Clinical Applications of MR-Linac in Oligometastatic Disease

Oligometastatic disease (OMD) is widely becoming recognized as a distinct state of limited disease burden where metastatic-directed therapies remain at the forefront as a strategy to improve patient outcomes. The role of stereotactic body radiation therapy (SBRT) for patients with OMD is of increasing interest to achieve long-term disease control and potentially improve survival. An increasing number of prospective studies utilizing SBRT to comprehensively treat all metastatic sites have suggested an association of ablative radiation with improved clinical outcomes. However, SBRT is not without risk, and while good results can be obtained with minimization of high dose radiation to surrounding normal tissues, conventional SBRT using CT onboard imaging has limits in defining the soft-tissue boundary between target and normal tissues. Further complicating the accurate delivery of SBRT are dynamic variations in the anatomy from physiologic processes that are not accounted for with conventional approaches. Tumor size may also evolve over the course of treatment, impacting dose to tumor and surrounding organs at risk. Technological advances and the development of MRI-guided radiation provide an exciting capability to better visualize the lesion and surrounding anatomy and adapt treatment in real time. This book chapter delves into the application of MRI-guided SBRT (MRgSBRT) for patients with OMD, including practical considerations and current ongoing trials. We also explore potential future directions and highlight opportunities for other clinical advances in patients with OMD using MRgSBRT as these technologies continue to evolve.