P13.01.A 11C-METHIONIN PET FOR RADIOTHERAPY TREATMENT PLANNING IN PATIENTS WITH RAPID EARLY PROGRESSION AFTER GLIOBLASTOMA SURGERY: PROSPECTIVE PHASE II TRIAL

Abstract

Abstract BACKGROUND Radiotherapy (RT) is a standard treatment for nearly all glioblastoma patients following initial surgery. Few retrospective studies indicate negative prognostic instances of progression during the planning magnetic resonance (MR) (up to 1 week before initiating RT), termed Rapid Early Progression (REP). The optimal RT management for REP patients remains uncertain. The objective of this prospective phase II trial (NCT05608395) is to assess impact of 11C-Methionine PET used for RT planning in REP glioblastoma patients. It is one of the first prospective clinical interventional trials focused on this specific cohort of patients. MATERIAL AND METHODS We enrolled glioblastoma, IDHwt, or Astrocytoma, IDHmt, WHO grade IV patients, who developed REP characterized by 1) increase in postoperative residuum by ≥ 25%, 2) appearance of new contras enhancing lesion, 3) unequivocal progression of the unresected satelite. Patients received treatment based on the Stupp or Perry protocol. Treatment response was evaluated using RANO criteria. RT target volumes were delineated as follows: Gross tumor volume included tumor cavity, enhancing lesion and 11C-MET PET (1.3 tumor-to-background ratio). The clinical target volume was GTV plus a modified 2cm margin reflecting surrounding organs at risk. Volumetric analyses of different radiotherapy target volume were performed using EclipseTM software including patterns of failure. RESULTS During 12/2020 - 12/2023, total of 31 patients were enrolled (16 treated via abbreviated RT course); median age 60 years, ECOG 0-1 in 28 patients, median follow up 20 months. No effect of 11C-MET PET - based radiotherapy treatment planning of GBM patients with REP was observed on PFS (median 3.4 months comparing to 4.9 in historical control cohort) and OS (12.3 months comparing to 15.7 months). Median MET volume was 7.3cm3 (43% of MRI volume), MET avidity was presented in 7 patients et least 1cm beyond MRI volume. Central recurrence was presented in 87% patients. CONCLUSION The optimal treatment of patients with REP is unknown and needs to be studied in more details including dose escalation studies with reduced target margins potentialy directed also by aminoacid PET examination. Adjustment of target radiotherapy volumes using 11C-MET PET did not lead to improved PFS or OS. Supported by NU20-03-00148.