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Title: Modelowanie terapeutycznych wiązek promieniowania za pomocą metody Monte Carlo
Authors: Pietrzak, Robert
Advisor: Konefał, Adam
Keywords: Metoda Monte Carlo; dozymetria; dozymetria kliniczna
Issue Date: 2017
Publisher: Katowice: Uniwersytet Śląski
Abstract: In this work models of two therapeutic beams of high-energy X-rays and protons were elaborated. The purpose of the investigation was the determination of significant parameters used in clinical dosimetry, basing on the elaborated models. The calculations were performed by means of computer simulations on the ground of the Monte Carlo algorithm. At the first stage of this work the head model of the Clinac 2300 linear accelerator by Varian was elaborated with the use of the professional MCNPX code. Verification of this model was carried out using the comparison between the calculated and measured depth-dose distributions in the standard dosimetry medium – water. The depth-dose distributions in water were determined for SSD = 100 cm and for three square radiation fields of 3 cm x 3 cm, 10 cm x 10 cm and 40 cm x 40 cm. Successful validation of the prepared model with the measuring system model made it possible to begin the next part of this investigation in which the energy spectra along the central axis of the beam and in the direction perpendicular to this axis in water were calculated. The spectral calculations were performed for the therapeutic 20 MV X-ray beam. The influence of the radiation field sizes on the shapes of the spectra in water were determined and the mean energy of the beam was calculated for the chosen irradiation conditions. At the second stage of this work the proton beams and the PTW 23343 Markus type ionization chamber used in clinical dosimetry were modeled. On the base of these models the perturbation factors 𝑝𝑤𝑎𝑙𝑙 , 𝑝𝑐𝑎𝑣 and the total perturbation factor 𝑝𝑞 were calculated for the punctual proton beam with energies of 15 MeV, 30 MeV, 60 MeV, 80 MeV. The influence of energy and spatial spread on the perturbation factors was determined. Moreover, the model of the real beam based on the passive system forming the proton beam in the Institute of Nuclear Physics of Polish Academy of Sciences in Bronowice was elaborated. The investigation basing on this model indicated that the depth-dose distributions obtained with the use of the water logic detectors and with the Marcus chamber model are compatible and they agree with the experimental results.
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