A One-Step Multi-Field Proton Flash Treatment Planning Method with Concurrent Optimization of Spot Weights, Range Modulator and Spot Scanning Path
Abstract
Purpose
FLASH radiation therapy, which utilizes FLASH effect with ultra-high-dose-rate (UHDR) radiation, has shown promising performance in achieving treatment goals with decreased risks on healthy organs of patients. However, a number of factors, including patient-specific range modulators (PSRMs) in the practical setup, and the scanning path within a specific field, can largely impact on the achievement of proton FLASH effect. This research work aims to propose a new one-step multi-field treatment planning algorithm to optimize spot weights, PSRM shapes and scanning path simultaneously to achieve better proton FLASH effect achievement in treatment.
Methods
The proposed algorithm utilizes a bi-level optimization structure, which divides the overall problem into an inner problem and an outer problem, and solves them alternately. In the inner problem, the algorithm alternately optimizes between spots weights and PSRM shapes using the alternating direction method of multipliers (ADMM) with the scanning path fixed. In the outer problem, the algorithm optimizes the scanning path using a custom genetic optimization algorithm with the other two factors fixed.
Results
Experimental results demonstrate that the proposed algorithm outperforms the Joint Range-Modulator and Spot Optimization (JSRO) approach as the baseline, which optimizes spot weights and PSRM shapes only, with particularly remarkable gains in lung cases. In one lung case, dose-rate coverage increases from 44.73% and 23.82% to 63.00% and 74.85% in two fields. In another lung case, dose-rate coverage increases from 40.79% and 49.22% to 66.08% and 66.65% in two fields. Besides coverage improvements, the proposed method also decreases the maximum target dose, indicating enhanced overall plan quality.
Conclusion
This research work proposes a one-step multi-field treatment planning algorithm that optimizes spot weights, PSRM shapes, and scanning path concurrently, and attains higher proton FLASH effect achievement compared to the baseline in experiments.