Real-Time Intrafraction Motion Management in Magnetic Resonance Imaging-Guided Adaptive Radiotherapy and Its Impact on Treatment Precision

Background and Purpose: Intrafraction motion remains a principal source of geometric uncertainty in external beam radiotherapy. Magnetic resonance imaging-guided adaptive radiotherapy (MRgART) uses continuous soft-tissue visualization throughout beam delivery to directly manage this uncertainty. This review critically evaluated the current state of real-time intrafraction motion management in MRgART, with emphasis on technological mechanisms, site-specific motion characteristics, clinical strategies, and the available evidence base. Materials and Methods: A structured narrative review of peer-reviewed literature, prospective registries, and international consensus documents published through March 2026 was conducted. PubMed/MEDLINE was searched using terms encompassing MR-Linac platforms, intrafraction motion, real-time gating, and adaptive radiotherapy. A total of 47 references meeting pre-specified inclusion criteria were synthesized. Results: Two commercial MR-Linac platforms dominated clinical practice: the 1.5 T system (>150 installed units) and the 0.35 T system (~55–65 operational units following corporate restructuring in 2024). Real-time beam gating reduced mean two-dimensional target displacement from 8.3 ± 4.3 mm (ungated) to 1.6 ± 0.6 mm (gated). A phase III randomized trial demonstrated that magnetic resonance imaging-guided stereotactic body radiotherapy for prostate cancer halved two-year late genitourinary toxicity compared with computed tomography-guided treatment (27% vs 51%; p = 0.004). A multi institutional phase II trial established that ablative pancreatic stereotactic body radiotherapy (50 Gy in 5 fractions) was deliverable with near-zero severe gastrointestinal toxicity and a median overall survival of 22.8 months from diagnosis. Artificial intelligence approaches achieved sub millimeter target localization at inference times of 8–36 milliseconds. Conclusions: Magnetic resonance imaging-guided intrafraction motion management was selectively transformative, enabling treatments previously limited by geometric uncertainty. Expansion of randomized evidence beyond prostate cancer, resolution of workflow efficiency constraints, and clinical deployment of artificial intelligence-assisted real time tracking represented the field’s foremost priorities.