- Email: [email protected]
New Recommendations for Occupational Radiation Protection
THE MEDICAL PHYSICS CONSULT
MAHADEVAPPA MAHESH, MS, PHD JAMES M. HEVEZI, PHD
New Recommendations for Occupational Radiation Protection Donald L. Miller, MD, Beth A. Schueler, PhD, Stephen Balter, PhD INTRODUCTION
Occupational radiation protection is a necessity whenever radiation is used. It is especially important for fluoroscopically guided and CT fluoroscopic procedures, in which occupational irradiation cannot be avoided. The International Commission on Radiological Protection (ICRP) publishes recommendations for occupational dose limits intended to limit the risk for stochastic effects to a level that is considered acceptable (ie, the dose limit denotes the value beyond which doses, and hence risks, would be generally considered unacceptable) [1]. In the United States, the National Council on Radiation Protection and Measurements (NCRP) publishes recommendations for maximum permissible dose (MPD) that generally, but not always, agree with ICRP recommendations for dose limits [2]. Regulatory bodies require that a worker not receive occupational exposure higher than the dose limits and also require implementation of the principle of optimization of protection. The expectation is that occupational doses will be considerably lower than the dose limits. There are two types of occupational dose limits in NCRP and ICRP recommendations. The first provides occupational dose limits for specific organs or tissues. The second establishes an acceptable risk level for cancer induction. Dose limits to workers for exposure of part of the body are expressed as equivalent dose for tissue (deterministic) effects in an organ or tissue and as effective dose for stochastic effects throughout the body. Effective dose is intended to be proportional 366
to the risk for radiation-induced cancer. In the United States, Nuclear Regulatory Commission regulations provide specific requirements for personal dosimetry when using radionuclides. When x-rays are used, the Occupational Safety and Health Administration and state regulations provide corresponding requirements. Different radiation quantities and units are used in these different regulations. For consistency, we use the ICRP notations for radiation quantities and units (Table 1) [1]. Unfortunately, the SI unit for both equivalent dose and effective dose is the sievert. Readers of the regulations and the literature need to be aware of the context in any particular situation. CURRENT RECOMMENDATIONS FOR OCCUPATIONAL DOSE LIMITS
Most countries have adopted the occupational dose limits recommended by the ICRP in 1990 [1,3]. In the United States, regulatory authorities consider ICRP and NCRP recommendations when setting dose limits but do not view them as binding. As of early 2012, the Nuclear Regulatory Commission is contemplating reducing the present MPD for effective dose from 50 mSv per year to the current ICRP dose limit of 20 mSv per year averaged over 5 consecutive years (100 mSv in 5 years) and 50 mSv in any single year. Additional restrictions apply to the occupational exposure of pregnant staff members. Current data do not justify precluding pregnant physicians or other workers from performing procedures in the labo-
ratory [4]. The ICRP recommends that the standard of protection for the conceptus should be broadly comparable to that provided for members of the general public [1]. The ICRP recommends that after a worker has declared her pregnancy, her working conditions should ensure that the additional dose to the conceptus does not exceed more than 1 mSv during the remainder of the pregnancy. In the United States, the NCRP recommendations are less stringent, with a 0.5mSv equivalent dose monthly limit for the conceptus (excluding medical and natural background radiation) once the pregnancy is declared [2]. Workers in the United States who do not wish to declare their pregnancy are not required to do so. Nonetheless, assessment of anticipated conceptus doses should be performed on the basis of current practice in the laboratory. Of note, the 2011 ICRP statement on tissue reactions recommends a lower equivalent dose limit for the lens of the eye [5]. The old and new ICRP dose limits and the current NCRP MPD are summarized in Table 1 [1,2,5]. Note the differences between the ICRP dose limits and the NCRP MPD for effective dose. Note also that the NCRP MPD for the lens of the eye has not changed and is still 150 mSv. WHY DID THE DOSE LIMIT FOR THE LENS OF THE EYE CHANGE?
