The Monte Carlo MCNPX program is used to simulate the transport process of proton beam incident the target region.The annihilation photon distribution is obtained by the reaction of16O (p,α) 13N,13 N β + decay and e + + e-→ 2γ to determine the relationship between the target position and the depth of Bragg peak.The simulation results show that when the energy of 60 MeV-150 MeV proton enters the muscle phantom,the position of the highest photon flux declining is Bragg peak position,the error is less than 2％;when the 90 MeV proton enters the muscle containing GTV,The position of Bragg peak shifted.At the same time,the position of the highest photon flux declining is Bragg peak position,the error is less than 1％;The target location which uses the method of Monte Carlo to determine is closer the ideal value.%本文利用MCNPX程序模拟了质子束入射靶区的输运过程.通过16O (p,α)13N、13N的β+衰变、e++e-→2γ,得到湮灭光子分布,确定靶区位置与Bragg峰深度的关系.模拟结果显示,能量为60MeV～ 150 MeV的质子入射肌肉组织模体时,湮灭光子通量下降梯度最大的位置为Bragg峰位置,位置偏差＜2％;当90 MeV质子入射含GTV(肿瘤靶区)的肌肉组织模体时,Bragg峰位置发生移动,此时湮灭光子通量下降梯度最大的位置与Bragg峰位置相同,位置偏差＜1％.利用MC法确定靶区位置,更接近理想位置.
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