不同材质Bolus致电子线放疗剂量分布差异研究

Background]: Boluses are utilized in the radiotherapy of superficial tumors, and a diverse range of materials is utilized in bolus fabrication. [Purpose]: To study the effects of different bolus materials on dose distributions during electron beam radiotherapy. [Methods]: The phase space files (PSFs) of electron beams from the IAEA official website were obtained to serve as the initial particle source. Using Geant4, the energy deposition of these beams in water were calculated and the physical parameters were validated. The superficial tumor radiotherapy models incorporating an overlying bolus were developed. Bolus thicknesses of 10 mm and 15 mm were employed at electron beam energies of 6 MeV and 9 MeV, respectively. The bolus materials evaluated included water, polystyrene, polylactic acid (PLA), silica-gel, and glycerol. The transport of electron beams within the models were simulated and a quantitative analysis comparing differences in maximum dose (Dmax), maximum dose depth (R100), superficial dose (D0), effective treatment depth (Reff), and dose distribution beyond the effective treatment depth among the models with different bolus materials were conducted. [Results]: As the bolus was composed by different materials, the difference of the Dmax is less than 3%, and for 10 mm and 15 mm bolus, the largest difference for R100, D0 and Reff are about 2 mm and 5 mm, 7% and 5%, 2.3 mm and 3.6 mm, respectively. The Dmax and D0 followed the order of polystyrenewaterPLAglycerolsilica-gel, and the R100 and Reff followed the order of polystyrenewaterPLAglycerolsilica-gel. The dose after Reff followed the order of polystyreneglycerolPLAwatersilica-gel, and with the depth of the tissue increases, the differences of relative average PDD gradually increase until the PDDs decrease to around 1%, with a maximum difference of about 10%. [Conclusions]: Bolus material has a significant impact on the dose distribution of electron beam radiotherapy. Reasonable selection of bolus material is of great significance for tumor radiotherapy and normal tissue protection.