The purpose of this study is to assess a real time motion tracking of lung tumors and important organs next to the tumor while breathing during a participant's radiation treatment. This will be assessed through a four-dimensional magnetic resonance imaging (MRI) scan before starting your radiation treatment and x-ray fluoroscopy images that are taken during radiation

Inclusion Criteria:

1. Adult (≥18 years) patients (both sexes) with histologically diagnosed Stage II-IIIb NSCLC
2. Patients to be treated with definitive external beam photon radiotherapy with or without systemic therapy (e.g., chemotherapy, immunotherapy).
3. No restrictions on number radiotherapy fractions, or location/number of lesions
4. ECOG performance status ≤ 3
5. Ability to undergo MRI scans
6. Patient has signed informed consent document and agreed to study procedures

Exclusion Criteria:

1. Pre-existing contraindications for MRI, such as any MRI-conditional or MRI-unsafe foreign objects within the body, non-removable ear cochlear or eye implant, aneurysm clip, cardiac pacemaker/wires, internal defibrillator, tissue expander, recent stent placement, penile prosthesis, medication patch, artificial limb, pregnancy, and claustrophobia
2. Women who are pregnant or trying to get pregnant (self-reported)
3. Pain in supine position or inability to raise arm above head in supine position