Low-dose Extrapolation of Radiation-Related Cancer Risk

Draft document: Low-dose Extrapolation of Radiation-Related Cancer Risk
Submitted by G Ches Mason, IAEA
Commenting as an individual

First, I'd like to congratulate the TG on an outstanding report. I think it stands alongside anything ICRP has done before and will serve as a key resource document for some time to come. I particularly appreciated the effort that has clearly gone into the writing, such that a non-specialist like myself has an opportunity of gaining some microbiological insight into this extraordinarily complex subject. I would also like to float a couple of questions which may or may not merit attention in the report. The first question has to do with the LNT debate and, in particular, whether it would be useful to comment in the report on another argument that seems to accompany the 'threshold' view. I think the report already deals admirably with the proposition that there could be some level of dose below which the fidelity of repair of radiation-induced DNA damage increases or the efficiency of elimination of damaged cells increases. But there is also the indirect argument suggesting that somehow (and I have no idea how) a low level of exposure to radiation stimulates the organism's overall efficiency of repair (including for non-radiation-induced SSB damage, which dominates) such that a reduction in that background dose could increase the overall incidence of cancer at the clinical level, and conversely. In lay terms, I guess the argument is an analogue of the notion that health and fitness correlate with exercise. Presumably, one would need to postulate that the background dose promotes the production of one or more of the proteins and other agents necessary for the repair process, or something similar, which seems implausible to me but I lack the biological knowledge to know whether such suggestions are feasible or nonsense. Could or should the report say something about this line of argument, or even put it to rest? At first blush, the thought that living organisms have evolved through selection in a sea of background radiation and that they might now therefore be optimally adapted has some appeal. But this is speculation and requires analysis. The second question is related. Chapter 6 provides a fascinating and innovative discussion of uncertainty and I found it extremely helpful. It further enhances an ethical judgement to presume LNT as a precautionary measure, I feel. However, the statistical analyses deal only with zero risk below a possible threshold. I wonder how the results would be affected if one tested the proposition put above that risk may become negative at low doses? Perhaps if the answer to the first question makes the idea sufficiently implausible, then there would be no need to do the arithmetic.