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).