S505
Clinical - Haemotology
ESTRO 2026
of DNA repair and radiosensitivity of different blood cell populations,” Sci Rep, vol. 11, no. 1, Dec. 2021, doi: 10.1038/s41598-021-81058-1 Keywords: Blood-sparring, CAR-T, lymphocyte- sparring
RT-C reducing average beam on time from 94 seconds (for RT-A) to 47 seconds (p<0.001), (Table 1).
Digital Poster Highlight 1615
Total body irradiation using VMAT improves dose homogeneity and enables better sparing of the lungs compared to conventional technique Anna Embring 1,2 , Marzia Palma 3,2 , Lotta Hansson 3,2 , Johan K Törlén 4,5 , Julia Söderström 6 , Lars Södergren 6 , Mathias Westermark 6 , Erik Almhagen 6,2 1 Department of Radiotherapy, Karolinska University Hospital, Stockholm, Sweden. 2 Department of Oncology-Pathology, Karolinska Insitute, Stockholm, Sweden. 3 Department of Hematology, Karolinska University Hospital, Stockholm, Sweden. 4 Cell Therapy and Allogeneic Stem Cell Transplantation (CAST), Karolinska Comprehensive Cancer Center, Karolinska University Hospital, Stockholm, Sweden. 5 Therapeutic Immunology and Transfusion Medicine, Department of Medicine Huddinge, Karolinska Insitute, Stockholm, Sweden. 6 Department of Nuclear Medicine and Medical Physics, Karolinska University Hospital, Stockholm, Sweden Purpose/Objective: Total body irradiation (TBI) is used as part of the conditioning regimen before allogeneic haematopoietic stem cell transplantation (HSCT) in certain haematological diseases. The delivery of TBI using conventional techniques (cTBI) varies significantly across different centres. TBI delivered using VMAT-technique enables more conformal dose distributions, better sparing of organs at risk, and greater treatment reproducibility. However, as VMAT- TBI is delivered with higher dose rates, concern has been raised about increased risk of radiation pneumonitis. This study aims to evaluate dose homogeneity, lung dose sparing, incidence of radiation pneumonitis, and impact on respiratory function (FEV1%) after TBI-containing HSCT conditioning in a
Conclusion: This study presents the first clinically implemented blood-sparing radiotherapy technique that explicitly accounts for the circulating nature of blood to protect circulating immune cells and potentially preserve CAR- T function. Reducing beam-on time below 60 seconds – through shorter arcs and FFF delivery – achieved the largest reductions in blood dose. Our technique may represent a new paradigm for post-CAR-T radiotherapy and could also mitigate radiotherapy- induced lymphopenia in other tumour sites. References: [1] Mikhaeel, G., et al. "Updated Results of RESTART Protocol (RadiothErapy bridging and conSolidaTion for CAR-T) in Large B-cell Lymphoma." International Journal of Radiation Oncology* Biology* Physics 123.1 (2025): S152-S153[2] C. Beekman et al., “A stochastic model of blood flow to calculate blood dose during radiotherapy,” Phys Med Biol, vol. 68, no. 22, p. 225007, 2023, doi: 10.1088/1361- 6560/ad02d6[2] D. Heylmann et al., “Comparison
retrospective cohort. Material/Methods:
Treatment plans and medical records from all patients treated with TBI at our institution, for which 3D dose distributions were available, were retrospectively analysed. Dose homogeneity was analysed using a homogeneity index (HI), defined as the volume of the clinical target volume (CTV) receiving 90-110% of the prescribed dose, divided by the volume of the CTV. FEV1% was recorded before and after HSCT, and change in FEV1% ( Δ FEV1) was calculated using FEV1%after – FEV1%before. Wilcoxon signed rank test
Made with FlippingBook - Share PDF online