Head and neck cancer (HNC) is the most common malignancy in the Indian males. Most of the cases of HNC present in locally advanced stage and requires a multidisciplinary management approach. Radical or adjuvant external beam radiotherapy (EBRT) is one of the important integral components of the management of HNC.

To find the incidence of hypothyroidism (HT) in patients of HNC treated with radiotherapy with or without concurrent chemotherapy.

A prospective, single institutional longitudinal observational study conducted at the department of radiotherapy, Institute of Post Graduate Medical Education and Research, Kolkata.

In this study, data of 118 patients were analysed. The median age at presentation was 56 years. The most common primary site of malignancy was oral cavity (39%). The patients were stage I, stage II and stage III as 11, 37·3 and 51·7% respectively. The median dose of EBRT was 66 Gy. HT statistically significantly correlated with primary site of malignancy (p = 0·001), dose of EBRT (p = 0·005). At the end of follow-up of 6 months, 39·8% developed HT.

The thyroid gland is an important organ at risk while considering EBRT to neck region. The inclusion of thyroid function test in routine follow-up is mandated.