The goal of this clinical trial is to see if a new combination of standard of care radiotherapy treatment prior to administering the study drugs obinutuzumab and glofitamab in relapsed/refractory Diffuse Large B Cell Lymphoma patients is effective. The main question it aims to answer is:
If you are able to tolerate the study treatments, and whether your cancer responds to the study treatment, compared with other reported studies of standard care treatments.
Participants will have three parts they need to complete over a 5 year period.
* Screening period over a 28 day period
* Treatment period - Radiotherapy followed by 12 treatment cycles every three weeks (total time approx. 37 weeks)
* Follow up, up to 4 years. Additional PET imaging studies will be performed in a cohort of patients (up to 6) who are willing to undergo infusions of 89Zr-Df-Crefmirlimab and 18F-Granzyme B for evaluation of the impact of radiotherapy plus glofitamab with relapsed diffuse large B-cell lymphoma.