|PART 4 OF COMMENTS IN 6 PARTS
Comments on Draft for Consultation
2005 RECOMMENDATIONS OF THE INTERNATIONAL
COMMISSION ON RADIOLOGICAL PROTECTION
David C. Kocher
SENES Oak Ridge, Inc.
Center for Risk Analysis
Oak Ridge, Tennessee, U.S.A.
Quantities Used in Radiological Protection (continued)
Paragraph (80). There is no obvious reason why age- and gender-specific tissue weighting factors couldn’t be developed. I would comment that the Commission’s approach perhaps could lead to inappropriate standards of protection when risks from exposure in childhood are substantially higher than risks from exposure of adults but age-averaged risks are determined primarily by the latter. There also are cancers for which radiation risks in males and females are significantly different.
I would also comment that when tissue weighting factors are age-averaged, there is a logical disconnect between tissue weighting factors and annual dose constraints or limits if the latter are applied to any age at exposure, rather than averaged over age. There probably are many situations for which the highest effective dose in any year is experienced by children, and it seems illogical to calculate effective doses to children using tissue weighting factors which are weighted toward values in adults.
Paragraph (81). At the time Publication 60 was issued, I felt that the Commission’s definition and use of “detriment” was rather artificial and arbitrary, and I continue to hold the same belief about the change in definition in the draft 2005 Recommendations. As I see it, a basic problem with detriment as defined and used by the Commission is that it masks the real issue, which is risk. Every other carcinogen is regulated on the basis of risk (generally risk of cancer incidence), and I see no reason not to do the same with radiation. Here again, when the Commission’s recommendations sidestep people’s basic concerns about prevention of disease, the Commission runs the risk of losing credibility and influence. Not everyone may be convinced that the various factors used to adjust cancer incidence data are appropriate for protection purposes, although the logic underlying this approach does make sense.
The Commission may argue that people’s concerns are being addressed more than in the past by starting with cancer incidence in estimating detriment, rather than cancer mortality as in Publication 60. However, I think that this is a rather weak argument when a lethality fraction is applied, which essentially converts incidence to mortality. So, detriment is not really based on cancer incidence, contrary to appearances, even though I agree that using data on cancer incidence as a basis for risk estimates instead of data on cancer mortality is a good idea.
Paragraph (82), first sentence. Is the use of “deterministic effects” intentional, given that this term was carefully avoided when “tissue reactions” were first discussed?
Paragraphs (87) and (88). I wonder if the commitment periods of 50 years for workers and adult members of the public and from time of exposure to age 70 for infants and children should be updated to reflect that life expectancies have increased substantially over the last few decades, especially in developed countries where radiological protection is of greatest concern. In many countries, the average life expectancy of an individual who reaches age 20 is well beyond 80 years, and the average life expectancy of a newborn is about 80 years.
The system of radiological protection for occupational exposure has been criticized for basically ignoring doses received by workers after they leave the workforce due to the presence of long-lived internal emitters in the body. Basing effective dose coefficients on a reasonable life expectancy of a young adult worker would help address this criticism. Another problem with the life expectancies assumed by the Commission is that average risks in a population of workers or in the general public are underestimated, perhaps by 15% or more, and the Commission could be criticized for this. For example, the nominal probability coefficient for fatal cancers in the whole population of 5% per Sv recommended in Publication 60 probably should be increased to about 6% per Sv, absent any other changes, to properly reflect average life expectancies in developed countries today.
Paragraph (91), last sentence. It seems to me that this statement is reasonable only if external doses from radiation sources for which the relative hazard is being characterized are unimportant compared with doses from internal exposure.
Paragraph (93), last sentence. This sentence mentions dose coefficients for occupational exposure. Won’t at least some of the ideas discussed in this paragraph be applied in developing dose coefficients for exposure of the public as well?
Paragraph (94), last sentence. Will it cause confusion that the biologically significant dose with respect to tissue reactions is given a different name than a similar dosimetric quantity for stochastic effects, especially when assessments of tissue reactions are based on the mean absorbed dose in an organ or tissue of concern?
Biological Aspects of Radiological Protection
Section 4.1 and Table 5. Does the fact that threshold doses in Table 5 apply to organs and tissues of adults lead to difficulties in preventing tissue reactions in children, who presumably are more radiosensitive than adults for many of the effects listed in the table? High acute exposures of children are a concern, for example, in cases of severe reactor accidents. Surely the Commission should say something about thresholds in infants and children.
Paragraph (105). In the middle of the fourth line, “judgements” presumably should be changed to “judgement” (the draft document is remarkably free of such errors). More importantly, if it has not done so already, I think that the Commission needs to document how it reached its judgment that DDREF should be 2.
