HYPOTHYROIDISM AFTER EXTERNAL RADIOTHERAPY FOR HEAD AND NECK-CANCER

Purpose: To study the development of thyroid hypofunction in patients with head and neck cancers admitted for external radiotherapy. Methods and Materials: Between November 1990 and July 1996, thyroid function was measured in 264 consecutive patients, where the entire thyroid gla nd or part of it was included in the target volume, The time to develo pment of hypothyroidism (HT) was calculated from the start of the radi otherapy. Results: The median follow-up period was 19 months. Seventee n patients (6%) developed elevated serum thyroid-stimulating hormone l evels with depressed (free) thyroxine levels (i.e., clinical HT), Elev ated serum thyroid-stimulating hormone level with normal (free) thyrox ine levels (i.e., chemical HT) developed in 57 (22%). The median time to clinical HT was 15 months (range: 7 to 32). The median time to chem ical HT was also 15 months (range: 2 to 28). The actuarial risk of dev eloping clinical or chemical HT 3 years after treatment was 15 and 40% , respectively, The incidence of chemical HT was significantly higher (p = 0.041) when the whole thyroid was included in the target volume c ompared to patients where only part of the thyroid was irradiated. The same trend was seen as regards clinical HT (p = 0.063), For those 20 patients who underwent laryngectomy, there was an increased risk of bo th chemical and clinical HT (p = 0.011 and 0.019, respectively), Incre asing age was associated with an increased risk of chemical HT (p = 0. 001), but not of clinical HT (p = 0.553). Sex, tumor site, radiation d ose, and combination of radiotherapy and chemotherapy were not signifi cant factors for thyroid hypofunction. Conclusion: Depressed thyroid f unction is common after external radiotherapy for cancers of the head and neck. Routine testing for possible thyroid hypofunction should be included in the follow-up procedures, even many years after end of rad iotherapy. (C) 1997 Elsevier Science Inc.