Extrapolation of Observed Low-Dose Risks to Lower Doses
At doses below those where significant risks have been demonstrated in human populations (below 50–100 mSv [protracted exposure] or 10–50 mSv [acute exposure]), we cannot use epidemiological data alone to establish the shape of the dose-response relation. All the dose-response relations shown in Figure 7.1 are possible descriptors of low-dose radiation oncogenesis—and different endpoints may well exhibit differently shaped dose-response relations.
a: linear extrapolation; b: downwardly curving (decreasing slope); c: upwardly curving (increasing slope); d: threshold; e: hormetic.
Linear Dose-Response Relations
At the low and intermediate doses that are amenable to statistically meaningful analysis, many data sets are available, both from epidemiological and laboratory studies, that are consistent with a linear dose-response relation. The data have been extensively reviewed in a recent NCRP Report,40 which concluded “although other dose-response relationships for the mutagenic and carcinogenic effects of low-level radiation cannot be excluded, no alternate dose-response relationship appears to be more plausible than the linear-nonthreshold model on the basis of present scientific knowledge,” and likewise in the recent BEIR-VII report “A comprehensive review of available biological and biophysical data supports a ‘linear-no-threshold’ (LNT) risk model—that the risk of cancer proceeds in a linear ...
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