Under the beam, beyond the tumor: An observational study of post-radiotherapy hypothyroidism in head and neck cancers

Background: Hypothyroidism is a frequently under-recognized late complication of radiotherapy (RT) in head and neck cancers. Its insidious onset and vague symptoms often delay diagnosis, affecting long-term quality of life. This study aimed to assess the incidence, timing, and severity of thyroid dysfunction following external beam radiotherapy (EBRT), and to identify correlations with clinical and treatment-related variables. Materials and Methods: A retrospective observational study was conducted on patients with head and neck malignancies treated with curative-intent EBRT using standard fractionation. Patients with preexisting thyroid disease or follow-up <6 months were excluded from the study. Thyroid function was assessed using serum thyroid-stimulating hormone (TSH) levels. Subclinical and overt hypothyroidism were defined by standard lab criteria. Associations with age, sex, radiation field, and dose distribution were analyzed. Results: Among 135 patients, 47 (35%) developed post-RT hypothyroidism. Subclinical cases made up 30% ( n = 41), whereas 6% ( n = 8) had overt hypothyroidism requiring treatment. Median time to TSH elevation was 8.2 months (range: 6–18 months). Higher incidence was seen in patients aged >50 years, females, and those receiving bilateral neck RT. A positive but nonsignificant correlation ( r = 0.28) was observed between radiation dose to lower cervical regions and TSH levels. Conclusion: Hypothyroidism is a common sequela of head and neck RT, often subclinical. Routine TSH monitoring starting at 6 months post-RT and annually thereafter is advised, particularly for older patients and those receiving bilateral neck irradiation. Early detection and treatment can improve survivorship and long-term quality of life.