  A significant challenge in Glioblastoma (GBM) management is identifying
pseudo-progression (PsP), a benign radiation-induced effect, from tumor
recurrence, on routine imaging following conventional treatment. Previous
studies have linked tumor lobar presence and laterality to GBM outcomes,
suggesting that disease etiology and progression in GBM may be impacted by
tumor location. Hence, in this feasibility study, we seek to investigate the
following question: Can tumor location on treatment-na\"ive MRI provide early
cues regarding likelihood of a patient developing pseudo-progression versus
tumor recurrence? In this study, 74 pre-treatment Glioblastoma MRI scans with
PsP (33) and tumor recurrence (41) were analyzed. First, enhancing lesion on
Gd-T1w MRI and peri-lesional hyperintensities on T2w/FLAIR were segmented by
experts and then registered to a brain atlas. Using patients from the two
phenotypes, we construct two atlases by quantifying frequency of occurrence of
enhancing lesion and peri-lesion hyperintensities, by averaging voxel
intensities across the population. Analysis of differential involvement was
then performed to compute voxel-wise significant differences (p-value<0.05)
across the atlases. Statistically significant clusters were finally mapped to a
structural atlas to provide anatomic localization of their location. Our
results demonstrate that patients with tumor recurrence showed prominence of
their initial tumor in the parietal lobe, while patients with PsP showed a
multi-focal distribution of the initial tumor in the frontal and temporal
lobes, insula, and putamen. These preliminary results suggest that
lateralization of pre-treatment lesions towards certain anatomical areas of the
brain may allow to provide early cues regarding assessing likelihood of
occurrence of pseudo-progression from tumor recurrence on MRI scans.
