Early treatment response assessment using ¹⁸F-FET PET compared to contrast-enhanced MRI in glioma patients following adjuvant temozolomide chemotherapy

Abstract

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 glioma patients after adjuvant temozolomide chemotherapy (TMZ). <b>Methods:</b> After biopsy or resection and completion of radiotherapy with concomitant TMZ, 41 newly diagnosed and histomolecularly characterized glioma patients (glioblastoma, 90%; age range, 20-79 y) were subsequently treated with adjuvant TMZ. MR and ¹⁸F-FET PET imaging were performed at baseline and after the second cycle of adjuvant TMZ. We obtained ¹⁸F-FET metabolic tumor volumes (MTVs) as well as mean and maximum tumor-to-brain ratios (TBR_mean and TBR_max, 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 and MRI parameters on survival was evaluated subsequently using univariate and multivariate survival estimates. <b>Results:</b> After 2 cycles of adjuvant TMZ chemotherapy, a treatment-induced reduction of MTV and TBR_max predicted a significantly longer PFS and OS (both <i>P</i> ≤ 0.03; univariate survival analyses) whereas RANO criteria were not significant (<i>P</i> > 0.05). Multivariate survival analysis revealed that TBR_max changes predicted a prolonged PFS (<i>P</i> = 0.012) and changes of MTV a prolonged OS (<i>P</i> = 0.005) independent of O⁶-methylguanine-DNA-methyltransferase promoter methylation and other strong prognostic factors. <b>Conclusion:</b> Changes of ¹⁸F-FET PET parameters appear to be helpful for identifying responders to adjuvant TMZ early after treatment initiation.