Thyroid V(50) is a risk factor for hypothyroidism in patients with nasopharyngeal carcinoma treated with intensity-modulated radiation therapy: a retrospective study.

BACKGROUND: We investigated the risk factors of radiation-induced thyroid dysfunction, then combined the clinical factors and optimum thyroid dosimetric parameters to predict the incidence rate of hypothyroidism (HT) and to guide individualized treatment. METHODS: A total of 206 patients with histologically proven nasopharyngeal carcinoma (NPC) treated at the Cancer Hospital of the University of Chinese Academy of Sciences between January 2015 and August 2018 were included. Dose-volume histogram (DVH) data, including mean dose, absolute volume, V(20), V(25), V(30), V(35), V(40), V(45), V(50,) V(55), and V(60) were extracted and used as dosimetric parameters. A logistic regression analysis model was built to identify predictors related to HT occurring within 2 years. RESULTS: Sex, N stage, thyroid volume, mean thyroid dose, and thyroid V(20) and V(50) were significantly different between patients with and without HT. Logistic regression analysis showed that N stage, thyroid volume, and thyroid V(50) were independent predictors of HT. The radiosensitivity of the thyroid decreased as the thyroid volume increased. Patients with N stage > 1 had significantly higher HT incidence (37.38%) than patients with N stage </=1 (13.11%). The incidence of HT was 54.55% in patients with thyroid V(50) > 24% and was 34.15% in patients with thyroid V(50) </= 24%. CONCLUSIONS: The incidence of HT is significantly associated with N stage, thyroid volume, and thyroid V(50). More attention should be paid to patients with NPC with thyroid volume </= 12.82 cm(3) and advanced N stage disease.