UNIty-Based MR-Linac Guided Adaptive RadioThErapy for High GraDe Glioma-4

Inclusion Criteria: * Histopathologically confirmed, based on biopsy or surgical resection, glioblastoma or WHO grade 4 astrocytoma (IDH wild type or mutant) * Deemed clinically appropriate for concurrent chemoradiotherapy (with temozolomide) with definitive/radical intent * Biopsy or surgical resection performed ≤ 12 weeks prior to study entry * Expected survival ≥ 12 weeks * ECOG performance status of 0, 1 or 2 * Sufficient estimated glomerular filtration rate (eGFR) of ≥ 30 mL/ min/1.73 m2 to allow administration of gadolinium-based contrast agent; patients with eGFR \< 30 mL/min/1.73 m2 not on dialysis may be allowed on the study after discussion of risks and benefits and approval by study neuroradiologist(s) * Completed written informed consent * Patient must be accessible for treatment and follow-up * Patients with multifocal or multicentric disease will be allowed per the discretion of the radiation oncologist Exclusion Criteria: * Contraindications to MRI examination as per standard MRI screening policy * Contraindication to Gadolinium-based contrast media * Enhancing disease involving any part of the brainstem on post-gadolinium T1-weighted MRI imaging for patients being treated using the short-course 15-fraction regimen * Inability to lie flat in a supine position for at least 30 minutes * Inability to tolerate immobilization in a head thermoplastic mask * Patients \> 140 kg and/or a circumference \> 60 cm (MRI scanner weight and bore size limits) * Prior therapeutic cranial irradiation * Leptomeningeal dissemination of disease * History of other malignancies with the exception of adequately treated non-melanoma skin cancer, or curatively treated other solid tumours with no evidence of disease for ≥ 2 years * Patients with any condition (e.g. psychological, geographical, etc.) that does not permit compliance with the protocol