Inclusion Criteria:

• * Pathological (histologically) proven diagnosis of prostatic adenocarcinoma within 365 days (1 year) prior to study registration.
• * History and physical exam with digital rectal exam of the prostate to establish clinical staging
• * Clinical stage T1-T2c (AJCC 7th edition) within 90 days of registration.
• * Prostate specific antigen (PSA) \< 20 ng/mL within 90 days prior to registration.
• * Gleason Score \< 7.
• * Eastern Cooperative Oncology Group(ECOG) Performance status 0-1.
• * Clinically negative lymph nodes evaluated by imaging (pelvic +/- abdominal CT or MRI scan).
• * Patients with lymph nodes equivocal or questionable by imaging are eligible without biopsy if the nodes are ≤ 1.5 cm in diameter; any node larger than this on imaging will require negative biopsy for eligibility, unless the node is know to be enlarged from prior scans and considered stable, per discretion of the treating physician.
• * Patients must be 18 years of age or older.
• * Patient must be able to provide study-specific informed consent prior to study entry.
• * Willingness and ability to complete the Expanded Prostate Cancer Index Composite (EPIC) Questionnaire.
• * No evidence of bone metastases (M0) on bone scan within 60 days prior to registration.
• * Bone scan is not required for patients enrolled with a single intermediate risk factor only, but this scan may be obtained at the discretion of the treating physician. Patients with 2 or 3 risk factors will require a negative bone scan for eligibility.
• * Equivocal bone scan findings are allowed if plain film x-rays are negative for metastasis.
• * Patient is able to start proton therapy or neo-adjuvant hormonal therapy, when recommended, within 12 weeks of registration.
• * No prior radiotherapy to the pelvic area.
• * No prior prostate cancer therapy such as: prostatectomy, cryotherapy, chemotherapy or hyperthermia.
• * Platelets ≥ 100,000 cells/mm3, Absolute neutrophil count (ANC) ≥ 1,800 cells/mm3, Hemoglobin ≥ 8.0 g/dl (Note: The use of transfusion or other intervention to achieve Hgb ≥ 8.0 g/dl is acceptable.)
• * Obs.: Patients with high risk factors, such as T3, Gleason 8-10 or PSA \> 20ng/mL who are not considered candidates for pelvic lymph node radiation treatment are still considered eligible for this study.

Exclusion Criteria:

• * • Prior radiotherapy to the pelvic area.
• * Prior prostate cancer therapy such as: prostatectomy, cryotherapy, or hyperthermia.
• * Prior systemic therapy (chemotherapy) for prostate cancer.
• * Evidence of distant metastases.
• * Regional lymph node involvement.
• * Previous or concurrent cytotoxic chemotherapy for prostate cancer.
• * Acquired Immune Deficiency Syndrome (AIDS) based upon current Centers for Disease Control (CDC) definition. Note however, that HIV testing is not required for entry into this protocol. The need to exclude patients with AIDS from this protocol is necessary because the treatments involved in this protocol may be significantly immunosuppressive. Protocol-specific requirements may also exclude immune-compromised patients.