Epidemiological Studies of Low-Dose Ionizing Radiation and Cancer: Rationale and Framework for the Monograph and Overview of Eligible Studies

Abstract

Whether low-dose ionizing radiation can cause cancer is a critical and long-debated question in radiation protection. Since the Biological Effects of Ionizing Radiation report by the National Academies in 2006, new publications from large, well-powered epidemiological studies of low doses have reported positive dose-response relationships. It has been suggested, however, that biases could explain these findings. We conducted a systematic review of epidemiological studies with mean doses less than 100 mGy published 2006-2017. We required individualized doses and dose-response estimates with confidence intervals. We identified 26 eligible studies (eight environmental, four medical, and 14 occupational), including 91 000 solid cancers and 13 000 leukemias. Mean doses ranged from 0.1 to 82 mGy. The excess relative risk at 100 mGy was positive for 16 of 22 solid cancer studies and 17 of 20 leukemia studies. The aim of this monograph was to systematically review the potential biases in these studies (including dose uncertainty, confounding, and outcome misclassification) and to assess whether the subset of minimally biased studies provides evidence for cancer risks from low-dose radiation. Here, we describe the framework for the systematic bias review and provide an overview of the eligible studies.

Figure 1.

Framework for the systematic bias assessment. *If aim is to assess whether there is evidence of an effect then priority is to identify biases away from null. CI = confidence interval; ERR = excess relative risk.

Figure 2.

A) Excess relative risk (ERR) per 100 mGy and 95% confidence intervals (CI) for all solid cancers (or site-specific solid cancers) following exposure in adulthood or at any age (Techa and Taiwanese residents) for the eligible studies. *90% confidence intervals. #Cohorts included in INWORKS. B) ERR per 100 mGy and 95% confidence intervals for all cancers (or site-specific solid cancers) following exposure in childhood for the eligible studies.

Figure 3.

A) Excess relative risk (ERR) at 100 mGy (and 95% confidence intervals [CIs]) for leukemia following exposure in adulthood or any ages (Taiwanese residents) for the eligible studies. *90% confidence intervals. #Cohorts included in INWORKS. ERR for Three Mile Island = 19. B) ERR at 100 mGy (and 95% confidence intervals) for leukemia following childhood exposure for the eligible studies.