Abstract
BACKGROUND: The prospective multi-site trial evaluating O-(2-[18F]-fluoroethyl)-L-tyrosine Positron Emission Tomography (FET-PET) in Glioblastoma (FIG) study is currently recruiting. This abstract aims to evaluate the impact of full central Nuclear Medicine physician (NMP) review of prospective FET-PET1 delineation of the biological target volume (BTV) for radiotherapy (RT) planning. MATERIAL AND METHODS: Adult GBM participants across 11 Australian sites undergo up to 3 FET-PET studies post-surgery/pre-chemo-RT [CRT] (FET-PET1), one month post CRT (FET-PET2) and at suspected progression evaluation timepoint (FET-PET3). Group 1 participants enter at timepoint 1 (FET-PET1 with MRI1), with Group 2 at timepoint 2. Adjuvant RT target volumes are derived per standard contrast MRI. These are compared to hybrid post-hoc RT volumes incorporating the FET-PET1 NM-derived BTV utilising MiM version 7.0 to evaluate the impact of FET PET on potential treatment planning. All trial sites and NMP have passed credentialling which included three benchmarking cases involving FET1-BTV delineation. RESULTS: Recruitment commenced in January 2021, with 253 (n=156 Group 1 and n=97 Group 2) participants enrolled to date, n=144 with evaluable FET-PET1 data. Trial credentialling demonstrated variations in FET-PET1-derived BTV in 25/72 (34.7%) -13 minor and 12 major. All n=144 prospective participant FET-PET1 with BTV delineation cases across 11 sites have undergone central NMP review, with 20/144 (13.9%) requiring resubmission. Reasons for resubmission/protocol deviation included incorrect imaging sequence selection within MiM workflow (n=3/20), static GTV overcontouring (n=12/20), dynamic volume of interest change in size/position during workflow (n=1/20) and static FET interpretation issues (n=3/20). Central radiation oncology review of hybrid BTV-derived RT volumes is underway. CONCLUSION: The importance of credentialling and full central review of all prospective FET-PET-derived BTV delineation in FIG trial participants is demonstrated. The FIG study remains the largest prospective multi-site study of its kind addressing the impact of FET-PET on radiation planning, management of pseudoprogression and prognostication.