Cancer Risk Assessment with Intermittent Exposure |
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Authors: | Duncan J Murdoch Daniel Krewski John Wargo |
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Institution: | Department of Statistics and Actuarial Science, University of Waterloo, Kingston, Ontario, Canada. |
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Abstract: | Applications of methods for carcinogenic risk assessment often focus on estimating lifetime cancer risk. With intermittent or time-dependent exposures, lifetime risk is often approximated on the basis of a lifetime average daily dose (LADD). In this article, we show that there exists a lifetime equivalent constant dose (LECD) which leads to the same lifetime risk as the actual time-dependent exposure pattern. The ratio C = LECD/LADD then provides a measure of accuracy of risk estimates based on the LADD, as well as a basis for correcting such estimates. Theoretical results derived under the classical multistage model and the two-stage birth-death-mutation model suggest that the maximum value of C, which represents the factor by which the LADD may lead to underestimates of risk, will often lie in the range of 2- to 5-fold. The practical application of these results is illustrated in the case of astronauts subjected to relatively short-term exposure to volatile organics in a closed space station environment, and in the case of the ingestion of pesticide residues in food where consumption patterns vary with age. |
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Keywords: | Multistage model birth-death-mutation model intermittent exposure time-dependent exposure relative effectiveness space-craft maximum allowable concentrations pesticide residues |
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