P03.20.a Defining Measurable Disease as Inclusion Criterion in Glioblastoma Trials - A Retrospective, Comparative Study of Pet Rano 1.0 vs. Rano 2.0 Criteria After Radiotherapy and First Progression

PURPOSE Response assessment in glioblastoma is based on the evaluation of contrast enhancement on MRI using RANO 2.0 criteria. ‘Measurable disease’ serves as an inclusion criterion for clinical trials both at baseline after radiotherapy and at first recurrence. The recently introduced PET RANO 1.0 criteria integrate amino acid PET into standardized response assessment. Our study compares the frequency of ‘measurable disease’ according to PET RANO 1.0 with MRI-based RANO 2.0 criteria at common inclusion timepoints for glioblastoma trials. METHODS This retrospective, single-center study included patients with IDH-wildtype glioblastoma who underwent [18F]FET-PET and MRI at the RANO 2.0 baseline up to 35 days after completion of radiotherapy or at first recurrence (max. time between scans: 28days). Two independent investigators assessed ‘measurable disease’ based on PET RANO 1.0 and RANO 2.0 criteria. Lesion size, uptake intensity (TBRmax, TBRmean), and their correlation with Karnofsky performance status (KPS) were evaluated. RESULTS A total of 109 patients (median age 58 years, IQR 53-68) were included, 43 at baseline and 66 at first recurrence. Using RANO 2.0, measurable disease was identified in 20/43 cases (46.5%) at baseline and in 43/66 (65.2%) at recurrence (median sum of cross-sectional diameters: 20.1mm, 21.3mm). In contrast, with PET RANO 1.0 a significantly higher proportion of patients showed measurable disease with 39/43 cases (90.7%) at baseline and 65/66 (98.5%) at first recurrence (median volume 12.6cm3, 17.5cm3; p<0.001). Baseline TBRmax showed a significant negative correlation with KPS (p<0.002, r<-0.345). CONCLUSION At baseline and first progression, PET RANO 1.0 criteria identify a significantly higher number of patients with measurable disease compared to standard MRI-based RANO 2.0 criteria. These findings suggest that PET-based assessment may provide a more detailed evaluation of disease burden which might broaden eligibility for glioblastoma trials. Prospective validation is warranted to establish the utility for patient stratification in clinical trials.