Linear accelerator and MLC Monte Carlo model in EGSnrc/BEAMnrc system; Model linearniho urychlovace a MLC v Monte Carlo systemu EGCnrc/BEAMnrc

In radiotherapy (RT) the Monte Carlo (MC) method is used especially as a golden standard for comparison with measured data, modelling of a detector response or a treatment planning system (TPS) calculation. In last years, using of an IMRT technique has been rapidly increasing in developed countries and also in Czech Republic. Benefit of IMRT is strongly dependent on a precise treatment planning and accurate target volume dose delivery. Precise dose delivering is interwoven with IGRT and for dose distribution verification the phantom measurement is usually performed. However, this way of verification may not discover possible dose distribution discrepancy between TPS and a patient. MC modelling is suitable especially for this situation. Recently increased interest in this field can be noticed in foreign authors works. Although IMRT technique is commonly used in our country this topic is not investigated. The MC simulation for IMRT is based on a verified linear accelerator treatment head model. In our case the model of Clinac 2100 C/D (Varian Medical System) is created. EGSnrc/BEAMnrc code is used for MC modelling. This system is adjusted especially for RT simulation. The model can be divided into several subsections. It is necessary to know precise accelerator treatment head geometrical parameters (from a producer) and convert them to EGSnrc/BEAMnrc. (authors)