Comparison of intravenous contrast-enhanced CT and ~(18)F-FDG PET/CT in delineation of tumor gross target volume in the patients with primary esophageal cancer

Objective To compare the difference of gross target volume(GTV) of primary tumor delineated by different observers in 18F-FDG PET/CT and intravenous contrast-enhanced CT images and to discus the feasibility of 18F-FDG PET/CT in the target contour of the esophageal cancer. Methods Image data of five esophageal cancer patients whom had 18F-FDG PET/CT simulation before radiotherapy were selected. Five radiation doctors were required to outline the primary tumor GTV on intravenous contrast-enhanced CT images and named as GTV-CT. Then the observers were asked to delineate the GTV by the threshold of 40 ﹪ SUVmax and physiological high uptake region were eliminate by visual. The GTV from 18F-FDG PET/CT were name as GTV-PET40vis. GTVs from different observer and different image set were analyzed. Results Means of GTV from different image set were as follow :GTV-CT(28.5 ± 11.8)cm3、GTV-PET 40 vis(15.3 ± 5.7)cm3. The means and variations of GTV-CT were significantly greater than those of GTV-PET 40 vis.Analysis of the target show that GTV-CT were larger than GTV-PET 40 vis in both axial and craniocaudal direction. Conclusions GTV acquired and adjusted by visually from 18F-FDG PET/CT by using 40 ﹪ SUVmax as the threshold had small volume and less variability than that of intravenous contrast- enhanced CT. We recommend this method to delineate the GTV of esophageal primary tumor in 18F-FDG PET/CT images.