Optimizing Spot Weight and Scanning Path for Enhanced Proton Flash Therapy Delivery
Abstract
Purpose
FLASH radiotherapy (FLASH-RT) has emerged as a promising technique that delivers radiation at ultra-high dose rates (UHDR), which significantly spares normal tissues while still effectively controlling tumors, referred to as the FLASH effect. In proton FLASH therapy, the scanning path of the proton spots plays a crucial role in determining the dose rate distribution. Optimizing the scanning trajectory is essential to ensure that UHDR conditions are met, which is vital for achieving the full potential of FLASH-RT. This study proposes a novel optimization approach, the Joint Spot Weight and Scanning Path Optimization (JSWSPO), to enhance FLASH coverage while improving treatment quality.
Methods
The JSWSPO approach is developed using a bi-level optimization framework. The outer loop of the optimization focuses on determining the scanning path to maximize dose-rate coverage, while the inner loop adjusts the spot weights to minimize the treatment planning objective function, subject to the fixed scanning path. The outer loop employs a genetic algorithm (GA), while the inner loop is solved using iterative convex relaxation (ICR) and the alternating direction method of multipliers (ADMM).
Results
The effectiveness of JSWSPO was validated by comparing it against three
Methods
standard intensity-modulated proton therapy (IMPT) with a fixed scanning path, JSWSPO with one outer iteration, and JSWSPO with ten iterations. In the head-and-neck case, the FLASH-dose-rate coverage improved from 67.84% with IMPT to 85.11% with the single iteration (SPO) and 86.27% with JSWSPO. Additionally, the treatment objective function value decreased from 3.79 (IMPT) to 3.64 (SPO) and 3.21 (JSWSPO). Notably, JSWSPO reduced the brainstem volume receiving ≥18 Gy from 0.43 cc (IMPT) to 0.35 cc, showing enhanced plan quality with iterative optimization.
Conclusion
The JSWSPO framework effectively optimizes both the scanning path and spot weights to enhance FLASH-dose-rate coverage and improve the quality of proton FLASH therapy treatment plans.