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Abstract
This is a review of historical trends, theoretical concepts and experimental data pertaining to the question of the shape of the dose-response curve for carcinogenesis in human beings exposed to low LET [linear energy transfer] radiation. The focus of the study is on the question of whether linear extrapolation data obtained at high doses and dose rates is a reasonable or unreasonable method of evaluating risk of cancer development following irradiation at low doses and/or low dose rates. Most, but not all, of the animal data indicate that linear extrapolation from high doses overestimates the risk at low doses or dose rates. A review of the mechanisms and possible dose response curves for each, suggests that this general principle may not be applicable to human radiation carcinogenesis. An analysis of dose response curves for 2 hit chromosome aberrations in mammalian cells shows that there is a linear component which dominates the response up to .apprx. 100 rads. Contrary to popular belief there are good data on cancer induction in humans by low doses and/or low dose rates of low LET radiation. Risk estimates at these low doses were not less than comparable risk estimates made from high doses. If anything, the data suggested the opposite. Linear extrapolation of human data from high doses (of up to around 100 rads) to low doses of low LET radiation may not overestimate the risk at low doses. Linear extrapolation of high to low doses probably underestimates the risk at low doses in some cases.