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Enhancing Nuclear Safety


Research

Thesis viva

Bayesian hierarchical approach to account for measurement error in the protracted low-dose exposure to ionizing radiation in the estimation of the risk of radiation-induced cancers. Application to a cohort of uranium miners


Sabine Hoffmann will defend her thesis

on Tuesday 12th December at 10:00 pm

at IRSN, building 01, auditorium

31 avenue de la Division Leclerc

92260 Fontenay-aux-Roses (France)



Abstract


In radiation epidemiology, exposure measurement error and uncertain input parameters in the calculation of absorbed organ doses are among the most important sources of uncertainty in the modelling of the health effects of ionising radiation. As the structures of exposure and dose uncertainty arising in occupational cohort studies may be complex, these uncertainty components are only rarely accounted for in this domain. However, when exposure measurement is not or only poorly accounted for, it may lead to biased risk estimates, a loss in statistical power and a distortion of the exposure-response relationship. The aim of this work was to promote the use of the Bayesian hierarchical approach to account for exposure and dose uncertainty in the estimation of the health effects associated with exposure to ionising radiation in occupational cohorts. More precisely, we proposed several hierarchical models and conducted Bayesian inference for these models in order to obtain corrected risk estimates on the association between exposure to radon and its decay products and lung cancer mortality in the French cohort of uranium miners. The hierarchical appraoch, which is based on the combination of sub-models that are linked via conditional independence assumptions, provides a flexible and coherent framework for the modelling of complex phenomena which may be prone to multiple sources of uncertainty. In order to compare the effects of shared and unshared exposure uncertainty on risk estimation and on the exposure-response relationship we conducted a simulation study in which we supposed complex and potentially time-varying error structures that are likely to arise in an occupational cohort study. We elicited informative prior distributions for average breathing rate, which is an important input parameter in the calculation of absorbed lung dose, based on the knowledge of three experts on the conditions in French uranium mines. In this context, we implemented and compared three approaches for the combination of expert opinion. Finally, Bayesian inference for the different hierarchical models was conducted via a Markov chain Monte Carlo algorithm implemented in Python to obtain corrected risk estimates on the lung cancer mortality in the French cohort of uranium miners associated with exposure to radon and its progeny.


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