Monte carlo simulation of linear accelerator and dosimetric quality assurance

Modelling and simulation in radiation related practices are popular and developing fields. Various algorithms, codes and softwares that make calculations with these algorithms have been developed to simulate transport of radiation. The need for devices and physical circumstances has reduced by means of that models and systems developed in computer environment could also be worked and tested in computer environment. Thus, cost and time advantages have been gained. Monte Carlo is a method that can be used to solve mathematical and physical problems by using simulation technique. A stochastic process can be simulated with random events with ragular random numbers. In this study, linear accelerator gantry has been modelled and simulated also many tests have been made with water phantom and ion chamber model by using MCNP code (Monte Carlo N-Particle) with Monte Carlo method. Dosimetric quality assurance of simulation has been made by the means of comparing simulation results and experimental results taken from linear accelerator. For this purpose, percent depth dose and dose profile measurements for flattening filter system and unfiltered (flattening filter free) system in 18 MV photon energy have been seperately examined and it has been concluded that they match up with experimental and theoretical values. Flux and spectrum analysis have been made for photoneutrons produced as a result of photonuclear reactions along with the photons and electrons in linear accelerator, and the contribution of materials in the gantry to the neutron production has been analysed. The subject of photoneutron is examined for filtered and unfiltered systems separately, and detailed information has been gained about neutrons produced in linear accelerator. This linear accelerator model and simulations could be used not only for medical purposes but also in research and development, design and shielding fields. The device could be operated in any energy level in addition to the particular energy level enabled by the medical linear accelerator softwares.