Thyroid Carcinomas After Irradiation for a First Cancer During Childhood

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Abstract
THYROID TISSUE is among the most radiosensitive tissues.1 After irradiation, the excess relative risk (ERR) of a thyroid tumor per dose unit decreases with increasing age at the time of irradiation.1-5 During the first decades after irradiation, the ERR of developing differentiated carcinoma and adenoma was 3 to 12 for a dose of 1 Gy of external low–linear energy transfer (LET) radiation delivered during childhood in 1 or a few fractions.1-8 Twenty years after irradiation, the ERR decreases with time; however, absolute excess risk increases for at least 40 years after irradiation.2-9 After external low-LET radiation delivered at a high dose rate during childhood, the dose-response relationship is essentially linear—at least from 0.1 Gy to a few gray.1-3,6-8 Although this aspect has not been studied sufficiently, it seems that identified risk factors for thyroid cancer, including reproductive factors, iodine intake, and body mass index, could modify the dose-response relationships after external low-LET irradiation.10,11