Assessment of treatment response in patients with glioblastoma multiforme using [18F]fluorethyl-L-tyrosine PET

Objectives The assessment of treatment response in patients with glioblastoma multiforme (GBM) is difficult. We evaluated the prognostic impact of PET using O-(2-[18F]fluoroethyl)-L-tyrosine (18F-FET) during treatment of patients with GBM.

Methods In a prospective study 25 patients with GBM were investigated by MRI and 18F-FET-PET after surgery (MRI-1/FET-1), 7-10 days (MRI-2/FET-2) and 6-8 weeks after completion of radiochemotherapy (MRI-3/FET-3). Volumes of the metabolically active tumor in 18F-FET-PET with a tumor/brain ratio (TBR) >1.6 (Tvol 1.6) and gadolinium contrast-enhancement on MRI (Gd-Volume), and the maximum and mean TBR (TBRmax/TBRmean) were determined. The prognostic impact of these parameters were tested by an approximation procedure with different cut-offs to determine the cut-off value best separating the patients in two prognostic groups. The median follow-up time was 13.8 (3-29) months. The prognostic impact of changes of the different parameters was evaluated using Kaplan-Maier estimates for disease-free survival (DFS) and overall survival (OS).

Results Changes of Tvol 1.6, TBRmax, and TBRmean between FET-1 and FET-2 or FET-3, respectively, were significant predictors of DFS and OS. In contrast, changes of the Gd-Volume between revealed no significant differences of DFS and OS.

Conclusions In comparison to Gd-Volumes on MRI, our data indicate that changes of Tvol 1.6, TBRmax, and TBRmean are better parameters to assess treatment response in GBM and to predict survival time