Immunotherapy With or Without SBRT in Patients With Stage IV Non-small Cell Lung Cancer

Inclusion Criteria: * Patients who are 18 years or older. * Performance Status 0-2 (ECOG) at time of consult with radiation oncology. * Pathologically proven non-small cell lung cancer (NSCLC) with evidence of metastatic disease. * Must have received 4 cycles of standard of care systemic therapy (usually this will consist of combination chemo-immunotherapy), with a CT chest abdomen pelvis that was performed after completion of these 4 cycles and demonstrates no evidence of progression per RECIST v1.1. * To be eligible for enrollment and randomization, patients must be within 180 days from their first dose of standard of care systemic therapy. Cycle 1 day 1 is defined as day 1. If enrolled on day 180, the patient would need to be randomized the same day. * Persistent active disease must be amenable to radiation treatment per the treating radiation oncologist, and patients must have at least one residual site of disease which can be identified by CT or PET/CT and targeted with radiation. * Patients who previously had earlier stage NSCLC treated definitively and have now developed new distant disease, are eligible for inclusion if they have undergone at least 4 cycles of standard of care systemic therapy for their metastatic recurrence, and they meet all criteria above. * There are no strict size or tumor number limitations in a given organ (lung, liver, abdomen pelvis, or spine). This is at the discretion of the treating radiation oncologist. Exclusion Criteria from Enrollment * More than 180 days has elapsed since day 1 of cycle 1 of standard of care systemic therapy. * Pregnant or lactating women. * The patient has received treatment for other carcinomas within the last three years (Except for cured non-melanoma skin cancer, low-risk prostate cancer, T1/T2 glottic cancer, stage 0 or stage I breast cancer, non-invasive bladder cancer, or treated in-situ cervical cancer). Prior lung cancer diagnosis now with oligometastatic recurrence is not an exclusion criteria. * Patients with major activating mutations in EGFR (del19, L858R, and T790M) or ROS 1 or ALK gene rearrangements are excluded Eligibility for Randomization * Once enrolled on study, patients will have a PET/MRI brain for restaging. Patients with no evidence of progression and 8 or fewer sites of active persistent disease per the treating physician are eligible for randomization. * If a PET has been performed within 30 days of enrollment with no evidence of progression per RECIST v1.1, then this scan may be used and does not have to be repeated prior to randomization. * If an MRI brain has been performed within 90 days of enrollment with no evidence of progression per RECIST v1.1, then this scan may be used and does not have to be repeated prior to randomization.