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Biological-equivalent-dose-based integrated optimization framework for fast-energy-switching Bragg peak FLASH-RT
Yiling Zeng1,2,3, Heng Li4, Qi Zhang1
1Department of Medical Physics, School of Physics and Technology, Wuhan University, Wuhan, China.
This study introduces an integrated optimization framework for FLASH radiotherapy, improving normal tissue sparing with single beam per fraction schedules. The developed framework effectively compensates for potential dose increases, enhancing treatment safety.
Area of Science:
- Medical Physics
- Radiation Oncology
- Radiotherapy Optimization
Background:
- Single beam per fraction (SBPF) schedules in FLASH radiotherapy meet dose thresholds and reduce beam switching uncertainties.
- SBPF may increase the biological equivalent dose in 2 Gy (EQD2) for normal tissues, posing a challenge for sparing.
- Optimizing FLASH plans requires balancing dose delivery, efficiency, and normal tissue protection.
Purpose of the Study:
- To develop an EQD2-based integrated optimization framework (EQD2-IOF) for Bragg peak FLASH plans using SBPF.
- To incorporate robust dose, delivery efficiency, and beam orientation optimization (BOO) into the EQD2-IOF.
- To enhance both normal tissue sparing and the FLASH effect in radiotherapy.
Main Methods:
- Utilized a superconducting gantry with fast energy switching (27 ms) and universal range shifters for FLASH plans.
- Implemented a simultaneous dose and spot map optimization (SDSMO) algorithm within a Bayesian optimization auto-planning framework.
- Developed a BOO algorithm using Tabu search for beam angle combination selection and a quantitative model for FLASH-enhanced dose distribution.
Main Results:
- EQD2-IOF plans showed no significant difference in target dose coverage (D2% and D98%) compared to manually optimized plans.
- EQD2-IOF plans achieved a significant reduction in mean EQD2 for the ipsilateral lung (10.5%) and normal tissue (11.5%) compared to manual plans.
- FLASH sparing in normal tissues receiving >70% of the prescription dose compensated for increased EQD2 when using SBPF schedules.
Conclusions:
- The EQD2-IOF automates SBPF FLASH-RT plan optimization for superior normal tissue sparing.
- The FLASH effect can compensate for potential fractionation repair loss in high-dose regions with fast (27 ms) energy switching.
- SBPF schedules require careful consideration with slower energy switching (500 ms) due to diminished FLASH effect.
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