Therapeutic radiation at a young age is linked to secondary thyroid cancer. The Late Effects Study Group.

TLDR

The study estimated thyroid cancer risk in 9,170 long‑term survivors of childhood cancer, using detailed treatment data from 23 cases and 89 matched controls. Compared with the general population, survivors had a 53‑fold higher thyroid cancer risk, which rose with time and radiation dose; 68 % of cancers occurred within the radiation field, and doses above 200 cGy were linked to a 13‑fold increase, with risk continuing to rise up to 6,000 cGy.

Abstract

We estimated the risk of thyroid cancer among 9170 patients who had survived 2 or more years after the diagnosis of a cancer in childhood. As compared with the general population, patients had a 53-fold increased risk (95% confidence interval, 34-80). Risk increased significantly with time since treatment for the initial cancer (P = 0.03). Detailed treatment data were obtained for 23 cases and 89 matched controls from the childhood cancer cohort. Sixty-eight % of the thyroid cancers arose within the field of radiation. Radiation doses to the thyroid of greater than 200 cGy were associated with a 13-fold increased risk (95% confidence interval, 1.7-104). The risk of thyroid cancer rose with increasing dose (P less than 0.001), but this was derived almost entirely from the increase from less than 200 to greater than 200 cGy. The risk of thyroid cancer did not decrease, however, at radiation doses as high as 6000 cGy.