Sometimes in electron radiotherapy, Bremsstrahlung photon is produced in accelerator head. This photon contamination creates various doses in electron beams. In this study, varian accelerator in electron mode has been simulated and the photon contamination depth dose for three energies 6, 9 and 12 MeV in Monte Carlo method was calculated. Also, electron depth dose curves in simulation and measurement were compared. The discrepancies between measurement and simulation of depth dose curves were calculated in high accuracy by a program that was written in FORTRAN language. The error average is less than 1.5% in semi-linear region for these three energies. Results show that the simulation has a good accuracy. Also, the graphs demonstrate that the dose of photon contamination is trivial versus electron dose. In phantom surface percentage photon contamination dose for these three energies ranged between 0.284% and 0.340% of maximum dose.

Clinical dosimetry and high precision in treatment system is an important characteristic in clinical process. Due to various limitations in clinical environment and detectors, it is difficult to achieve a detailed information experimentally (Zhu et al., 2001; and Ding, 2002). One of the main advantages of Monte Carlo technique is the provision and identification of a detailed history of each particle. Therefore, Monte Carlo simulation can be used in collecting information that cannot be measured experimentally (Ding, 2002). In radiological science, Monte Carlo techniques have provided more applied information in beam simulation. By improving the computer technologies, it can use various Monte Carlo methods in radiotherapy. Monte Carlo simulation is an accurate tool in prospect of dose distribution and quantities in patient radiotherapy. The Monte Carlo method can model all electron and photon reactions and prospected dose distribution in improved geometry with high accuracy (Brady et al., 2006). Photon contribution dose in a clinical electron beam provides a little dose in patient, major part of this X-ray dose is produced by the accelerator exit window tube, monitor chamber, scattering foil, X-ray collimators and electron applicator. The structure and geometry of these various parts can be optimized for producing the least number of Bremsstrahlung contamination (Mackie and Scrimger, 1982; and El-Khatib et al., 1991).

In linear accelerators with scattering foil, the foil is the main source in photon contamination (Geyer et al., 2006). In many linear accelerators, scattering foils are used to generate broad beams but these foils cause Bremsstrahlung contamination especially in high energies (Sorcini et al., 1997). The atomic number and thickness of a scattering foil have a mass effect on this Bremsstrahlung (Zhu et al., 2001). In this study, the dose that occurred due to photon contamination in 6, 9 and 12 MeV electron beams of depth doses curve was measured by MCNP code. Also the depth dose curve from measurement and simulation of Varian clinical linear accelerator was compared.

Physics Journal, Electrical Transport Properties, Transmission Electron Microscopy, Magnetotransport Data, Antiferromagnetic Semiconductors, Chemical Precipitation Method, Nanocrystalline Manganites, Perovskite Structure, Citrate-gel Method, Polycrystalline Perovskite Material, Debye Scherrer Formula.