Early Treatment Response Assessment Using 18F-FET PET Compared with Contrast-Enhanced MRI in Glioma Patients After Adjuvant Temozolomide Chemotherapy

Abstract

Background: The goal of this study was to compare the value of contrast-enhanced MRI and O-(2-[18F]fluoroethyl)-L-tyrosine (18F-FET) PET for response assessment in gliomapatients after adjuvant temozolomide chemotherapy (TMZ). Methods: After biopsy or resection and completion of radiotherapywith concomitant TMZ, 41 newly diagnosed andhistomolecularlycharacterizedgliomapatients (glioblastoma,90%; age range, 20-79 y) were subsequently treated with adjuvant TMZ.MR and 18F-FETPET imagingwereperformedatbaseline andafter the second cycle of adjuvant TMZ.We obtained 18F-FETmetabolic tumor volumes (MTVs) as well as mean and maximum tumor-to-brain ratios (TBRmean and TBRmax, respectively). Threshold values of 18F-FET PET parameters to predict outcome were established by receiver-operating- characteristic analyses using a median progression-free survival (PFS) of ≥ 9 mo and overall survival (OS) of ≥ 15 mo as reference. MRI response assessment was based on the Response Assessment in Neuro-Oncology (RANO)working group criteria. The predictive value of changes of 18F-FET PET andMRI parameters on survival was evaluated subsequently using univariate andmultivariate survival estimates. Results: After 2 cycles of adjuvant TMZ chemotherapy, a treatmentinduced reduction of MTV and TBRmax predicted a significantly longer PFS and OS (both P ≤ 0.03; univariate survival analyses) whereas RANOcriteriawere not significant (P.0.05).Multivariate survival analysis revealed that TBRmax changes predicted a prolonged PFS (P = 0.012) and changes of MTV a prolonged OS (P = 0.005) independent of O6-methylguanine-DNA-methyltransferase promoter methylation and other strong prognostic factors. Conclusion: Changes of 18F-FET PET parameters appear to be helpful for identifying responders to adjuvant TMZ early after treatment initiation.