SUBJECT: CORAR COMMENTS TO THE ICRP ON EARLY AND LATE EFFECTS OF RADIATION IN NORMAL TISSUES AND ORGANS: THRESHOLD DOSES FOR TISSUE REACTIONS AND OTHER NON-CANCER EFFECTS OF RADIATION IN A RADIATION PROTECTION CONTEXT.
These comments are submitted on behalf of the Council on Radionuclides and Radiopharmaceuticals (CORAR)1. CORAR members have numerous employees who are occupationally exposed to ionizing radiation. CORAR is consequently committed to support the development of recommendations that optimize radiation protection programs. In the attached comments we chose to focus on the radiation protection of skin and extremities. Our perspective is based on the practical experience of managing significant quantities of radioactive materials in our industry and recent research on deterministic effects (tissue reactions).
CORAR recommends that this new ICRP publication should report the relevant scientific results in sufficient detail to enable the Commission to fully consider their implications on the system of radiological protection. It appears to us that this report should provide more details on threshold doses for tissue reactions in the hands and skin of the hands. This is needed to support the consideration and potential selection by the ICRP of a less restrictive occupational dose limit for extremities.
In the USA the National Council on Radiation Protection and Measurements (NCRP) and the U.S. Nuclear Regulatory Commission NRC) both recognized that allowing more occupational exposure to the extremities would result in less occupational exposure to more radiation sensitive tissues and organs in the whole-body for certain groups of radiation workers. CORAR provided an explanation of this need to adjust extremity dose limits to optimize radiological protection to the ICRP on September 14th, 2006 and is reissued in the attached comments on ICRP 103 with revised terminology and updated references.
CORAR appreciates that the Committee reviewed research on skin dose effects. However, this scientific literature has more detailed information on tissue reactions from small area skin dose that is needed for the ICRP to make a decision on appropriate extremity dose limits.
CORAR is also concerned about the choice of 1% incidence to define a threshold dose. The normal practice in Radiation Protection has been to select 5% as the threshold for accepting radiological data as being significant. Consequently we recommend that if 1% is to be used the choice should be fully explained or a pertinent explanation referenced.
CORAR appreciates the update on tissue reactions in the lens of eye and circulatory systems. More research is needed to substantiate these new findings. The ICRP shall need to determine the potential consequences of changing dose limits for these organs. The risk should be considered for practical life time occupational conditions and the long latency period for these tissue reactions.
We appreciate the opportunity to provide these comments and would be glad to provide clarification or additional comments if needed.
Leonard R. Smith, CHP.
Cochair CORAR Manufacturing Quality and Safety Committee.
1. CORAR is a North American trade association that includes members who are the major manufacturers and distributors of radiopharmaceuticals, radioactive sources and research radiochemicals used for therapeutic and diagnostic medical applications and for industrial, environmental and biomedical research and quality control.
March 31, 2011
CORAR COMMENTS ON ICRP 103 RECOMMENDATIONS OF THE INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION 2007
Page 50 Paragraph (60)
“… the Commission judges that the occupational and public dose limits, including the limits on equivalent dose for the skin, hands/feet and eye, given in Publication 60 (ICRP, 1991b) remain applicable for preventing the occurrence of deterministic effects (tissue reactions);”
Page 99 Paragraph (245) Table 6, Recommended dose limits in planned exposure situations
“Type of Limit
Occupational… Annual equivalent dose in:
Skin 500 mSv Averaged over 1 cm2 area of skin regardless of the area exposed.
Hands and feet 500mSv”
ICRP Skin Dose Limit: 500 mSv Averaged Over 1 cm2.
1. CORAR recognizes that the International Commission on Radiological Protection’s (ICRP) recommended occupational annual skin dose limit of
500 mSv provides adequate protection against ionizing radiation as follows:
a. The limit is highly protective against stochastic effects.
b. For a given average skin dose, the risk of stochastic effects will be less when the exposure is non-uniform.
c. The limit is highly protective against stochastic effects for both uniform and non-uniform exposure.
d. The limit is protective against deterministic effects (tissue reactions) when skin exposure is uniform.
e. ICRP’s occupational annual dose limit of 500 mSv averaged over 1 cm2 area of skin is intended to provide adequate protection against deterministic effects (tissue reactions) when skin exposure is non-uniform.
