Developing CAR‐T‐sparing Radiotherapy ‐ early dosimetric results

Background/objective: Radiotherapy (RT) is an effective treatment for residual lymphoma following CD19 chimeric antigen receptor T-cell (CAR-T) therapy. However, there are concerns regarding the potential effect of RT on CAR-T, particularly early after infusion. We initiated a prospective protocol to explore different planning parameters and techniques dose blood, thus CAR-T cells, in order develop “CAR-T sparing RT” Methods: analysed 33 plans 11 lesions 7 patients. Each lesion was planned 3 times; (1) conventional plan using volumetric modulated arc therapy (VMAT) technique, (2) with optimisation blood vessels region as well blood-rich organs bone marrow, (3) same 2 but delivered Flattening Filter-Free (FFF) beams increase rate. Plans were compared regards target volume (PTV) coverage, homogeneity, at risk (OAR) doses including vessels, rate beam-on time. Results: Using techniques, mean major reduced by 12% VMAT plan. The time 60% due organ not significantly affected. There no detrimental overall quality terms PTV coverage homogeneity. measures employed varied cases depending volume, anatomical location, proximity vessels. Examples clinical will be presented meeting. Conclusion: Reduction radiation possible variety technical adjustments reduction Further work continues understand relative contribution individual optimise post-CAR-T setting. Keywords: Aggressive B-cell non-Hodgkin lymphoma, Cellular therapies, Radiation Therapy Conflicts interests pertinent abstract. N. G. Mikhaeel Honoraria: Gilead, Educational meeting honoraria, Oct 2022