Belarusian in utero cohort: A new opportunity to evaluate the health effects of prenatal and early-life exposure to ionising radiation.

In April 1986, the Chernobyl nuclear accident resulted in wide-scale contamination of Belarus with significantly elevated levels of radioiodine isotopes, mainly iodine-131 (131I), and long-lived radiocaesium isotopes, mainly caesium-137 (137Cs). Various groups of the population were affected by exposure to ionising radiation, including pregnant women and their foetuses. This paper describes the methods and results related to the establishment of a cohort of 2965 Belarusian people exposed in utero due to Chernobyl fallout. The cohort consists of individuals whose mothers resided in the most radioactively contaminated areas in Belarus at the time of the accident. Prenatal and postnatal doses to the thyroid due to intake of 131I, external irradiation and ingestion of radiocaesium isotopes were estimated for all cohort members. Ongoing research on this unique cohort will provide important information on adverse health effects following prenatal and postnatal exposure to radioiodine and radiocaesium isotopes, for which available epidemiological data are scant.

Thyroid Dose Estimates for a Cohort of Belarusian Persons Exposed in Utero and During Early Life to Chernobyl Fallout.

Thyroid radiation doses were estimated for a cohort of 2,965 Belarusian persons who were exposed in utero and during early life to fallout from the Chernobyl nuclear power plant accident. Prenatal and postnatal doses to the thyroid due to intake of I, external irradiation from radionuclides deposited on the ground, and ingestion of cesium isotopes (Cs and Cs) were calculated for all cohort members. Dose estimation was based on personal interviews with subjects' mothers; the interviews collected data on subjects' residential history, consumption by mothers during time of pregnancy and breast-feeding, as well as consumption by subjects after birth. Direct instrumental measurements of radioactivity in mothers and the study subjects, if available, were also used for calculation of doses. Intake of I by mothers was found to be the predominant pathway for thyroid exposure for the study subjects. The average thyroid dose due to all exposure pathways was estimated to be 137 mGy (median dose of 25 mGy, maximal dose of 14.8 Gy), including 130 mGy (median dose of 17 mGy, maximal dose of 14.8 Gy) from I intake, 4.9 mGy (median dose of 3.0 mGy, maximal dose of 102 mGy) due to external irradiation, and 2.5 mGy (median dose of 1.7 mGy, maximal dose of 47 mGy) due to ingestion of Cs. The dose estimates will be used to evaluate the radiation-related risk of thyroid cancer and other thyroid diseases in this unique cohort.