2605 - Modeling the Interplay between Microscale Energy Deposition and Oxygen Depletion in FLASH Ion Beam Therapy
Presenter(s)
S. Shen1,2, H. Sun3, H. Zhu4, J. Yang3, Z. Dou3, Y. Yin2, and T. Dai5; 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, 3Department of Radiation Physics, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, jinan, China, 4Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Guangzhou 510060, China, Guangzhou, China, 5Thayer School of Engineering, Dartmouth College, Hanover, NH
Purpose/Objective(s): The integration of FLASH radiotherapy with ion beam therapy offers a potential paradigm shift in the therapeutic index. This study establishes a mechanistic framework to quantify the interplay between micrometer-scale energy deposition and time-dependent oxygen depletion across various ion species.
Materials/Methods: Microdosimetric lineal energy spectra for protons, helium, lithium, beryllium, boron, and carbon ions were simulated using the GATE Monte Carlo platform. An analytical model was developed by integrating stochastic microscale energy deposition, oxygen depletion kinetics, and oxygen-dependent biological response. We investigated the Linear-Quadratic parameter a and the FLASH Sparing Effect (FSE) across a range of dose rates (0.1–1000 Gy/s), dose-averaged lineal energies (yD), and oxygen concentrations (O2).
Results: The model successfully characterized the FLASH effect across diverse physical and chemical conditions. The parameter a reached a saturation plateau at high O2 levels for all ion species. FSE increased with environmental O2 up to a dose-rate-dependent maximum before declining. A critical finding was the non-monotonic relationship between FSE and yD: the sparing effect initially increased, peaked, and subsequently converged toward unity in the high-LET region. Furthermore, the FSE-LET relationship exhibited distinct ion-species dependency, indicating that microscale track structure significantly influences oxygen-mediated protection.
Conclusion: We established a quantitative microdosimetric framework that reveals the complex interplay between physical energy distribution and chemical oxygen dynamics. Our findings indicate that optimal normal tissue protection is highly sensitive to the combination of ion species and oxygenation levels, providing a theoretical basis for the biological optimization of FLASH ion beam treatment planning.