In addition, they were asked if they have exceeded federal radiation dose guidelines in the year prior to the study and if they have ever been asked to modify their work habits by a radiation safety officer. Finally, they were asked whether or not they believe their radiation dose poses any
health risk to them and, if so, what concerns them the most about their exposure. Three commercial thermoluminescent dosimetry (TLD) badges (Landauer, Glenwood, Ill) were sent via United States mail to each project participant. Prior to mailing, each set of badges was marked with the participant's project code number and the three badges were clearly labeled "outside," "inside," or "control." The project participants were instructed to wear the "inside" badge under lead at waist level, to wear the "outside" badge over lead at upper chest level, and to keep the "control" badge remote from any source of artificial radiation, such as in an office. The project participants kept the TLD badges for approximately 2 months, and then returned their badge sets to the authors. The 2-month study period was chosen because it was considered long enough to acquire dose readings above background, long enough to reflect an adequate sample of case mix and practice pattern for each person, and brief enough to make excess background exposure of the badges unlikely. Dosimetry readings were performed by the commercial supplier. Deep dose readings (1cm deep to skin surface) were used for all calculations. Deep dose readings are calculated by the dosimeter supplier using an estimate of the penetrating ability of the radiation obtained by using filters in the TLD holder. Deep dose is more closely related to radiation risk than skin surface dose and was used for this reason. At the conclusion of the 2-month dosimetry data acquisition period, the participants completed a final questionnaire, indicating the exact dates between which they wore the TLD badges (designated as "start" and "stop" dates), how many weeks they spent away from clinical duties during the study period, and whether they believed the badge doses would accurately reflect their actual radiation exposures. For each individual, the actual number of days the badges were worn
Marx et a1
599
-
Volume 3 Number 4
Table 1 Questionnaire Items Included in Statistical Analysis Frequency Scale for Statistics Questionnaire Item Sex Male, female early t 2 a l body dose set by many states, implying that supplemental lead shielding for the head and neck is warranted for this erouo. Furthermore, under-lead doses in this study were lower than previously reported ones, and use of a l-mmthick lead apron minimized dose to the torso. The large difference between overlead and under-lead doses in this study of interventional radiologists, who work in a relatively "high-dose" radiation environment, implies that there is a need to incorporate the estimation of total body ED into clinical use, particularly as concerns about the possible ill effects of low-energy radiation are rising and as lowering of permissible occupational exposure levels mav be near at hand. Imolementatio; of ED for monitorini and regulating purposes will produce a more relevant index of radiation hazards. We suggest that the CRCPD and individual states require that the estimated ED, rather than individual point dosimeter readings, be used for monitoring purposes. u
.
References 1. Begg FR, Hans LF. Radiation exposure to angiographer during coronary arteriography using the U arm image amplifier. Cathet Cardiovasc Diagn 1975; 1:261-265. 2. Balter S, Sones FM, Brancato R. Radiation exposure to the operator performing cardiac angiography with U-arm systems. Circulation 1978; 58:925-932. 3. Britton CA, Wholey MH. Radiation exposure of personnel during digital subtraction angiography. Cardiovasc Intervent Radio1 1988; 11:108-110. 4. Bush WH, Jones D, Brannen GE. Radiation dose to personnel during percutaneous renal calculus removal. AJR 1985; 145:1261-1264. 5. Lowe FC, Auster M, Beck TJ, Chang R, Marshall FF. Monitoring radiation exposure to medical personnel during percutaneous nephrolithotomy. Urology 1986; 28:221-226. 6. Santen BC, Kan K, Velthuyse HJM,
606
Journal of Vascular and Interventional Radiology
November 1992
