Monte-Carlo simulation of high energy photon beams created by flattening-filter free medical linear accelerator

In this thesis, it was aimed to model and verify the Monte Carlo simulation of more than 10 MV energy Flattening Filter Free (FFF) linear accelerator. In addition, the proprieties of Bremsstrahlung photon beams were evaluated depending on the target structure and nucleus to reduce the potential difficulties in medical irradiation where high-energy photon beams are being used. The simulation of 18 MV FFF Elekta Synergy linear accelerator was created using FLUKA\Flair Monte Carlo (MC) program. This simulation was verified with experimental data obtained from the water phantom. The effects of the PRECISION card, EM-CASCA card, and photon, electron transport limit values on the simulation results were investigated. It was determined that the PRECESIO card and the EM-CASCA card did not affect the simulation results. At the same time, assigning high-energy electron transport limit values to regions that would not affect the calculation results and it did not affect the simulation results. Therefore, the computation time has been reduced. Linear accelerator simulations were modelled for WRe and Ta materials of different thicknesses. The Percentage Depth Dose (PDD) and profile of the FFF photon beam obtained from these simulations were evaluated. In conclusion, the MC simulation of the FFF linear accelerator was modelled and verified in the study. This simulation is the method that can be used to design the new target structure.