ACPSEM guideline: commissioning and quality assurance of Magnetic Resonance Imaging Linear Accelerators.

MRI-guided radiotherapy introduces unique quality assurance (QA) requirements due to magnetic field effects on dose delivery, imaging-dependent workflows, adaptive planning and system specific considerations. Consistent, vendor agnostic guidance is needed to support safe commissioning, clinical implementation, and ongoing performance monitoring across MRI-Linac platforms. This guideline defines minimum recommended MRI-Linac commissioning and QA practices to support consistent and safe clinical operation across services. It was developed by the MRI-Linac QA sub-group of the Magnetic Resonance Imaging Linac Working Group using an evidence-informed, consensus-based approach. Key international standards, task group reports, vendor documentation, and peer-reviewed literature relevant to the MRI-Linac were reviewed. Candidate QA tests were mapped to clinical risks and system functions, then organized into commissioning and routine QA domains with suggested cadence. Recommendations were refined through iterative working group review, with emphasis on implementation and auditability. The resulting commissioning recommendations are grouped into domains addressing key performance and safety areas for MRI-Linacs. Additionally, a minimum test set is proposed with suggested frequencies and tolerances where supported by evidence. Adoption of this guideline supports harmonized MRI-Linac QA practice, improved reproducibility across sites, and enhanced patient safety. The framework is designed to be implementable across platforms and evolve as MRI-guided radiotherapy workflows, vendor capabilities, and the evidence matures.