A novel QA method for adaptive aperture position verification of proton therapy system

Accurate Adaptive Aperture (AA) leaf positioning is essential for some proton therapy systems to ensure precise dose delivery and patient safety. However, conventional quality assurance (QA) methods can be suboptimal or inefficient for routinely assessing the dynamic nature of AA in the Mevion S250i HYPERSCAN system. This study introduces a novel automated QA method to verify AA positions utilizing a scintillation detector. A specialized QA plan consisting of 7 rectangular fields was generated in the RayStation treatment planning system (TPS) and delivered using the Mevion S250i HYPERSCAN proton therapy system. Dose distributions were measured with an IBA Lynx PT scintillation detector. A MATLAB-based software tool automated the analysis of leaf positions, full-width half maximum (FWHM), and valley positions by comparing measured dose distributions with TPS calculations. Leaf positioning errors between measured and planned values demonstrated excellent agreement, with deviations mostly below 1 mm. Quantitative analysis of FWHM, valley positions, field centers, and delivery log data revealed average differences well within submillimeter tolerances, confirming the high accuracy and reproducibility of AA leaf positioning. The developed QA method provides an efficient and robust solution for routine verification of AA leaf positions in the Mevion S250i HYPERSCAN system, ensuring the reliability of proton beam-shaping for clinical treatments.