UNITy-BasED MR-Linac Adaptive Simultaneous Integrated Hypofractionated Boost Trial for High Grade Glioma in the Elderly

Inclusion Criteria: * Patient age ≥ 65 years * Histopathologically confirmed, based on biopsy or surgical resection, glioblastoma or WHO grade 4 astrocytoma, IDH-mutant * Biopsy or surgical resection performed ≤ 6 weeks prior to study entry * Deemed suitable by the treating physicians for 15 daily fractions of radiation, delivered daily over 3 weeks, with concurrent temozolomide chemotherapy * Expected survival ≥ 12 weeks * ECOG performance status of 0, 1 or 2 * Able (sufficiently fluent in English) and willing to complete QOL questionnaires; however, inability to complete the questionnaires will not make the patient ineligible for the study * 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 Exclusion Criteria: * Contraindications to MRI as per standard MRI screening policy * Contraindication to Gadolinium-based contrast media * Inability to lie flat in a supine position for at least 90 minutes * Inability to tolerate immobilization in a head thermoplastic mask * Patients \> 140 kg and/or a circumference \> 60 cm * Prior dose-limiting cranial irradiation * T1w post-gadolinium enhancing disease involving the brainstem * Leptomeningeal dissemination of disease * Patients with any condition (e.g. psychological, geographical, etc.) that does not permit compliance with the protocol