Post-treatment Ultrasensitive Positron Emission Tomography in Nasopharyngeal Carcinoma Patients

Inclusion Criteria: * Patients must be informed of the investigational nature of this study and given written informed consent. * Aged between 18-70, male/female. * Staged III or IV (AJCC 8th) NPC patients with histologically confirmed non-keratinizing nasopharyngeal carcinoma (including differentiated type and undifferentiated type, WHO II and III). * Received induction chemotherapy and/or concurrent chemoradiotherapy. ECOG scale 0-1. * Fertile women should practice contraception during the study period. * HGB ≥90g/L ,WBC ≥4\*109/L , PLT ≥100\*109/L, * With normal liver function test (ALT and AST ≤2.5\*ULN, TBil ≤2.0\*ULN) * With normal renal function test (serum creatinine ≤1.5\*ULN) Exclusion Criteria: * Women in pregnancy or lactation * Prior malignancy except adequately treated basal cell, squamous cell skin cancer, or cervical cancer in situ. * Any severe intercurrent disease, which may bring unacceptable risk or affect the compliance of the trial, for example, unstable cardiac disease requiring treatment, renal disease, chronic hepatitis, diabetes with poor control (fasting plasma glucose \>1.5×ULN), and emotional disturbance. * Already involved in other clinical trial. * Mental disorder, civil disability, limited capacity for civil conduct.