Julius HW. Exposure of the radiologist to scattered radiation during angiography. Radiology 1975; 115: 447-450. Linos DA, Gray JE, McIlrath DC. Radiation hazard to operating room personnel during operative cholangiography. Arch Surg 1980; 115:1431-1433. Gustafsson M, Lunderquist A. Personnel exposure to radiation at some angiographic procedures. Radiology 1981; 140:807-811. Jeans SP, Faulkner K, Love HG, Bardsley RA. An investigation of the radiation dose to staff during cardiac radiological studies. Br J Radiol 1985; 58:419-428. Tryhus M, Mettler FA, Kelsey C. The radiologist and angiographic procedures: absorbed radiation dose. Invest Radiol 1987; 22:747-750. Baker DG. Radiology: is there an occupational hazard?. Am Ind Hyg Assoc J 1988; 49:17-20. Riley RC, Birks JW, Palacios E, Templeton AW. Exposure of radiologists during special procedures. Radiat Phys 1972; 104:679-683. Woolson RF. Statistical methods for analysis of biomedical data. New York: Wiley; 1987. X-ray protection. NCRP Report no. 1. Bethesda, Md: National Council on Radiation Protection and Measurements, 1931. X-ray protection. NCRP Report no. 3. Bethesda, Md: National Council on Radiation Protection and Measurements, 1936. Medical x-ray protection up to two million volts. NCRP Report no. 6. Bethesda, Md: National Council on Radiation Protection and Measurements, 1949. Permissible dose from external sources of ionizing radiation (1954) including maximum permissible exposure to man: addendum to Na-
tional Bureau of Standards Handbook 59. NCRP Report no. 17. Bethesda, Md: National Council on Radiation Protection and Measurements, 1958. Basic radiation protection criteria. NCRP Report no. 39. Bethesda, Md: National Council on Radiation Protection and Measurements, 1971. Recommendations on the limits for exposure to ionizing radiation. NCRP Report no. 91. Bethesda, Md: National Council on Radiation Protection and Measurements, 1987. 1990 Recommendations of the International Commission on Radiological Protection. ICRP Publication 60. Ann ICRP 1991; 21:l-25. Recommendations of the International Commission on Radiological Protection. ICRP Publication 26. Ann ICRP 1977; 1:l-53. Implementation of the principle of as low as reasonably achievable (ALARA) for medical and dental personnel. NCRP Report No. 107. Bethesda, Md: National Council on Radiation Protection and Measurements, 1990. Committee on the Biological Effects of Ionizing Radiations, National Research Council. Health effects of exposure to low levels of ionizing radiation (BEIR V). Washington, DC: National Academy Press; 1990. Kumazawa S, Nelson DR, Richardson AC. Occupational exposure to ionizing radiation in the United States: a comprehensive review for the year 1980 and a summary of trends for the years 1960-1985. Environmental Protection Agency. 52011-84-005. Springfield, Va: National Technical Information Service; 1984. Conference of Radiation Control Program Directors. Suggested state regulations for control of radiation. 8th ed. Rockville, Md: Food and
Drug Administration, Center for Devices and Radiological Health, 1990; 1:F12. Bushong SC. Personnel monitoring in diagnostic radiology: revisited-again! Health Phys 1989; 56:565566. Faulkner K, Harrison RM. Estimation of effective dose equivalent to staff in diagnostic radiology. Phys Med Biol 1988; 33:83-91. Exposure of the U.S. population from occupational radiation. NCRP Report no. 101. Bethesda, Md: National Council on Radiation Protection and Measurements, 1989. Ionizing radiation exposure of the population of the United States. NCRP Report no. 93. Bethesda, Md: National Council on Radiation Protection and Measurements, 1987. Langmead WA, Farmer FT. Positioning of film badges. Br J Radiol 1971; 44:481-482. Brateman L. A plea for sensible film badge placement in diagnostic radiology. Health Phys 1989; 56: 567-568. Webster EW. EDE for exposure with protective aprons. Health Phys 1989; 56:568-569. Meinhold CB. Use of effective dose equivalent for external radiation exposures. Health Phys 1989; 56:569570. Structural shielding design and the evaluation for medical use of x rays and gamma rays of energies up to 10 MeV. NCRP Report No. 49. Bethesda, Md: National Council on Radiation Protection and Measurements, 1976. Gertz EW, Wisneski JA, Gould RG, Akin JR. Improved radiation protection for physicians performing cardiac catheterization. Am J Cardiol 1982; 50:1283-1286.
Occupational Radiation Exposure to Interventional Radiologists: A Prospective Study1 M . Victoria Marx, M D Loren Niklason, PhD ElizabethA. Mauger, MS Index terms: Fluoroscopy Interventional procedures * Radiology and radiologists Radiations, exposure to patients and personnel Radiations, measurement
-
JVIR 1992; 3:597-606 Abbreviations: CRCPD = Conference of Radiation Control Program Directors, ED = effective dose, EDE = effective dose equivalent, ICRP = International Commission on Radiological Protection, NCRP = National Council on Radiation Protection and Measurements, PYD = projected yearly dose, TLD = thermoluminescent dosimetry
From the Departments of Radiology (M.V.M., L.N.) and Biostatistics (E.A.M.), University of Michigan Hospitals, 1500 E Medical Center Dr, Ann Arbor, MI 481090030. From the 1991 SCVIR annual meeting. Received March 17, 1992; revision requested May 7; revision received August 6; accepted August 7. Address reprint requests to M.V.M.
