Dosimetric measurements of the medical LINAC device using phantoms are an important procedure to determine the correct delivery dose on the target volume. The percentage depth dose values of RW3, SW557, ABS, epoxy, PRESAGE phantom materials obtained from a simulation program were compared with those experimentally measured with water phantom at 6 and 18 MV photon energy spectrums. The values of energy spectrums of photons were taken from the database of Elekta Synergy Linear Accelerator device and defined in GATE/Geant4 simulation program. The mean percentage dose differences for all these materials were compared with water phantom and the closest phantom material to water was determined as SW557 at 6 and 18 MV photon energies. The mass attenuation coefficients, the effective atomic numbers and electron densities of water-equivalent phantom materials and some selected human organs were found for both monoenergetic photons and 6, 18 MV photon energy spectrums using GATE simulation code. Furthermore, a new approximation method was developed to calculate the mass attenuation coefficient for the photon energy spectrums. There was determined to be good agreement between the numerical calculations of the approximation method and the simulation results, with a difference of less than 4% between them.
Keywords: Effective atomic number; GATE/Geant4 simulation; ICRU tissue; Mass attenuation coefficient; Radiotherapy; Water equivalent phantom materials.
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