Magnetic Resonance Imaging-Guided Radiation Therapy: Advances and Opportunities for Thoracic Malignancies

Magnetic resonance imaging-guided radiation therapy (MRgRT) is a recent technological innovation integrating a linear accelerator within a magnetic resonance imaging (MRI) machine. There are several potential advantages of MRgRT that can increase the therapeutic ratio of thoracic radiation, especially for central tumors adjacent to multiple OARs, high-risk patients undergoing re-irradiation, or patients with pulmonary comorbidities. These advantages address several limitations of CT-based stereotactic body radiation therapy (SBRT) including online adaptation for inter-fraction anatomical changes, intra-fraction motion management, and improved soft tissue visualization. By reducing dose to organs at risk, MRgRT may allow for safe delivery of SBRT to historically high-risk, centrally located lung tumors. In addition, there are many promising areas of ongoing investigation including further optimization of thoracic MRI sequences and incorporation of functional MRI to guide dose escalation. In this chapter, we discuss the potential benefit, clinical workflow, current limitations, and future directions of MRgRT for thoracic tumors.