2005 ICRP Recommendation

Draft document: 2005 ICRP Recommendation
Submitted by Kenzo Fujimoto, National Institute of Radiological Sciences
Commenting on behalf of the organisation

COMMENTS ON THE DRAFT OF ICRP NEW RECOMMENDATIONS 28 December 2004 The Working Group on International Issue in Japan Health Physics Society* has been discussing the draft of ICRP new recommendations. Our comments are provided below based on the consensus among the Working Group. We hope an improved new recommendation will be made taking into account our comments as well as others. Our comments are focused only on the following four points that will have a large impact on regulatory bodies and society when the new recommendations are published, although many aspects have been discussed in the Working Group. Comment A: Relationship between dose constraints and dose limits Comment B: Maximum dose constraints Comment C: LNT Comment D: Annual dose limits for individual organs or tissues Comment A: Relationship between dose constraints and dose limits The term gdose limith and its values remain in the new draft. However, its importance is now less and greater priority is placed on gdose constrainth. As seen in the paragraphs S5, 8, 133,137, 155 and 185 the ICRP has upgraded the importance of dose constraints, which formerly form an integral part of the optimisation of protection (see paragraph 121 in Publication 60). This is a big change in the radiological protection system and causes several problems shown below. The emphasis on dose limits over dose constraints should be maintained, or at least the two should be at the same level. Problem 1. Once dose constraints have legal power as mentioned in the new draft (see paragraph 121), the present radiological protection system implemented in many countries throughout the world cannot be used any more without a drastic change of regulations. Therefore, it is not acceptable to make such a drastic change to the concept of dose constraints. Problem 2. The social impact of the change in priority between dose limits and dose constraints is very big since dose limits, not dose constraints, have been implemented as a legal requirement in the present radiological protection system in many countries. Therefore, dose limits should be retained as a more important requirement than dose constraints. Problem 3. Radiation workers have been monitored by personal dosimeters and exposure can be controlled by direct comparison with dose limits. In addition to dose limits, dose constraints have been set for each workplace in Japan so that occupational exposure can be controlled with confidence. Therefore, it is not necessary to emphasize the importance of dose constraints for occupational exposure. Problem 4. If dose constraints are emphasized as in the new draft, it would result in more strict control on individual dose. For example, if a plant X is considered as a single source and a constraint of 10 mSv is set for the plant, the radiation workers who work only in plant X are controlled more strictly than by present dose limit. Problem 5. The suggested dose constraints would be applied even to emergency and controllable existing exposure, so that the dose must be reduced to a level that is lower than the dose constraint regardless of its feasibility when optimisation process is applied to emergency or existing situation. This new approach therefore is considerably different from the present approach for intervention and may cause problems in its implementation. Problem 6. In the process of optimisation the present system of protection based on dose limits has more options to choose different measures than the new scheme with obligatory constraints. Emphasizing dose constraints would lose this advantage. Problem 7. The recommended approach would result in double regulatory controls with dose constraints and dose limits. Proposal for revision: 1. The titles of Table S1 and Table 7 should be changed to gImportant dose levels of concern for a single sourceh. 2. Dose constraints are applied to source-related radiological protection and dose limits are applied to individual-related ones. Therefore, it should be clearly mentioned that dose limits can be defined as values that are equal or larger than dose constraints. Once this concept is adapted, there should be no more conflict between the values shown in Table S1 and Table 7 and the annual dose limit of 50 mSv for radiation workers. 3. The ICRP should leave the details of how to use dose constraints and dose limits to national authorities in the same manner as mentioned in paragraph 149. 4. The ICRP should mention that dose constraints should be used in accordance with dose limits, taking into consideration of the situation in each country. 5. The ICRP should mention that it is not always necessary to change the radiological protection system to the one based on dose constraints when the present protection system based on dose limits works properly for the safety of workers and the public. 6. The use of dose constraints should be flexible, taking into account the exposure time, such as working hours or occupancy factors. 7. The revisions suggested above should be made in the relevant paragraphs, such as S3, S5, 8, 88, 133, 137, 156, 164, 165 and 185. Comment B: Maximum dose constraints 1. It is not persuasive to use natural background level as the basis of dose constraint derivation. The reasoning for the derivation of four values shown in Table S1 and Table 7 should be provided. One hundred times or one one hundredth of the annual average dose due to natural radiation is not a reason that will persuade the general public. Moreover, there is no reason to choose 20 mSv as one of the maximum dose constraints. 2. The choice of annual natural radiation exposure as the basis for maximum dose constraints should be made based on scientific, social and psychological reasoning. 3. The ICRPfs historical approach based on risk evaluation should be maintained for setting the dose constraints or dose limits. The reasoning based on risk should not be abandoned just because it is not easy to explain to the general public. The problem does not come from risk assessment but rather from poor risk communication. Therefore, each level proposed in Table S1 and Table 7 should be based on risk. One simple solution is to provide risk estimates in the tables. 4. Radiation protection is itself one of the forms of risk control. Dose constraints and dose limits should be defined based on risk. Although there are some difficulties in a scientific approach based on risk, we have to do our best to estimate it and define a radiation protection system based on it. The proposed approach based on natural background level could be far more vague and not persuasive, especially where the background level is ten times higher than the world average. This could be a source of misunderstanding. 5. Using the dose due to natural background radiation is useful for risk communication, especially for the maximum dose constraint of 1 mSv that is often erroneously regarded as a line of demarcation between safe and dangerous but not used for the standard of levels of concern. 