" SCVIR, 1992
This study investigates the occupational radiation dose to interventional radiologists and the operator-controlled factors that may affect dose. Thirty interventional radiologists wore radiation badges over and under lead aprons for 2 months and answered a questionnaire. The relationships between dose and caseload, case mix, experience, optional fluoroscopy features, lead apron type, and additional lead shielding were evaluated. Mean projected yearly dose (PYD)over lead was 49.1 mSv (1mSv = 100 mrem) but was 66.6 mSv for persons performing 1,000 or more cases per year and 31.0 mSv for those performing fewer than 1,000 cases per year (P= .027). Mean PYD under lead was 0.9 mSv but was 1.3 mSv for persons with 0.5-mm lead coverage and 0.4 mSv for those with 1.0-mm lead coverage (P= .002). No other significant correlation was found. Conclusions are that caseload and apron thickness are the primary determinants of total body dose, that over-lead dose is high enough to warrant additional lead shielding for the head and neck, and that a double-thicknessapron lowers under-lead dose by two-thirds. The large difference between under-lead and over-leaddoses suggests that use of a collar badge alone for monitoring purposes is not predictive of total-body effective dose for this group of radiation workers. lNTERVENT10NAL radiologists specialize in the performance of invasive diagnostic and therapeutic procedures with use of fluoroscopic guidance. While occupational radiation exposure is something that all interventional radiologists accept, most have a vague feeling that their exposure levels are "high." Daily use of C-arm or U-arm fluoroscopy (1,2), manual injection of contrast material during digital subtraction angiography (3), and frequent performance of lengthy procedures with the operator in close proximity to the patient (4,5) are among the factors that contribute to elevated exposure. Previous investieations have documented Droce" dure-specific and body part-specific exposures (1-9), but few (10-12) have looked a t exposure levels over time for physicians performing a wide range of fluoroscopically guided interventions. To our knowledge,
none have studied operator-controlled factors that might affect occupational radiation absorbed dose. The time has come to evaluate critically the occupational radiation exposure received by interventional radiologists for several reasons. First, the radiation dose received by individual interventional radiologists is likely to be rising because fluoroscopically guided interventional procedures are becoming more common, complex, and lengthy. Second, the specialty of interventional radiology is growing, and this population may be an increasingly significant segment of the medical worker population. In addition, in the relatively near future, it may be necessary for the specialty of interventional radiology to respond to changes in government regulations concerning permissible occupational radiation exposure. Finally, and perhaps most important,
598
Journal of Vascular and Interventional Radiology
November 1992
the population of physicians performing fluoroscopically guided interventional procedures includes not only interventional radiologists (who have formal training in radiation physics and radiation safety) but cardiologists, vascular surgeons, urologists, orthopedic surgeons, and gastroenterologists. Evaluation of the occupational radiation exposure to interventional radiologists may, therefore, have relevance to a much broader segment of health care workers. The goal of this investigation is to calculate, as accurately as possible, the projected yearly over-lead and under-lead radiation doses to a population of interventional radiologists and to identify what operator-controlled factors contribute to dose.
