EFFICIENT MONTE CARLO MODELING FOR GAMMA KNIFE PERFEXION

Monte Carlo (MC) simulations constitute the most accurate tool for dosimetric analysis in small radiation fields, such as those generated by the Leksell Gamma Knife Perfexion (LGK-PFX) system. However, implementing a fully detailed model of the system is computationally demanding, both in terms of processing time and geometric complexity, due to the explicit inclusion of the 576 collimators distributed throughout the device. To address this limitation, we present an efficient and accurate model based on a single phase-space file (PSF) generated from a source–collimator simulation for each collimator size (4, 8, and 16 mm), computed using PenEasy Monte. The resulting PSF is subsequently rotated to the required orientations to reproduce the system response. This approach drastically reduces the effective computational burden, as each reference PSF is generated only once and can then be reused to simulate any desired LGK-PFX configuration. Compared with full-system models that require hundreds of hours of computation and storage on the order of terabytes, the proposed rotating-PSF strategy enables Monte Carlo simulations with moderate computational resources, making MC-based verification feasible in a clinical context. The model was validated by comparing MC-generated dose distributions with measurements performed using EBT4 radiochromic films at Ruber International Hospital (Madrid), as well as with data provided by Elekta and other MC-based studies. A 7%–0.5 mm gamma analysis of the dose profiles showed pass rates above 95%. Output factors (OFs) for the 4 mm and 8 mm collimators were 0.848 ± 0.011 and 0.889 ± 0.011, respectively, in a cubic water phantom. Overall, the rotating PSF approach preserves dosimetric accuracy while substantially improving computational efficiency, providing a practical and clinically relevant solution for dosimetry with the LGK-PFX system. • Rotating PSF model developed for efficient Monte Carlo simulation of LGK Perfexion. • Simulation time and computational cost are greatly reduced with preserved accuracy. • Gamma pass rates above 95% validated against EBT4 radiochromic film measurements. • Flexible simulation of single sectors, sector combinations, or full LGK-PFX geometry.