A 62-year-old woman with a 40-pack-year smoking history and severe chronic obstructive pulmonary disease with early-stage right upper lobe non-small cell lung cancer (NSCLC) was treated with stereotactic ablative radiotherapy (SABR). Two years after treatment, a surveillance computerized tomography scan showed lesions of the posterior 4th and 5th ribs including expansion of the medulla that was unusual and of concern for possible malignant infiltration. A follow-up magnetic resonance imaging (MRI) scan revealed these lesions to be healing fractures post-radiotherapy. Although generally well tolerated, SABR is known to produce inflammatory and fibrotic changes both in-field and in organs at risk, and rib fractures are a well-established adverse event. MRI has high diagnostic accuracy and sensitivity for rib fractures and was able to rule out malignant spread. This case demonstrates the need for regular follow-up following SABR for early-stage NSCLC, as well as the challenge of interpreting indeterminate post-SABR radiography findings.