Author: Paul Boisseau, Eric S. Diffenderfer, Andrew Friberg, Wenbo Gu, Matthew Nichols, Kan Ota, Xiaokun Teng, Boon-Keng Kevin Teo, Lingshu Yin, Jennifer Wei Zou 👨🔬
Affiliation: Department of Radiation Oncology, University of Pennsylvania, Pyramid Technical Consultants, Inc., University of Pennsylvania 🌍
Purpose: Traditional quality assurance procedures for proton pencil beam energies involve water tank setups or multiple solid water phantoms and are time-consuming. This study demonstrates that an innovative multi-layer Faraday cup (MLFC) can provide a convenient, fast and accurate QA method for proton pencil beam energies. It allows variable beam energy measurements with fine energy resolution without setup adjustments.
Methods: The MLFC (Pyramid, MLFC-128 250MeV) measures charge deposition in 128 stacked copper layers, with a hexagonal energy filter (MicroHexTM) enabling pencil beam energy measurements with fine energy resolution. In this study, we measured the deposited charges for 100 to 226.7 MeV pristine pencil beams and correlated the energies with the peak positions from Gaussian fitting of the channel charge distribution. In addition, we simulated the charge distributions of the pencil beams in the MLFC structures using TOPAS Monte Carlo (MC) package.
Results: Both the measurements and simulations demonstrated a linear relationship between the charge peak positions and the pencil beam ranges in copper and water. The MLFC achieved a 1 MeV energy measurement resolution for clinical pencil beams. Our TOPAS MC simulation demonstrated that the hexagonal filter improved energy measurement resolution by distributing charge collection across multiple copper layers. Repeated measurements confirmed the system's reliability.
Conclusion: The MLFC provides a fast, practical, and precise solution for proton beam energy QA using a calibration curve that correlates the fitted charge peak position with beam energy. Its ability to measure multiple energies with a single setup makes it an effective tool for routine clinical workflows, offering significant advantages over traditional methods.