FUNCTIONAL HYPOTHYROIDISM IN PATIENTS RECEIVING CONCURRENT CHEMORADIATION FOR HEAD AND NECK SQUAMOUS CELL CARCINOMA.

Introduction: Head and neck cancers are the fth most common globally and second most prevalent in India, with 77,000 annual cases. Radiotherapy, often combined with chemotherapy, is a standard treatment but frequently results in radiation-induced hypothyroidism (RIHT), with incidence rates ranging from 4% to 79%. RIHTsignicantly impacts quality of life, yet thyroid function testing is rarely routine. Hypothyroidism, a common late effect, is irreversible and requires lifelong hormone replacement. Preventive strategies are crucial to minimize this complication in patients undergoing radical radiotherapy with concurrent chemotherapy for head and neck squamous cell carcinoma. Aim & Objectives: This study examines the incidence of radiation-induced hypothyroidism in patients with HNSCC receiving chemoradiation and explores preventive strategies to reduce its occurrence and associated morbidity. Materials and Methods: This prospective study, conducted at GSLMedical College from October 2019 to April 2021, involved patients with head and neck squamous cell carcinoma receiving radical radiotherapy. Eligible patients underwent thyroid function tests before, after treatment, and six months post-radiotherapy. Dose-volume metrics were analyzed, and statistical assessments were performed using SPSS 22.0 and R version 3.2.2. Signicance was set at p < 0.05. The study aimed to evaluate the incidence of radiation-induced hypothyroidism and explore preventive strategies. Results: In our study, 17 out of 31 patients (54.8%) developed radiationinduced hypothyroidism (RIHT) at 6 months post-radiotherapy, with 13 (41.9%) showing clinical hypothyroidism (mean TSH 7.77 ± 2.93, p < 0.001). T4 and T3 levels showed no signicant difference between hypothyroid and euthyroid patients. Cold intolerance occurred in 12.9%, weight gain in 16.1%, dry skin in 29%, and constipation in 35.5% of patients. The mean thyroid dose was similar between hypothyroid (6570.29±587) and euthyroid groups (6541.35±601.13), with no statistically signicant difference. Long-term follow-up is crucial, as RIHT incidence increases over time. Conclusion: Radiation-induced hypothyroidism (RIHT) is a common complication of head and neck radiotherapy, with our study reporting a 54.8% incidence at 6 months. While no clear dose-response relationship was identied, smaller thyroid volumes increased the risk of hypothyroidism. Early detection and long-term follow-up are essential to prevent progression from subclinical to clinical hypothyroidism. Further research is needed to improve predictive models and minimize thyroid exposure during treatment.