The phenomenon of pseudoprogression (PsP) on standard imaging can make response assessment difficult in patients with glioblastoma who have undergone standard chemoradiation treatment (CRT). PsP mimics tumor progression on standard imaging, yet is thought to represent a positive biological response to treatment. Recent efforts to define rCBV thresholds to distinguish tumor from treatment effect has enabled the creation of fractional tumor burden (FTB) maps. FTB maps quantify the percent of tumor within an enhancing lesion. This study shows that, within 4-months post-CRT, FTB is a better indicator of PFS and OS than median rCBV or methylation status alone.