Measurable disease as baseline criterion for response assessment in glioblastoma: A comparison of PET -based (PET RANO 1.0) and MRI-based (RANO) assessments

Background: Recently, criteria based on amino acid positron emission tomography (PET) have been proposed for response assessment in diffuse gliomas (PET RANO 1.0). In this study, we compare the prevalence of measurable disease according to PET RANO 1.0 with magnetic resonance imaging (MRI)-based Response Assessment in Neuro-Oncology (RANO) criteria in glioblastoma.

Methods: We retrospectively identified patients with newly diagnosed IDH-wild-type glioblastoma who underwent [18F] Fluoroethyltyrosine (FET) PET and MRI after resection or biopsy and before radio-/radiochemotherapy. Two independent investigators analyzed measurable disease according to PET RANO 1.0 or MRI-RANO criteria. Additionally, lesion size, congruency patterns, and uptake intensity on [18F]FET PET images were assessed.

Results: We evaluated 125 patients including 49 cases after primary resection and 76 cases after biopsy. Using PET criteria, 113 out of 125 patients (90.4%) had measurable disease, with a median PET-positive volume of 15.34 cm3 (8.83-38.03). With MRI, a significantly lower proportion of patients had measurable disease (57/125, 45.6%; P < .001) with a median sum of maximum cross-sectional diameters of 35.65 mm (26.18-45.98). None of the 12 patients without measurable disease on PET had measurable disease on MRI. Contrariwise, 56/68 patients (82.4%) without measurable disease on MRI exhibited measurable disease on PET. Clinical performance status correlated significantly with PET-positive volume and MRI-based sum of diameters (P < .0059, P < .0087, respectively).

Conclusions: [18F]FET PET identifies a higher number of patients with measurable disease compared to conventional MRI in newly diagnosed glioblastoma. PET-based assessment may serve as a novel baseline parameter for evaluating residual tumor burden and improving patient stratification in glioblastoma studies. Further validation in prospective trials is warranted.