This is a dose escalation study using the CyberKnife radiotherapy device for small surgical or medically untreatable renal tumors. Patients with renal tumors 5cms or less in diameter will be accrued onto this study. The ability of CyberKnife to ablate these renal tumors and maintain renal function with dose escalation will be assessed.

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:

• Tumor size 5 cm or less
• Radiographic evidence of malignancy or Histologically verified primary renal malignancy.
• If the kidney biopsy is inconclusive but the radiologist determines that the tumor based on the CT/MRI is highly suspicious for cancer, you may participate
• Patients with highly suspicious lesions on CT or MRI
• One -three gold fiducials placed in or around tumor
• Contradiction or patient refusal to partial or complete nephrectomy
• Age 18 or greater
• KPS score 70 or greater

Exclusion Criteria:

• Irreversible coagulopathies that preclude fiducial placement