Comparison of Tumor Target Volume on Four-Dimensional Computed Tomography and 18F-FDG PET/CT in Lung Cancer

Objective: The correlation between 18F-fluorodexyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) and four-dimensional computed tomography (4DCT) based-tumor volumes is unclear. This prospective study was conducted to determine the optimal threshold of PET/CT for gross tumor volume (GTV) delineation using 4DCT as the standard reference for locally advanced lung cancer patients.Material and Methods: Ten patients with histologically proven primary lung cancer who underwent radiotherapy fromJune 2017 to March 2018 in Ramathibodi Hospital were enrolled in the study. The 4DCT simulation and 18F-FDG PET/CT simulation were performed on the same position and same date. Eight standard uptake value (SUV) thresholds of SUV 1.5.0-2.0 and 15.0-35.0% of maximum SUV were selected for contouring in order to be compared with 4DCT based tumor volumes. The comparison methods used were the mean percentage volume change, dice similarity coefficient (DSC), and 3D-centroid shift of the targets between 18F-FDG PET/CT-based gross tumor volume (GTVPET) and internal gross tumor volume (IGTV) from 4DCT.Results: The largest and smallest volume of primary tumors were 422.6 cm3 and 5.9 cm3. GTVPET contoured using SUV 1.5 (GTVPET1.5) approximated closely to IGTV in all the parameters, including volume change, DSC, and 3D-centroid shift. The best median percentage volume change, median DSC, and median centroid shift between IGTV and GTVPET1.5 were 5.55, 0.745 and 0.37, respectively.Conclusion: GTVPET contoured by 18F-FDG PET at SUV1.5 corresponded most closely to the IGTV in all parameters. Further study with a larger sample size and clinical outcome analysis is needed.