MR-Guided Radiotherapy
Radiotherapy (RT) plays a crucial role in cancer management, serving as a curative or palliative treatment for at least 75% cancer patients. As technology evolves, image-guided intensity-modulated RT has become the gold standard for high-dose clinical RT. One significant advancement in this field is the integration of magnetic resonance imaging (MRI) into the RT workflow, called MRI-guided RT.
Key benefits of MRI-guided RT include superior soft tissue contrast, improved organ motion visualization and providing precise tumor physiologic structure far superior to conventional computed tomography (CT) scans. This enhanced contrast aids in accurate tumor delineation and organ-at-risk identification. Real-time MRI allows clinicians to track organ motion during treatment sessions. This capability is particularly valuable for tumors affected by continuous or sporadic movements, such as those in the breast, lung, gut, kidneys, bladder, liver, and rectum. In addition, MRI-guided RT enables precise imaging of tissue, enhancing treatment planning and delivery accuracy.
Offline and Online MRI-Guided RT
Offline MRI-guided RT is already being used for treatment planning in brain, prostate and head and neck cancers as well as stereotactic body radiotherapy, outside of RT sessions. Online MRI-guided RT via MRI-guided linear accelerator (MRI-Linac) combined system are also being used for planning, adaptation of organ movement (interfraction and intrafraction), and monitoring. Online MRI-guided RT, helps in tumors of breast, lung, gut, kidneys, bladder, liver, and rectum that are affected by continuous or sporadic movements during treatment sessions. This aids in increased safety of organs, and providing for a more effective dose escalation while limiting toxicity. Recent studies have demonstrated successful adaptive RT using MRI-Linac systems, allowing for hypofractionation and ablative doses with minimal toxicity in interfraction organ motion and intrafraction organ motion occurring in the pancreas.
Some key ongoing developments in MRI will further facilitate advances in both offline and online MRI-guided RT. Furthermore, manufacturers are integrating AI algorithms to enhance MRI imaging speed. Cancers that may move on day to day basis include intestines, rectum, prostate, liver and lungs. Whilst treating patients on MR-LINAC, the system acquires an image of the day with the patient on treatment couch. Any shape or position change of the tumour is then re-planned in real time before each day’s radiation treatment delivery.
The current focus of online MRI-guided RT is adaptation to anatomic changes. In the longer term, biomarkers derived from quantitative MRI techniques are expected to enable adaptation to physiologic structure and treatment response. At present, the use of MRI-Linac in routine clinical practice is limited to interfraction adaptation.
In summary, MRI-guided RT represents a paradigm shift in personalized and precision oncology. As technology evolves, cost-effective real time MRI-guided RT will become available for all patients undergoing RT.