The primary goal of this study is to assess whether using recent advances in technology to treat high intermediate risk and high-risk prostate cancer (HrPCa) can improve clinical outcomes, measured as recurrence-free survival at 2 years after treatment. The advances we propose to use are 1) Prostate-Specific Membrane Antigen (PSMA) Positron Emission Tomography/Magnetic Resonance Imaging (PET/MR), obtained before and after radiation; and 2) the ViewRay MRIdian Linac system, which is a radiation treatment machine that has live MRI imaging during treatment delivery and the ability to deliver a simultaneous integrated boost (SIB) to high-risk nodules seen on MRI.
   
   Stereotactic body radiation therapy (SBRT) targets the entire prostate gland with radiation. Due to advances in treatment planning, high risk nodules within the prostate can be targeted to a higher dose, while treating the surrounding prostate tissue to a lower dose. By selectively targeting only high-risk nodules to a higher radiation dose, instead of treating the entire gland to a higher dose, we hope to maximize tumor control without increasing side effects. Furthermore, we will use the ability of the ViewRay to adapt to changes in your anatomy during 5-treatment SBRT, to provide a more conformal treatment. 
   
   PSMA PET is obtained using Gallium-68 labeled PSMA-HBED-CC (study drug). This is a radioactive agent designed to bind to PSMA, which is found in high concentration on prostate tumor cells. The study drug is considered investigational, which means it has not been approved by the U.S. Food and Drug administration (FDA). However, it has been used in Europe for the last 4-5 years and several thousand patients have been injected safely with this study drug; we have also used this study drug at our institution safely. It is believed that by using PSMA PET with MR, we will be able to see smaller tumors in the prostate gland, lymph nodes and distant sites, than is otherwise possible today.
   
   Subjects will also have the option of providing stool microbiome and blood samples prior to treatment, and at end of treatment and first follow up, which will be part of an exploratory study to look at changes in the immune system and bacterial species during treatment.