• Bogdana Suchorska, Marcus Unterrainer, Annamaria Biczok, Marketa Sosnova, Robert Forbrig, Peter Bartenstein, Jörg-Christian Tonn, Nathalie Lisa Albert, and Friedrich-Wilhelm Kreth.
• Department of Neurosurgery, Ludwig-Maximilians University, University Hospital Munich, Marchioninistr. 15, 81377, Munich, Germany. Bogdana.Suchorska@med.uni-muenchen.de.
• J. Neurooncol. 2018 Sep 1; 139 (3): 721-730.

BackgroundMonitoring treatment response after chemotherapy of gadolinium-(Gd)-negative gliomas is challenging as conventional MRI often indicates no radiological changes. We hypothesize that 18F-FET-PET can be used as a biomarker for response assessment in Gd-negative gliomas undergoing chemotherapy.MethodsSixty-one patients harboring Gd-negative WHO grade II or III glioma receiving alkylating agents (temozolomide or CCNU/procarbacine) were included. All patients underwent MRI and 18F-FET-PET before chemotherapy and 6 months later. We calculated T2-volume, 18F-FET-PET based biological tumour volume (BTV) and maximal tumour-to-brain ratio (TBRmax). Moreover, dynamic PET acquisition was performed using time-activity-curves (TACs) analysis. For MRI-based response assessment, RANO criteria for low-grade glioma were used. For 18F-FET-PET, following classification scheme was tested: responsive disease (RD) when a decrease in either BTV ≥ 25% and/or TBRmax ≥ 10% occurred, an increase in BTV ≥ 25% and/or TBRmax increase > 10% characterized progressive disease (PD), minor changes ± 25% for BTV and ± 10% for TBRmax were regarded as stable disease (SD). Post-chemotherapy survival (PCS) and time-to-treatment failure (TTF) were calculated using the Kaplan-Meier method.Results18F-FET-PET based response has shown patients with RD to have the longest TTF time (78.5 vs 24.6 vs 24.1 months, p = 0.001), while there was no significant difference between patients with a SD and PD. A comparable pattern was observed for PCS (p < 0.001). T2-volume based assessment was not associated with outcome.Conclusion18F-FET-PET is a promising biomarker for early response assessment in Gd-negative gliomas undergoing chemotherapy. It might be helpful for a timely adjustment of potentially ineffective treatment concepts and overcomes limitations of conventional structural imaging.

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