Detection of Circulating Tumor DNA After Stereotactic Ablative Radiotherapy in Patients With Unbiopsied Lung Tumors

The goal of this observational study is to determine if liquid biopsies from patients with stage I non-small cell lung cancer (NSCLC) can add to the diagnosis of a small lung cancer, or can better detect recurrent lung cancer compared to the standard of care procedures used for diagnosing this type of cancer. The main question\[s\] it aims to answer are: * Primary Objective: 1\) To assess whether liquid biopsy for molecular residual disease during follow-up can predict a recurrence of lung cancer * Secondary Objectives: 1. To assess the impact of SABR on detection rates of ctDNA in patients undergoing SABR for early-stage lung tumors. 2. To correlate positivity by blood-based cancer detection platforms and pre-treatment probability of malignancy using the Brock and Herder models. Study investigators will also assess the rate of detection for targetable mutations in this patient population, and to correlate ctDNA findings, in patients without tissue confirmed disease. Blood samples from participants will collected at eight (8) time-points: before the participant's first radiation treatment, following their first treatment and then at their 3-month, 6-month, 9-month, 12-month, 18-month and 24-month follow-up visits.