Inclusion Criteria:

          1. Histologically proven prostate adenocarcinoma.

               -  Gleason score 2-7 (reviewed by reference lab at UM).

               -  Biopsy within one year of date of enrollment.

          2. Clinical stage ≤ T2 based on DRE and/or ≤ T3a based on MRI (if done); N0-Nx; M0-Mx
             (AJCC 7th Edition)

               -  T-stage and N-stage determined by physical exam and available imaging studies
                  (CT, and/or MRI of the pelvis; see section 4.5). For MRI, questionable
                  extracapsular extension is permitted. To distinguish blood from tumor the ideal
                  study would be to acquire T2, T1 noncontrast and T1 dynamic contrast enhanced
                  sequence, although this is not required. A small amount of extracapsular
                  extension is permitted, as long as it can be included in the clinical target
                  volume (CTV) and the constraints are met.

               -  M-stage determined by physical exam, CT or MRI. Bone scan not required unless
                  clinical findings suggest possible osseous metastases.

          3. Prostate-Specific Antigen (PSA) < 20 ng/ml, obtained no greater than 3 months prior to
             enrollment.

          4. Patients belonging in one of the following risk groups:

               -  Low:

                    -  Clinical stage* T1-T2; Gleason ≤ 6, PSA ≤ 10 & <50% biopsy cores positive.

               -  Intermediate:

                    -  Clinical stage T2b-T2c; Gleason ≤ 6, PSA ≤ 10 & <50% biopsy cores positive.

                    -  Clinical stage T1-T2; Gleason ≤ 6, PSA ≤ 10 & ≥50% biopsy cores positive.

                    -  Clinical stage T1-T2; Gleason = 7, PSA ≤ 10 & <50% biopsy cores positive or
                       T1-T2; Gleason ≤ 6 & PSA >10 and < 20 & < 50% biopsy cores positive.

                    -  MRI stage T3a with evidence of extraprostatic extension is allowed.

                    -  Clinical stage is based on digital rectal exam (DRE). Seminal vesicle
                       invasion on MRI is not eligible. T1a should be permitted if subsequent
                       peripheral zone biopsies show tumor.

          5. Prostate volume: ≤ 80 cc.

               -  Determined using: volume = π/6 x length x height x width.

               -  Measured from CT or MRI ≤90 days prior to enrollment.

          6. Zubrod performance status 0-1.

          7. No prior total prostatectomy or cryotherapy of the prostate.

               -  Prior suprapubic prostatectomy, transurethral resection and laser ablation are
                  permitted.

          8. No prior radiotherapy to the prostate or lower pelvis.

          9. No implanted hardware or other material that would prohibit appropriate treatment
             planning or treatment delivery, in the investigator's opinion.

         10. No chemotherapy for a malignancy in the last 5 years.

         11. No history of an invasive malignancy (other than this prostate cancer, or
             nonmetastatic basal or squamous skin cancers) in the last 5 years.

         12. 4-6 months of androgen deprivation therapy (ADT) are allowed for intermediate risk
             patients. This must be declared prior to randomization. This may not have been started
             more than 2 months prior to randomization.

         13. Patient must be able to have gold fiducial markers placed in the prostate (if on
             anticoagulants, must be cleared by a primary care physician or cardiologist), or if
             patient already has fiducial marker placed, they must be in accordance with the
             protocol specifications (Section 4.2.2). NOTE: If a method of intrafraction prostate
             tracking is available which does not require fiducial markers, this will be adequate
             for this trial (i.e. 4D transperitoneal ultrasound, onboard MRI guidance).

         14. Ability to understand and the willingness to sign a written informed consent document.

         15. Willingness to fill out quality of life/psychosocial forms.

         16. Age >= 35 and =< 85 years.

         17. IPSS (AUA) score ≤12

        Exclusion Criteria:

          1. Does not have a diagnosis of prostate adenocarcinoma.

          2. Patient has clinical T3a or any evidence of T3b disease.

          3. Patient has stage N1 or M1 disease.

          4. Patients has a PSA of greater than 20 ng/ml, obtained no greater than 3 months prior
             to randomization.

          5. Patient does not meet any of the risk groups outlined in section 3.1.4.

          6. Prostate volume greater than 80 cc.

          7. Zubrod performance status 2 or greater.

          8. Prior total prostatectomy.

          9. Prior radiation therapy to the prostate or lower pelvis.

         10. Implanted hardware which limits treatment planning or delivery (determined by the
             investigator).

         11. Chemotherapy within the past 5 years.

         12. Diagnosis of an invasive malignancy within 5 years (other than current prostate cancer
             or non-metastatic basal or squamous skin cancers or non-metastatic curatively treated
             papillary thyroid carcinoma).

         13. The use of more than 2 months of androgen deprivation therapy (ADT) prior to
             randomization, or plans for ADT to be continued for greater than 6 months.

         14. Inability to have gold fiducial markers placed in the prostate, or fiducial markers
             already placed that are not in accordance with the protocol (Section 4.2.2). NOTE: If
             a method of intrafraction prostate tracking is available which does not require
             fiducial markers, this will be adequate for this trial (i.e. 4D transperitoneal
             ultrasound, onboard MRI guidance).

         15. Unwilling or inability to give informed consent.

         16. Not willing to fill out quality of life/psychosocial questionnaires.

         17. IPSS score > to 12.

         18. Age < 35 and > 85 years.