The incidence of hypothyroidism after radiotherapy for head and neck cancer

The incidence of hypothyroidism after radiotherapy for head and neck cancer. Objectives: To identify the incidence of radiation-induced hypothyroidism (HT) after head and neck radiotherapy.Furthermore, we wanted to correlate patient and treatment characteristics with the incidence of HT in order to identify predictive factors for radiation-induced HT.

Methodology: We examined the values of thyrotropin, i.e., the thyroid-stimulating hormone (TSH), in head and neck cancer patients who received a combination treatment of radiotherapy and chemotherapy between 2005 and 2012. HT was defined as having a TSH value of > 10 mIU/L or whenever the patient started to take substitution therapy after treatment. We correlated the radiotherapy mean dose to the thyroid gland (Dmean), the pretreatment volume of the thyroid gland, sex, age, type of concomitant treatment, tumour localization, and T and N classification with the incidence of HT.

Results: We were able to obtain data from 72 patients. From these 72 patients, 48 (66%) had a normal thyroid function and 25 (34%) had developed HT. The mean follow-up for these patients was 55 months (range: 21 to 103 months). Out of the 25 patients with HT, 8 (32%) were diagnosed within the first year of follow-up. Increasing Dmean is a significant risk factor for developing HT. Increasing thyroid volume, on the other hand, was correlated with less HT in our patient cohort.

Conclusions: In our study, the incidence of HT is 34%. We also noticed that HT can even develop shortly after treatment. Patients with a higher Dmean to the thyroid gland and lower pretreatment thyroid gland volumes are more at risk.