Hippocampus Avoidance During Intensity Modulated Radiotherapy for T4 Nasopharyngeal Carcinoma Patients

Inclusion Criteria: 1. Histologically or cytologic confirmed nasopharyngeal carcinoma 2. ECOG performance scale 0-2 3. Tumor stage is T4N0-3M0-1 according to 8th American Joint Commission on Cancer edition 4. Adequate hepatic, renal and hematologic functions (hemoglobin ≥ 90g/L, platelets ≥ 100×10\^9/L, neutrophils ≥ 1.5×10\^9/L, serum transaminase \< 2.5×the upper limit of normal(ULN), (If liver metastases, serum transaminase\< 5×the ULN), creatinine clearance rate \> 60ml/min. 5. Informed consent signed. Exclusion Criteria: 1. History of malignant tumors. 2. Any severe complications contraindicated chemotherapy or radiotherapy. 3. Medical history of central nervous system, cognitive or psychological diseases; 4. Pregnant or nursing women. 5. Patients with mental disease cannot complete the questionaire. 6. MRI contraindication -