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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, V20, V25, V30, V35, V40, V45, V50, V55, and V60 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 V20 and V50 were significantly different between patients with and without HT. Logistic regression analysis showed that N stage, thyroid volume, and thyroid V50 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 V50 > 24% and was 34.15% in patients with thyroid V50 ≤ 24%.Conclusions: The incidence of HT is significantly associated with N stage, thyroid volume, and thyroid V50. More attention should be paid to patients with NPC with thyroid volume ≤ 12.82 cm3 and advanced N stage disease. [ABSTRACT FROM AUTHOR]

Objective: To evaluate the effect and acute toxicity of late course conformal radiotherapy combined with chemotherapy for stage III and IV a nasopharyngeal carcinoma (NPC)., Methods: Ninety-six patients with stage III and IV a NPC were randomly divided into 2 groups: test group (n = 46, undergoing late course conformal radiotherapy combined with chemotherapy) and control group (n = 50, undergoing conventional radiotherapy). Both groups were treated with one-period chemotherapy, including cisplantin, 5-fluouracil, and calcium folinate, before and after the radiotherapy. The radiotherapy of the test group consisted of 2 phases: 36.0 approximately 40.0 Gy in 18 approximately 20 fractions over 3.5-4 weeks as the first phase using conventional technique was delivered with 2 lateral opposing faciocervical fields, and then 30.0-46.0 Gy in 15-23 fractions over 3-4.5 weeks as the second phase using three-dimensional conformal radiotherapy (3D-CRT)., Results: The rates of complete remission (CR), partial remission (PR), and no change (NC) of the test group were 95.65%, 4.35%, and 0, not significantly different from those in the control group (90.00%, 10.00%, and 0, P = 0.287). The 1-year survival rate of the test group was 100%, not significantly different from that of the control group (96.00%, P = 0.170). The nasopharyngeal 1 year control rate of the test group was 97.83%, significantly higher than that of the control group (78.00%, P = 0.03). The distant metastasis rate of the test group was 8.70%, not significantly different from that of the control group (12.00%, P = 0.596). The incidence rates of radiological caries and irradiation-induced otitis media in the test group was 4.25% and 17.39% respectively, both significantly lower than those in the control group (26.00% and 42.00% respectively, P = 0.004 and P = 0.000). There was no significant difference in the incidence of nausea, vomiting, leukopenia, and severity of acute mucositis between these 2 groups., Conclusion: Late course conformal radiotherapy combined with chemotherapy effectively improves the disease control, delays the distant metastasis, and alleviates radioactivity damnification.