Localized prostate cancer can be treated in 5 sessions using a precise, targeted form of radiation known as stereotactic body radiation therapy (SBRT), with low toxicity. Despite these advances, overall outcomes for aggressive (high risk) prostate cancer remain poor, with 10-year recurrence-free survival of approximately 65% regardless of treatment modality. Recurrences are typically distant and carry poor prognosis, with 5 year survival of 25%. The investigators propose to utilize the latest advances in cancer imaging (PSMA Positron Emission Tomography (PET)/Magnetic Resonance Imaging (MR)) and radiation delivery (MR-guided radiation therapy with real-time adaptive planning), to deliver a personalized radiation treatment that targets the areas of greatest risk of recurrence in the prostate with improved precision, and as a result improve clinical outcomes for individuals with high risk prostate cancer. PSMA PET/MR is a novel imaging modality, not yet widely available, that augments the tissue detail provided by MR. The combination of PSMA PET with MR results in improved delineation of intraprostatic nodules and higher diagnostic accuracy for detection of metastatic disease compared to conventional imaging. PSMA PET/MR imaging data is readily transferable to a MR-based linear accelerator (MR-LINAC), a novel, innovative platform that allows direct visualization of the tumor during treatment, and permits real-time individualized correction for motion with online adaptive radiation planning.