Delineation of Reducing Clinical Target Volume for Early-stage Nasopharyngeal Carcinoma Patients

Inclusion Criteria: 1. histologically confirmed NPC (WHO II-III) 2. stage I-IIb according to the 6th AJCC/UICC 3. no previous treatment for NPC 4. between 18 and 70 years old 5. KPS ≥ 80 scores 6. adequate organ function (white blood cell ≥ 4.0×109/L; absolute neutrophil count ≥ 1.5×109/L; hemoglobin ≥ 100g/L; platelet count ≥ 100×109/L; total bilirubin, aspartate aminotransferase and alanine aminotransferase ≤ 1.5X upper limit normal; and creatinine clearance rate ≥ 30 mL/min) Exclusion Criteria: 1. fine-needle aspiration biopsy, incisional or excisional biopsy of neck lymph node, or neck dissection prior IMRT 2. disease progression during IMRT 3. presence of distant metastasis 4. pregnancy or lactation 5. previous malignancy or other concomitant malignant disease