Reduced vs Conventional Dosage Intensity-modulated Radiotherapy for Chemotherapy-sensitive Stage II-III Nasopharyngeal Carcinoma

Inclusion Criteria: 1. Histologically confirmed non-keratinizing nasopharyngeal carcinoma (differentiated or undifferentiated type, i.e., WHO type II or type III). 2. Staged as T1-3N1-2M0, T2-3N0M0 (stage II-III) at diagnosis (according to the 8th AJCC edition). 3. Aged between 18-70 years. 4. Karnofsky scale (KPS)≥70. 5. Normal bone marrow function. 6. Evaluated as PR or CR after 3 cycles of GP induction chemotherapy. 7. EBV DNA copy number decreased to 0 copies/mL after 3 cycles of GP induction chemotherapy. 8. Normal liver and kidney function: 1. total bilirubin, AST and ALT levels of no more than 2.5 times the upper normal limit; 2. creatinine clearance rate of at least 60 mL/min or creatinine of no more than 1.5 times the upper normal limit. 9. Given written informed consent. Exclusion Criteria: 1. Histologically confirmed keratinized squamous cell carcinoma (WHO type I) or basal squamous cell carcinoma. 2. Recurrent or metastatic nasopharyngeal carcinoma. 3. Evaluated as SD or PD after 3 cycles of GP induction chemotherapy. 4. EBV DNA copy number of more than 0 copies/mL after 3 cycles of GP induction chemotherapy. 5. Pregnancy or lactation (Pregnancy tests should be considered for women in childbearing age, and effective contraception should be emphasized during treatment.) 6. Other invasive malignant diseases in the past, other than cured basal cell skin carcinoma, squamous cell carcinoma, cervical carcinoma in situ. 7. Primary and regional lesions have been treated with chemotherapy or surgery (except diagnostic purpose) 8. Any severe disease, which may cause unacceptable risk factors or affect compliance with the trial, for example, unstable heart disease requiring treatment, kidney disease, chronic hepatitis, poorly controlled diabetes (fasting blood glucose \> 1.5×ULN), and mental illness.