S504
Clinical - Haemotology
ESTRO 2026
1 Department of Medical Physics and Clinical Engineering, Guy´s and St Thomas´ Hospital, London, United Kingdom. 2 Nuffield Department of Population Health, University of Oxford, Oxford, United Kingdom. 3 Department of Radiation Oncology, Harvard Medical School, Boston, USA. 4 Department of Clinical Oncology, University College London, London, United Kingdom. 5 Department of Clinical Oncology, Guy´s and St Thomas´ Hospital, London, United Kingdom. 6 Department of Haematology, King´s College Hospital, London, United Kingdom. 7 Department of Radiation Oncology, University of Washington, Seattle, USA Purpose/Objective: Radiotherapy is an effective treatment for residual lymphoma early after CD19 chimeric antigen receptor T-cell therapy (CAR-T). However, there are concerns that it may impair CAR-T cell viability and function. To address this, we developed and clinically implemented a novel blood-sparing radiotherapy technique that, for the first time, not only considers sparing blood rich organs and vessels, but also the time element for circulating blood. Material/Methods: As part of the RESTART protocol [1], we treated 20 lesions in 16 post CAR-T lymphoma patients from 2 institutions. Each lesion was planned using 3 radiotherapy techniques (total 60 plans). 1. RT-A: conventional VMAT;2. RT-B: blood-sparing optimisation (reduced number of arcs and angles, contouring and dose-optimisation for blood vessels (BV) and blood-rich organs);3. RT-C: as RT-B, but delivered with flattening-filter-free (FFF) beams to shorten beam-on time by using higher dose rate (1400MU/min instead of 600MU/min).The prescription dose for plan comparison was 30Gy/10#. Fractional blood doses were estimated using a published stochastic blood-flow model [2], computing the proportion of circulating blood receiving 0 Gy, >0.05 Gy, and >0.5 Gy per fraction. Doses to target volumes and organs-at-risk (OARs) and beam on time for each plan were calculated and compared between plans using paired Wilcoxon tests with Bonferroni correction. Results: RT-C (FFF delivery) achieved the greatest blood-sparing effect. On average, 29.2% of blood received 0 Gy with RT-C versus 16.9% (RT-B) and 15.5% (RT-A) (p<0.001). The fraction of blood receiving >0.05 Gy—a threshold for radiosensitive lymphocytes [3]—was also significantly lower with RT-C. Both RT-B and RT-C markedly reduced mean doses to blood vessels and bone marrow, while maintaining comparable OAR doses (Table 1). PTV coverage (V95%) decreased slightly ( − 2/3%) with RT-B and -C due to fewer arcs but remained clinically acceptable. Beam on time reduction had the largest impact on blood dose, with
Oncology, University Hospital Heidelberg, Heidelberg, Germany. 15 Department of Radiation Oncology, University Hospital of Cologne, Cologne, Germany. 16 Klinik für Strahlentherapie und Radioonkologie, University Hospital Bonn, Bonn, Germany. 17 Kinik für Strahlentherapie und Radioonkologie, Medizinische Hochschule Hannover, Hannover, Germany. 18 Klinik für Strahlentherapie, Universitätsklinikum Schleswig- Holstein, Kiel, Germany. 19 Department of Radiation Oncology, University Hospital, LMU Munich, Munich, Germany. 20 Department of Radiotherapy and Radiation Oncology, University Hospital Munster, Munster, Germany Purpose/Objective: To evaluate the efficacy of various radiotherapy (RT) regimens with or without systemic therapy in patients with primary cutaneous diffuse large B-cell lymphoma, leg type (pcDLBCL). Material/Methods: A total of 93 patients from 20 institutions were included. Patients received a median total radiation dose of 36 Gy (range, 8-50) and a median dose of 2 Gy per fraction (range, 1.5-5 Gy). Clinical parameters, treatment modalities, local control (LC), progression- free survival (PFS), and overall survival (OS) were analyzed. Results: The median duration of LC was not reached. The LC rates at 1 year and 3 years were 95% and 90%, respectively. Moderate-dose regimens (30–36 Gy) achieved similar rates of LC compared to higher-dose regimens, while lower doses (< 30 Gy) were associated with inferior LC. The addition of systemic chemotherapy did not significantly improve LC, PFS, or OS. The radiation treatment was well tolerated, with grade 3 toxicities reported in only 16% of patients. Conclusion: Moderate-dose RT achieves high local control in pcDLBCL, comparable to higher doses, with favorable tolerability. Routine addition of chemotherapy may not improve outcomes. Dose reduction strategies could be considered in selected patients. Keywords: primary cutabeous NHL, deescalation, radiotherapy Mini-Oral 1364 Developing blood-sparing radiotherapy following CAR-T for lymphoma Georgios Ntentas 1,2 , Chris Beekman 3 , Amy G. H. Smith 1 , Harald Paganetti 3 , Suganya Sivabalasingham 4 , Jessica L Brady 5 , Karimali Keshwani 4 , Robin Sanderson 6 , Clemens Grassberger 7 , Rubina Begum 1 , Meera Patel 5 , Andrea Kuhnl 6 , N. George Mikhaeel 5
Made with FlippingBook - Share PDF online