The optimal threshold of 18F-FLT PET and 18F-FDG PET to estimate the length of gross tumor volume in patients with squamous cell carcinoma of the thoracic esophagus verified by pathological examination

e15665 Background: To determine the optimal method of using 3-deoxy-3-18F-fluorothymidine (FLT) positron emission tomography (PET) to estimate gross tumor length in esophageal carcinoma, and compared with that of 18F- fluorodeoxyglucose(FDG) PET. Methods: Twenty patients with esophageal squamous cell carcinoma treated with radical surgery were enrolled and detected by FLT PET, eighteen of them underwent FDG PET scan. Gross tumor volumes (GTVs) were delineated using seven different methods with FLT PET: visual interpretation, standardized uptake value (SUV) 1.3, SUV 1.4, SUV 1.5, and 20% of maximum standard uptake value (SUVmax), 25% SUVmax,30% SUVmax, on FLT PET imaging, and three different methods with FDG PET: visual interpretation, SUV 2.5, and 40%SUVmax on FDG PET imaging. The length of tumors on FLT PET scan were measured and recorded as LFLTvis, LFLT1.3, LFLT1.4, LFLT1.5, LFLT20%, LFLT25%, and LFLT30%, and FDG PET scan were measured and recorded as LFDGvis, LFDG2.5, and LFDG40%, respectively, and co...