Iatrogenc hypothyroidism: A consequence of external beam radiotherapy to the head & neck malignancies

Background: Hypothyroidism is a known consequence of external beam radiotherapy to the neck encompassing part or whole of the thyroid gland for over 40 years. Still thyroid function tests are not a part of routine follow up of head - neck cancer patients treated with radiotherapy with or without surgery and / or chemotherapy.
Aim: Aim of this study was to find out the incidence of hypothyroidism in head - neck cancer patients treated with radiotherapy with or without chemotherapy where radiation portals included most or whole of the thyroid gland.
Materials and Methods: From September 2001 to November 2003, 187 patients with head-neck malignancies were treated with external beam radiotherapy whose radiation portals included part or whole of the thyroid gland with / without chemotherapy. Thyroid function tests were done at the beginning of treatment, at six weeks after completion of radiotherapy and thereafter at six weeks interval for two years.
Results: Out of 187 patients, five were excluded from the study as they were found to be hypothyroid before the initiation of treatment. Another four were excluded from result analysis because they underwent laryngectomy for uncontrolled disease. Of the patients attending the follow up clinic, 17.8 % and 21.8 % were found to have clinical and sub-clinical hypothyroidism at two year.
Conclusion: As a significant number of patients develop hypothyroidism following radiotherapy to the neck, thyroid function tests should be included in the routine follow up protocol of such patients. But certain questions have emerged from this study which need a large randomized study to find out the answers.

Keywords
Iatrogenic hypothyroidism, Thyroid function tests, Head & neck malignancies, Teletherapy