Comparative Analysis of Outcome, Recurrence Patterns and Dosimetry in Glioblastoma Patients Treated According to RTOG versus EORTC Contouring Guidelines

Background Optimal radiotherapy target volume delineation for glioblastoma (GBM) remains debated, with distinct guidelines from the RTOG and the EORTC. Direct comparisons of clinical outcomes based on these guidelines are lacking. This study compared overall survival (OS), progression-free survival (PFS), functional status, and dosimetry in GBM patients treated per RTOG or EORTC protocols at a single institution. Methods We retrospectively analyzed 149 patients with isocitrate dehydrogenase (IDH) wildtype, CNS WHO grade 4 GBM treated with chemoradiotherapy (60 Gy) per RTOG (n=106) or EORTC (n=43) guidelines between 2016–2023. OS, PFS, KPS changes, and radiation exposure to organs at risk (OARs) were compared. Results No significant difference was found between groups for OS (median 17.0 months, p=0.6) or PFS (median 7.1 months, p=0.4). O⁶-methylguanine-DNA methyltransferase (MGMT) promoter methylation was prognostic for OS (Hazard Ratio [HR] 0.45, p<0.001) and PFS (HR 0.41, p<0.001). A KPS score <70 before or after radiotherapy, or at first follow-up, predicted worse OS (HR 2.8–3.4, all p<0.001), but not PFS. The RTOG group had significantly lower KPS at first follow-up (p=0.031). RTOG target volumes were significantly larger (p<0.001) and associated with higher radiation doses to brainstem, chiasm, optic nerves, hippocampi, pituitary, and greater tissue volume receiving at least 1 Gy (V1Gy) (all p≤0.007). Conclusions While RTOG and EORTC guidelines yielded comparable survival outcomes, the RTOG protocol was associated with larger irradiated volumes, higher OAR exposure, and greater decline in early post-treatment performance status. These findings support the clinical relevance of volume-sparing strategies in GBM radiotherapy.