MRI-Guided Radiation Therapy for Prostate Cancer: The Next Frontier in Ultrahypofractionation

SIMPLE SUMMARY: Prostate cancer treatment with radiation therapy has advanced significantly over the years. Leveraging the proposed low [Formula: see text] / [Formula: see text] ratio of prostate cancer, radiation therapy for the definitive treatment of upfront prostate cancer has moved from conventionally fractioned approaches to ultrahypofractionated fractionation schemes that require increased precision in both treatment planning and treatment delivery. MRI-guided radiation therapy (MRIgRT) enables this precision-based approach by improving visualization of the prostate and the surrounding structures, enabling safer dose escalation with reduced toxicity profiles relative to CT-guided radiation therapy. Real-time gating and on-table adaptive treatment further reduce dose to normal structures. Treatment efficacy and reduced toxicity must be balanced with ongoing challenges pertaining to MRIgRT workflow and training. In this review, we focus on the utility of MRIgRT in the treatment of prostate cancer and highlight ongoing trials using ultrafractionated MRIgRT. ABSTRACT: Technological advances in MRI-guided radiation therapy (MRIgRT) have improved real-time visualization of the prostate and its surrounding structures over CT-guided radiation therapy. Seminal studies have demonstrated safe dose escalation achieved through ultrahypofractionation with MRIgRT due to planning target volume (PTV) margin reduction and treatment gating. On-table adaptation with MRI-based technologies can also incorporate real-time changes in target shape and volume and can reduce high doses of radiation to sensitive surrounding structures that may move into the treatment field. Ongoing clinical trials seek to refine ultrahypofractionated radiotherapy treatments for prostate cancer using MRIgRT. Though these studies have the potential to demonstrate improved biochemical control and reduced side effects, limitations concerning patient treatment times and operational workflows may preclude wide adoption of this technology outside of centers of excellence. In this review, we discuss the advantages and limitations of MRIgRT for prostate cancer, as well as clinical trials testing the efficacy and toxicity of ultrafractionation in patients with localized or post-prostatectomy recurrent prostate cancer.