ESTRO 2025 - Abstract Book

S675

Clinical - CNS

ESTRO 2025

1507

Digital Poster Clinical outcomes and QoL in glioblastoma patients treated with MR-guided adaptive radiotherapy using a 1.5T MR-Linac in an Australian setting Kurl Jamora 1 , Morikatsu Wada 1 , Richard Khor 1 , Hui Gan 2 , Augusto Gonzalvo 3 , Lawrence Sher 2 , Eddie Lau 4 , Mark Tacey 1 , Georgia Barjaktarovic 5 , Sandra Fisher 1 , Felicity Height 1 , Andrew M Scott 6 , Sweet Ping Ng 1 1 Department of Radiation Oncology, Austin Health, Melbourne, Australia. 2 Department of Medical Oncology, Austin Health, Melbourne, Australia. 3 Department of Neurosurgery, Austin Health, Melbourne, Australia. 4 Department of Radiology, Austin Health, Melbourne, Australia. 5 Department of Radiation Oncology, Townsville University Hospital, Townsville, Australia. 6 Department of Molecular Imaging and Therapy, Austin Health, Melbourne, Australia Purpose/Objective: The magnetic resonance linear accelerator (MRL) enables daily adaptation of radiation therapy plans. This study presents our institutional experience with the clinical outcomes and quality of life (QoL) of glioblastoma patients treated using a 1.5 Tesla (T) MR-Linac (MRL). Material/Methods: We identified glioblastoma patients enrolled in a prospective registry (FIRM study) who were treated with MRL between August 2021 and May 2024. Acute toxicity was assessed until 19 weeks post-radiotherapy initiation. QoL was evaluated at baseline and at regular follow-ups using the EORTC QLQ-C30 and QLQ-BN20 questionnaires. Cumulative overall survival was estimated using Kaplan-Meier analysis. Results: A total of 28 patients were included, with a median follow-up of 11.6 months (range 0.5–30.6 months). The mean age at registration was 63 years; 15 were male, and 27 had an ECOG performance status of 0-1. Eleven patients underwent gross total resection, 9 had subtotal resection, and 8 had biopsy only. All were IDH-wild type; 10 were MGMT promoter-methylated, 16 were non-methylated, and 2 had unknown status. Concurrent temozolomide was administered to 25 patients. This was the first radiation course for 25 patients, while 3 received re-irradiation at the same primary site. Sixteen patients (57.1%) were treated with 60 Gy in 30 fractions, 11 (39.3%) with 40 Gy in 15 fractions, and one (3.6%) with 35 Gy in 10 fractions. The mean interval from CT/MRI simulation to radiotherapy start was 12.6 days. All patients completed prescribed fractions on the MRL. Initially, in-room time averaged 40 minutes; this has since reduced to 20 minutes. Twelve patients (42.9%) required Adapt-To-Shape or re-planning within the first week due to tumor progression, indicated by increased T2/FLAIR signal beyond the initial clinical target volume on daily MRL imaging. Acute Grade 2 fatigue occurred in 6 patients (21%), and no Grade 3-4 toxicities were reported. QoL assessments showed a decline in QLQ-C30 global health status score at 3 months (mean difference [MD] -15.08 [95% CI: -27.98 to -2.18]) and 12 months (MD -12.04 [95% CI: -33.31 to 9.23]). Future uncertainty (QLQ-BN20) improved at 6 months (MD -12.78 [95% CI: -22.47 to -3.09]), while communication deficit worsened at 3 months (MD +17.99 [95% CI: 2.44 to 33.54]). The 1-year cumulative overall survival rate was 77.2% (95% CI: 67.3% to 84.5%). Conclusion: Treatment of glioblastoma with MR-guided adaptive radiotherapy is feasible, with manageable acute toxicities and adaptive capabilities to address tumor changes.

Keywords: MRL, glioblastoma, MRgRT