British Journal of Radiology (2007) 80, 498
© 2007 British Institute of Radiology
doi:
Annals of the ICRP Publication 99: Low dose extrapolation of radiation-related cancer risk.By J Valentin. pp. 142, 2006 (Elsevier, UK), £73.99 ISBN 008-044958-1
P P Dendy
The first sentence of the Introduction to this small book states that "The purpose of the present report is to summarise scientific evidence relevant to the quantification of cancer risk associated with radiation exposure at (effective) doses of interest for radiation protection, particularly doses below current recommended limits for protection of radiation workers (e.g. 20 mSv/year) and the general public (e.g.1 mSv/year)". Because many examinations in diagnostic radiology result in effective doses of approximately 1 mSv or less, a lot of BJR readers will be interested to know if the report has anything new to say on risks at such very low doses.
The main body of the text is divided into five chapters: epidemiological considerations; low dose risk — biology; cellular consequences of radiation-induced damage; carcinogenic effects of ionising radiation; and quantitative uncertainty analysis.
Chapter 2 provides a good overview of epidemiological data and demonstrates, yet again, that there is no direct credible epidemiological evidence of radiation-related risk associated with exposures of the order of 1 mGy, nor is there much prospect of obtaining any, because the extrapolated risk factor, based on the linear-no-threshold (LNT) model, is so small. Although this chapter relies heavily upon medical exposures, it is written from the stand-point of general radiation protection, not diagnostic radiology. Indeed, one entry in Table 2.1 would suggest to a non-specialist that the effective dose from a single screening mammogram is 3 mSv.
BJR readers who are not radiobiologists may find the other chapters heavy going, but there are well-written conclusions and these, together with the Guest Editorial and the Executive Summary, get the message over.
For the practical purposes of radiation protection, and this includes optimisation in diagnostic radiology, the LNT model remains the most prudent risk model and can be readily interpreted and implemented. However, there is accumulating radiobiological evidence that makes the dose–response relationship increasingly uncertain at very low doses of ionising radiation, and, by implication, any extrapolation from higher doses. The risk from a single effective dose of 1 mSv, if any, is still unknown.
