ESTRO 2021 Abstract Book

S137

ESTRO 2021

dose (cGy)

p_o (Pa)

∂t_1 (µs)

∂t_2 (µs)

∂x (mm)

2a 40 5.0 1.0 0.5 -1.0 2b 39 5.1 -0.2 0.7 -0.4 2c 41 5.0 -0.4 0.9 -0.3 2d 36 10.1 0.5 0.0 -0.2 2e 36 8.5 -1.2 0.0 1.2 2f 41 10.3 0.5 -0.2 -0.2

Conclusion Thermoacoustic range verification is feasible for a hypofractionated protocol delivering 6 Gy/fraction at a conventional dose rate. Improving receive sensitivity by another 20 dB is WIP and could enable adaptive planning for 2 Gy fractionation or online verification before an entire hypofractionated dose is delivered at a conventional dose rate. SNR is proportional to dose/pulse so FLASH delivery with short (FWHM<6 us) pulses would increase efficiency and could enable online verification before 1 Gy is delivered.

Proffered papers: Proffered papers 13: Haematology / Paediatrics / Sarcoma

OC-0206 Radiotherapy as bridging strategy in Large B-cell lymphoma patients selected for CAR T-cell therapy A. Niezink 1 , M. Beijert 2 , J. van Doesum 3 , C.T. Muijs 2 , J.A. Langendijk 2 , D.M. Busz 2 , A.P. Crijns 2 , T. van Meerten 3 1 University Medical Center Groningen / University of Groningen , Radiation Oncology, Groningen, The Netherlands; 2 University Medical Center Groningen / University of Groningen, Radiation Oncology, Groningen, The Netherlands; 3 University Medical Center Groningen / University of Groningen, Hematology, Groningen, The Netherlands Purpose or Objective Patients with Large B-cell lymphoma (LBCL) who have refractory or relapse disease after two lines of systemic therapy (ST) have a very poor prognosis. However, for these patients anti-CD19 chimeric antigen receptor T- cell (CART) therapy has emerged as a potential curative treatment regime as approximately half of the patients achieve long-term disease-free survival. CAR T-cells are generated from autologous T-cells, collected through an apheresis procedure. The logistics and production are time consuming and may take up to 4-6 weeks. Many patients in which CART therapy (CARTT) is indicated have symptomatic and progressive disease during the production period. Bridging therapy, referred to therapy administered after apheresis until CART infusion may be indicated. Early reports on radiotherapy (RT) as a bridging strategy have shown feasibility, safety and effectivity, but patient numbers were limited. Here we present our experience with bridging in patients selected for CART therapy in a relatively large cohort. The current analysis focuses on the evaluation of the response rates. Materials and Methods All patients treated with CARTT are included in a prospective data registration program including data on patient and tumor characteristics, treatment, toxicity and outcomes. For this analysis all patients with LBCL who underwent apheresis for CARTT were included. Bridging therapy may consist of steroids, chemotherapy, RT or a combination of these treatments. Responses to bridging therapy were based on 18 F-Fluordeoxyglucose