Int J Radiat Oncol Biol Phys. 2018 Nov 15; 102(4): 1024–1028.
Purpose: Response criteria of glioblastoma after chemoradiation do not account for metabolic changes that occur after treatment. The purpose of this study is to evaluate the utility of positron emission tomography (PET) imaging with C11 methionine (MET) (MET-PET) for detecting changes that occur after chemoradiation therapy and the value of molecular biomarkers for predicting the magnitude of metabolic response. Methods and materials: Patients with newly diagnosed glioblastoma undergoing standard chemoradiation treatment were enrolled in this prospective imaging study, with MET-PET scan performed within 3 days after surgical resection and again at 4 weeks after completion of chemoradiation. Near contemporaneous contrast-enhanced magnetic resonance imaging was performed within 2 weeks of each MET-PET scan. MET-PET imaging was analyzed for maximum standardized uptake value (SUV), SUVmean, and SUVvolume on a multimodality workstation. Results: A total of 18 patients underwent baseline postoperative MET-PET imaging, 14 of whom underwent postchemoradiation MET-PET imaging. Among those who showed residual MET-avid disease on immediate postoperative MET-PET scans and underwent postchemoradiation MET-PET imaging (n = 10), mean ΔSUVmax was -40% (range -100% to 0%), mean ΔSUVmean was -35% (range -100% to 0%), and mean ΔSUV volume was -64% (range -100% to 0%). The Δtumor/brain reference was -40% (range -100% to 0%) using SUVmax and -35% (range -100% to 0%) using SUVmean. In contrast, none of the T2-weighted images on contrast-enhanced magnetic resonance imaging showed a >25% reduction in abnormal T2/fluid-attenuated inversion recovery signal on visual assessment. ΔSUVmax, ΔSUVmean, and ΔSUVvolume correlated with O6-methylguanine-DNA methyltransferase (MGMT) promoter methylation status (P = .01), but not with epidermal growth factor receptor or c-MET amplification status. All patients were IDH-1 wildtype. Conclusions: MET-PET scanning shows a significant decrease in metabolic signal at 1 month after chemoradiation compared with the immediate postoperative period, even when T2/fluid-attenuated inversion recovery changed little. MGMT promoter methylation status further predicts differential metabolic responses. MET-PET may be a useful tool for delineation of radiation targets and assessment of response.