Hypothyroidism after radiotherapy to the neck

PURPOSE: The purpose of this study was to investigate the incidence and possible predictors of hypothyroidism after radiotherapy to the neck, focusing on radiation dose-volume factors. METHODS AND MATERIALS: Thyroid function was measured in 169 patients treated with radiation ports including the thyroid, between 1989 and 2000. Hypothyroidism was determined with an endpoint of elevated serum thyroid stimulating hormone(TSH) levels > 10.0 microU/ml. In 60 patients, radiation dose-volume factors were calculated; e.g., total volume of the thyroid, mean radiation dose to the thyroid, and %-volume of the thyroid which received radiation doses of no less than 10-70 Gy(V10-V70). The evaluated risk factors for hypothyroidism included these dose-volume factors, sex, age, primary disease, combined chemotherapy, and follow-up period. RESULTS: Hypothyroidism was detected in 33 (19.5%) of the 169 patients. None of them had clinical symptoms of hypothyroidism. V10, V20, and V30 seemed to be possible predictors of hypothyroidism and had a significant impact on the peak level of serum TSH. CONCLUSION: Radiation dose-volume factors of the thyroid seemed to correlate with the incidence of hypothyroidism, and V10, V20, and V30 had a significant impact on the peak level of serum TSH.