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Cancer risk assessment with intermittent exposure
D J Murdoch1, D Krewski, J Wargo
1Department of Statistics and Actuarial Science, University of Waterloo, Kingston, Ontario, Canada.
Summary
Estimating carcinogenic risk with intermittent exposures can be inaccurate. A lifetime equivalent constant dose (LECD) offers a more precise measure than the lifetime average daily dose (LADD), often revealing significant risk underestimates.
Area of Science:
- Environmental Health
- Toxicology
- Risk Assessment
Background:
- Carcinogenic risk assessment commonly estimates lifetime cancer risk.
- Intermittent or time-dependent exposures are often approximated using the lifetime average daily dose (LADD).
Purpose of the Study:
- To introduce the concept of a lifetime equivalent constant dose (LECD) for accurate risk assessment.
- To develop a method for evaluating the accuracy of LADD-based risk estimates.
- To provide a basis for correcting risk estimates derived from LADD.
Main Methods:
- Theoretical derivation of LECD under the classical multistage model.
- Theoretical derivation of LECD under the two-stage birth-death-mutation model.
- Calculation of the ratio C = LECD/LADD to quantify risk estimation accuracy.
Main Results:
- A lifetime equivalent constant dose (LECD) exists, yielding the same lifetime risk as time-dependent exposures.
- The ratio C (LECD/LADD) measures the accuracy of LADD-based risk estimates.
- Theoretical models suggest the LADD may underestimate risk by a factor of 2- to 5-fold (maximum C value).
Conclusions:
- LECD provides a more accurate method for carcinogenic risk assessment with variable exposures.
- The LADD approximation can lead to significant underestimation of cancer risk.
- Findings are applicable to scenarios like astronaut exposures and dietary pesticide residue intake.