Inclusion Criteria:
1. Patients aged 18 or older.
2. Patients with an Eastern Cooperative Oncology Group (ECOG) performance status of 0-2.
3. Patients with confirmed tumor location using advanced imaging to ensure accurate classification of ultra-central NSCLC.
4. Ability to undergo bronchoscopy and Endobronchial ultrasound (EBUS) with adequate fiducial placement
5. Histologically or cytologically confirmed clinical stage T1-T2 N0 M0 NSCLC (AJCC 9th edition), with maximum tumor diameter ≤5 cm.
6. Absence of overt radiological or bronchoscopy assessed gross endobronchial invasion, invasion of the trachea, esophagus, major blood vessels, or other mediastinal structures.
7. 4D-CT (computed tomography) scans will be required to evaluate tumor motion and verification at time of simulation:
○ Screening for ultra-central tumor deformation between inhalation and exhalation extremities will be performed via 4D-CT to avoid inappropriate margins for significant tumor motion or deformation.
8. Ultra-central tumors must include:
o Gross Tumor Volume (GTV) or Planning Target Volume (PTV) located within 1 cm (centimeter) of the Proximal Bronchial Tree (PBT) and/or at least one of the following: (1) GTV or protocol PTV within 1 cm of the PBT; or (2) GTV within 5 mm of or abutting/overlapping the esophagus, heart/pericardium, aorta, pulmonary artery, or pulmonary vein.
9. Patients are eligible to receive SBRT:
* Patients deemed suitable for SBRT based on multidisciplinary evaluation;
* Medically inoperable, decline surgery or high surgical risk as determined by a thoracic surgeon or multidisciplinary tumor board;
* No prior overlapping thoracic radiation exceeding dose constraints for critical structures;
* Adequate pulmonary function to tolerate procedure;
* A minimum of two gold fiducials will be placed in or adjacent to the tumor via bronchoscopy and will be tracked/evaluated by the treating radiation oncologist and/or physicist/dosimetrist to determine quality of fiducial placement for trial inclusion.
10. Patients are eligible to receive radiation therapy:
* Candidate for CyberKnife radiosurgery using Synchrony motion management;
* 4D-CT is required to evaluate tumor motion. Patients with \>1.5 cm excursion in any dimension will require a 5 mm PTV margin and remain eligible only if all mandatory Organs-at-risk (OAR) dosimetric and planning constraints can be met; otherwise, they are ineligible for protocol treatment.
* OAR constraints will be prioritized over target coverage. Patients who cannot meet mandatory airway, esophagus, great vessel, heart, spinal cord, and lung constraints are not eligible for protocol treatment.
11. Female patients of childbearing potential must have a negative pregnancy test prior to treatment and agree to contraception during and for a defined period after treatment.
12. Patients who can comply with follow-up visits and treatment plans.
13. Patients who can provide written informed consent prior to study procedures.
Exclusion Criteria:
1. Patients with evidence of nodal involvement (N1-N3) or distant metastases (M1).
2. Patients with previous radiation therapy to the thorax that would result in overlap with the planned treatment field.
3. Patients with tumor-associated bronchial compression, defined as visible deformation or narrowing of the trachea, mainstem bronchus, or bronchus intermedius on diagnostic CT, simulation CT, or bronchoscopy.
4. Patients receiving concurrent chemotherapy, immunotherapy, or targeted therapy during SBRT.
5. Patients with active connective tissue disease (e.g., lupus, scleroderma, polymyositis, rheumatoid arthritis).
6. Patients with interstitial lung disease of any etiology.
7. Patients on Vascular Endothelial Growth Factor (VEGF) inhibitors.
8. Patients with tumor invasion of any major airways, esophagus, or major blood vessels.
9. Patients with evidence of endobronchial disease.
10. Patients who fail to place fiducial markers for Synchrony tracking.
11. Patients who require alternate fractionation scheduling.
12. Patients who are pregnant or are breastfeeding.
13. Patients who are unable to lie flat for the duration of treatment (approximately 45-60 minutes per fraction).
14. Patients with psychiatric illness or social situation that would limit compliance with study requirements.
15. Patients who are unable to or unwilling to give informed consent.
