中文摘要：

束流扩展是研究质子治疗大体积深度肿瘤的基础，利用Monte Carlo多粒子模拟软件Fluka2006．3b．10，计算质子经过单阻止柱双散射体后束流横向分布特性，与相同条件下由Highland公式经解析计算相比较．结果表明：在束流分布均匀性大于95％的范围内，Fluka计算得到的质子通量小于由Highland公式经解析计算得到的结果，膜薄的条件下二者符合好于膜厚的条件．束流扩展半径随着两个散射膜厚度的增加而增大，束流利用率先增加后减小，最大值是16．9％．

英文摘要：

Beam spreading is the foundation of proton therapy for large area and depth tumor. The characteristics of proton lateral beam distribution for a solid beam stopper double scattering system are investigated using Monte Carlo muhi-particle transport code Fluka and the results are compared with analytical computation by using Highland formula under the same conditions. It is found that proton fluence obtained by Fluka is lower than that by analytical computation with Highland formula in the region where the variation in uniformity is ± 2.5 % and they coincide better with thin-foil than with thick-foil. For a solid beam stopper double scattering system, as the thickness of foils increases, the radius of beam spreading increases, but the efficiency of beam use age increases firstly and then decreases, the maximum value is about 16.9%.