ACUTE RADIATION THYROIDITIS

Purpose: Radiation-induced thyroid dysfunction is considered a late ef fect, We prospectively assessed acute reactions of the thyroid to exte rnal neck irradiation. Methods and Materials: This study included 22 p atients in whom the thyroid was incidentally exposed to therapeutic do ses of radiation. Thyroid function tests included measurements of seru m thyroid stimulating hormone (TSH), free and total triiodothyronine ( T3) and thyroxine (T4), thyroglobulin, and antithyroid antibodies. The se tests were performed before radiotherapy (baseline values), after a pproximately 40 Gy had been administrated, 2 weeks after the end of ra diotherapy, and 3 and 6 months after the beginning of radiotherapy. Re sults: Mean serum levels of TSH were 1.53, 0.55, 0.78, 2.14, and 7.57 mu U/ml before radiotherapy, after 40 Gy irradiation, 2 weeks after th e end of radiotherapy, and 3 and 6 months after radiotherapy, respecti vely. Thus, levels of TSH exhibited two phases: a significant decrease during radiotherapy (thyrotoxic phase) and an increase after radiothe rapy (hypothyroid phase) (baseline vs. 40 Gy: p < 0.0001, baseline vs. 6 months: p = 0.003). Increases of thyroid hormones were subtle durin g radiotherapy. Conclusions: We believe that radiation promotes releas e of excessive amounts of thyroid hormones during radiotherapy owing t o suppression of TSH secretion. In addition to the late damage (hypoth yroidism), thyrotoxicosis occurs when the thyroid gland receives a the rapeutic doses of external radiation. Copyright (C) 1996 Elsevier Scie nce Inc.