6. Table S1 and Table 7 should be revised based on risk estimation. As was done in Publication 60, the dose level should be derived based on the acceptable risk in the present society and then the dose should be compared with that due to natural radiation to understand the size of the dose. 7. Practice, existing controllable exposure and emergency situations are all mixed in Table S1 and Table 7. It would be nice to mention all these in the same table. However, it is necessary to explain the differences since the ways of handling these situations are not the same. A new paragraph should be inserted after paragraph 163, although paragraph 21 touched on the differences and paragraph 5 also mentioned that it has not been always easy to explain different applications. 8. gMinimum value of any constrainth is also shown in Table S1 and Table 7. It is not appropriate for this to appear in the tables with other maximum constraints since it is not a maximum value. The suggested revision is to change of title of these tables to gImportant dose levels of concern for a single sourceh. 9. It is necessary to demonstrate how to derive a dose constraint from the maximum dose constraint. 10. It is necessary to describe clearly the way to define action levels or levels for intervention actions from dose constraints, although some approaches are shown in paragraphs 179 and 192 for action levels for radon and levels for intervention actions, respectively. 11. It is necessary to describe clearly how to handle a situation for radiation protection in which the doses or concentrations are lower than action levels or levels for intervention actions. The approach is shown only in the case of radon exposure. The same approach should be taken in all other situations as well, i.e., gFor occupational exposure, below these levels the system of protection is not applied and the resulting doses should not be recorded in the workerfs records. For the public, there should be no attempt to reduce exposures further, as they should not be regarded as controllable exposures subject to regulatory actions.h This approach could also be applied to evacuation, relocation, sheltering and iodine prophylaxis in an emergency situation. Comment C: LNT. 1. There have long been arguments on the LNT hypothesis. However, neither the absence nor the existence of a threshold can be proved due to the uncertainties involved in the estimation of risks for low dose radiation. Under these circumstances it is reasonable and appreciated that the ICRP takes a practical approach regarding the radiation effects, i.e., the LNT. 2. It is also appreciated that the ICRP stated clearly in paragraph 54 that effective doses based on the LNT hypothesis should not be used to assess risks of stochastic effects in retrospective situations for exposures in identified individuals, nor should it be used in epidemiological evaluations of human exposure. 3. Although the LNT hypothesis is an assumption for the purpose of radiological protection, the general public tends to believe that it proves that radiation is harmful no matter how low is the dose. Fears of this kind are the reason for artificial abortions among mothers who received only small radiation doses due to the Chernobyl nuclear accident (Ref.1). The fear of radiation among the general public hinders the use of radiation for our benefit. It is therefore necessary to be very cautious when mentioning the effects of low dose exposure. (Ref. ‚P) Knudsen, L. B.: Legally induced abortions in Denmark after Chernobyl. Biomed. Pharmacother. 45, 229-231 (1991). 4. It is necessary to not emphasize the effects due to low dose exposure. Suggested modifications in several paragraphs are shown below. i1j The underlined parts in paragraph S6 shown below should be deleted since these explanations are too strong to express the effect due to tiny exposure. iS6juIn all situations the constraints are complemented by the requirement to optimise the level of protection achieved. 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. The Commission therefore recommends that further, more stringent, measures should be considered for each individual source.v i2j With the practical approach in mind, the last sentence of paragraph 38 seems exaggerated. The word ganyh should be deleted. i3j The word, gscientificallyh in paragraph 101 should be deleted since the LNT hypothesis is adapted for practical purposes rather than scientifically. i4j In the last sentence in paragraph 187 the phrase, geven at small doses above the natural backgroundh should be deleted. It is not necessary to emphasize the risk due to small doses.. 5. As the recommendations of the ICRP have a great influence not only on regulatory bodies and radiological protection experts, but also on our society, the ICRP should make more efforts to clear up the misunderstanding of the general public on low dose exposure. Therefore, it might be useful to include the following new paragraph in Chapter 5.2 as well as after paragraph S6. The new text explains the LNT hypothesis and its usage in some more detail. i1j Exposure of a few mSv has no significant health effects, as can be judged from the fact that the world average annual dose due to natural radiation is estimated to be 2.4 mSv and some places have more than ten times higher than the average. Strict control of radiation even at low dose levels is required simply to monitor the effectiveness of radiation protection, not because low dose levels pose any danger to workers or to the public. i2j The ICRP adopts the LNT hypothesis for practical reasons: it is simple, easy to use, agrees relatively well with scientific assumptions and allows us to sum doses. i3j The ICRP recognises that the health effects due to exposure of a few mSv could not be detected although the risk could be estimated using the LNT hypothesis. i4j The LNT hypothesis should not be used to assess risks of stochastic effects in retrospective situations for exposures in identified individuals, nor should it be used in epidemiological evaluations of human exposure since it is defined for radiation protection purposes. Comment D: Annual dose limits for individual organs or tissues We agree with the approach of the ICRP in paragraph 94 to distinguish between (1) the radiation weighted dose (Sv) which is defined for the protection of organs or tissue based on stochastic effects, and (2) the RBE-weighted absorbed dose (Gy-Eq) developed to estimate the level of tissue reactions. If we follow the new approach, we have to use the term of RBE-weighted absorbed dose for the annual dose limits for individual organs or tissues shown in Table 9 since the limits are to prevent tissue reactions. *The Working Group on International Issue in Japan Health Physics Society Chair: K. Fujimoto, National Institute of Radiological Sciences (for further contact: kenzofuj@nirs.go.jp) T. Iimoto, The University of Tokyo N. Ishigure, National Institute of Radiological Sciences T. Kikuchi, Jichi Medical School Radioisotope Center S. Miyazaki, The Kansai Electric Power CO., INC. K. Oda, Kobe University of Mercantile Marine K. Sakai, Central Research Institute of Electric Power Industry K. Saito, Japan Atomic Energy Research Institute K. Shinohara, Japan Nuclear Cycle Development Institute I. Urabe, Fukuyama University K. Yamaguchi, Osaka University Hospital