Modeling of the siemens artiste linear accelerator device with using Monte Carlo Method and evaluation of parameters effecting to energy

The main purpose of radiotherapy is to give the highest radiation dose to the tumor and to deliver minimum dose to the healthy tissues surrounding tumor. To achieve this purpose, the dose distribution must be compared and verified with a high accuracy method. The Monte Carlo method simulates interaction possibilities for various physical processes and to solve the problem by using random numbers. This method uses reliable distribution functions that control each interaction of photons and electrons in air and matter. As the Monte Carlo method tracks each particle throughout its lifetime and takes into account all the interactions it does, this method is the most accurate method for simulation of radiotherapy treatments. In this study, we have investigated initial electron parameters of Siemens Artiste linear accelerator (LINAC) with 6 MV photon beam by using the Monte Carlo method. It is essential to define all the characteristics of initial electrons hitting the target i.e. mean energy and full width of half-maximum (FWHM) of the spatial distribution intensity, which is needed to run Monte Carlo simulations. Measurement data of percent depth dose (PDD) and lateral dose profile were obtained in water by a farmer ion chamber. In additional, we have used film dosimetry in different depth for PDD and lateral dose. At the first step, Siemens Artiste LINAC head geometry was modeled using BEAMnrc code after the specifications of LINAC obtained from the manufacturer. The BEAMnrc of LINAC head components include the exit window, target, primary collimator, flattening filter, monitor chamber, Y Jaws and X multi leaf collimator (MLC). At the second step, the phase space files were used as input file to DOSXYZnrc simulation to determine the dose distribution in water phantom that was created by DOSXYZnrc program. The dose distributions for PDD and beam lateral dose profile have been calculated in water phantom. All the results were obtained at source-surface distance (SSD) of 100 cm and in 10 x 10 cm2 field. It was concluded that there existed a good conformity between Monte Carlo simulation and measurement data when we used electron mean energy 6.3 MeV and 0.30 cm FWHM value as initial parameters. We have observed that FWHM values affect very little on PDD and we see the electron mean energy and FWHM values affect on lateral dose profile. However, these effects are between tolerance values. The initial parameters especially depend on components of LINAC head. A small change in electron parameters creates strong effects on the dose. Therefore, electron parameters should be well defined. Within the scope of this thesis, the phase space file obtained from Monte Carlo Simulation can be used in dose scattering, MLC leakage, checking and comparing the dose distribution occurring anywhere on the patient and in various radiation studies. Keywords: Monte Carlo, Simulation, BEAMnrc, DOSXYZnrc, Siemens Artiste.