Fiducial markers vs. PET/CT for esophageal cancer GTV delineation for radiotherapy treatment planning using a standard SUV threshold and background uptake method.

70 Background: Often in esophageal targets that move with respiration, endoscopically implanted fiducial markers are placed under ultrasound guidance within 1 cm from the superior and inferior tumor border. Our group has previously reported the stability of this method. 3D 18F-FDG PET/CT is obtained for initial staging of esophageal cancer and has altered the tumor volume in many sites. The correlation of these two methods for GTV delineation is currently undefined. Methods: Twenty-one patients with esophageal cancer were selected for this retrospective, IRB-approved analysis. Each patient underwent fiducial placement (by one of six endoscopists) at the inferior and superior borders of the tumor and received PET/CT prior to Radiotherapy (RTx). PET/CT images were imported into an image analysis software system for measurements. The distance between fiducial markers and MTV defined by 2.5 SUV contour (method 1) and MTV using a threshold above mean liver uptake (method 2) was calculated. The fiducials were l...