Thyroid cancer after exposure to radioactive 131I

The thyroid gland is susceptible to radiation carcinogenesis, and the thyroid cancer risk decreases with increasing age at exposure, with a low risk above 20 years of age at exposure. The risk is best described be a linear dose-response relationship down to 0.1 Gy. Epidemiological studies of patients have not observed any increased risk for thyroid cancer after I-131 exposure, but the statistical power to detect risks in children is limited. The Chernobyl accident led to substantial I-131 exposure in Belarus, the Russian Federation and Ukraine. About 4 000 cases of thyroid cancer have been diagnosed among those who were children and adolescents in 1986, including about 3 000 in the age group 0 - 14 years. The risk per Gy from I-131 in young subjects may be less than that seen after external low-LET radiation. A recent case-control study found a threefold risk for thyroid cancer among children from severely iodine-deficient areas, as compared with those living in lesser iodine-deficient areas. A threefold risk reduction was observed among those children receiving stable iodine compared with those not receiving iodine.