Relation of External Beam Radiotherapy Dose with Subclinical Hypothyroidism in Patients undergoing Adjuvant Neck Radiation after Surgery for Squamous Cell Carcinoma of Head and Neck.

The objective of this study was to find out the radiation dose relationship with subclinical hypothyroidism in the postoperative head and neck squamous cell carcinoma patients, who underwent adjuvant neck external beam radiotherapy. It was a prospective cohort study done between June 2018 and January 2020. One hundred patients, who were fulfilling the criteria of histological proven postoperative head and neck squamous cell carcinoma (SCC) of AJCC 2018 stage I to III, were enrolled. Patients were irradiated for 50 Gy to the bilateral lower neck on a linear accelerator. A CT scan face and neck with contrast along with T3, T4, and TSH was done before and after 4 weeks of chemoradiotherapy. All the patients were kept on surveillance for every three months for one year with the above-mentioned CT scan and thyroid function test. Ten patients (10%) had received radiation dose less than 30 Gy to the thyroid gland, while 90 patients (90%) had received radiation dose >30 Gy to thyroid gland. After one year of completion of treatment, 27.8% patients (n = 25) developed subclinical hypothyroidism among those patients (n = 90), who received radiation dose more than 30 Gy to thyroid gland. None of the patients had subclinical hypothyroidism among those patients (n =10), who received radiation dose below 30 Gy to thyroid gland (p= 0.062). Key Words: Head and neck cancer, Neck radiotherapy, Subclinical hypothyroidism.