The purpose of this study is to determine the effects of CyberKnife radiosurgery in patients with early stage prostate cancer.

The investigators hypothesize that hypofractionated stereotactic radiotherapy via the CyberKnife® can deliver tumor ablating doses of radiation to prostate tumors safely and effectively while sparing the adjacent tissues (rectum, bladder, ureters, urethra, penile bulb, and bowel) from receiving damaging doses of radiation.

The CyberKnife system is a type of radiation machine that uses a special system to precisely focus large doses of x-rays (radiation) on the tumor. The device is designed to concentrate large doses of radiation onto the tumor so that injury from radiation to the nearby normal tissue will be minimal.

Inclusion Criteria:

• Male Age ≥ 21
• Histologically proven prostate adenocarcinoma
• Clinical stage T1b-T2b, N0-Nx, M0-Mx (AJCC 6th Edition)
• PSA ≤ 20 ng/ml
• Prostate volume ≤ 100 cc

Patients belonging in one of the following risk groups:

• Low:

  • CS T1b-T2a and Gleason 2-6 and PSA ≤ 10

• Intermediate:

  • CS T2b and Gleason 2-6 and PSA ≤ 10, OR
  • CS T1b-T2b, and Gleason 2-6 and PSA ≤ 20 ng/ml OR Gleason 7 and PSA ≤ 10 ng/ml

Exclusion Criteria:

• Any histology other than adenocarcinoma
• Age < 21
• KPS <= 40 <70
• ECOG Performance Status ≥ 2
• Patient weight >350 lbs. (table limitation)
• Prior XRT to prostate or lower pelvis
• Prior surgery or cryotherapy to prostate
• Implanted hardware or other material that would prohibit appropriate treatment planning or treatment delivery, in the investigator's opinion
• Chemotherapy for a malignancy in the last 5 years
• History of an invasive malignancy (other than this prostate cancer, or basal or squamous skin cancers) in the last 5 years
• Hormone ablation for 2 months prior to enrollment, or during treatment