IRB-approved retrospective analysis of older adults with GBM diagnosed from 2019-2022. Records were reviewed to describe clinical variables, radiation course, development of PsP by RANO criteria, and interventions to manage symptomatic pseudoprogression. Pearson’s chi-squared test was used to determine an association between course of treatment, development of PsP, receipt of temozolomide (TMZ), and clinical interventions.

50 patients were identified (29 M), median age =74 (range 69-95), median KPS 80 (range 60-100), median overall survival (OS) was 12 months. 23 patients were MGMT methylated, 22 unmethylated, and 5 indeterminate. MGMT methylation status was not predictive of PsP. 28/50 had gross total resection. 32/50 received HfRT and 21 of these 32 also received TMZ, vs. 16/18 in the standard RT group. 56.25% of pts receiving HfRT developed pseudoprogression compared to 44.44% in the standard RT group (p=0.42). Among pts receiving HfRT, addition of TMZ was associated with PsP (p=0.10). Pts who developed PsP were more likely to require clinical interventions if they received HfRT compared to standard RT (p=0.11).

HfRT did not clearly increase risk of pseudoprogression, but our findings suggest that addition of TMZ may increase risk of pseudoprogression in older patients. Greater statistical power or a prospective cohort study would allow evaluation of whether certain chemoradiation regimens increase the likelihood of pseudoprogression development.