Focal Therapy With Stereotactic Body Radiation Therapy (SBRT) for Patients With a Single Prostate Tumor

Background: The current standard treatment of prostate cancer is either surgery or radiation. Typically, this includes either the removal or radiation of the whole prostate gland. Many people now seek out focal therapy options to decrease the side effects of treatment. Until now, several forms of physical destruction with heat (thermal ablation), cold (cryotherapy), sound waves (HIFU), laser (FLA), and electrical energy (IRE). A new type of radiation (SBRT) may be an effective way to cure men of early-stage prostate cancer with fewer side effects than standard treatments. Objective: To see how people with untreated localized prostate cancer will respond to focal therapy with SBRT. Eligibility: People aged 18 years and older with untreated localized prostate cancer (prostate cancer which has not spread outside of the prostate gland). Design: * Participants will undergo screening including blood tests, an MRI, a PSMA PET/CT (18F-DCFPyL), and a biopsy. * Small, non-radioactive, gold seeds about the size of a grain of rice will be placed in and/or around the tumor to help target the radiation treatment. * Radiation (SBRT) will occur in 2 separate sessions about 1 week apart. No sedation is used, these sessions are painless. Each session will take about 1-2 hours. Participants can go home afterwards. * Follow-up will continue for 2 years with repeat scans (MRI and PSMA PET/CT) and blood (PSA) tests. * After two years, a biopsy will be done to understand the impact of this new treatment on prostate cancer.