Voxel model of individual cells and its implementation in microdosimetric calculations using GEANT4

Accurate dosimetric calculations at cellular and sub-cellular levels are crucial to obtain an increased understanding of the interactions of ionizing radiation with a cell and its nucleus and cytoplasm. Ion microbeams provide a superior opportunity to irradiate small biological samples, e.g., DNA, cells, and to compare their response to computer simulations. However, the phantoms used to simulate small biological samples at cellular levels are often simplified as simple volumes filled with water. As a first step to improve the situation in comparing measurements of cell response to ionizing radiation with model calculations, a realistic voxel model of a KB cell was constructed and used together with an already constructed geometry and tracking 4 (GEANT4) model of the horizontal microbeam line of the Centre d'Etudes Nucléaires de Bordeaux-Gradignan (CENBG) 3.5 MV Van de Graaf accelerator at the CENBG, France. The microbeam model was then implemented into GEANT4 for simulations of the average number of particles hitting an irradiated cell when a specified number of particles are produced in the beam line. The result shows that when irradiating the developed voxel model of a KB cell with 200 α particles, with a nominal energy of 3 MeV in the beam line and 2.34 MeV at the cell entrance, 100 particles hit the cell on average. The mean specific energy is 0.209 ± 0.019 Gy in the nucleus and 0.044 ± 0.001 Gy in the cytoplasm. These results are in agreement with previously published data, which indicates that this model could act as a reference model for dosimetric calculations of radiobiological experiments, and that the proposed method could be applied to build a cell model database.