Could Water Replace Muscle Tissue Used in Electron and Photon Beams?: A Monte Carlo Study

This study was conducted to evaluate the use of different phantom materials (muscle_ICRP, muscle_ICRU, and water) using Geant4-GAMOS Monte Carlo method. GAMOS which based on the Geant4 toolkit developed by European Organization for Nuclear Research (CERN) is a Monte Carlo simulation software. The material composition and density of muscle skeletal (ICRP), muscle striated (ICRU), and water (ICRU) used in this simulation were provided by Geant4 cross section data. Simulation objects consist of world, detector, source, and phantom. The phantom material used was distinguished. The source was placed inside a tube while detector was placed inside phantom. The detector was separated 2 cm from source in +x direction. The photon and electron beam with varied energies 0.5, 1.0, 1.5, and 2.0 MeV was used as source. The simulation time for each simulation was different depend on the incident particle type, particle energy, and phantom material composition. Electron beam takes longer time simulation than photon beam for varied phantom materials. The Rayleigh scattering, Compton scattering, and the photo-electric effect were occurred in each simulation but gamma conversion into electron and positron pairs only discovered in 1.5 and 2.0 MeV photon beam. The positron was produced because of pair production interaction. The energy histogram collected in this simulation shows that the muscle (ICRP and ICRU) material can be replaced by water if the muscle depth from the skin surface is not more than 2 cm. This results also were confirmed by comparing the mass coefficient attenuation and stopping power ratio curves between muscle (ICRP and ICRU) and water material extracted using other Monte Carlo software, EGSnrc.