It is my understanding that new data on dose-response in Japanese atomic-bomb survivors may indicate a need to revisit assumptions about DDREF in extrapolating from high acute doses to lower doses, although the situation may be complicated when mortality and incidence data for all solid tumors do not show the same form of a dose-response (recent data for one endpoint show curvature, whereas data for the other endpoint look linear). It seems possible that DDREF may be considerably more uncertain than indicated by previous data. These developments bear watching.
Paragraphs (111) and (112) and Table 6. To me, this way of presenting risk information illustrates the Commission’s lack of enthusiasm about embracing risk in a system of radiological protection. None of the probability coefficients in Table 6 are risks and, thus, they do not represent quantities of primarily interest to people, and it seems illogical to use probability coefficients in Table 6 for purposes of prospective assessments of risk in general terms or comparisons with other risks when they do not represent risk. In paragraph (112), last sentence, the Commission notes that a nominal probability coefficient for fatal cancer in the whole population may be estimated from cancer incidence data in Table A1.a of Annex A, but nowhere is it shown how the nominal probability coefficient is derived (although a knowledgeable reader can guess) and a probability coefficient for fatal cancer in workers is not given. Most importantly, probability coefficients for cancer incidence are not presented at all, even though they are of interest in many situations (e.g., in comparing risks due to radiation with risks normally estimated for other carcinogens).
Paragraph (118), last sentence. I am ignorant about cancer risks from in utero irradiation. However, the reference to a dose of 100 mSv as some kind of protection standard does not seem reasonable to me, although I suppose that it all depends on what “specific protection case,” “prolonged exposure,” and “well below” mean. In paragraph (175), the Commission essentially recommends that the dose to the fetus should not be much higher than 1 mSv. There is a lot of room between these two doses, and the two statements do not seem compatible to me.
The General System of Protection
Section 5.2. I don’t have any particular difficulties with these discussions. Indeed, the Commission’s arguments seem reasonable. I do, however, have two concerns. The first is whether the role of a dose limit from all controllable sources combined for normal situations has been de-emphasized too much. Similar to the principle of justification discussed in a previous comment, I am concerned that another bedrock principle of radiation protection is somehow being cast aside. I appreciate that dose limits are rarely important in controlling actual exposures, but they do represent statements about limits on barely tolerable risk, which are not found in protection systems for other carcinogens. I wonder if the relationship between dose limits and dose constraints and the importance of dose constraints in ensuring compliance with dose limits has been made sufficiently clear in these discussions.
As noted in a previous comment, I also believe that the Commission needs to give a clear definition of what is meant by a “normal situation” to which dose limits apply and how it differs from an “existing controllable situation” involving routine exposure. For example, exposure to radon in homes certainty is a “normal situation” by any reasonable layman’s definition but is viewed by the Commission as “an existing controllable exposure.” Nowhere in this section is the meaning of “normal situation” discussed (I submit that the meaning is not obvious). Clear discussions of the meaning of “existing controllable exposure” also are needed, especially as it differs from “normal situation.”
Paragraph (136), last sentence. I believe that this statement is important, and it may call for some amplification. For example, dose constraints for normal situations need to be well below the maximum recommended values in order to ensure that applicable dose limits for all normal situations combined are met. I believe that this important point should not be lost.
Also, does the Commission intend to discuss on what basis regulatory agencies should set dose constraints at levels below maximum recommended values? This seems important.
Paragraph (137), second sentence. On what basis is action to reduce dose or risk virtually certain to be warranted? Is it because the associated risk is intolerable, or is it because application of the principle of optimization almost certainly will indicate that the allowable dose should be lowered? It seems important to explain this.
Paragraph (139). It seems to me that the Commission’s need to distinguish between Optimization of Protection and ALARA, especially to emphasize that the former is a much broader concept, is partly the result of a problem of the Commission’s own making. The common interpretation that the ALARA principle is applied using quantitative cost-benefit analysis, which the Commission certainly encouraged, rather blatantly ignores the “social factors” aspect of ALARA. If proper attention had been paid all along to social factors and how they change over time in implementing the ALARA principle, there probably would be little need for a different and more broadly defined principle of optimization.
Figure 2, cartoon in upper right. I am pleased to see the inclusion of a “mining” icon in this figure. As noted previously, national authorities have often ignored mining wastes and other wastes from exploitation of energy sources when an activity resulting in increased radiation exposure of workers or the public is not nuclear-related. It should be clear that these kinds of waste are included in the system of radiological protection.
Paragraph (143), last sentence, paragraph (146), second sentence, and paragraph (148), third sentence. These statements seem reasonable, but I wonder how the Commission would classify an individual who works as a receptionist at a facility where x ray machines are operated (say) and receives incidental exposure to radiation while working, even though working with radiation sources is not part of their job. Would such an individual be subject to dose constraints and associated monitoring and information requirements for occupational exposure, or would such an individual be considered a member of the public?