ESTRO 2021 Abstract Book

S242

ESTRO 2021

Between April 2019 & January 2021 a total of 27 pts have received bridging RT. Of these 23 have been infused (1 not infused due to COVID19, 1 due to cardiac function & 2 pending). The CAR-T therapy was delivered in 1 Haematology Institution, but bridging RT in 9 different referring centres. Pt and disease characteristics and RT details are shown in table 1. The median time from CT planning scan to start of RT was 10 days (4-42). The median time between apheresis and start of RT was 5 days (-37-21; 3 patients received RT prior to apheresis at -37,-35 &-29 days) and median time between end of RT and CAR-T infusion was 19 days (10-116). No pts were delayed due to RT toxicity. Toxicity data was available for 22 pts. 10 (45.5%) reported no toxicity. Only 1 pt had grade 3 toxicity (vomiting & diarrhoea) and RT was stopped. The most common toxicities were skin reaction (n=5) & fatigue (n=4). 25/27 (92.6%) pts underwent a PET-CT between bridging RT & infusion. In 22 (88%) pts there was response in treatment field (CMR=2, PMR=20). In 13 (59.1%) of those pts there was evidence of progressive disease (PD) outside the field, but none were prevented from receiving CAR-T infusion due to PD. With median FU of 8.8 (0.6-20.6) months from date of CAR-T infusion, 12/ 23 (52.2%) infused pts have relapsed, (2 infield, 5 out of field, 5 in both) with a local control rate of 69.6%; CMR (12; 52.2%) and PMR (4; 17.4%). 7 pts have died since infusion, 6 due to PD and 1 due to sepsis. Median PFS was 5.1 months (95% CI 0.0-11.9 months) and median OS 17.8 months (95% CI 12.7-22.9 months). 1 pt had infusion delayed due to COVID19 infection and died of PD. Conclusion RT was a safe and effective bridging option in this cohort of DLBCL pts pre CAR-T therapy. With close collaboration between Haematologists and Radiation Oncologists, it is possible to deliver a course of radical dose RT in the narrow window between apheresis and infusion, even across a wide geographical network. Further work is required to determine which pts benefit most from bridging RT and the optimal dose and schedule.