2. The skin dose limit of 500 mSv averaged over I cm2 was last recommended in ICRP 59(1), ICRP 60(2) and NCRP 116(3). Since these publications were in preparation, animal studies have been published which implies a need to reevaluate this recommended limit.
Recent Animal Studies on the Effects of Small Area Skin Irradiation.
3. NCRP 130 (4), published in 1999, summarizes the results of animal studies that provide additional information on the effects of low energy (i.e. maximum energy less than 500 keV) beta radiation on small areas of skin and the effects of low energy beta and gamma radiation.
4. These studies imply that the 500 mSv averaged over 1 cm2 skin dose limit is more conservatively protective against deterministic effects (tissue reactions) than is necessary.
5. In NCRP 130, a new limit of 500 mGy averaged over 10 cm2 is recommended for skin dose from single irradiation events due to “hot particles”. This limit was considered adequate to prevent the breakdown of the skin barrier and prevent subsequent infection.
NCRP Statement No 9. (5)
6. The U.S. Nuclear Regulatory Commission requested the National Council on Radiation Protection and Measurements (NCRP) to investigate the feasibility of establishing a skin dose limit that would be applicable to all skin dose geometries.
7. The NCRP published the results of this investigation in Statement No 9 on March 30, 2001. The NCRP recommended an annual limit of 0.5 Gy averaged over the most highly exposed 10 cm2 of skin at a tissue depth of 70 μm.
8. This new recommended limit was applicable to radiation exposure from “hot particles” on the skin or on hair or clothing near the skin, small area skin contamination and exposure to small areas of skin by external radiation beams.
9. This limit was considered sufficient to prevent the breakdown of the skin barrier and subsequent infection.
10. To ensure that the NCRP recommendation was sufficiently protective, the NRC sponsored reviews of potential health implications that confirmed that stochastic effects on the skin were negligible and deterministic effects (tissue reactions) in worst-case scenarios were slight and acceptable. (6) (7)
NRC Revision of Skin Dose Limit Regulation. (7)
11. On April 5, 2002, the U.S. Nuclear Regulatory Commission published a revision of the regulatory annual dose limit, specifying it as a shallow-dose equivalent of 50 rem (0.5 Sv) to the skin of the whole-body or the skin of any extremity.
12. The assigned shallow-dose equivalent is defined in the regulation as the dose equivalent at a tissue depth of 0.007 centimeter (7mg/cm3) averaged over the contiguous 10 cm2 of skin of the whole-body or extremity receiving the highest external exposure.
13. This new annual limit is elegantly applicable to both large area and small area skin irradiation and is also compatible with the extremity dose limit, simplifying compliance.
14. The US requirement to determine the dose equivalent at a tissue depth of 0.007 centimeters is different from regulatory requirements in other countries. For example, in the UK it is permissible to determine the dose at the applicable affected tissue depth.
15. CORAR recommends that the ICRP considers adopting an annual skin dose limit of 500 mSv averaged over 10 cm2.
16. This recommended limit should provide a similar level of protection as the ICRP’s other occupational limits and would therefore be more compatible with them.
17. CORAR recommends that skin dose should be assessed at the applicable affected tissue depth, particularly when occupational dose approaches or exceeds the recommended skin dose limit. This practice is necessary to ensure that the significance of skin dose is properly evaluated with respect to the significance of dose to other tissues. This practice is also preferred because it directly produces a skin dose record that more accurately documents the actual dose to the relevant tissue that must be protected.
18. However, CORAR recognizes that, when evaluating past exposure and planning future exposure, the potential for exposing different areas of skin with different applicable tissue depths should be comprehensively considered and appropriate operational controls implemented to accommodate the reasonably possible exposure conditions.
19. CORAR recommends that the ICRP should consider promoting the use of a default value for the skin tissue depth of 70 μm when exposure conditions are uncertain or impractical to evaluate to the necessary level of detail.
20. CORAR provides the following additional references that support this recommendation.(8) (9) (10)
Justification of the CORAR Recommendation.
21. The primary justification for CORAR’s recommended skin dose limit is that it facilitates the optimization of the radiological protection of the highest exposed radiation worker group in the U.S.
22. CORAR recommends that the ICRP should consider whether conditions in other countries warrant a revised skin dose limit.
