Objective:To assess the effect of Bolus materials(a material has the same effect with tissue)on dose distribution of electron beam radiotherapy on chest wall after surgery for breast cancer.Methods:Radiotherapy model of chest wall after modified radical mastectomy for breast cancer was constructed in this study.Based on the 6 MeV electron beam phase space file(PSF),which came from the International Atomic Energy Agency(IAEA)official website,and the Geant4 Monte Carlo software package,the research calculated the dose distributions of the electron beam radiotherapy of 5 kinds of different materials included water,polystyrene,polylactic acid,glycerol and silica-gel in Bolus materials,and compared the differences of the dose distributions between chest wall and lung tissue.Results:The Bolus materials have a relatively minor effect on the depth of maximum dose(dmax)of electron beams on the chest wall.The dmax maximum difference that was caused by Bolus with 10mm thickness only was 2mm.The Bolus materials with 10mm thickness have a notable effect on dose distribution,particularly in the posterior edge of the chest wall and shallow lung tissue.The order of Bolus materials corresponding to the dose in the posterior edge of the chest wall,from large to small,was polystyrene,water,polylactic acid,silica-gel and glycerol.For Bolus materials with 5 mm thickness and 10 mm thickness,the dose differences were approximate 8%and 15%,respectively.In shallow lung tissue,the corresponding Bolus materials with doses from large to small were water,polystyrene,polylactic acid,silica-gel and glycerol.For Bolus materials with 5 mm thickness and 10 mm thickness,the maximum dose differences were approximate 50%and 70%,respectively.Conclusion:The effect of Bolus materials has larger effect on the dose distribution of electron beam radiotherapy on the chest wall.The reasonable selection of Bolus materials is contributed to ensure the dose of target region,and minimize dose deposition of lung tissue.
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