Non-malignant Thyroid Diseases after a Wide Range of Radiation Exposures

Abstract

Background The thyroid gland is one of the most radiosensitive human organs. While it is well known that radiation exposure increases the risk of thyroid cancer, less is known about its effects in relation to non-malignant thyroid diseases. Objectives The aim of this review is to evaluate the effects of high and low dose radiation on benign structural and functional diseases of the thyroid. Methods We examined the results of major studies from cancer patients treated with high-dose radiotherapy or thyrotoxicosis patients treated with high doses of iodine-131, patients treated with moderate to high dose radiotherapy for benign diseases, persons exposed to low doses from environmental radiation and survivors of the atomic bombings who were exposed to a range of doses. We evaluated radiation effects on structural (tumors, nodules), functional (hyper- and hypothyroidism), and autoimmune thyroid diseases. Results Following a wide range of doses of ionizing radiation, an increased risk of thyroid adenomas and nodules was observed in a variety of populations and settings. The dose response appeared to be linear at low to moderate doses, but in one study there was some suggestion of a reduction in risk above 5 Gy. The elevated risk for benign tumors continues for decades following exposure. Considerably less consistent findings are available regarding functional thyroid diseases including autoimmune diseases. In general, associations for these outcomes were fairly weak and significant radiation effects were most often observed following high doses, particularly for hypothyroidism. Conclusions A significant radiation dose-response relation was demonstrated for benign nodules and follicular adenomas. The effects of radiation on functional thyroid diseases are less clear, partly due to the greater difficulties studying these diseases.

Non-cancer morbidity among Estonian Chernobyl cleanup workers: a register-based cohort study

“…Ron and Brenner29 summarised the evidence of benign thyroid diseases after radiation exposure. They concluded that associations have been weak and elevated risk occurred mainly in participants with high doses, exposed at young ages and in women.…”

Durable donor engraftment after radioimmunotherapy using α-emitter astatine-211–labeled anti-CD45 antibody for conditioning in allogeneic hematopoietic cell transplantation

“…Although a strong relationship exists between hypothyroidism and high-dose external or internal 131 I irradiation (30-80 Gy and Ͼ 185 MBq), the association is less for the low-dose ranges used in the current study. 48 Whether the subclinical hypothyroidism in the current animals is a consequence of RIT cannot be ruled out. However, histopathologic changes in the thyroid were not observed in any of the dogs treated with higher doses of 211 At; and taking the short half-life of 211 At into account, it is unlikely that the thyroid received a high enough dose to induce a state of deficiency.…”

Thyroid neoplasia risk is increased nearly 30 years after the Chernobyl accident

“…2.07; 95% CI: 0.28–10.31) . Epidemiologic data on radiation risk of FA are sparse because it is difficult to distinguish adenoma from certain benign thyroid lesions and follicular carcinoma …”