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Submitted by Kenneth L. Mossman, Arizona State University
   Commenting as an individual
Document Low-dose Extrapolation of Radiation-Related Cancer Risk
The use of the linear no-threshold (LNT) theory in radiation protection remains controversial. Central estimates of and uncertainties in radiogenic cancer risks at low dose depend on the underlying predictive theory. Regulators and decision-makers use risk estimates to make risk management decisions. This ICRP report provides important scientific analyses of current epidemiological and radiobiological data regarding the shape of the dose response curve for radiation carcinogenesis. I offer the following comments for the Task Force’s consideration:

1. Throughout the report LNT is referred to as a hypothesis. In the context of the present report LNT is a theory, not a hypothesis. There are clear distinctions between theory, hypothesis, and models. Hypotheses are scientific questions that lead to experiments that test a theory (in some scientific experiments the underlying hypothesis does not test a specific theory). Theories are often expressed mathematically and are used to predict an outcome when conditions (i.e., parameter values) are specified. A useful reference that makes clear distinctions between theory and hypothesis is Barbour, I.G. Religion and Science, San Francisco: Harper Collins Publishers; 1997. Do not be fooled by the title-this is an excellent book that discusses, among other things, the nature of scientific inquiry.

2. The lack of balance in the report is a serious deficiency. As far as I know, no one on the Task Force is an advocate of theories other than LNT. The report reads like a consensus document when, in fact, no scientific consensus exists regarding the appropriateness of LNT or any other predictive theory in radiation protection. There is considerable discussion of thresholds but in general alternatives to LNT are given little attention. As a scientific document, the ICRP should present all scientific perspectives.

3. The dose and dose-rate effectiveness factor (DDREF) is discussed as an important source of risk uncertainty. However, DDREF is only a correction for dose-rate, not dose. In any particular exposure scenario DDREF is constant over the range of doses of interest. The Task Force should consider discussing dose extrapolation as a source of uncertainty. What is the uncertainty in risk when extrapolating from 200 mSv to 2 mSv (all other sources of uncertainty being accounted for)?

Thank you for the opportunity to comment on this important report.