Reduced Dose Radiotherapy vs Standard Dose Radiotherapy for Early Stage Nasopharyngeal Carcinoma

All the patients receive intensity-modulated radiotherapy. If patients receive CR and EBV DNA undetectable when completing 50.88Gy radiation, they will continue to receive radiotherapy until 61.48Gy, then the patients would be randomised assigned ( 1:1 ) to reduced dose group (observation) or standard dose group (continue to receive radiotherapy until 69.96Gy). Patients with stage IA will receive radiotherapy alone, and patients with stage IB will receive concurrent chemoradiotherapy. For patients with stage IB, those assigned to reduced dose group will receive a total of 2 cycles cisplatin concurrent chemotherapy, with 100mg/m2 per cycle; those assigned to standard dose group will receive a total of 3 cycles cisplatin concurrent chemotherapy, with 100mg/m2 per cycle. This study investigates whether administering reduced dose is non-inferior to standard dose radiotherapy in terms of 3-year locoregional relapse-free survival (LRRFS) rate for stage I nasopharyngeal carcinoma patients who are sensitive to radiotherapy. The primary endpoint is 3-year locoregional relapse-free survival.