|CORAR comments, Part 1 of 2
The Council on Radionuclides and Radiopharmaceuticals (CORAR)1 appreciates the opportunity to comment on the proposed ICRP recommendations. CORAR is a collaborating organization with the NCRP and has many years of experience in communicating the potential impact of proposed radiation protection standards, guidance and regulations.
CORAR members distribute radionuclides to the worldwide research and medical community and are consequently concerned that national and international radiation protection recommendations be uniform and practical.
We hope these comments are of value to the ICRP and would be glad to provide clarification or further information as needed.
1. (S6) “…This is because there is presumed to be some probability of health effects even at small increments of exposure to radiation above the natural background….”
a. While CORAR understands that social and economic factors must be considered when developing radiation protection standards we still expect that the ICRP should fully utilize the scientific evidence as a basis for recommendations.
b. CORAR perceives that the current scientific understanding is that there may be a probability of health effects at low exposure, but that these cannot be quantified for doses that are less than 50 mSv (5 rem)..
c. Hence scientific basis for optimizing radiation protection should recognize that the risk of health effects ranges from zero to some observable value. CORAR recommends that the ICRP uses this scientific understanding as a basis for optimization and not “presumption” or “assumption” of risk.
2. “Table S2. Recommended Exclusion Levels”
It’s not clear how other low levels of naturally occurring radionuclides in the biosphere such as 14C are to be excluded.
3. (38) “For protection purposes, it is assumed that these effects increase with increasing radiation dose, with no threshold, and that any increment of exposure above natural background produces a linear increment of risk.”
a. The proposal to base protection on an assumption will seem inappropriate to the radiation protection community. It would be preferable to recommend the dose response model and state or reference its scientific basis.
b. However, this assumption appears to conflict with the current scientific understanding. It is not currently known whether there are deleterious effects from receiving an effective dose of less than about 50 mSv (5 rem).
c. Considering the current scientific understanding of the dose response relationship, the effects should be considered to linearly correlate with effective dose exceeding about 50 mSv (5 rem) and be uncertain below 50 mSv (5 rem).
d. The ICRP should consider whether there is sufficient scientific evidence to provide a range of values for the dose response relationship below 50 mSv (5 rem). For example, a range of effects could be considered with a lower value of zero at zero effective dose. Other values of the range could be determined by extrapolation using plausible dose response models between zero and 50 mSv (5 rem).
e. It is not clear why the assumption will serve “protection purposes”. If the assumed LNT model is incorrect, it’s use may provide no protection. This needs to be considered in the context of protection from all risks including risks, which are not radiological. Since there are only finite resources to reduce risks, overall protection can only be secured if the resources are properly allocated to reduce the most significant risks.
f. Hence to provide overall protection it is important that radiation risk is properly compared with other risks and their associated uncertainties, so that limited protection resources are most effectively utilized.
4. (48) “The averaging of absorbed dose and the summing of mean doses in different organs and tissues of the human body, as given in the definition of all the protection quantities, is only possible under the assumption of a linear dose-response relationship with no threshold (LNT). All protection quantities rely on these hypotheses”.
a. We understand that the use of the LNT model simplifies protection estimates. However, if the LNT model is determined to be incorrect, these protection estimates are also most likely to be incorrect too and would certainly have to be reevaluated.
b. The practicality of the use of the LNT model is not a justification for its validity.
Shouldn’t the equation for “E” include a term that accounts for intake through intact and damaged skin?
6. (93) “ICRP Committee 2 is considering how best to give advice for assessing radiation doses from intakes of radionuclides…..”
In selecting model based conversion coefficients, the ICRP should consider the ease that these could be adjusted to enable actual cases to be accurately evaluated.
7. (95) “Apart from some exposures of medical patients and some serious emergency situations, which have to be managed separately, the control of stochastic effects will avoid the occurrence of most, and probably all, tissue reactions”.
Other exceptions are the control of dose to the lens of the eye, skin and extremities where deterministic effects dominate and are the critical concern.
8. (99) Table 5
It would be useful to include 1% incidence rates for small area (10 cm2) skin exposures. Also a note on the size of the “large areas” would be useful.
9 (101) “… it is scientifically reasonable to assume that in general and for practical purposes cancer risk will rise in direct proportion to absorbed dose in organs and tissues..”
It’s not clear why the ICRP thinks it scientifically reasonable to use LNT in the low dose range when there are no measurements to validate this hypothesis. Why not accept that the dose response relationship is unknown and make appropriate recommendations on this basis?
10. (127) ….“the presumed proportional relationship between dose and stochastic effects….”
This presumption appears to be a weak basis for protection. However, the determination of this relationship at doses above about 50 mSv (5rem) should be stated as scientifically reasonable and not merely a “presumption”.
11. (132) “… They [i.e., proposed ICRP restrictions] provide a level of protection for individuals that should be considered as obligatory and not maintaining these levels of protection should be regarded as a failure….
