Inclusion Criteria:

• Patient must be over the age of 18 years
• Histological confirmation of primary NSCLC
• Pulmonary nodule size less than or equal to 5 cm
• The following stage of NSCLC patients are eligible:
• Stage I: T1, N0, M0 or T2, N0, M0 (Tumor size </= 5cm)
• Stage II: T3, N0, M0 (Chest wall invasion only, Tumor size </= 5cm)
• ECOG/Zubrod status of 0, 1, or 2
• In order to be considered medically inoperable, the patient must meet at least one major criteria or a minimum of 2 criteria as described below:

MAJOR CRITERIA:

• FEV1 < 50% or predicted postoperative FEV1 < 40%
• DLCO < 50% or predicted postoperative DLCO < 40%
• Exercise induced maximal exercise oxygen consumption(M VO2)< 15/kg/min
• Thoracic surgery consultation should be obtained from a Board Certified Thoracic Surgeon who in collaboration with a Radiation Oncologist should determine that the patient is not a surgical candidate.

MINOR CRITERIA:

• Age > 80 years
• Pulmonary hypertension (defined as a pulmonary artery systolic pressure > than 40 mm Hg
• Oxygen requirement
• Congestive heart failure (any 3 of the following must be documented: dyspnea, peripheral edema, chest x-ray with interstitial edema or cardiomegaly, rales or congestion)
• Poor left ventricular function (defined as an ejection fraction of 40% or less)
• Severe cerebral (with CVA or recent TIA) or severe peripheral vascular disease
• Diabetes Mellitus with severe organ damage
• Females of child bearing age must be using a reliable form of birth control
• PET-CT scan completed within 6 weeks of registration

Exclusion Criteria:

• Prior history of cancer within the last 5 years or concurrent cancer other than basal cell or squamous cell carcinoma
• Weight exceeds the tolerances of the institution's imaging and CyberKnife platform/couch
• Thoracic radiation therapy in the same field as the planned treatment area
• Patient has completed chemotherapy within less than 30 days of treatment
• Stage T2 with tumor size > 5 cm; Stage T3 (except T3 by virtue of chest wall invasion only and </= 5 cm); Stage T4
• Presence of N1, N2 or N3 disease
• Pancoast tumors
• Current distant metastases (M1)
• Female with child-bearing potential who refuses to take a pregnancy test prior to treatment
• Pregnant or nursing female
• Active systemic or pulmonary infection
• Undergoing systemic therapy within 2 weeks after last fraction of radiation