Current treatment options for primary renal cancer include surgery or ablative techniques—all are invasive or minimally invasive options. The completely noninvasive treatment option of stereotactic radiation therapy (SABR), which has become standard of care in many cancer sites, has not been explored for primary renal cancer. With multiple technological advances, it is now feasible to safely treat a moving intra-abdominal tumor such as that in a kidney. This proposed clinical trial evaluates the efficacy of SABR in treating patients with early renal cancers. Growing renal masses will first be biopsied to confirm the diagnosis of renal cancer. Patients will then undergo treatment with SABR of 3-5 fractions completing within three weeks. Treatment response will be evaluated using sequential MRI scans and a second tumor biopsy one year after treatment. Monitoring of treatment toxicity and kidney function will also be performed.