Author: Zongsheng Hu, Yuting Li, Radhe Mohan, Emil Schueler, Uwe Titt 👨🔬
Affiliation: The University of Texas MD Anderson Cancer Center, Department of Radiation Physics, The University of Texas MD Anderson Cancer Center 🌍
Purpose: In previous work, we developed an irradiation system for pre-clinical ultra-high-dose-rate(FLASH) radiotherapy experiments based on synchrotron proton beamline. However, the beam current limitations of the synchrotron system posed challenges in achieving high dose and high dose rate simultaneously. In this study, we introduce a novel design enabling uniform spread-out Bragg peak (SOBP) dose coverage at higher achievable doses and dose rates, accommodating preclinical FLASH experiments with a broader range of dose and dose rate conditions.
Methods: The design relied on modulating a single pencil beam spill. To enhance dose and dose rate, the first scatterer from previous design was removed, and all components were re-engineered and reoptimized using Monte Carlo simulations, including a cone-shaped flattening filter to transform the Gaussian shape transverse beam profile into flat, a ridge filter composed stepped pyramids arrays to generate the SOBP, a range compensator to correct range variations caused by the flattening filter and a collimator to minimize penumbrae. The ridge filter was fabricated with a resin-based 3D printer, while other components were manufactured and installed on the beamline. The system underwent comprehensive validation to evaluate its performance.
Results: The new design achieves a 10 mm-diameter circular field and 20-mm SOBP modulation, delivering a dose of 45 Gy at dose rate of 448 Gy/s at the center of SOBP—double the capability of the previous design. The lateral dose profile flatness at SOBP center is 3.9% and 4.8% for the x and y direction, respectively. Due to 3D printing uncertainties, the longitudinal dose uniformity within the SOBP is ± 5.3%.
Conclusion: This new beamline design increased performance in dose rate and dose per spill by about 100 % compared to the previous design and demonstrates the feasibility of using synchrotron-generated proton beams to achieve sufficiently high doses and dose rates for FLASH radiobiology experiments.