The response of the lens to radiation has traditionally been considered a tissue reaction, with a threshold dose below which the effect is highly unlikely to occur. In the past, the threshold dose for detect-
Published by Elsevier Inc. on behalf of American College of Radiology 0091-2182/12/$36.00 ● DOI 10.1016/j.jacr.2012.02.006
The Medical Physics Consult 367
Table 1. Dose limits (maximum permissible doses) for occupational exposure Dose Quantity Previous ICRP occupational dose limit Effective dose Annual
Equivalent dose Lens of the eye
Skinⴱ Extremities (hands and feet) NCRP maximum permissible dose Effective dose Annual Cumulative Equivalent dose Lens of the eye Skinⴱ Extremities (hands and feet)
Current
[1]
[5]
20 mSv/y averaged over 5 consecutive years (100 mSv in 5 years) and 50 mSv in any single year
Unchanged
150 mSv/y
20 mSv/y averaged over defined periods of 5 years, with no single year exceeding 50 mSv Unchanged Unchanged
500 mSv/y 500 mSv/y [2] 50 mSv/y 10 mSv ⫻ age (y)
Unchanged Unchanged
150 mSv/y 500 mSv/y 500 mSv/y
Unchanged Unchanged Unchanged
Note: ICRP ⫽ International Commission on Radiological Protection; NCRP ⫽ National Council on Radiation Protection and Measurements. ⴱ
Averaged over 1 cm2 of the most highly irradiated area of the skin.
able human lens opacities was considered to be 2 Gy for a single acute exposure and 5 Gy for protracted exposure. For cataract with visual impairment, the thresholds were considered to be 5 and 8 Gy, respectively [2,3]. More recent data from populations exposed to lower doses of radiation suggest that lens opacities occur at exposures substantially lower than 2 Gy [5,6]. Statistical analysis of the available data suggests a possible absence of a threshold dose, or that if one does exist, it could be ⬍0.1 Gy. There have been reports of radiation-induced cataracts in interventionalists who have performed procedures for a number of years and of doses to the lens approaching the annual limit of 150 mSv during angiographic procedures [6]. With typical reported interventional workloads, the radiation dose to the lens may exceed the current threshold for tissue reactions after several years of work if radiologic protection devices are not used and radiologic protection principles are not followed [7]. Several surveys of cardiologists and support staff members working in catheterization labora-
tories in Latin America and Asia found a high percentage of lens opacities attributable to occupational radiation exposure [6]. These recent data, and the mechanistic uncertainties regarding cataract development, highlighted the need for a detailed reappraisal of the radiosensitivity of the lens of the eye. The ICRP recently reviewed epidemiologic evidence for lens tissue reactions and now considers the threshold in absorbed dose to the lens of the eye to be 0.5 Gy (500 mGy, equivalent to 500 mSv) [5]. As a result, the ICRP now recommends a dose limit for the lens of the eye of 20 mSv per year, averaged over 5 years (Table 1) [5]. OCCUPATIONAL EXPOSURE
Numerous publications have reported staff radiation levels for various types of interventional procedures. Data for interventional radiologic procedures are summarized in NCRP report 168 [8]. In some circumstances, values of effective dose ⬎ 20 mSv per year could result from a workload of 1,000 cases yearly. Doses to the lens of the
eye and the hand can be high for interventional radiologic procedures, particularly when over-table x-ray tube equipment is used. However, with appropriate attention to dose reduction and personal protection, and when personal dosimeter readings are properly interpreted, most interventionalists will have values of effective dose substantially less than 10 mSv per year, most likely in the range of 2 to 4 mSv per year [8,9]. RECOMMENDATIONS FOR OCCUPATIONAL RADIATION PROTECTION
Recommendations for occupational radiation protection are widely available and should be followed [8,9]. Over-table x-ray tube equipment should not be used for interventional fluoroscopic procedures. As noted above, the ICRP recommends lowering the dose limit for the lens of the eye. This recommendation should underscore the importance of proper eye protection. When used properly, ceilingsuspended shields are extremely effective [10]. Leaded eyeglasses are an alternative when the use of ceiling
368 The Medical Physics Consult
suspended shields is not feasible. These eyeglasses may be used in combination with disposable tungstenantimony scatter-shielding drapes for even greater protection [10]. Leaded eyeglasses with protective side shields provide more protection than eyeglasses without these features. They help minimize both scatter that approaches the operator from the side and scatter from the operator’s own head [8]. The principal disadvantage of leaded eyeglasses is their weight and discomfort, as they are considerably heavier than normal eyeglasses. Proper fit is important to minimize discomfort. CONCLUSIONS
Interventional radiologists should be aware of the recent changes in the international recommendations for occupational dose limits and the differences between international and US recommendations. With appropriate attention to dose reduction
