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Abstract

Scope: The main purpose is the investigation and analysis of radiotherapy techniques for small fields, as well as the detailed list of devices that support this method. Also, the optimal shielding material and combination of parameters for electrons and photons transfer to a tissue target through a simulation of a radiotherapy device was searched.. Methods and Materials: PENELOPE code was used, a ready-made free Monte Carlo code system. The system consists of a cylindrical long hole collimator with 4cm diameter. A single energy source of γ photons was used as the irradiation source at a distance of 100cm from the test tissue and inside the collimator. The shielding materials were Iron (Fe), Lead (Pb) and Tungsten (W) in thicknesses of 1cm, 3cm and 5cm 2MeV, 4MeV, 6MeV, 8MeV and 10MeV. Each simulation had a duration of 900sec (15min) or 107 photon stories. The results were extracted from spatial dose distribution diagrams, two- and three-dimensional, and from the cylindrical dose distribution. The spatial distribution was investigated for 10cm tissue depth, and the cylindrical distribution for 15cm tissue depth, with 1cm step. Results: A small percentage of radiation is constantly present very close to the limits of the irradiated surface, but outside them, which increases as the irradiation energy increases. Lead and Tungsten shielding is generally stronger than Iron shielding. We also observe an increase in radiation away from the irradiated area (> 5cm) in the Iron shield. Conclusion: Lead and Tungsten shielding give the best dose absorption results compared to Iron shielding. The two optimal parameter combinations are 5cm Lead shield with 4MeV radiation energy and 5cm Tungsten shield with 8MeV radiation energy.