A proton dose calculation algorithm for conformal therapy simulations based on Moliere's theory of lateral deflections
A proton dose calculation algorithm for conformal therapy simulations based on Moliere's theory of lateral deflections
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DOI：
10.1118/1.598222
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发表时间：
1998-04-01
期刊：
影响因子：
3.8
通讯作者：
Deasy, JO
中科院分区：
文献类型：
--
作者：
Deasy, JO
提出了一种计算治疗能量范围（100-250 MeV）内质子剂量分布的算法。目标是为二维或三维模拟可能的强度调制质子治疗递送方案提供精确的铅笔束剂量分布。该算法基于莫里哀的侧向偏转理论，该理论准确地描述了入射带电粒子的侧向偏转分布。该理论通过通常的铅笔束近似应用于非均匀目标，该近似假设来自给定铅笔束的所有质子在每个深度穿过相同的材料。通过蒙特卡罗计算的宽场中心轴深度-剂量曲线进行影响-剂量转换，该曲线考虑了由于核碰撞和距离离散引起的衰减。通过在深度处使用径向分布函数的最佳拟合高斯近似来提高计算速度。给出了250 MeV和160 MeV条件下具有代表性的铅笔束和展开布拉格峰计算。在Bragg峰处，在水中计算的半最大值时横向全宽度与预期的理论横向值一致，在160 MeV时在1%以内，在250 MeV时在3%以内。该算法与卷积方法的不同之处在于，密度或原子组成的任何不均匀性的深度影响都以严格的方式考虑。该算法与基于费米-埃格斯的方法的不同之处在于，它严格考虑了原子电子的非小角散射和屏蔽效应。计算负担只比使用不那么严格的费米-埃格斯理论所期望的稍微大一点。(C) 1998美国医学物理学家协会。[s0094 - 2405(98) 02204 - 4]。
An algorithm is developed for computing proton dose distributions in the therapeutic energy range (100-250 MeV). The goal is to provide accurate pencil beam dose distributions for two-dimensional or three-dimensional simulations of possible intensity-modulated proton therapy delivery schemes. The algorithm is based on Moliere's theory of lateral deflections, which accurately describes the distribution of lateral deflections suffered by incident charged particles. The theory is applied to nonuniform targets through the usual pencil beam approximation which assumes that all protons from a given pencil beam pass through the same material at each depth. Fluence-to-dose conversion is made via Monte Carlo calculated broad-field central-axis depth-dose curves, which accounts for attenuation due to nuclear collisions and range straggling. Calculation speed is enhanced by using a best-fit Gaussian approximation of the radial distribution function at depth. Representative pencil beam and spread-out Bragg-peak computations are presented at 250 MeV and 160 MeV in water. Computed lateral full-widths-at-half-maximum's in water, at the Bragg peak, agree with the expected theoretical lateral values to within 1% at 160 MeV and to within 3% at 250 MeV. This algorithm differs from convolution methods in that the effect of the depth of any inhomogeneities in density or atomic composition are accounted for in a rigorous fashion. The algorithm differs from Fermi-Eyges based methods by accounting in a rigorous way for the effect of nonsmall-angle scattering and screening due to atomic electrons. The computational burden is only slightly greater than that expected using the less-rigorous Fermi-Eyges theory. (C) 1998 American Association of Physicists in Medicine. [S0094-2405(98)02204-4].