Brief Summary: This phase II trial studies the effect of adaptive radiation planning in reducing side effects associated with radiation treatment and immunotherapy in patients with stage II-IV non-small cell lung cancer. Prior to radiation, patients undergo simulation, where they are positioned on the treatment table in a manner that can be reproduced each time they receive treatment in order to reach the tumor exactly at the same spot each time. However, a patient's tumor may shrink as they receive radiation, exposing healthy tissue to radiation as well. Adaptive radiation planning involves re-designing a treatment plan at set intervals. The purpose of this study is to see whether establishing set time points through adaptive radiation planning, regardless of whether the doctor notices a significant decrease in tumor size, will reduce some of the side effects associated with radiation treatment and immunotherapy.

Detailed Description: PRIMARY OBJECTIVE: I. To evaluate whether implementing set intervals for radiation replanning reduces cardiopulmonary toxicity and preserves healthy lung and heart tissue, with the intention of establishing a new standard treatment modality. OUTLINE: Patients undergo computed tomography (CT) stimulation with or without intravenous (IV) contrast over 1.5 hours on days -15 to -1, then undergo standard of care (SOC) chemoradiation on days 1-40. Patients also undergo additional CT scan simulations without IV contrast over 20 minutes each on days 15 and 29. After completion of study, patients are followed up at 3-12 weeks, and then every 6 months for approximately 2 years.