2048 - FLASH Effect Modeling for Ion-beam Radiation Therapy Based on Microdosimetry
Presenter(s)
S. Shen1,2, W. Li2, X. Fan1,2, S. Wang1,2, J. Zhu3, Y. Yin2, and T. Dai2; 1Department of Graduate, Shandong First Medical University, Shandong Academy of Medical Sciences, Jinan, China, 2Department of Radiation Oncology Physics and Technology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China, 3Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Shandong Provincial Key Medical and Health Laboratory of Pediatric Cancer Precision Radiotherapy (Shandong Cancer Hospital), Jinan, China
Purpose/Objective(s): The FLASH effect has attracted significant attention in the field of ion beam radiotherapy. However, understanding and modeling the underlying mechanisms of this effect at microscopic scales remains challenging. This study aims to present a modeling approach for the FLASH effect in ultra-high-dose-rate ion beam radiotherapy, based on microdosimetry.
Materials/Methods: Microdosimetric linear energy spectra were calculated for various ion beams (proton, helium, lithium, beryllium, boron, and carbon) using the GATE Monte Carlo software package. An analytical model was developed by integrating the dynamic oxygen depletion equation and calculating the oxygen enhancement ratios based on microdosimetric quantities. The FLASH sparing effect (FSE) is defined as the ratio of DFLASH/DCONV, where DCONV and DFLASH are the reference absorbed dose delivered at the conventional dose rate and ultra-high dose rate resulting in the same biological effect, respectivelly. Quantifications of the FSE were then performed for ion beams with various dose rates (0.1-1000 Gy/s) and linear energy transfer LET (1.04-508.2 keV/µm).
Results: The FSE decreases with increasing LET and tends to approach unity in the high LET region. This trend has been observed for cells with different radiosensitivities. The LQ parameter a demonstrates a dependence on oxygen concentration across all radiation modalities, with varying LET values and dose rates. The FSE increases with higher environmental oxygen concentrations but decreases in the high LET region for ion beams with different LET values and dose rates.
Conclusion: A quantitative framework for better understanding the mechanisms of the FLASH effect and its application to ion beam therapies with microdosimetric approach has been established. The model suggests that the FLASH effect is significant at intermediate level. Ion beams with LET less than 180 keV/µm is required to induce FLASH sparing effects in normal tissue.