MATERIALS AND METHODS In March 1990,35 interventional radiologists were invited to participate in a prospective evaluation of their occupational radiation exposures. Thirty of the initial 35 subjects (86%)completed the project and comprise the final study group. The group included 22 men and eight women from 17 institutions. There were 18 faculty members and nine fellows-in-training from 14 teaching hospitals, and three interventionalists from three non-teaching institutions. Each member of the study group completed three phases of the project, including completing a lengthy preliminary questionnaire, wearing dosimetry badges for a predetermined time period, and completing a short final questionnaire. The preliminary questionnaire was used to acquire basic demographic data, as well as information about practice patterns, fluoroscopy equipment and habits, radiation protection practices, and compliance with standard departmental monitoring procedures. With respect to practice patterns, project participants were asked how many interventional procedures they perform per year, what percentage of their practices are spent doing
interventional procedures, what percentage ', of their interventional work is diagnostic and what percentage is therapeutic, how much of their work involves fluoroscopy (rather than computed tomographic [CT] or ultrasonographic [US] guidance), how many years after residency have they been practicing primarily interventional radiology, and what are their future plans with regard to practice pattern. They were also asked how many weeks per year they spend away from clinical duties (ie, meeting and vacation time). On the topic of fluoroscopy, participants were asked what types of x-ray equipment they use, including the diameter of the image intensifier of each unit. They were also asked how often (always, frequently, sometimes, rarely, or never) they employ each of the following fluoroscopy features: lead collimators, high-dose fluoroscopy, magnification fluoroscopy, pulsed fluoroscopy, and last-image hold. In addition, they were asked how often they manually inject contrast material during acquisition of digital angiographic images and how often they stand behind an extra lead shield while doing so. Radiation protection questions included what style (front coverage or wrap-around) and thickness (millimeters lead equivalent) lead aprons participants wear and how often they check their aprons for defects. The group members were asked how often (always, frequently, sometimes, rarely, or never) they use the following additional types of shielding: thyroid shield, leaded glasses, leaded gloves, or a movable leaded-glass barrier. With regard to monitoring procedures, the participants were asked how many departmental dosimetry badges they are normally assigned, and where and how often they wear their dosimeters. In addition, they were asked if they have exceeded federal radiation dose guidelines in the year prior to the study and if they have ever been asked to modify their work habits by a radiation safety officer. Finally, they were asked whether or not they believe their radiation dose poses any
health risk to them and, if so, what concerns them the most about their exposure. Three commercial thermoluminescent dosimetry (TLD) badges (Landauer, Glenwood, Ill) were sent via United States mail to each project participant. Prior to mailing, each set of badges was marked with the participant's project code number and the three badges were clearly labeled "outside," "inside," or "control." The project participants were instructed to wear the "inside" badge under lead at waist level, to wear the "outside" badge over lead at upper chest level, and to keep the "control" badge remote from any source of artificial radiation, such as in an office. The project participants kept the TLD badges for approximately 2 months, and then returned their badge sets to the authors. The 2-month study period was chosen because it was considered long enough to acquire dose readings above background, long enough to reflect an adequate sample of case mix and practice pattern for each person, and brief enough to make excess background exposure of the badges unlikely. Dosimetry readings were performed by the commercial supplier. Deep dose readings (1cm deep to skin surface) were used for all calculations. Deep dose readings are calculated by the dosimeter supplier using an estimate of the penetrating ability of the radiation obtained by using filters in the TLD holder. Deep dose is more closely related to radiation risk than skin surface dose and was used for this reason. At the conclusion of the 2-month dosimetry data acquisition period, the participants completed a final questionnaire, indicating the exact dates between which they wore the TLD badges (designated as "start" and "stop" dates), how many weeks they spent away from clinical duties during the study period, and whether they believed the badge doses would accurately reflect their actual radiation exposures. For each individual, the actual number of days the badges were worn
Marx et a1
599
-
Volume 3 Number 4
Table 1 Questionnaire Items Included in Statistical Analysis Frequency Scale for Statistics Questionnaire Item Sex Male, female early t 2 a l body dose set by many states, implying that supplemental lead shielding for the head and neck is warranted for this erouo. Furthermore, under-lead doses in this study were lower than previously reported ones, and use of a l-mmthick lead apron minimized dose to the torso. The large difference between overlead and under-lead doses in this study of interventional radiologists, who work in a relatively "high-dose" radiation environment, implies that there is a need to incorporate the estimation of total body ED into clinical use, particularly as concerns about the possible ill effects of low-energy radiation are rising and as lowering of permissible occupational exposure levels mav be near at hand. Imolementatio; of ED for monitorini and regulating purposes will produce a more relevant index of radiation hazards. We suggest that the CRCPD and individual states require that the estimated ED, rather than individual point dosimeter readings, be used for monitoring purposes. u
.
