NIMG-41. MULTI-SITE, PROSPECTIVE TRIAL EVALUATING FET-PET IN GLIOBLASTOMA (FIG) STUDY (TROG 18.06): PRELIMINARY RESULTS OF CENTRAL NUCLEAR MEDICINE REVIEW OF FET-PET BIOLOGIC TARGET VOLUME DELINEATION FOR RADIATION PLANNING

Abstract BACKGROUND To provide an update from the multi-site trial evaluating O-(2-[18F]-fluoroethyl)-L-tyrosine Positron Emission Tomography (FET-PET) in Glioblastoma (FIG) study and 2) assess the impact of central Nuclear Medicine physician (NMP) review of prospective FET-PET1 delineation of the biological target volume (BTV) for radiotherapy (RT) planning. Material and methods Up to 210 adult GBM participants across 11 Australian sites will undergo FET-PET post-surgery/pre-chemo-RT [CRT] (FET-PET1), one month post CRT (FET-PET2) and at suspected progression (FET-PET3). Group 1 participants enter at timepoint 1 (FET-PET1 with MRI1), with Group 2 entering at timepoint 2. Adjuvant RT target volumes are derived per standard contrast MRI with hybrid post-hoc RT volumes then incorporating the FET-PET1 NM-derived BTV utilising MiM version 7.0. All trial sites and NMP have passed credentialling which included three benchmarking cases involving BTV delineation. RESULTS Trial recruitment commenced in January 2021, with 189 (n=126 Group 1 and n=63 Group 2) participants enrolled to date, with a target of 140 Group 1 participants. During trial credentialling, results demonstrated variations in FET-PET1-derived BTV in 25/72 (34.7%) - 13 minor and 12 major.Currently, 42 of 112 participant FET-PET1 with BTV delineation cases across 10 sites have undergone central review, with 7/42 (16.7%) requiring resubmission. Reasons for resubmission/protocol deviation included incorrect imaging sequence selection within the MiM workflow (n=3), Static GTV overcontouring (n=3) and dynamic volume of interest change in size/position during MiM workflow use (n=1). CONCLUSION The FIG trial will complete recruitment in 2024 with analyses planned at one year post CRT completion. Despite improvements in resubmission rates compared to the credentialling phase, central review of prospective FET-PET1-derived BTV delineation remains important in ensuring protocol adherence. The FIG study is the largest prospective multi-site study of its kind addressing FET-PET’s impact on adjuvant radiation planning and its role in management of pseudoprogression and prognostication.