MRI-Guided Radiation Therapy for Prostate Cancer: Less Is More When Technology and Evidence Intersect

The delivery of radiation therapy for prostate cancer has advanced considerably over the past decade, marked primarily by improvements in image guidance and hypofractionation. While these advances have added to patient convenience and lowered toxicity profiles from radiotherapy, there remain additional opportunities to further improve the therapeutic ratio. MRI-guided radiotherapy (MRIgRT) is an emerging treatment planning and delivery paradigm that promises further improvements in the therapeutic ratio through better visualization of prostate and surrounding normal tissue anatomy, leading to improved target delineation and OAR avoidance. Real-time treatment gating further enables PTV margin reduction, which has been rigorously evaluated in a randomized fashion to result in more favorable toxicity profiles compared to legacy CT-based treatment planning and delivery approaches. Additional advantages of MRIgRT, including expanding indications for hypofractionation across the prostate cancer continuum, incorporating functional imaging in treatment planning, deploying on-table adaptive treatment planning and delivery, and real-time dose accumulation calculations, are aggressively under study. This chapter outlines the evidence base supporting the use of MRIgRT for the treatment of prostate cancer while exploring potential pitfalls of MRIgRT in the space. We also highlight ongoing clinical trials seeking to further innovate MRIgRT for prostate cancer by leveraging both commercial treatment platforms currently available.