B: 3D radiotherapy can only prescribe 54 Gy in tumor and lymph node (dark green line) while 60 Gy isodose line does not cover the whole lymph node (yellow line). 5 1.3 VALUES OF F-FDG PET / CT IN STAGING, RADIOTHERAPY PLANNING, AND PROGNOSIS OF UPPER THIRD ESOPHAGEAL CANCER 1.3.1 Metabolic parameters of 18F-FDG PET / CT The standard uptake value (SUV) is the most commonly used parameter and is calculated by the formula: SUV (g ml) = Tumor activity concentration (kBq ml) Injected dose (MBq) x Lean body mass The basic metabolic parameters of 18F-FDG PET include: - SUVmax is the maximum SUV value measured in the tumor - SUVmean is calculated as the mean SUV of the whole tumor - SUVpeak is the highest SUVmean value of a spherical region of interest with a volume of 1 ml in the tumor - MTV is the metabolic volume of the lesion, determined by the SUV threshold.