S1774
Physics - Dose prediction/calculation, optimisation and applications for particle therapy planning
ESTRO 2026
Results: All cases achieved the prescribed dose coverage (D99% = 19.0 Gy) with acceptable dose homogeneity (mean HI = 1.21 ± 0.04) using the same universal bolus (Figure 1, Table 1). The mean skin dose (Dmean) was 19.32 ± 0.91 Gy. FLASH dose-rate objectives were met across all simulations, with DRmean,skin values ranging from 68.5 to 505.3 Gy/s at beam currents well below the technical limit (mean = 73.9 ± 59.4 nA). Robustness analysis showed ≤ 3.0% variation in D99% for 9 out of 10 mice under combined setup and range uncertainties. One outlier (mouse RM10) exceeded tolerance due to a marked gross tumour volume shape deviation, suggesting potential benefit from morphology-based bolus stratification.
throughput, UHDR proton Bragg Peak irradiations in small animals using a universal bolus design. The validated setup enables future in vivo FLASH studies in breast cancer-relevant tissues and provides a robust experimental platform for investigating LET- dependent biological effects and optimising FLASH delivery parameters under clinically realistic
constraints. References:
Kristensen, L., et al. 2025. Electron vs proton FLASH radiation on murine skin toxicity. Radiother Oncol, 206, 110796.Diffenderfer, E. S., et al. 2022. The current status of preclinical proton FLASH radiation and future directions. Med Phys, 49, 2039-2054.Charaghvandi, R. K., et al. 2017. Redefining radiotherapy for early-stage breast cancer with single dose ablative treatment: a study protocol. BMC Cancer, 17, 181 Keywords: FLASH, proton therapy, small animal model Research on Lattice Optimization with Dual Degrees of Freedom Based on Real-Time Deformable Registration in Spatially Fractionated Radiation Therapy Yi Peng, Ke Yuan, Feng Yang, Xin Xin, Junxiang Wu, Tianli Qiu, Xianliang Wang Department of Radiation Oncology, Sichuan Cancer Hospital and Institute, Chengdu, China Purpose/Objective: Lattice radiotherapy is the most advanced and predominant treatment modality in spatially Digital Poster 4318 fractionated radiation therapy (SFRT). Conventional lattice radiotherapy relies on clinicians manually delineating lattice points, leading to irregular distribution and inconsistent dose delivery. The hexagonal close packing (HCP) lattice arrangement offers a geometrically regular pattern with alternating high- and low-dose regions, yet its rigid structure often fails to conform to irregular tumor anatomy, resulting in insufficient dose coverage in certain tumor areas. Therefore, the key focus of this study is to develop a customized lattice arrangement tailored to individual tumor anatomy to improve dose coverage. Material/Methods: Based on CT imaging and tumor contour data, a three- dimensional discrete mesh model of the tumor is reconstructed. Using the geometric center of the tumor as a reference, a preliminary lattice array is preset in a hexagonal close packing (HCP) configuration. The lattice array is then redefined with two degrees of freedom (geometric center and rotation angle), and an optimization system iteratively
Conclusion: This in silico validation demonstrates the feasibility of delivering conformal, single spot PBS, high-
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