Development and verification of a Geant4 model of the electron beam mode in a clinical linear accelerator

At present, a significant number of studies are focused on the development of novel methodologies for the fabrication of dosimetry phantoms. One of these methods is to produce heterogeneous samples by 3D printing. In order to select the most appropriate parameters for such products, it is necessary to conduct numerical simulations. In this work, we developed the model of a beam-forming system using a medical linear accelerator as a reference. This model was used to determine simulation parameters and corresponding dose distributions of an electron beam with nominal energies of 6, 12, and 15 MeV in a homogeneous water phantom. These parameters were, in fact, adapted to provide maximum agreement between simulated distributions and those experimentally obtained with the clinical linear accelerator. The beam simulation was performed using the Geant4 Monte Carlo toolkit. The simulation geometry of the accelerator treatment head includes scattering foil and a flattening filter, which are designed for electron beam broadening. Additionally, the beam-forming system was incorporated to collimate the beam to the required size. A metal applicator was included to reduce the contribution of electron scattering in air. The main simulation parameters were iteratively tuned by comparing simulation results with experimentally obtained data. It is shown that the simulated percentage depth dose and transverse profiles for electron beams in water phantom are in good agreement with the experimental data obtained with a cylindrical ionization chamber. This demonstrates that the methodology employed in the development of the numerical model of the medical linear accelerator is vendor-independent, readily implementable, and allows for rapid calculations. Furthermore, the model can be applied for a variety of purposes, including the selection of parameters for the fabrication of heterogeneous dosimetry phantoms.