Postradiotherapy hypothyroidism: radiation dose response and chemotherapeutic radiosensitization at less than 40 Gy.

To analyze our experience with iatrogenic hypothyroidism, we prospectively followed 84 patients, seen from 1984 to 1990, who had been diagnosed with either Hodgkin's disease (HD) or head and neck (H&N) carcinoma and subsequently treated with radiotherapy. Within these two diagnostic groups were subgroups whose treatment differed as to dose of therapeutic irradiation received or adjunctive use of chemotherapy. Approximately 50% of all patients and of each subgroup developed either clinical or subclinical hypothyroidism during follow-up. However, among the HD patients who received irradiation plus chemotherapy, a dose-response relationship below a threshold limit of dose received, probably 40 Gy, was observed.