Cancer Incidence after In Utero Exposure to Ionizing Radiation in Techa River Residents

Health effects of in utero exposure to ionizing radiation, especially among adults, are still unclear. The aim of this study was to analyze cancer risk in a cohort of subjects exposed in utero due to releases of nuclear waste into the Techa River in the Southern Urals, taking into account additional postnatal exposure. Analysis for solid cancer was based on 242 cases among 10,482 cohort members, accumulating 381,948 person-years at risk, with follow-up from 1956-2009, while analysis for hematological malignancies was based on 26 cases among 11,070 persons, with 423,502 person-years at risk, with follow-up from 1953-2009. Mean doses accumulated in soft tissues and in red bone marrow during the prenatal period were 4 mGy and 30 mGy, respectively. Additional respective mean postnatal doses received by cohort members were 11 and 84 mGy. Poisson regression analysis was used to estimate the excess relative risk (ERR) of cancer incidence related to in utero and postnatal doses. No association was observed for in utero exposure with solid cancer risk [ERR per 10 mGy: -0.007; 95% confidence interval (CI): <-0.107; 0.148] or with hematological malignancy risk (ERR/10 mGy: -0.011; 95% CI: <-0.015; 0.099). However, ERR of solid cancer increased significantly with increasing postnatal dose (ERR/10 mGy: 0.11; 95% CI: 0.04; 0.22). The very wide confidence intervals in these ERR results are similar to those of studies performed on the LSS cohort and the offspring of the Mayak Female Worker Cohort, as well as case-control studies of effects after in utero medical exposure. There were limitations of this study, with decreased statistical power, due to the low prenatal doses received by most of the cohort members, the small number of cancer cases and the absence of cohort members over the age of 59 years (living cohort members had reached 49-59 years of age). Further aging of the cohort and extension of the follow-up period will enhance the statistical power of this study in the future. There is a shortage of cohort studies reporting on the effects of prenatal radiation exposure, as well as information on chronic exposure during the prenatal period. Therefore, further research of this unique cohort will be a useful addition to the published literature on this subject, and a valuable means of elucidating the long-term effects of low-dose radiation exposure in the fetus. (C) 2017 by Radiation Research Society