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The Application Of EGS Code In Studying Electron Detection And The Effects Of Mask On Radiotherapeutic Dose Distribution

Posted on:2008-12-15Degree:MasterType:Thesis
Country:ChinaCandidate:Y Q ZhaoFull Text:PDF
GTID:2144360242464136Subject:Particle Physics and Nuclear Physics
Abstract/Summary:PDF Full Text Request
EGS(Electron-Gamma Shower)code is a Monte Carlo generic package which can simulate the transport of electron and photon in arbitrary conditions from keV to TeV, In this paper, we use the Monte Carlo code to study some problems which are difficult to solve by numerical calculating method and experimental method in practical work. This paper's mainly content as follows:(1) The preparatory work. In order to better understand the law of the interaction between electron and the matter and the dose distribution characteristic when the electron transport through the matter. We do some preliminary simulation work with a variety of ways in this paper, including: the shape of the energy spectrum and its change when the electron beam transport through a certain thickness of the material; the fluence and the planar fluence depth distribution of electron beam; Electronic back-scattering law, the monoenergetic electron absorption, electron bremsstrahlung and dose distribution of the electron(2) monoenergetic electron absorption experiment results and impact factors. Use the EGS code to study the monoenergetic electron's absorption in aluminum and the influence factors of experiment. Simulative results and experimental results are compared, when the simulative conditions consistent with the experimental conditions, they are consistent. The difference of the two semi-absorption thickness is not more than 3%. We also discussed how the experimental conditions affect the semi-absorption thickness value of the monoenergetic electron. The results showed: collimator, the aluminum windows of detector, the distance between the absorption material and the aluminum windows affect the measurement of the semi-absorption thickness value. Reducing the thickness of aluminum windows, shorten the distance between the absorption material and the aluminum windows can improve the measurement accuracy.(3) In the radiotherapy treatment process, effects of thermoplastic mask on dose distribution of radiotherapeutic beams. We use the BEAMnrc code that was specifically made for radioactive sources to study the effects of thermoplastic mask on X(y)-rays and electron dose. We found that the effects vary with the different materials, different density, different thickness and different structure of mask. The conclusions as follows: for X(γ) -rays, the use of mask will increase the surface dose. The greater density and thickness and the smaller mesh size of the mask, the more surface dose. The surface dose of no-mesh mask is more than that of the mask with mesh. For the electron beam, Mask moves the PDD curve forward and increases the surface dose. When the mask is thicker and the mesh size of the mask is smaller, the distance of the PDD curve moving forward is greater and the surface dose also is more. When there is no-mesh, the results are greater than that of mask with mesh. The simulation conclusions are consistent with the experimental conclusions, which provide a reliable theoretical basis for the radiation therapy program.
Keywords/Search Tags:Monte Carlo Method, EGS Code, BEAM Code, Semi-absorption thickness, Thermoplastic mask, PDD
PDF Full Text Request
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