Supplementary Material for: Mistaken Metastasis: Radiation-Induced Rib Fracture Mimicking Malignancy on CT Case Report

A 62-year-old woman with a 40-pack-year smoking history and severe chronic obstructive pulmonary disease (COPD) 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 (CT) 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 (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. Magnetic resonance imaging 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 stereotactic ablative radiotherapy for early-stage NSCLC, as well as the challenge of interpreting indeterminate post-stereotactic ablative radiotherapy radiography findings.