and personal protection, occupational dose can be kept within the most stringent recommendations. Advances in our understanding of the risk for radiation-induced cataract have led to a dramatic decrease in the recommended dose limit or the lens of the eye. Eye protection should be used routinely. REFERENCES 1. International Commission on Radiological Protection. The 2007 recommendations of the International Commission on Radiological Protection. ICRP publication 103. Ann ICRP 2007;37:1-332. 2. National Council on Radiation Protection and Measurements. Limitation of exposure to ionizing radiation. NCRP report no 116. Bethesda, Md: National Council on Radiation Protection and Measurements; 1993. 3. International Commission on Radiological Protection. 1990 recommendations of the International Commission on Radiological Protection. ICRP publication 60. Ann ICRP 1991;21:1-201. 4. Best PJ, Skelding KA, Mehran R, et al. SCAI consensus document on occupational radiation exposure to the pregnant cardiologist
and technical personnel. Catheter Cardiovasc Interv 2011;77:232-41. 5. International Commission on Radiological Protection. Statement on tissue reactions 2011. Available at: http://www.icrp.org/ docs/ICRP Statement on Tissue Reactions. pdf. Accessed March 13, 2012. 6. Rehani MM, Vano E, Ciraj-Bjelac O, Kleiman NJ. Radiation and cataract. Radiat Prot Dosim 2011;147:300-4. 7. Vano E, Gonzalez L, Fernández JM, Haskal ZJ. Eye lens exposure to radiation in interventional suites: caution is warranted. Radiology 2008;248:945-53. 8. National Council on Radiation Protection and Measurements. Radiation dose management for fluoroscopically guided interventional medical procedures. Report no 168. Bethesda, Md: National Council on Radiation Protection and Measurements; 2010. 9. Miller DL, Vañó E, Bartal G, et al. Occupational radiation protection in interventional radiology: a joint guideline of the Cardiovascular and Interventional Radiology Society of Europe and the Society of Interventional Radiology. Cardiovasc Intervent Radiol 2010;33:230-9. 10. Thornton RH, Dauer LT, Altamirano JP, Alvarado KJ, St Germain J, Solomon SB. Comparing strategies for operator eye protection in the interventional radiology suite. J Vasc Interv Radiol 2010;21:1703-7.
Donald L. Miller, MD, is from the Center for Devices and Radiological Health, US Food and Drug Administration, Silver Spring, Maryland. Beth A. Schueler, PhD, is from the Department of Radiology, Mayo Clinic, Rochester, Minnesota. Stephen Balter, PhD, is from the Department of Radiology and Department of Medicine, Columbia University, New York, New York. Donald L. Miller, MD, US Food and Drug Administration, Center for Devices and Radiological Health, 10903 New Hampshire Avenue, Silver Spring, MD 20993; e-mail: [email protected].
MAHADEVAPPA MAHESH, MS, PHD JAMES M. HEVEZI, PHD
New Recommendations for Occupational Radiation Protection Donald L. Miller, MD, Beth A. Schueler, PhD, Stephen Balter, PhD INTRODUCTION
Occupational radiation protection is a necessity whenever radiation is used. It is especially important for fluoroscopically guided and CT fluoroscopic procedures, in which occupational irradiation cannot be avoided. The International Commission on Radiological Protection (ICRP) publishes recommendations for occupational dose limits intended to limit the risk for stochastic effects to a level that is considered acceptable (ie, the dose limit denotes the value beyond which doses, and hence risks, would be generally considered unacceptable) [1]. In the United States, the National Council on Radiation Protection and Measurements (NCRP) publishes recommendations for maximum permissible dose (MPD) that generally, but not always, agree with ICRP recommendations for dose limits [2]. Regulatory bodies require that a worker not receive occupational exposure higher than the dose limits and also require implementation of the principle of optimization of protection. The expectation is that occupational doses will be considerably lower than the dose limits. There are two types of occupational dose limits in NCRP and ICRP recommendations. The first provides occupational dose limits for specific organs or tissues. The second establishes an acceptable risk level for cancer induction. Dose limits to workers for exposure of part of the body are expressed as equivalent dose for tissue (deterministic) effects in an organ or tissue and as effective dose for stochastic effects throughout the body. Effective dose is intended to be proportional 366
to the risk for radiation-induced cancer. In the United States, Nuclear Regulatory Commission regulations provide specific requirements for personal dosimetry when using radionuclides. When x-rays are used, the Occupational Safety and Health Administration and state regulations provide corresponding requirements. Different radiation quantities and units are used in these different regulations. For consistency, we use the ICRP notations for radiation quantities and units (Table 1) [1]. Unfortunately, the SI unit for both equivalent dose and effective dose is the sievert. Readers of the regulations and the literature need to be aware of the context in any particular situation. CURRENT RECOMMENDATIONS FOR OCCUPATIONAL DOSE LIMITS
