NIMG-84. PREDICTION OF RESPONSE TO LOMUSTINE-BASED CHEMOTHERAPY IN GLIOMA PATIENTS AT RECURRENCE USING MRI AND FET PET

Abstract

Abstract BACKGROUND This study evaluates O-(2-[18F]fluoroethyl)-L-tyrosine (FET) PET and contrast-enhanced MRI for early response assessment in glioma patients at recurrence treated with lomustine-based chemotherapy. METHODS Thirty-six adult patients with WHO CNS Grade 3 or 4 gliomas (glioblastoma, 69%) at recurrence (median number of recurrences, 1; range, 1-3) were retrospectively identified. Besides MRI, serial FET PET scans were performed at baseline and early after chemotherapy initiation (median number of cycles, 2). Mean and maximum tumor-to-brain ratios (TBR), metabolic tumor volumes (MTV), the occurrence of new distant hotspots with a mean TBR > 1.6 at follow-up, and the dynamic parameter time-to-peak were derived from all FET PET scans. Threshold values of PET parameters were defined using receiver operating characteristic analyses to predict progression-free survival (PFS) of ≥ 6 months and overall survival (OS) of ≥ 12 months. MRI response assessment was based on RANO criteria. Using univariate and multivariate survival estimates, the predictive value of FET PET parameters and RANO criteria were subsequently evaluated. RESULTS After treatment initiation, the median follow-up time was 11 months (range, 3-71 months). Relative changes of the mean and maximum TBR, MTV, and RANO criteria predicted a significantly longer PFS (all P< 0.003) and OS (all P< 0.05). At follow-up, the occurrence of new distant hotspots (n≥ 1) predicted a worse outcome, with significantly shorter PFS (P=0.001) and OS (P< 0.001). Changes of the dynamic parameter time-to-peak did not predict a significantly longer PFS or OS (P > 0.05). Multivariate survival analyses revealed that new distant hotspots at follow-up had the highest significance level to predict non-response (P< 0.001; hazard ratio, 8.578), independent of RANO criteria, IDH mutation status, and O6-methylguanine-DNA-methyltransferase promoter methylation. CONCLUSIONS FET PET seems to be a powerful tool for identifying responders to lomustine-based chemotherapy early after treatment initiation.