Inclusion Criteria:  Have an ECOG Performance Status of ≤ 2. Refer to Appendix A. Have histologically proven diagnosis of non-small cell lung cancer (NSCLC). Stage cT1-3N0M0 with tumor size < 6 cm. Prior systemic therapy allowed but no systemic therapy 4-6 weeks prior to stereotactic body radiation therapy SBRT (see exclusion criteria), during SBRT, or 2 weeks after SBRT. Tumors located within 2 cm in all directions of any mediastinal critical structures, including the bronchial tree, esophagus, heart, brachial plexus, major vessels, spinal cord, phrenic nerve, and recurrent laryngeal nerve, as defined by the International Association for the Study of Lung Cancer (IASLC) (27). Participant is considered to be either medically or surgically inoperable by physicians, or participant declines surgery. Participants of child-bearing potential must agree to use adequate contraceptive methods (e.g., hormonal or barrier method of birth control; abstinence) prior to study entry.  Should a woman become pregnant or suspect she is pregnant while she or her partner is participating in this study, she should inform her treating physician immediately.  Participant must understand the investigational nature of this study and sign an Independent Ethics Committee/Institutional Review Board approved written informed consent form prior to receiving any study related procedure  Exclusion Criteria:  Contraindication to stereotactic body radiation therapy (SBRT) (including the inability to cooperate with any aspect of SBRT such as the inability to lie still and breathe reproducibly) Prior radiation to the volume of lung or mediastinum currently involved by tumor Plan for the patient to receive other concomitant antineoplastic therapy (including standard fractionated radiation, chemotherapy, biological therapy, vaccine therapy, and surgery) while on this protocol, except at disease progression Received an investigational agent within 30 days prior to enrollment Participants who have had chemotherapy or radiotherapy within 4 weeks (6 weeks for nitrosoureas or mitomycin C) prior to entering the study or those who have not recovered from adverse events due to agents administered more than 4 weeks earlier. Participants with known brain metastases should be excluded from this clinical trial because of their poor prognosis and because they often develop progressive neurologic dysfunction that would confound the evaluation of neurologic and other adverse events. Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements. Pregnant or nursing female participants. Unwilling or unable to follow protocol requirements. Any condition which in the Investigator's opinion deems the participant an unsuitable candidate to receive SBRT