Date of Award

2002

Embargo Period

8-1-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biometry and Epidemiology

College

College of Graduate Studies

First Advisor

David G. Hoel

Second Advisor

Daniel T. Lackland

Third Advisor

Stuart R. Lipsitz

Fourth Advisor

Lawrence C. Mohr

Fifth Advisor

Donald Frey

Abstract

Many late effects from exposure to ionizing radiation, including cancers, have been described in the literature. The identification and quantification of radiation-induced health effects is an important and complex issue. Recommendations for radiation safety and protection from the International Commission on Radiological Protection are made using a linear no threshold risk model on epidemiological data. A major obstacle in this process is the limited availability of data to directly measure the health effects of radiation on human populations. One way to circumvent this problem IS to use experimental data from laboratory animals and extrapolate across species to man. The cancer incidence and mortality data from the Japanese atomic bomb survivors was adjusted for uncertainty that exists in the dose estimates, systematic error in the neutron dose estimates, and a dose-dependent relative biological effectiveness. A threshold term was included in the -Poisson regression model as a surrogate for nonlinearity in the dose response curve. The research suggests that the threshold improves the fit of the model for the solid tumor incidence, as well as the leukemia incidence and mortality data (although the mortality data was not a significant improvement). In our study, B6CF 1 mice were used to assess the shape of the dose response curve and the effects of fractionation at low doses. The Cox proportional hazards model was used to as an empirical model, while the two-stage clonal expansion model was used as the biologically based cancer model in which information on the carcinogenesis process is incorporated into the model. The two models resulted in similar descriptions of the dose response curves, cancer risks, neutron relative biological effectiveness and dose rate effectiveness factor associated with exposure to ionizing radiation. The analyses indicate that the dose response curve appears linear in the low dose region, and fractionation reduces the effectiveness of gamma exposure while increasing the effectiveness of neutron exposure.

Rights

All rights reserved. Copyright is held by the author.

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