The Effect of Sodium Fluoride Application on the Prevention of Radiation Caries in NPC Patients

Inclusion Criteria: * a. Patients with histologically confirmed non-keratinizing NPC (including differentiated type and undifferentiated type, world health organization \[WHO\] II or III). b. Original clinical staged as II-IVa (according to the 8th AJCC edition) c. Male or female who are not pregnant. d. No evidence of distant metastasis (M0). e. Age between 18-60 years. f. WBC≥4×109/L, PLT≥100×109/L, HGB≥90g/L. g. Normal liver function test: Alanine Aminotransferase (ALT), Aspartate Aminotransferase (AST) \<1.5×upper limit of normal (ULN) concomitant with alkaline phosphatase (ALP) ≤2.5×ULN, and bilirubin ≤ULN. i. With normal renal function test (creatinine clearance rate≥60 ml/min or creatinine\< 1.5×ULN. j. The Eastern Cooperative Oncology Group (ECOG) Performance status less or equal to 1. k. Patients must be informed of the investigational nature of this study and give written informed consent. l. Patients receive nasopharyngeal and neck radiotherapy. m. After pre-radiotherapy oral examination, no less than 2 functional teeth in any 1/6 segment of the mouth. Exclusion Criteria: * a. With clinical stage of I and IVb (according to the 8 th AJCC edition). b. Patients with tumor recurrence or distant metastasis. c. Prior malignancy except adequately treated basal cell or squamous cell skin cancer, in situ cervical cancer. d. History of previous radiotherapy (except for non-melanomatous skin cancers outside intended RT treatment volume). e. Prior chemo…