23. In the 1980’s radiation protection staff in the U.S. nuclear power industry had the following concerns about skin exposure to hot particles:
a. There was a need to timely detect hot particles to enable them to be promptly removed to minimize exposure.
b. There was a need to determine the skin dose to demonstrate compliance with the regulatory limit.
c. The time taken to prevent, detect, remove and assess “hot particles” in the presence of ambient penetrating radiation caused an increase in whole body dose to the operators and radiation protection staff or to operators during leaving and reentering the radiation area to monitor.
d. It was perceived that efforts to minimize the dose from “hot particles” were resulting in more serious risk of stochastic effects due to increased whole body dose.
24. “Hot particle” control was primarily a concern of the nuclear fuel-cycle industry in the U.S.. However, it was recognized that similar, if less common, conditions of non-uniform skin exposure occur in other occupations in the U.S.. These conditions include:
a. Small area skin contamination due to the transfer of beta emitting radionuclides through undetected pin-holes in gloves or the penetration of gloves when handling equipment with rough surfaces. These conditions are commonly encountered in nuclear medicine, nuclear pharmacy, radiopharmaceutical manufacturing, radiochemical manufacturing and biomedical research operations.
b. Leakage radiation from shielded syringes used to dispense gamma, x-ray and/or beta emitting radionuclides in nuclear pharmacy, biomedical research and radiopharmaceutical manufacturing quality control operations.
c. Occupational non-uniform radiation encountered during medical procedures including computerized tomography, brachytherapy and fluoroscopy, and particularly interventional cardiology and radiology.
25. In many of these conditions, the worker is subject to both non-uniform skin dose, mostly to the hands, and a lower amount of whole-body exposure.
26. In the U.S. the annual number of medical procedures using ionizing radiation is increasing about 5 to 10% each year. Furthermore, new medical technologies often involve greater exposure.
27. This trend increases the occupational exposure of physicians, medical support staff, and radiopharmaceutical dispensing technologists. These workers are emerging as the highest exposed group in the country.
28. This is currently the main reason that it is impractical in the U.S. to implement an occupational annual effect dose limit of 20 mSv for all radiation workers.
29. Strategies to minimize exposure include: automating dispensing operations, improving the efficiency of procedures, using a team approach to reduce the exposure of critical individuals and maintain accurate occupational dosimetry that is not over-conservative. For example, the use of robotic dispensing systems has greatly reduced exposure from P-32-radiochemical processing in the manufacturing industry. However, these controls are often more difficult to effectuate in the hospital.
30. The implementation of a less restrictive skin-dose limit is another method to reduce whole-body exposure and optimize protection.
1. ICRP. “The Biological Basis for Dose Limitation in the Skin”, ICRP Publication 59, Annals of the ICRP 22, 1991.
2. ICRP, “1990 Recommendations of the International Commission on Radiological Protection”, ICRP Publication 60, Annals of the ICRP 21, 1991.
3. NCRP, “Limitation of Exposure to Ionizing Radiation”, NCRP Report No 116, 1993.
4. NCRP, “Biological Effects and Exposure Limits for “Hot Particles:, “ NCRP Report No 130, 1999.
5. NCRP, “Statement No 9, Extension of the Skin Dose Limit for Hot Particles to Other External Sources of Skin Irradiation”, 2001.
6. J. Baum, “Analysis of Potential Radiobiological Effects Related to a Unified Skin Dose Limit”, Health Physics, June 2001, pp. 537-543.
7. NRC, “Revision of the Skin Dose Limit”, Federal Register, Vol. 67, No 66, April 5, 2002.
8. Hopewell, J.W., Coggle, J.E., Wells, J., Hamlet, R., Williams, J.P., and Charles, M.W.; “The acute effects of different energy beta-emitters on pig and mouse skin.” British Journal of Radiology, Suppl. 19, 1986, pp 47-51.
9. Charles, M.W., Hopewell J.W., and Coggle, J.E.; “Recent trends in radiobiology of skin and repercussions for dose limitation and personal dosimetry.” Radiation Theory and Practice, Proceedings of the 4th International Symposium of the Society for Radiological Protection.
10. Charles, M.W.; “General considerations on the choice of dose limits, averaging areas and weighting factors for the skin in the light of revised skin cancer risk figures and experimental data on non-stochastic effects.” INT. J. Radiat. Biol., 1990, Vol. 57. No4, pp. 841-858.