Background: Stereotactic body radiation therapy (SBRT) is the primary alternative to surgery for patients with clinical stage I or II non -small cell lung cancer (NSCLC) who have significant comorbidity that precludes safe resection and for those who refuse surgery. Methods: Patients with clinical stage I or II NSCLC treated with SBRT in our institution between January 2015 and December 2019 were retrospectivel...