A retrospective study of thyroid functional status in patients treated with radiation therapy over head and neck region for squamous cell carcinoma of head and neck

Head and neck cancer is the sixth most common carcinoma in the world.Management of head neck cancer is either surgery or radiotherapy (RT) for early stage tumour and surgery combined with radiotherapy, radical radiotherapy or concurrent chemoradiotherapy (CCRT) for advanced stages. One of the most common clinical late effects of thyroid gland irradiation in patients exposed to therapeutic doses to the neck is hypothyroidism. To estimate the prevalence of hypothyroidism in post radiation head neck cancer patients where radiation portal included total or most of the thyroid gland and o calculate the Odds ratio for the development of subclinical or clinical hypothyroidism. From February 2018 to May 2019, 102 patients with histopathologically proven advanced (stage III, IV) squamous cell carcinoma of head and neck region (excluding patients with thyroid malignancy and prior neck surgery) who were treated with radical external beam radiotherapy (68-70 Gy) delivered by Cobalt 60 Teletherapy machine with conventional fractionation over head and neck region at least 6 months back were studied. Thyroid function tests (T3, T4, TSH, f-T4) were done at 6 months,9 months and 12 months after completion of radiotherapy. Out of the 102 patients with mean age of 50.9 (±9.4) years, 64 (62.7%) were males and 38 (37.3%) were females. Most common Primary tumour site was larynx (36.1%). CCRT was given to 65.7% of patients and 75.5% of patients had stage-III disease. Two patients were lost to follow-up. Overall, 35% developed hypothyroidism of which 18% were clinical (high TSH, low f-T4) and 17% were sub-clinical hypothyroidism (high TSH, normal f-T4) at one year of follow-up. No significant associations were found with age, gender, stage and addition of chemotherapy. In comparison with control group (patients attending other OPDs, N=200) odds ratio for the development of hypothyroidism was found to be 3.5 (subclinical-4.9, Clinical- 1.9). Hypothyroidism is an under‑recognized morbidity of external beam radiation to the neck. Recognizing hypothyroidism early and treating it prevents associated complications. Hence, thyroid function tests should be done during routine follow up.