Low dose radiation risks for women surviving the a-bombs in Japan: generalized additive model.

Greg Dropkin

doi:10.1186/s12940-016-0191-3

Abstract

BackgroundAnalyses of cancer mortality and incidence in Japanese A-bomb survivors have been used to estimate radiation risks, which are generally higher for women. Relative Risk (RR) is usually modelled as a linear function of dose. Extrapolation from data including high doses predicts small risks at low doses. Generalized Additive Models (GAMs) are flexible methods for modelling non-linear behaviour.MethodsGAMs are applied to cancer incidence in female low dose subcohorts, using anonymous public data for the 1958 – 1998 Life Span Study, to test for linearity, explore interactions, adjust for the skewed dose distribution, examine significance below 100 mGy, and estimate risks at 10 mGy.ResultsFor all solid cancer incidence, RR estimated from 0 – 100 mGy and 0 – 20 mGy subcohorts is significantly raised. The response tapers above 150 mGy. At low doses, RR increases with age-at-exposure and decreases with time-since-exposure, the preferred covariate. Using the empirical cumulative distribution of dose improves model fit, and capacity to detect non-linear responses. RR is elevated over wide ranges of covariate values. Results are stable under simulation, or when removing exceptional data cells, or adjusting neutron RBE. Estimates of Excess RR at 10 mGy using the cumulative dose distribution are 10 – 45 times higher than extrapolations from a linear model fitted to the full cohort. Below 100 mGy, quasipoisson models find significant effects for all solid, squamous, uterus, corpus, and thyroid cancers, and for respiratory cancers when age-at-exposure > 35 yrs. Results for the thyroid are compatible with studies of children treated for tinea capitis, and Chernobyl survivors. Results for the uterus are compatible with studies of UK nuclear workers and the Techa River cohort.ConclusionNon-linear models find large, significant cancer risks for Japanese women exposed to low dose radiation from the atomic bombings. The risks should be reflected in protection standards.Electronic supplementary materialThe online version of this article (doi:10.1186/s12940-016-0191-3) contains supplementary material, which is available to authorized users.

Highlights

Analyses of cancer mortality and incidence in Japanese A-bomb survivors have been used to estimate radiation risks, which are generally higher for women
Basis dimension k=10 was sufficient when tested by gam.check or modelling residuals against covariates
P5ae, P5se, P5ad and P5sd were cross-validated (Appendix B) in A+, to test the proportion of deviance explained and the estimated Relative Risk (RR)|10 mGy with 90% Bayesian posterior confidence interval (CI), see Additional file 1: Table S1

Summary

Introduction

Analyses of cancer mortality and incidence in Japanese A-bomb survivors have been used to estimate radiation risks, which are generally higher for women. The 1958–1998 incidence cohort was analysed by Preston and co-workers [1], whose main model assumes a linear dose response. Pierce and Preston [2] found a significant dose response for all solid cancer incidence in the 0 – 100 mGy range. Some cancer studies find non-linear responses to radiation [5,6,7,8] and there are some significant results at low doses [9,10,11,12,13,14,15,16]. Low dose radiation risk was reviewed in 2003 [17] and remains a focus of research [18]

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Discussion

Conclusion