Evaluation of Bridging Radiation Therapy Before CAR T-Cell Infusion for the Treatment of Relapsed or Refractory Large B-Cell Lymphoma

Inclusion Criteria: * Documented informed consent of the participant and/or legally authorized representative. * Assent, when appropriate, will be obtained per institutional guidelines. * Age: \>= 18 years. * Eastern Cooperative Oncology Group (ECOG) =\< 2 or Karnofsky Performance Status (KPS) \>= 60. * Histologically confirmed large B-cell lymphoma. * Relapsed/refractory disease. * Planned to undergo commercial CAR T-cell infusion within 3 months of enrollment. * 6 or fewer sites (treatable with a maximum of 3 isocenters) of FDG-PET avid disease, treatable with a a maximum of 3 isocenters. * Measurable disease e.g., at least 1.5 cm on CT/MRI or by Response Evaluation Criteria in Solid Tumors 1.1 (RECIST 1.1). * Fully recovered from the acute toxic effects (except alopecia) to =\< grade 1 to prior anti-cancer therapy. * Women of childbearing potential (WOCBP): negative urine or serum pregnancy test (performed within 30 days prior to day 1 of protocol therapy). * If the urine test is positive or cannot be confirmed as negative, a serum pregnancy test will be required. Exclusion Criteria: * Prior CD19-directed therapy. * Radiation therapy within 21 days prior to day 1 of protocol therapy. * Central nervous system (CNS) disease. * History of allergic reactions attributed to compounds of similar chemical or biologic composition to study agent. * Active diarrhea. * Clinically significant uncontrolled illness. * Active infection requiring antibiotics. * Other active malignancy. * Females only: Pregnant. * Any other condition that would, in the investigator's judgment, contraindicate the patient's participation in the clinical study due to safety concerns with clinical study procedures. * Prospective participants who, in the opinion of the investigator, may not be able to comply with all study procedures (including compliance issues related to feasibility/logistics).