Inclusion Criteria:
1. Pathologically (histologically or cytologically) proven diagnosis of non-small cell lung cancer (NSCLC); if the risk of biopsy is unacceptable, pathologic confirmation is not required providing there is serial growth on serial (\>=2) CT imaging and/or FDG avidity that is strongly suggestive of a primary NSCLC.
2. Stage T1-3, N0, M0 (UICC/AJCC Staging, 8th Ed.), tumor size \< 6 cm, prior to registration, based upon the following minimum diagnostic workup:
1. History/physical examination within 4 weeks prior to registration
2. CT scan with contrast (unless medically contraindicated) within 12 weeks of registration. The CT scan will include the entirety of both lungs, the mediastinum, liver and adrenal glands; the primary tumor dimensions will be measured on CT. Note: Patients with lesions that cannot be visualized by CT scan are not eligible for the study.
3. Whole body positron emission tomography (PET) scan within 12 weeks of registration, using FDG with adequate visualization of the primary tumor and draining lymph node basins in the hilar and mediastinal regions.
4. Mediastinal lymph node sampling by any technique is encouraged but not required. Patients with hilar or mediastinal lymph nodes \<1 cm and no abnormal hilar or mediastinal uptake on PET will be considered N0. Patients with \> 1 cm hilar or mediastinal lymph nodes on CT or abnormal PET (including suspicious but nondiagnostic uptake) may still be eligible if directed tissue biopsies of all abnormally identified areas are negative for cancer.
3. ECOG performance status 0-2;
4. age \>18;
5. Ultra-central tumor location: tumours whose planning target volume (PTV) is expected to touch or overlaps the central bronchial tree, esophagus, pulmonary vein, or pulmonary artery as determined at the time of consultation.
Exclusion Criteria:
1. Prior invasive malignancy (except non-melanomatous skin cancer) unless disease free for a minimum of 2 years (e.g. carcinomas in situ of the breast, oral cavity, or cervix are permissible); previous lung cancer, if the patient is disease-free for a minimum of 2 years is permitted.
2. Any prior thoracic radiotherapy.
3. Any prior chemotherapy for the study cancer (cancer proposed to be treated on the study).
4. Prior surgery for the study cancer.
5. Plans for the patient to receive other local therapy (including standard fractionated radiotherapy and/or surgery) while on this study, except at disease progression;
6. Plans for the patient to receive systemic therapy (including standard chemotherapy or biologic targeted agents), while on this study, except at disease progression.
7. Pregnancy.
8. The following autoimmune and connective tissue diseases will be excluded: Scleroderma and Systemic lupus erythematosus
9. patients with interstitial lung disease (ILD).
