Patients confirmed to have T1-T3 N1-N3 (Stage IIIA-IIIC) or select Stage IV primary adeno- or squamous cell-carcinoma of the lung will be treated per standard of care; concurrent chemoradiotherapy for 6 to 6.5 weeks, followed by consolidative immunotherapy. A CT simulation scan is obtained with the patient in the treatment position allowing the radiation oncologist to delineate intended tumor targets and organs at risk (OAR). Using specialized treatment planning software, a radiation plan is generated with the goal of maximizing tumor coverage with intended prescription dose and minimizing unintended radiation dose to OARs below established thresholds. The primary intervention of this trial will be sparing the thoracic bone marrow. This will be done by delineating the thoracic bone marrow on the CT simulation scan and applying vertebral marrow-specific OAR constraints during treatment planning to optimally spare radiation dose to this structure during treatment

The only intervention that will occur during the radiation treatment planning process will be the application of evidence-based radiation dose limitations to the vertebral bone marrow during treatment plan optimization in order to attempt to limit Grade 3 Lymphopenia (G3L) toxicity.

The primary end point will be evaluating whether implementing dosimetric constraints to the bone marrow will decrease rates of G3L toxicity in the peripheral blood compared to expected rates of 40% in large series examining toxicities during chemoradiation. Values will be expressed as a percentage rates of G3L lymphopenia.

Overall Survival (OS), as measured from time of enrollment in the study

Progression Free Survival (PFS), either distant or local measured on routine surveillance imaging