18F-DCFPyL Imaging as a Method to Assess Treatment Response to Stereotactic Body Radiation Therapy

Background: Identifying medium- and high-risk prostate cancer early may allow for treatments to work. But identification can be hard. Researchers want to see if a radiotracer used during PET scans can help. Objective: To test how an imaging agent called 18F-DCFPyL detects response to standard prostate cancer treatment. Eligibility: People ages 18 and older with newly diagnosed prostate cancer who have no evidence of distant metastatic disease and plan to get stereotactic body radiation therapy (SBRT) with or without androgen deprivation therapy (ADT). Design: Participants will be screened with: Medical history Physical exam Blood tests MRI Participants will have baseline MRI and PET/CT scans. For the MRI, they may get a contrast agent by IV injection. For the PET/CT scan, they will get an IV injection of 18FDCFPyL. About 1 to 2 hours later, they will get the PET/CT scan. During the scans, participants will lie on their back and remain still for 45 minutes to 1 hour. These scans will be repeated at different points during the study. Participants will get SBRT with or without ADT. Participants will complete questionnaires about their quality of life. Participants will be asked about any symptoms they are having. They will also be asked about medications they are using. They may have a physical exam. Participants will give blood and urine samples. They will give a tumor sample from a biopsy they have had in the past. After treatment, participants will have follow-up visits. These will occur 1 month after treatment, then every 3 months for a year, and then every 6 months for 1 more year.

* INCLUSION CRITERIA: * Biopsy proven localized prostate cancer in whom stereotactic body radiation treatment (SBRT) with or without neoadjuvant androgen deprivation therapy (ADT) is planned for definitive management (NIH laboratory of pathology confirmation is not required). * Must have at least 1 MRI detected, biopsy proven localized prostate cancer. * Age \>= 18 years * ECOG performance status \ 2 times the upper limit of normal. * Weighing \> 350 lbs (weight limit for scanner table), or unable to fit in imaging gantry. * Evidence of tumor spread beyond the prostate/seminal vesicles (lymph nodes, metastases). * Contraindications to radiation or SBRT.