Risk factors of early thyroid dysfunction after definitive radiotherapy in nasopharyngeal carcinoma patients

Abstract Background To explore the patterns and risk factors of early thyroid dysfunction in nasopharyngeal carcinoma (NPC) patients within 1 year after intensity‐modulated radiation therapy (IMRT). Methods Patients with NPC who received definitive IMRT between April 2016 and April 2020 were included. All patients had normal thyroid function before definitive IMRT. The chi‐square test, Student's T ‐test, Mann–Whitney U test, Kaplan–Meier method, receiver operating characteristics curve, and Cox proportional hazard analysis were used for statistical analysis. Results A total of 132 NPC patients were identified. Of these patients, 56 (42.4%) had hypothyroidism and 17 (12.9%) had hyperthyroidism. The median time to hypothyroidism and hyperthyroidism was 9 months (range, 1–12 months) and 1 month (range, 1–6 months) after definitive IMRT, respectively. In patients with hypothyroidism, 41 (73.2%) had subclinical hypothyroidism and 15 (26.8%) had clinical hypothyroidism. In those with hyperthyroidism, 12 patients (70.6%) had subclinical hyperthyroidism, and five patients (29.4%) had clinical hyperthyroidism. Age, clinical stage, thyroid volume, and V45 were independent risk factors for early radiation‐induced hypothyroidism within 1 year after IMRT. Patients aged <47 years, stage III/IV disease, or pre‐irradiation thyroid volume < 14 cm 3 had higher risks of developing hypothyroidism. Conclusion Primary subclinical hypothyroidism was the most common subtype of early thyroid dysfunction in NPC patients within 1 year after IMRT. Age, clinical stage, thyroid volume, and V45 were independent risk factors for early radiation‐induced hypothyroidism in NPC patients.