Author: Zachary M. Diamond, Pretesh Patel, Sibo Tian, Yinan Wang, Xiaofeng Yang, David Yu, Ahmal Jawad Zafar, Jun Zhou 👨🔬
Affiliation: Emory University, Department of Radiation Oncology and Winship Cancer Institute, Department of Radiation Oncology and Winship Cancer Institute, Emory University 🌍
Purpose: High spatial resolution in pin ridge filter (pRF)-based proton planning may be constrained by the 1mm dose grid resolution in commercial treatment planning systems. This study investigates the dose calculation accuracy of modularized pRF-based plans, focusing on dose grid alignment and beam angle dependencies.
Methods: A pRF was generated using a previously reported iterative spot reduction algorithm in RayStation using a 1mm dose grid resolution. Dose accuracy was evaluated under lateral perturbations (up to 0.5mm) and gantry beam angles (up to 45°) compared to a reference dose distribution at 0° with pRF aligned to the dose grid. Rotated dose distributions at oblique angles were transformed to 0° using SimpleITK for comparison. Gamma analysis thresholds of 3%/3mm, 3%/2mm, and 2%/2mm quantified dose distribution accuracy. Rotational perturbations were tested by rotating and reversing the dose distribution to validate interpolation effects.
Results: For lateral perturbations, gamma passing rates were 99.1±0.4%, 98.2±0.7%, and 96.6±1.2% for 3%/3mm, 3%/2mm, and 2%/2mm, respectively, with minimum passing rates of 97.85%, 95.99%, and 93.48%. Rotational perturbations yielded mean passing rates of 98.5±0.1%, 96.7±0.1%, and 93.6±0.7% for 3%/3mm, 3%/2mm, and 2%/2mm, with minimum rates of 98.30%, 96.51%, and 92.45%. Rotation and anti-rotation tests showed gamma passing rates of 99.7%, 99.6%, and 99.3% for 3%/3mm, 3%/2mm, and 2%/2mm, respectively, at 10% dose thresholds.
Conclusion: This study establishes the feasibility of accurate dose calculation in pRF-based proton plans, demonstrating high gamma passing rates under dose grid alignment and beam angle perturbations. These findings provide a framework for optimizing pRF-based planning to account for dose grid uncertainties and improve clinical accuracy.