P12.17.B VARIATIONS IN RADIOLOGICAL DEFINITION AND CLINICAL DECISION-MAKING OF TUMOR PROGRESSION IN PATIENTS WITH GLIOMA AFTER CHEMORADIATION: RESULTS FROM THE PERISCOPE PROJECT

Abstract BACKGROUND Determining radiological progression in glioma patients after chemoradiotherapy remains challenging, particularly due to the difficulty of distinguishing true progression from treatment-related changes such as pseudoprogression. Clinical decision-making often relies on subjective interpretation of MRI scans, which may delay the recognition of true tumor growth. Volumetric criteria such as RANO, which define progression as a ≥40% increase in enhancing tumor volume, offer a more objective alternative. In this study, we compare the timing of progression as determined by volumetric RANO criteria to the timing of progression as established by clinical evaluation, aiming to assess whether volumetric assessment identifies progression in glioma patients after chemoradiotherapy. MATERIAL AND METHODS In this multicenter observational study involving 15 Dutch hospitals, we prospectively collected clinical data, treatment decisions, and MRI scans from a total of 322 patients with glioma post-chemoradiation. All MRI scans were centrally stored at Health RI, and tumor volumes were automatically segmented using the in-house developed segmentation pipeline, Glioseg. Tumor volume increases according to the RANO criteria (≥40% volume increase) were systematically compared with the clinically determined time of progression. Currently, preliminary results are reported from 7 centers (n=199). RESULTS In this preliminary cohort, 86 patients were excluded due to having only one MRI session. 57 patients (50%) showed discrepancies between clinical progression and RANO-based volumetric progression. Progression per RANO occurred earlier than the clinical diagnosis in 27 patients (24%), while 30 patients (26%) did not meet RANO criteria despite being clinically labeled as progressive. CONCLUSION Preliminary results demonstrate that RANO volumetric assessment can identify tumor progression earlier than clinical evaluation in a substantial proportion of glioma patients post-chemoradiotherapy. This highlights the added diagnostic value of standardized volumetric criteria in reducing subjectivity and enabling more timely treatment decisions. Ongoing analysis of the full cohort will further elucidate the clinical impact of these discrepancies.