(133) The most fundamental level of protection is the source – related restriction called a dose constraint….”
a. Considering that the ICRP annual occupational effective dose constraint is 20 mSv (2 rem), CORAR is concerned that a small number of highly skilled radiation workers in the radiopharmaceutical manufacturing and distribution industry would be adversely impacted.
b. The current practice of limiting total effective dose to 50 mSv (5 rem) in one year and 100 mSv (10 rem) in 5 years enables the selection of the most highly skilled worker to complete a task. Implementation of the proposed annual constraint will necessitate the use of additional less skilled workers and significantly increase the collective dose.
c. If the LNT hypothesis correctly characterizes risk at these occupational dose levels the 20 mSv (2 rem) dose constraint will cause conflict with ICRP’s recommendation to optimize protection. Hence there is a need to reconsider the 2 rem dose constraint and the validity of the LNT hypothesis for this level of occupational exposure.
d. The ICRP has not indicated the scientific basis for this change from ICRP60.
12. (143) “…The Commission therefore limits its use of the phrase “occupational exposure (to radiation) to exposures incurred at work as a result of situations that can reasonably be regarded as being the responsibility of the operating management.”
The ICRP should clarify the responsibility for controlling radon exposure in the work place. Perhaps there is a need to reference sections (179) and (180).
13. (164) “…This sets the maximum of the Commission’s constraint to restrict exposure of individual members of the public following an accident,….”
It’s not clear in this paragraph whether the 100 mSv (10 rem) constraint applies to the emergency worker or to the member of the public.
14. (175) “…the methods of protection at work for women who may be pregnant should provide a level of protection for any conceptus broadly comparable to that provided for members of the general public. This is reasonable since while the mother may have chosen to be a radiation worker, the unborn child has not made such a decision….The working conditions of a pregnant worker, after declaration of pregnancy, should be such as to make it unlikely that the additional radiation weighted dose to the fetus will exceed about 1 mSv during the remainder of the pregnancy”
a. CORAR agrees with the policy and more protection needed for an unborn child. However, the fact that the unborn child has not made a decision is not relevant. The exposure of the unborn child should not be treated any different than if the pregnancy caused the mother to have other similarly radiosensitive tissue. In either case it’s the mother who must decide whether to be a radiation worker and the government to decide on the appropriate dose constraint.
b. The appropriate dose limit should be 5 mSv (500 mrem) not 1 mSv (100 mrem) because the mother, and consequently the unborn child, derives benefit from the mother choosing to be a radiation worker.
15. (181) “…In its 1977 Recommendations for occupational exposure…the Commission used a comparison of the then estimated fatal risk associated with average worker exposures with average accident fatality rates in industries widely regarded as “safe”…..However, comparisons with average accidental death rates in industries not associated with radiation are not very satisfactory, particularly as the mortality rates apply to averages over single sectors of industries, whereas dose limits apply to individuals”.
a. Risk to radiation workers should be compared with risks to other occupational sectors. The risk assessment for radiation workers should include the total occupational risk including the risk from radiation exposure. Since the average occupational radiation exposure is likely to be comparable with natural background radiation for most occupations the component of risk for radiation will be uncertain and should be expressed as a range from zero to a plausible maximum value.
b. Comparison of the risk of long term radiation exposure at the recommended limits for individuals could be compared with the small occupational groups that are at highest acceptable risk.
16 (186) Table 9
“ 2Averaged over 1 cm2 area of skin regardless of the area exposed”.
This recommendation appears to be incompatible with other dose limits. Recent research on radiation effects for small area skin exposure from “hot” particles and skin contamination indicates that the dose should be averaged over 10 cm2 not 1 cm2 or alternatively the dose limit should be 5 Sv (500 rem) averaged over 1 cm2 (Reference NCRP Statement No.9 (see also the attached CORAR position paper).
17. (187) “This is because of the presumption that there is some risk of adverse health effect from exposures to ionizing radiation, even at small doses above the natural background.”
See above comments on sections (S6) (38) and (127). The choice of the word “presumption” appears unfortunate as the basis for scientific recommendations.
18. (207) “…the development of exclusion criteria would be beneficial in the practical application of protection and avoid the excessive regulation of radiation sources, both natural and artificial.”
a. CORAR agrees with this statement, but recommends that it should be expanded and specific benefits described.
b. Benefits of excluding low-level or uncontrollable radiation sources from regulatory control include preserving the use of limited radiation protection resources for controlling more significant exposure conditions and practices. Excessive regulation of ionizing radiation has caused many researchers to abandon the use of radioactive materials and replace them with non-radiometric methods using hazardous materials that are less safe and have greater adverse environmental impact. This topic would be a good subject for future ICRP and NCRP evaluation and report.
19. Table A1 Summary of Nominal risks and Detriment
It’s not clear what units apply to these parameters.