P18.02.B ANALYSIS OF TUMOR RELAPSE PROBABILITY AND OVERALL SURVIVAL PREDICTION FOLLOWING CONCOMITANT RADIOTHERAPY WITH TEMOZOLOMIDE USING FET PET IN PATIENTS WITH GLIOBLASTOMA

Abstract BACKGROUND Early after surgery and completion of concomitant radiotherapy with temozolomide, the evaluation of tumor relapse probability and overall survival prediction is of considerable interest for the management of patients with glioblastoma. MATERIAL AND METHODS Sixty-three adult glioblastoma patients (mean age 55.4 years, SD ± 14.6) who received dynamic PET imaging using the radiolabeled amino acid O-(2-[18F]fluoroethyl)-L-tyrosine (FET) after surgery or biopsy and completion of concomitant radiotherapy with temozolomide, were retrospectively included in the study. Static FET PET parameters such as maximum and mean tumor-to-brain ratios (TBRmax/TBRmean) and metabolic tumor volumes (MTV) and the dynamic FET PET parameter time-to-peak (TTP) were obtained. The prognostic value of FET PET parameters was evaluated concerning the progression-free and overall survival (PFS, OS). Using receiver-operating-characteristic (ROC) analyses, threshold values for FET PET parameters were acquired. Subsequently, univariate and multivariate survival estimates were performed to assess the prognostic value of these parameters to predict a significantly longer PFS (as a surrogate for tumor relapse probability) and OS. RESULTS ROC analysis revealed that the parameter TBRmax was the most powerful parameter to predict both a significantly longer PFS (17.8 vs. 9.0 months; P=0.003; threshold, 2.85) and OS (33.2 vs. 18.4 months; P=0.002; threshold, 2.75). MTV had a similar prognostic value for both PFS (15.9 vs. 7.2 months; P=0.002; threshold, 34.0 mL) and OS (28.2 vs. 14.4 months; P=0.003; threshold, 32.6 mL). At a lower level of significance, TTP was only prognostic for a significantly longer OS (27.7 vs. 17.5 months; P=0.037; threshold, 25 minutes). TBRmax and MTV remained significant in multivariate survival analysis, indicating independent predictors for both a significantly longer PFS and OS (all P≤0.04). CONCLUSION Our results suggest that FET PET parameters were highly prognostic in patients with newly diagnosed glioblastomas at an early stage of first-line therapy for predicting favourable PFS and OS.