Inclusion Criteria:

• Diagnosis of adenocarcinoma of the prostate.
• Localized prostate cancer, as confirmed by staging with PSA, biopsy, Gleason score, DRE, and clinical stage.
• Low-risk, intermediate-risk, or high-risk disease, based on NCCN Prostate Cancer Risk Group Guidelines and Joint AUA/ASTRO/SUO Guidelines.
• If patient has high-risk disease, nuclear medicine bone imaging must be performed to document the absence of overt metastatic disease in bones.
• Candidate for definitive prostate radiotherapy (either IMRT or proton).
• If patient is to be treated with IMRT, all treatment must be planned with IMRT; if patient is to be treated with protons, all treatment must be planned with protons (including pelvic nodes if treated).
• No previous prostate cancer treatment, with the exception of short-term (≤ 6 months) ADT according to NCCN guidelines.
• Age 30-80 years old at the time of consent.
• Life expectancy estimate (LEE) of ≥10 years.
• ECOG/Zubrod Performance Status 0-2.
• Non-English speaking patients may be enrolled.

Exclusion Criteria:

• Findings of metastatic disease (nodal or distant, N1 or M1).
• Very low-risk or very high-risk prostate cancer based on NCCN Prostate Cancer Risk Group Guidelines and Joint AUA/ASTRO/SUO Guidelines.
• Prior prostate surgical procedure, including transurethral resection of the prostate (TURP) and GreenLight Laser Therapy.
• History of invasive rectal malignancy or other pelvic malignancy, regardless of disease-free interval.
• Active inflammatory bowel disease (i.e., patients requiring medical interventions or who are symptomatic) or documented history of inflammatory bowel disease requiring intervention.
• Prior pelvic RT for any reason.
• Documented lack of psychological ability or general health permitting completion of the study requirements and required follow-up.
• Documented diminished capacity to understand the risks and benefits of participation in research and to autonomously provide informed consent.