MR-Linac adaptive GBM RT shows FLAIR (FHR) omission doesn’t shift failures or survival

UNITED (NCT04726397) is a prospective Phase 2 MR-guided, weekly online-adaptive chemoradiotherapy approach for newly diagnosed glioblastoma using a small GTV-to-CTV margin (CTV=GTV+5mm); clinicians variably extended the CTV to include peritumoral FLAIR-hyperintense region (FHR) beyond 5mm (NF n=24; FHR not included despite being present [FNI] n=27; FHR included [FI] n=47). At progression (69 recurrences/98 patients), failures were predominantly central (65–72%) with no difference by contouring strategy (p=0.717), and recurrent GTV (rGTV) coverage within the CTV was high and similar across groups (median 97.9%; p=0.105) with comparable estimated rGTV dose. Median PFS was 10.5 vs 8.0 vs 8.6 months (NF/FNI/FI; p=0.279) and median OS was 16.9 vs 15.8 vs 13.4 months (p=0.389), with no significant differences on multivariable analysis—outcomes landing broadly in the expected newly diagnosed GBM chemoRT range (classic Stupp regimen median OS ~14.6 months).