This study will explore the best dose of radiation to be used when treating stage I-III non-small cell lung cancer (NSCLC) with stereotactic body radiation therapy (SBRT) or hypo-fractionated radiotherapy (HypoFrx-RT) that is delivered in combination with an immune checkpoint inhibitor. Treatments with SBRT or HypoFrx-RT for locally confined NSCLC show positive response which may be further augmented when they are combined with an immune checkpoint inhibitor. Currently, it is not understood what radiation dose is most suitable for such combined treatments and their clinical efficacy in the treatment of early stage (ES) NSCLC. Therefore, this study can help researchers gain insight into what a safe and effective SBRT or HypoFrx-RT dose will be when such radiotherapeutic approaches are combined with concurrent and adjuvant administration of an immune checkpoint inhibitor in the treatment of ES NSCLC.