GEANT4-based Monte Carlo Simulation of Beam Quality Correction Factors for the Leksell Gamma Knife® Perfexion™

With the publication of TRS-483 in late 2017 the IAEA has established an international code of practice for reference dosimetry in small and non-standard fields based on a formalism first suggested by Alfonso et al. in 2008. However, data on beam quality correction factors ($k_{Q_{msr,}{Q}_0}^{f_{msr,}{f}_{ref}}$) for the Leksell Gamma Knife® Perfexion™ is scarce and what little data is available was obtained under conditions not necessarily in accordance with the IAEA's recommendations. This study constitutes the first systematic attempt to calculate those correction factors by applying the new code of practice to Monte Carlo simulation using the GEANT4 toolkit. $k_{Q_{msr,}{Q}_0}^{f_{msr,}{f}_{ref}}$ values were determined for three common ionization chamber detectors and five different phantom materials, with results indicating that in most phantom materials, all chambers were well suited for reference dosimetry with the Gamma Knife^®. Similarities and differences between the results of this study and previous ones were also analyzed and it was found that the results obtained herein were generally in good agreement with earlier PENELOPE and EGSnrc studies.