Most countries have adopted the occupational dose limits recommended by the ICRP in 1990 [1,3]. In the United States, regulatory authorities consider ICRP and NCRP recommendations when setting dose limits but do not view them as binding. As of early 2012, the Nuclear Regulatory Commission is contemplating reducing the present MPD for effective dose from 50 mSv per year to the current ICRP dose limit of 20 mSv per year averaged over 5 consecutive years (100 mSv in 5 years) and 50 mSv in any single year. Additional restrictions apply to the occupational exposure of pregnant staff members. Current data do not justify precluding pregnant physicians or other workers from performing procedures in the labo-
ratory [4]. The ICRP recommends that the standard of protection for the conceptus should be broadly comparable to that provided for members of the general public [1]. The ICRP recommends that after a worker has declared her pregnancy, her working conditions should ensure that the additional dose to the conceptus does not exceed more than 1 mSv during the remainder of the pregnancy. In the United States, the NCRP recommendations are less stringent, with a 0.5mSv equivalent dose monthly limit for the conceptus (excluding medical and natural background radiation) once the pregnancy is declared [2]. Workers in the United States who do not wish to declare their pregnancy are not required to do so. Nonetheless, assessment of anticipated conceptus doses should be performed on the basis of current practice in the laboratory. Of note, the 2011 ICRP statement on tissue reactions recommends a lower equivalent dose limit for the lens of the eye [5]. The old and new ICRP dose limits and the current NCRP MPD are summarized in Table 1 [1,2,5]. Note the differences between the ICRP dose limits and the NCRP MPD for effective dose. Note also that the NCRP MPD for the lens of the eye has not changed and is still 150 mSv. WHY DID THE DOSE LIMIT FOR THE LENS OF THE EYE CHANGE?
The response of the lens to radiation has traditionally been considered a tissue reaction, with a threshold dose below which the effect is highly unlikely to occur. In the past, the threshold dose for detect-
Published by Elsevier Inc. on behalf of American College of Radiology 0091-2182/12/$36.00 ● DOI 10.1016/j.jacr.2012.02.006
The Medical Physics Consult 367
Table 1. Dose limits (maximum permissible doses) for occupational exposure Dose Quantity Previous ICRP occupational dose limit Effective dose Annual
Equivalent dose Lens of the eye
Skinⴱ Extremities (hands and feet) NCRP maximum permissible dose Effective dose Annual Cumulative Equivalent dose Lens of the eye Skinⴱ Extremities (hands and feet)
Current
[1]
[5]
20 mSv/y averaged over 5 consecutive years (100 mSv in 5 years) and 50 mSv in any single year
Unchanged
150 mSv/y
20 mSv/y averaged over defined periods of 5 years, with no single year exceeding 50 mSv Unchanged Unchanged
500 mSv/y 500 mSv/y [2] 50 mSv/y 10 mSv ⫻ age (y)
Unchanged Unchanged
150 mSv/y 500 mSv/y 500 mSv/y
Unchanged Unchanged Unchanged
Note: ICRP ⫽ International Commission on Radiological Protection; NCRP ⫽ National Council on Radiation Protection and Measurements. ⴱ
Averaged over 1 cm2 of the most highly irradiated area of the skin.
able human lens opacities was considered to be 2 Gy for a single acute exposure and 5 Gy for protracted exposure. For cataract with visual impairment, the thresholds were considered to be 5 and 8 Gy, respectively [2,3]. More recent data from populations exposed to lower doses of radiation suggest that lens opacities occur at exposures substantially lower than 2 Gy [5,6]. Statistical analysis of the available data suggests a possible absence of a threshold dose, or that if one does exist, it could be ⬍0.1 Gy. There have been reports of radiation-induced cataracts in interventionalists who have performed procedures for a number of years and of doses to the lens approaching the annual limit of 150 mSv during angiographic procedures [6]. With typical reported interventional workloads, the radiation dose to the lens may exceed the current threshold for tissue reactions after several years of work if radiologic protection devices are not used and radiologic protection principles are not followed [7]. Several surveys of cardiologists and support staff members working in catheterization labora-
tories in Latin America and Asia found a high percentage of lens opacities attributable to occupational radiation exposure [6]. These recent data, and the mechanistic uncertainties regarding cataract development, highlighted the need for a detailed reappraisal of the radiosensitivity of the lens of the eye. The ICRP recently reviewed epidemiologic evidence for lens tissue reactions and now considers the threshold in absorbed dose to the lens of the eye to be 0.5 Gy (500 mGy, equivalent to 500 mSv) [5]. As a result, the ICRP now recommends a dose limit for the lens of the eye of 20 mSv per year, averaged over 5 years (Table 1) [5]. OCCUPATIONAL EXPOSURE
