Purpose: To investigate the incidence of hypothyroidism after radiotherapy of laryngeal cancer, including the possible factors that could predict the onset of hypothyroidism.
Materials and methods: We report this study on patients treated by radiotherapy as part of the treatment for laryngeal cancer in the Department of Oncology in Eastern Finland. Sixty-five males and seven females were treated with radiotherapy between 1974-1995.Thyroid function was determined by measuring serum thyroid stimulating hormone, and serum free thyroxine (FT4). The studied risk factors for hypothyroidism included age, treatment modalities, radiation dose and energy, height of the radiation field, and follow-up time.
Results: Hypothyroidism was detected in 17 (24%) of the 72 patients. Hypothyroidism was clinically unsuspected in all but one patient. Hypothyroidism was more common, if the height of the radiation field was >/=7 cm, or the patient had been operated. Hypothyroidism was less common if less than a half of the thyroid bed was irradiated.
Conclusion: The detection of hypothyroidism clinically is difficult, and the rate of hypothyroidism warrants routine assessment of thyroid function after irradiation of laryngeal cancer.