Stereotactic Body Radiotherapy (RT) for Non-Small Cell Lung Cancer

Inclusion Criteria: * Must have been treated at University of Health Network with SBRT for an early-stage NSCLC (T1N0M0; T2N0M0; or T3N0M0 chest wall primary tumours only). * On follow-up thoracic CT scans, patients must have changes in the previously targeted lung parenchyma that fit into one of the following three patterns: - Changes that on CT and clinical grounds are felt to be related to fibrosis * Changes that on CT and clinical grounds are suspicious for recurrence * Equivocal changes (uncertain whether the changes represent fibrosis or recurrence) * Must be greater than 18 years in age * Must be able to attend regular follow-up including radiologic investigations and clinical visits * Written informed consent Exclusion Criteria: * Standard contraindications to MRI study (e.g. ferromagnetic prosthesis, pacemaker/implanted defibrillator, metallic implant in eye, severe claustrophobia, etc…) * Contraindications to Gadolinium contrast-agent. May include a history of allergic reaction to following previous administration of gadolinium or poor renal function (calculated creatinine clearance \< 30 mL/min). * Patients with surgical resection of the treated portion of lung following their SBRT, although surgical resection of other parts of the lung is allowed.