Numerous publications have reported staff radiation levels for various types of interventional procedures. Data for interventional radiologic procedures are summarized in NCRP report 168 [8]. In some circumstances, values of effective dose ⬎ 20 mSv per year could result from a workload of 1,000 cases yearly. Doses to the lens of the
eye and the hand can be high for interventional radiologic procedures, particularly when over-table x-ray tube equipment is used. However, with appropriate attention to dose reduction and personal protection, and when personal dosimeter readings are properly interpreted, most interventionalists will have values of effective dose substantially less than 10 mSv per year, most likely in the range of 2 to 4 mSv per year [8,9]. RECOMMENDATIONS FOR OCCUPATIONAL RADIATION PROTECTION
Recommendations for occupational radiation protection are widely available and should be followed [8,9]. Over-table x-ray tube equipment should not be used for interventional fluoroscopic procedures. As noted above, the ICRP recommends lowering the dose limit for the lens of the eye. This recommendation should underscore the importance of proper eye protection. When used properly, ceilingsuspended shields are extremely effective [10]. Leaded eyeglasses are an alternative when the use of ceiling
368 The Medical Physics Consult
suspended shields is not feasible. These eyeglasses may be used in combination with disposable tungstenantimony scatter-shielding drapes for even greater protection [10]. Leaded eyeglasses with protective side shields provide more protection than eyeglasses without these features. They help minimize both scatter that approaches the operator from the side and scatter from the operator’s own head [8]. The principal disadvantage of leaded eyeglasses is their weight and discomfort, as they are considerably heavier than normal eyeglasses. Proper fit is important to minimize discomfort. CONCLUSIONS
Interventional radiologists should be aware of the recent changes in the international recommendations for occupational dose limits and the differences between international and US recommendations. With appropriate attention to dose reduction
and personal protection, occupational dose can be kept within the most stringent recommendations. Advances in our understanding of the risk for radiation-induced cataract have led to a dramatic decrease in the recommended dose limit or the lens of the eye. Eye protection should be used routinely. REFERENCES 1. International Commission on Radiological Protection. The 2007 recommendations of the International Commission on Radiological Protection. ICRP publication 103. Ann ICRP 2007;37:1-332. 2. National Council on Radiation Protection and Measurements. Limitation of exposure to ionizing radiation. NCRP report no 116. Bethesda, Md: National Council on Radiation Protection and Measurements; 1993. 3. International Commission on Radiological Protection. 1990 recommendations of the International Commission on Radiological Protection. ICRP publication 60. Ann ICRP 1991;21:1-201. 4. Best PJ, Skelding KA, Mehran R, et al. SCAI consensus document on occupational radiation exposure to the pregnant cardiologist
and technical personnel. Catheter Cardiovasc Interv 2011;77:232-41. 5. International Commission on Radiological Protection. Statement on tissue reactions 2011. Available at: http://www.icrp.org/ docs/ICRP Statement on Tissue Reactions. pdf. Accessed March 13, 2012. 6. Rehani MM, Vano E, Ciraj-Bjelac O, Kleiman NJ. Radiation and cataract. Radiat Prot Dosim 2011;147:300-4. 7. Vano E, Gonzalez L, Fernández JM, Haskal ZJ. Eye lens exposure to radiation in interventional suites: caution is warranted. Radiology 2008;248:945-53. 8. National Council on Radiation Protection and Measurements. Radiation dose management for fluoroscopically guided interventional medical procedures. Report no 168. Bethesda, Md: National Council on Radiation Protection and Measurements; 2010. 9. Miller DL, Vañó E, Bartal G, et al. Occupational radiation protection in interventional radiology: a joint guideline of the Cardiovascular and Interventional Radiology Society of Europe and the Society of Interventional Radiology. Cardiovasc Intervent Radiol 2010;33:230-9. 10. Thornton RH, Dauer LT, Altamirano JP, Alvarado KJ, St Germain J, Solomon SB. Comparing strategies for operator eye protection in the interventional radiology suite. J Vasc Interv Radiol 2010;21:1703-7.
Donald L. Miller, MD, is from the Center for Devices and Radiological Health, US Food and Drug Administration, Silver Spring, Maryland. Beth A. Schueler, PhD, is from the Department of Radiology, Mayo Clinic, Rochester, Minnesota. Stephen Balter, PhD, is from the Department of Radiology and Department of Medicine, Columbia University, New York, New York. Donald L. Miller, MD, US Food and Drug Administration, Center for Devices and Radiological Health, 10903 New Hampshire Avenue, Silver Spring, MD 20993; e-mail: [email protected].