• To determine biochemical disease free survival (using both ASTRO and Phoenix definitions) and measure the rates of acute and late genitourinary and gastrointestinal toxicities following CyberKnife radiosurgery. [ Time Frame: 5 years ] [ Designated as safety issue: No ]
  
• To compare the CyberKnife biochemical disease free survival rates (bDFS) to published HDR monotherapy bDFS rates reported in the literature. [ Time Frame: 5 years ] [ Designated as safety issue: No ]
  

• To measure the rates of local failure, distant failure, clinical-disease free survival, disease-specific survival, overall survival and quality of life. [ Time Frame: 5 years ] [ Designated as safety issue: No ]
  

Radiation: CyberKnife Stereotactic Radiosurgery
38 Gy delivered in 4 fractions of 9.5 Gy per fraction

In this study, CyberKnife radiosurgery will be used to produce dose distributions comparable to those created by HDR brachytherapy treatment, without the use of invasive catheters. The radiosurgery volumes will closely be made to resemble HDR brachytherapy therapeutic volumes with similar dose limitation objectives to adjacent normal tissues.

The CyberKnife Robotic Radiosurgery System is a unique radiosurgical system capable of treating tumors anywhere in the body noninvasively and with sub-millimeter accuracy. The CyberKnife System delivers radiation using a precise targeting methodology allowing a focal treatment margin around the target, thus limiting the volume of adjacent tissue receiving high doses radiation. This in turn allows the delivery of high doses of radiation to the prostate over a short series of treatments.

Inclusion Criteria:

• Patient must be at least 18 years of age
• Histologically proven prostate adenocarcinoma
• Biopsy within 1 year of date of registration
• Clinical Stage T1b-T2b, N0, M0
• Patients belonging to one of the following risk categories:
• Low Risk: CS T1b-T2a, Gleason Score 2-6, PSA < or = 10 ng/ml
• Intermediate Risk: CS T2b, Gleason Score 2-6, PSA < or = 10 ng/ml or CS T1b-T2b, Gleason Score 2-6, PSA < or = 20 ng/ml or CS T1b-T2b, Gleason Score 7 and PSA < or = 10 ng/ml
• Prostate Volume < or = 100 cc
• ECOG performance status 0-1

Exclusion Criteria:

• Clinical Stage T2c or greater
• Prior prostatectomy or cryotherapy of the prostate
• Prior radiotherapy fo the prostate or lower pelvis
• Implanted hardware or other material that would prohibit appropriate treatment planning or delivery
• History of an invasive malignancy other than basal or squamous skin cancers in the last 5 years
• Hormone ablation for two months prior to enrollment or during treatment