Low-dose Extrapolation of Radiation-Related Cancer Risk

Draft document: Low-dose Extrapolation of Radiation-Related Cancer Risk
Submitted by Sylvain Saint-Pierre, World Nuclear Association
Commenting on behalf of the organisation

24 March 2005 - World Nuclear Association Dr. Roger Clarke and Dr. Lars-Erik Holm International Commission on Radiological Protection SE-171 16 Stockholm Sweden Subject: WNA’s RPWG Key Review Comments on ICRP C1 Task Group Report Dear Dr. Clarke and Dr. Holm, The World Nuclear Association (WNA) is pleased to provide its key review comments on the subject ICRP draft report entitled: “Low-dose Extrapolation of Radiation related Cancer Risk – Draft of Dec 10, 2004” These review comments were prepared by the WNA’s Working Group on Radiological Protection (RPWG). The RPWG is composed of experienced RP professionals drawn from a wide range of nuclear industry sectors in various countries who have been constructively involved in the ongoing international RP debate. Review Comments 1. The draft report seems to be a comprehensive compilation of the relevant scientific information and analysis on low doses which, as mentioned in the report introduction, roughly correspond to doses of about 10 mSv. 2. This report structures this scientific information well and makes progress in analysing it. However, given that some significant on-going scientific works that underpin the basic knowledge on low doses are in the process of being updated (e.g. UNSCEAR and US NAS), it would seem more logical to complete these updates first and then to have their findings accounted for in the development of the C-1 report. Otherwise, this report may in a relatively short timeframe be considered incomplete, if not obsolete, and would not serve effectively as a primary reference for the scientific basis of the next generation of ICRP recommendations. Given this, while our review comments are preliminary, we believe that they can add value and constructively contribute to the development of the current draft report. 3. The report repeatedly put forward a rationale in favour of the so-called “linear, no-threshold” (LNT) hypothesis. Down to ‘low doses’ and even lower, this rationale tends to be weaker as scientific data and evidence are also weaker. However, it is noted that the report comparisons to the extreme and idealistic notion of a universal scientific threshold - below which there would be absolutely zero risk! – add an extra level of weakness. The report would benefit from being more neutral and cautious here, including for the related conclusions. Notwithstanding this, the fact remains that at such low levels, the question of whether ‘purely’ scientifically valid relations (linear or other) or a universal threshold can be found or not, is rather a ‘purely’ scientific matter that cannot provide a legitimate basis for sound public RP policy. 4. The report’s overall conclusion seems partly unclear: “… the evidence as a whole does not favour the existence of a universal threshold, and there seems to be no particular reason to factor the possibility of a threshold into risk calculations for purposes of radiation protection.” (p.12) What is the precise meaning of the second clause? Can it mean that for radiation protection purposes, there would be no room for a practical threshold (not necessarily ‘purely’ scientifically valid) below which risk calculations would be considered as irrelevant for sound public RP policy? If so, it can be easily argued (e.g. based on ALARA, and its essential aim of achieving a reasonable balance of risks and benefits) that down to very low and extremely low doses, such a practical threshold does have an important role to play in making sound RP policies even if it would bear some tiny theoretical risks. – The WNA Position Statement on “Risks of Low-Dose Ionising Radiation” (see the attached electronic “pdf” file) provides a broad perspective on this topic, and ends by emphasising “the need to establish a consistent international approach to defining a level of dose below which it is widely deemed legitimate to maintain that an individual is adequately protected from ionising radiation, whether natural or man-made.” Moreover, it adds that “At such a low level – below which there would be an agreed absence of valid health concerns – it would be unjustified to allocate more resources to controlling sources of small radiation exposure because any such effort could only impair the many peaceful uses of nuclear technology, from which much human benefit is attained.” 5. The report mentions and discusses some important non-scientific issues in relation to low doses and the related thresholds, but this information is generally not well focused, is sometimes unclear or lacks coherence, and overall tends to miss some of the most essential points. The quotes from the draft report that are reproduced herein in Annex A illustrate the kinds of non-scientific issues that we have noted in the draft report. One essential point that is notably missed is a discussion of the important role that a practical threshold should play in making sound RP policies. The overall conclusion that can be derived from this is that the C-1 report is most likely not a suitable place for discussing and addressing non-scientific issues and for making judgment calls on practical radiological protection purposes, in particular on those that relate to public policies and practical thresholds. The fact that ICRP leadership in the low dose debate plays an important role in improving public understanding and perception of radiation and of its associated risks is another key factor in suggesting that non-scientific issues are best to be addressed outside of the scientific scope of the C-1 draft report. Otherwise, there would be a real risk that scientific issues become unduly discounted relative to increasing social concerns about lower radiation risk that would not be based on any rationale. What seems more appropriate here is that the matter of adopting a practical threshold (corresponding to some tiny theoretical risk) on the basis of a reasonable balance between scientific and non-scientific issues should be seriously considered by ICRP (at the upper level - e.g. Committee 4 or the Main Commission itself). If there would be added value, this process could possibly include seeking further scientific input from the C-1 Task Group on the practical threshold considered. 6. Direct or indirect suggestions in the Conclusions that, based on epidemiological or experimental carcinogenesis studies, there is evidence of radiation risk down to doses of the order of 10 mGy, and even lower doses of the order of 1 mGy warrant further explanations and evidence. What is missing here is a balanced discussion that would present the weight of evidence that supports linearity down to about 100 mGy against the much more limited evidence and data that would support linearity at lower doses. 7. The report does not seem to include an assessment of data on populations that live in high background radiation areas - that precisely correspond to the low dose levels that are of prime interest in this study. This potential shortcoming should be thoroughly examined and, if relevant, it should be well addressed in the next draft report. 8. Considering the emerging topics of radiation-related adaptive response, genomic instability, and bystander effects, we note that the current level of understanding is insufficient and that further studies are needed. We appreciate this opportunity to contribute to the ICRP’s open consultation process, and we look forward to working further with you in exploring ways to improve the current RP system. Yours sincerely, Sylvain Saint-Pierre Director for Environment and Radiological Protection World Nuclear Association ANNEX A The following quotes from the draft report illustrate the kinds of non-scientific issues that we have noted in the draft report: - Quantitative uncertainty approach: “Central to the approach is recognition of the fact that radiation protection is a political process,…” (p.16) - Avoiding or benefiting from radiation-related risk: “The problem is inherently political…” (p.21) - Estimation of cancer risk following radiation exposure: “Public and regulatory interest is usually with exposures at radiation doses far lower than those at which useful information about risk can be obtained by studying populations which such exposures.” (p.21) - Estimation of risk at low doses and low dose rates: “Most public concern is with exposures to less than 50 mSv,…” (p.31)