S361
Clinical - CNS
ESTRO 2026
Harmonisation of Radiotherapy Quality Assurance. https://rtqaharmonization.org/resources (Accessed Oct 30, 2025). 4. Niyazi M, Andratschke N, Bendszus M, et al. ESTRO-EANO guideline on target delineation and radiotherapy details for glioblastoma. Radiother Oncol. 2023;184:109663. doi:1 0.1016/j.radonc.2023.109663. Keywords: Radiotherapy, Glioblastoma, RTQA Reirradiation outcomes in patients with recurrent glioblastoma treated with either hypofractionated or conventionally fractionated radiation therapy Max G. Felland 1 , Lydia Golden 2 , Nicole Sanda 2 , Caryn Martin 2 , Elizabeth Bowser 2 , Clara Ferreira 2 , Rebecca Todd 2 , Susan Arnold 3,4 , Jessica Lawrence 2,5 , William Breen 6 , Mark Folkertsma 7 , Liam Chen 4,8 , Garret Fitzpatrick 4,8 , Grace Tobin 4,9 , Kaili Ranta 2,4 , Kathryn Dusenbery 2,4 , Lawrence R Kleinberg 10 , Andrew Venteicher 4,11 , Matthew Hunt 4,11 , Elizabeth C. Neil 4,9 , Richard Evans 12 , Stephanie Terezakis 2,4 , Joseph Moore 2,4 , Lindsey Sloan 2,4 1 Medical School, University of Minnesota, Minneapolis, USA. 2 Department of Radiation Oncology, University of Minnesota Medical Center, Minneapolis, USA. Digital Poster 1267 3 Department of Veterinary Clinical Sciences, University of Minnesota, St. Paul, USA. 4 Masonic Cancer Center, University of Minnesota Medical School, Minneapolis, USA. 5 Department of Surgical and Radiological Sciences, University of California Davis, Davis, USA. 6 Department of Radiation Oncology, Mayo Clinic, Rochester, USA. 7 Department of Radiology, University of Minnesota Medical Center, Minneapolis, USA. 8 Department of Pathology, University of Minnesota Medical Center, Minneapolis, USA. 9 Department of Neurology, University of Minnesota Medical Center, Minneapolis, USA. 10 Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University School of Medicine, Baltimore, USA. 11 Department of Neurosurgery, University of Minnesota Medical Center, Minneapolis, USA. 12 Clinical and Translational Science Institute, University of Minnesota, Minneapolis, USA Purpose/Objective: Reirradiation remains a central treatment strategy for patients with recurrent glioblastoma (rGBM). Although outcomes of various hypofractionated radiotherapy (HFRT) regimens have been evaluated for this patient population1, few studies have directly compared conventionally fractionated RT (CFRT) and HFRT within the same institution. Here, we analyze overall survival (OS) and patterns of failure (POF) in rGBM patients treated with HFRT or CFRT.
Conclusion: No association was observed between RTQA
compliance and clinical outcomes, possibly because most radiotherapy plans were pC and deviations were minimal, leading to a ceiling effect. Accordingly, when radiotherapy is planned and delivered to contemporary standards, modest contouring variations don't translate into differences in survival or toxicity; this lack of correlation supports the safety of adopting narrower target margins recommended by recent ESTRO-EANO guidelines [4]. In contrast, brain- PTV mean dose emerged as an indicator for outcomes and toxicity. These findings support a selective, risk- adapted QA strategy focusing on clinically meaningful dosimetric metrics (e.g., mean doses, homogeneity and conformity indices), to guide and monitor narrower margins when biologically and technically justified. References: 1. Jomy J, Sharma R, Lu R, et al. Clinical impact of radiotherapy quality assurance results in contemporary cancer trials: a systematic review and meta- analysis. Radiother Oncol. 2025;207:110875. doi:10.10 16/j.radonc.2025.110875. 2. Roth P, Gorlia T, Reijneveld JC, et al. Marizomib for patients with newly diagnosed glioblastoma: A randomized phase 3 trial. Neuro Oncol. 2024;26(9):1670-1682. doi:10.1093/neuonc/noae053. 3. Global
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