Inclusion Criteria:  Patients ≥18 years old Newly diagnosed RCC by biopsy (preferred) or radiologic evidence of growth on surveillance over two consecutive assessments (6-12 months) Primary lesion >3 cm, or recurrent lesion following local ablative therapy Medically inoperable or patient who refuses surgery following assessment by experienced urologist, and discussed in a multidisciplinary setting ECOG 0-2 Written informed consent Participants must be able to understand the English-language or with the aid of a translator  Exclusion Criteria:  Primary Lesion >20cm Evidence of distant metastatic disease Previous abdominal RT in vicinity of kidney preventing definitive SBRT History of major radiosensitivity syndrome Second invasive malignancy within the past 3 years (excluding non-melanomatous skin cancer) Currently pregnant or lactating