NIMG-48. MEASURABLE DISEASE AS BASELINE CRITERION FOR RESPONSE ASSESSMENT IN GLIOBLASTOMA TRIALS – A COMPARATIVE STUDY OF MRI-BASED (RANO 2.0) VERSUS PET-BASED (PET RANO 1.0) ASSESSMENT

Abstract Response assessment in glioblastoma relies on measuring contrast enhancement on MRI according to RANO 2.0 criteria, and ‘measurable disease’ often serves as inclusion criterion for clinical trials. Recently, criteria based on amino acid PET have been proposed for response assessment in clinical trials (PET RANO 1.0). Here, we compare ‘measurable disease’ as defined by PET RANO 1.0 with the standard MRI-based RANO 2.0 criteria in glioblastoma patients. In this retrospective single-center study, we identified patients with newly diagnosed IDH-wildtype glioblastoma who underwent [18F]FET PET and MRI after resection or biopsy and before chemoradiotherapy. Two independent investigators analyzed ‘measurable disease’ according to PET RANO 1.0 versus MRI-based RANO 2.0 criteria. Additionally, lesion size and uptake intensity, including maximal and mean target-to-background ratio, were assessed. We evaluated 136 patients with 76 cases after biopsy and 60 after microsurgical resection. Using RANO 2.0, 35/76 patients (46.1%) had measurable disease in the biopsy group, and 25/60 (41.6%) in the resected group (median sum of maximum cross-sectional diameters: 39.7mm and 28.0mm, respectively). Utilizing PET RANO 1.0, a significantly higher proportion (overall 123/136, 90.4%; 66/76 (86.8%) after biopsy; 57/60 (95.0%) after resection) had measurable disease (p<0.001). None of the 10 patients in the biopsy group nor of the 3 patients in the resected group without measurable disease on PET had measurable disease on MRI. Contrariwise, 32/41 patients (73.2%) in the biopsy group and 30/35 (85.7%) in the resected group without measurable disease on MRI exhibited measurable disease on PET. PET RANO 1.0 identifies a significantly higher number of patients with ‘measurable disease’ compared to conventional MRI-based criteria in the perioperative period of glioblastoma. PET-based assessment may thus serve as a novel baseline parameter for evaluating treatment response in glioblastoma trials, that may allow the enrollment of larger patient populations. Further validation in prospective trials is warranted.