【摘 要】
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Purpose:To develop a pencil beam algorithm(PBA)for dose calculation of proton beams in both homogeneous and heterogeneous media.Methods:The proton PBA consisted of the integral depth-dose and the off-
【机 构】
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Key Laboratory of Neutronics and Radiation Safety,Institute of Nuclear Energy Safety Technology,Chin
【出 处】
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The 15th Asia-Oceania Congress of Medical Physics (AOCMP2015
论文部分内容阅读
Purpose:To develop a pencil beam algorithm(PBA)for dose calculation of proton beams in both homogeneous and heterogeneous media.Methods:The proton PBA consisted of the integral depth-dose and the off-axis lateral dose.The integrated depth dose was extracted from Monte Carlo(MC)simulation of 101 monoenergetic beams incident(50-250 MeV)in a water phantom,and performed one-dimensional scaling by the mass stopping power ratio to account for density heterogeneities.Fermi-Eyges scattering theory with material dependent scattering powers was used to transport pencil beams,and the characteristic width of elastic scattering events was determined by the differential Molière scattering theory; thus the incorporation of those scattering powers allowed PBA to calculate the accurate lateral spread profile of the beam in heterogeneous media.The large angle and non-elastic nuclear scattering events,which were also known as nuclear halo and modeled through two components:one Gaussian and one Cauchy-Lorentz distribution,of which parameters,widths and amplitudes,were determined by a nonlinear least squares fit of MC simulated single pencil beam dose profile in water.Results:Our PBA was validated against MC simulations of a simplified beamline in 5 benchmarking phantoms including homogeneous water/bone phantoms,and others with longitudinal and lateral heterogeneities for 2 field sizes(4×4,10×10 cm2).Agreements were quantified by calculating the percentage of points within 3 or 2 percent dose difference(PDD)or 2 mm distance to agreement(DTA).For all phantom geometries benchmarked,our PBA yielded 98%of dose points passed with PDD 3%or DTA 2 mm,and at least 95%of dose points passing PDD 2%or DTA 2 mm.Conclusion:The PBA developed in this work provided excellent results compared with MC simulations,and enables accurate dose calculation for implementation of Intensity Modulated Proton Therapy using dynamic scanning beam delivery system.
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