Spatial discrepancies between FET PET and conventional MRI in patients with newly diagnosed glioblastoma

P14.32 SPATIAL DISCREPANCIES BETWEEN FET PET AND CONVENTIONAL MRI IN PATIENTS WITH NEWLY DIAGNOSED GLIOBLASTOMAP. Lohmann1, P. Stavrinou2, K. Lipke1, E. K. Bauer3, G. Ceccon3, J. Werner3, G. R. Fink1,3, N. J. Shah1,4, K. Langen1,5, N. Galldiks1,3; 1Institute of Neuroscience and Medicine (INM-3,-4), Research Center Juelich, Juelich, Germany, 2Department of Neurosurgery, Faculty of Medicine and University Hospital Cologne, University of Cologne, Cologne, Germany, 3Department of Neurology, Faculty of Medicine and University Hospital Cologne, University of Cologne, Cologne, Germany, 4Department of Neurology, University Hospital RWTH Aachen, Aachen, Germany, 5Department of Nuclear Medicine, University Hospital RWTH Aachen, Aachen, Germany.BACKGROUND: In patients with glioblastoma, the tissue showing contrast enhancement (CE) in MRI is usually the target for resection or radiotherapy. However, the solid tumor mass typically extends beyond the area of CE. Amino acid PET can detect tumor parts that show no CE. We systematically investigated tumor volumes delineated by amino acid PET and MRI in newly diagnosed, untreated glioblastoma patients. MATERIAL AND METHODS: Preoperatively, 50 patients with subse-quently neuropathologically confirmed glioblastoma underwent O-(2-[18F]-fluoroethyl)-L-tyrosine (FET) PET, fluid-attenuated inversion recovery (FLAIR), and CE MRI. Areas of CE were manually delineated. FET PET tumor volumes were segmented using a tumor-to-brain ratio ≥ 1.6. The per-centage of overlapping volumes (OV), as well as Dice and Jaccard spatial similarity coefficients (DSC; JSC), were calculated. FLAIR images were evalu-ated visually. RESULTS: In 86% of patients (n = 43), the FET PET tumor volume was significantly larger than the volume of CE (21.5 ± 14.3 mL vs. 9.4 ± 11.3 mL; P < 0.001). Forty patients (80%) showed both an increased uptake of FET and CE. In these 40 patients, the spatial similarity between FET and CE was low (mean DSC, 0.39 ± 0.21; mean JSC, 0.26 ± 0.16). Ten patients (20%) showed no CE, and one of these patients showed no FET uptake. In 10% of patients (n = 5), increased FET uptake was present out-side of areas of FLAIR hyperintensity. CONCLUSION: Our results show that the metabolically active tumor volume delineated by FET PET is signifi-cantly larger than tumor volume delineated by CE. The data strongly suggest that the information derived from FET PET should be integrated into the management of newly diagnosed glioblastoma patients. FUNDING: This work was supported by the Wilhelm-Sander Stiftung, German