THYROID-DYSFUNCTION FOLLOWING RADIOTHERAPY FOR HEAD AND NECK-CANCER

Purpose: To determine the frequency of hypothyroidism (both subclinical and clinical) following external beam radiotherapy to the whole of the thyroid gland in the treatment of squamous cell cancers of the head and neck. Methods and Materials: One hundred and four patients who had completed radiotherapy 30 days to 5 years earlier (84 patients) or who were scheduled for radiotherapy (20 patients) had a single measurement of serum-free thyroxine and thyroid stimulating hormone levels between August 1991 and May 1992. Results: None of the 20 patients assessed prior to treatment showed thyroid dysfunction. Twenty of 84 (23.8%) previously treated patients had subclinical (9.5%) or clinical (14.3%) hypothyroidism. By 5 years, up to 40% of patients may become hypothyroid. Thyroid underactivity was significantly more common in patients having both laryngectomy (including hemi-thyroidectomy) and radiotherapy compared to radiotherapy alone (p < 0.001). Hypothyroidism had not been suspected clinically in any patient tested. Conclusion: In view of the frequency and potential morbidity of this complication, thyroid function testing should become a routine part of posttreatment follow-up for these patients.