This is a prospective phase II study of Stereotactic Ablative Radiotherapy (SABR) in patients with Non-Small Cell Lung Cancer (NSCLC) and co-existent Interstitial Lung Disease (ILD), to determine oncologic and toxicity outcomes. Patients will be divided into 3 separate cohorts based on the ILD-GAP index.

For patients with ILD and concurrent early-stage lung cancer who are not candidates for surgery, data showing high rates of toxicity have led to a difficult clinical dilemma, since there are few alternate treatment options. The option of delivering no treatment whatsoever, which avoids any risk of treatment-related toxicity, is associated with a high risk of death due to the lung cancer itself.

Stereotactic ablative radiotherapy (SABR) is a newer radiotherapy approach which uses modern radiotherapy planning and targeting technologies to precisely deliver larger, ablative doses of radiotherapy. SABR has been associated with high rates of local control. A major advantage of SABR is that in general, the toxicity profile is very favorable, even in patients with substantial co-morbid conditions.

It is possible that currently-used doses and fractionations of SABR, when given with strict planning criteria to minimize the risk of lung toxicity, have only a modest risk of treatment-related toxicity and represent the best possible approach.

This study will examine SABR versus a historical control of untreated stage I non-small cell lung cancer with Overall survival (OS) as the endpoint. OS was selected as it objectively reflects the potential benefits of treatment (i.e. extended survival), the harms of treatment (grade 5 toxicity), and the natural history of the ILD disease process itself.

Inclusion Criteria:

• Stage T1-2, N0, M0 (AJCC Staging, 8th Edition - i.e. tumor size ≤ 5 cm) prior to registration.
• Not a candidate for surgical resection, determined by any of the following:
• Consultation with a thoracic surgeon
• Discussion at Multidisciplinary Team (MDT) rounds with a surgeon present
• Patient refusal of surgery
• Pathologically (histologically or cytologically) proven diagnosis of non-small cell lung cancer (NSCLC) is not required, but strongly recommended.
• If the risk of biopsy is unacceptable, pathologic confirmation is not required providing there is growth over time on Computed Tomography (CT) imaging and/or Fluorodeoxyglucose (FDG) avidity that is strongly suggestive of a primary NSCLC.
• Eastern Cooperative Oncology Group (ECOG) performance status 0-3;
• Age ≥ 18;
• Life expectancy > 6 months
• Fibrotic interstitial lung disease of any subtype, as diagnosed by a respirologist/pulmonologist.

Exclusion Criteria:

• 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.
• Prior thoracic radiotherapy
• Plans for the patient to receive other local therapy while on this study, except at disease progression;
• Plans for the patient to receive systemic therapy (including standard chemotherapy or biologic targeted agents), while on this study, except at disease progression. Patients are allowed to receive anti-fibrotic agents used in the treatment of IPF or non-IPF fibrotic ILD (e.g. nintedanib, pirfenidone), or steroids, if those are part of their current ILD treatment regimen. Other immunosuppressive drugs such as mycophenolate, azathioprine, cyclophosphamide, and rituximab must be stopped for 2 weeks prior and 2 weeks after treatment.
• Active pregnancy
• Concurrent administration of any drugs with known radiosensitive effects (e.g. Methotrexate).