Cancer risks attributable to low doses of ionizing radiation: Assessing what we really know

doi:10.1073/pnas.2235592100

Cancer risks attributable to low doses of ionizing radiation: Assessing what we really know

^aCenter for Radiological Research, Columbia University, 630 West 168th Street, New York, NY 10032; ^cClinical Trials Service Unit, Radcliffe Infirmary, Oxford OX2 6ME, United Kingdom; ^dRadiation and Genome Stability Unit, Medical Research Council, Oxfordshire OX11 ORD, United Kingdom; ^eRadiation Epidemiology Branch, National Cancer Institute, Bethesda, MD 20892; ^fLaboratory of Radiobiology, Harvard School of Public Health, Boston, MA 02115; ^gBiostatistics Branch, National Cancer Institute, Rockville, MD 20892; ^hRadiation Effects Research Foundation, Hiroshima 732-0815, Japan; ⁱEnvironmental Carcinogenesis Division, Environmental Protection Agency, Research Triangle Park, NC 27711; ^jOffice of Radiation and Indoor Air, Environmental Protection Agency, Washington, DC 20460; ^kDepartment of Mathematics, University of California, Berkeley, CA 94720; ^lDepartment of Epidemiology, Johns Hopkins University, Baltimore, MD 21205; ^mBiology Department, Brookhaven National Laboratory, Upton, NY 11973; and ⁿDepartment of Medical Physics, Memorial Sloan–Kettering Cancer Center, New York, NY 10021

Contributed by Richard Doll, August 29, 2003

Abstract

High doses of ionizing radiation clearly produce deleterious consequences in humans, including, but not exclusively, cancer induction. At very low radiation doses the situation is much less clear, but the risks of low-dose radiation are of societal importance in relation to issues as varied as screening tests for cancer, the future of nuclear power, occupational radiation exposure, frequent-flyer risks, manned space exploration, and radiological terrorism. We review the difficulties involved in quantifying the risks of low-dose radiation and address two specific questions. First, what is the lowest dose of x- or γ-radiation for which good evidence exists of increased cancer risks in humans? The epidemiological data suggest that it is ≈10–50 mSv for an acute exposure and ≈50–100 mSv for a protracted exposure. Second, what is the most appropriate way to extrapolate such cancer risk estimates to still lower doses? Given that it is supported by experimentally grounded, quantifiable, biophysical arguments, a linear extrapolation of cancer risks from intermediate to very low doses currently appears to be the most appropriate methodology. This linearity assumption is not necessarily the most conservative approach, and it is likely that it will result in an underestimate of some radiation-induced cancer risks and an overestimate of others.

Footnotes

↵ b To whom correspondence should be addressed. E-mail: djb3{at}columbia.edu.
Abbreviations: CI, confidence interval; LSS, Life-Span Study; RR, relative risk.