Hypofractionated MR-guided radiotherapy for glioblastoma: Institutional online adaptive workflow using MR-linac

To describe the feasibility and clinical implementation of hypofractionated Magnetic Resonance-guided Radiotherapy (MRgRT) using an MR-Linac system in a newly diagnosed glioblastoma (GBM) patient, with a focus on adaptive planning, tumor volume dynamics, and workflow efficiency. A 74-year-old male with GBM underwent gross total resection followed by MRgRT. Treatment planning used high-resolution MR and CT fusion. Online adaptation was performed using "adapt-to-shape" and "adapt-to-position" protocols. Target volumes were delineated using co-registered postoperative imaging. Volumetric changes and treatment workflow metrics were recorded. The patient completed 15 fractions of hypofractionated RT (40.05 Gy in 2.67 Gy/fraction) without delays or complications. Adaptive MRgRT enabled precise target coverage and accounted for significant anatomical changes. The gross tumor volume (GTV) increased from 32.25 cc postoperatively to 69.55 cc at fraction 6 (+112.32%), with corresponding increases in CTV and PTV. T2/FLAIR abnormalities also expanded by up to +83.67%. Median treatment time per fraction was 27.1 minutes (range: 19.3 to 68.5), with imaging, contouring, and planning contributing most to extended durations during adaptive fractions. Treatment was well tolerated, with only grade 2 asthenia reported. This case illustrates the feasibility and potential clinical value of MRgRT for GBM. Real-time adaptive planning enables clinicians to respond dynamically to tumor and cavity changes, potentially improving target coverage and reducing toxicity. Further studies are warranted to assess its impact on outcomes and to explore the integration of functional imaging into adaptive workflows.