Quantitative PET/CT Analysis for Tumor Response

PET/CT scans were performed as previously described (14 (link)). A GE ADW4.6 workstation (GE Healthcare, Waukesha, WI, USA) was used to display images, which were interpreted by two experienced nuclear medicine physicians. For the semi-quantitative analysis, the threshold of the volumes of interest (VOIs) was set at 0.5 by PETVCAR (GE Healthcare). The maximum SUV (SUVmax) was defined as the value of the highest pixel and average SUV (SUVmean) as the mean SUV related to the tumor burden. To determine the peak SUV corrected for lean body mass (SULpeak), the reviewer placed a sphere or cube as the VOI around the hottest lesions (up to five lesions, no more than two per organ). Within this VOI, the software searched for the 1.0-cm³ sphere that encompassed the voxels with the highest average SUL. For background activity, a 3-cm-diameter spherical VOI was delineated in the right lobe of the liver or in the descending thoracic aorta for patients with liver involvement. Response of SULpeak (%) was defined as (sum of baseline SULpeak—sum of follow-up SULpeak)/(sum of baseline SULpeak) × 100. Target lesions on follow-up scans were not necessarily the same as target lesions at baseline (13 (link)).