References 1. Begg FR, Hans LF. Radiation exposure to angiographer during coronary arteriography using the U arm image amplifier. Cathet Cardiovasc Diagn 1975; 1:261-265. 2. Balter S, Sones FM, Brancato R. Radiation exposure to the operator performing cardiac angiography with U-arm systems. Circulation 1978; 58:925-932. 3. Britton CA, Wholey MH. Radiation exposure of personnel during digital subtraction angiography. Cardiovasc Intervent Radio1 1988; 11:108-110. 4. Bush WH, Jones D, Brannen GE. Radiation dose to personnel during percutaneous renal calculus removal. AJR 1985; 145:1261-1264. 5. Lowe FC, Auster M, Beck TJ, Chang R, Marshall FF. Monitoring radiation exposure to medical personnel during percutaneous nephrolithotomy. Urology 1986; 28:221-226. 6. Santen BC, Kan K, Velthuyse HJM,
606
Journal of Vascular and Interventional Radiology
November 1992
Julius HW. Exposure of the radiologist to scattered radiation during angiography. Radiology 1975; 115: 447-450. Linos DA, Gray JE, McIlrath DC. Radiation hazard to operating room personnel during operative cholangiography. Arch Surg 1980; 115:1431-1433. Gustafsson M, Lunderquist A. Personnel exposure to radiation at some angiographic procedures. Radiology 1981; 140:807-811. Jeans SP, Faulkner K, Love HG, Bardsley RA. An investigation of the radiation dose to staff during cardiac radiological studies. Br J Radiol 1985; 58:419-428. Tryhus M, Mettler FA, Kelsey C. The radiologist and angiographic procedures: absorbed radiation dose. Invest Radiol 1987; 22:747-750. Baker DG. Radiology: is there an occupational hazard?. Am Ind Hyg Assoc J 1988; 49:17-20. Riley RC, Birks JW, Palacios E, Templeton AW. Exposure of radiologists during special procedures. Radiat Phys 1972; 104:679-683. Woolson RF. Statistical methods for analysis of biomedical data. New York: Wiley; 1987. X-ray protection. NCRP Report no. 1. Bethesda, Md: National Council on Radiation Protection and Measurements, 1931. X-ray protection. NCRP Report no. 3. Bethesda, Md: National Council on Radiation Protection and Measurements, 1936. Medical x-ray protection up to two million volts. NCRP Report no. 6. Bethesda, Md: National Council on Radiation Protection and Measurements, 1949. Permissible dose from external sources of ionizing radiation (1954) including maximum permissible exposure to man: addendum to Na-
tional Bureau of Standards Handbook 59. NCRP Report no. 17. Bethesda, Md: National Council on Radiation Protection and Measurements, 1958. Basic radiation protection criteria. NCRP Report no. 39. Bethesda, Md: National Council on Radiation Protection and Measurements, 1971. Recommendations on the limits for exposure to ionizing radiation. NCRP Report no. 91. Bethesda, Md: National Council on Radiation Protection and Measurements, 1987. 1990 Recommendations of the International Commission on Radiological Protection. ICRP Publication 60. Ann ICRP 1991; 21:l-25. Recommendations of the International Commission on Radiological Protection. ICRP Publication 26. Ann ICRP 1977; 1:l-53. Implementation of the principle of as low as reasonably achievable (ALARA) for medical and dental personnel. NCRP Report No. 107. Bethesda, Md: National Council on Radiation Protection and Measurements, 1990. Committee on the Biological Effects of Ionizing Radiations, National Research Council. Health effects of exposure to low levels of ionizing radiation (BEIR V). Washington, DC: National Academy Press; 1990. Kumazawa S, Nelson DR, Richardson AC. Occupational exposure to ionizing radiation in the United States: a comprehensive review for the year 1980 and a summary of trends for the years 1960-1985. Environmental Protection Agency. 52011-84-005. Springfield, Va: National Technical Information Service; 1984. Conference of Radiation Control Program Directors. Suggested state regulations for control of radiation. 8th ed. Rockville, Md: Food and
Drug Administration, Center for Devices and Radiological Health, 1990; 1:F12. Bushong SC. Personnel monitoring in diagnostic radiology: revisited-again! Health Phys 1989; 56:565566. Faulkner K, Harrison RM. Estimation of effective dose equivalent to staff in diagnostic radiology. Phys Med Biol 1988; 33:83-91. Exposure of the U.S. population from occupational radiation. NCRP Report no. 101. Bethesda, Md: National Council on Radiation Protection and Measurements, 1989. Ionizing radiation exposure of the population of the United States. NCRP Report no. 93. Bethesda, Md: National Council on Radiation Protection and Measurements, 1987. Langmead WA, Farmer FT. Positioning of film badges. Br J Radiol 1971; 44:481-482. Brateman L. A plea for sensible film badge placement in diagnostic radiology. Health Phys 1989; 56: 567-568. Webster EW. EDE for exposure with protective aprons. Health Phys 1989; 56:568-569. Meinhold CB. Use of effective dose equivalent for external radiation exposures. Health Phys 1989; 56:569570. Structural shielding design and the evaluation for medical use of x rays and gamma rays of energies up to 10 MeV. NCRP Report No. 49. Bethesda, Md: National Council on Radiation Protection and Measurements, 1976. Gertz EW, Wisneski JA, Gould RG, Akin JR. Improved radiation protection for physicians performing cardiac catheterization. Am J Cardiol 1982; 50:1283-1286.
