MULTIPLE SCATTERING THEORY APPLIED TO ELECTRON DOSIMETRY

电子束越来越多地被用于辐射 癌症的治疗，因为它们的快速剂量衰减将最大限度地减少 超出治疗范围的关键健康组织的照射 音量。不幸的是，对于治疗计划的目的并不是 还可以常规地计算吸收剂量分布 准确地说，尤其是在组织不均匀的情况下 和身体的曲度。在穿透身体时，高能电子 经历了多次碰撞和曲折，尽管 主要是向前，路径。直到最近，才有一些 调查人员已经开始应用费米-艾格斯多重散射 对电子剂量计算问题的理论认识 这一理论将电子束的行为描述为 合理的第一近似值，至少在齐次或 水平分层介质。然而，费米-艾吉斯理论 不能直接应用于计算电子剂量 具有局部化不均匀的配置的分布， 而某种近似的铅笔束求和方法必须是 如果费米-艾奇斯理论要被 使用。 这个正在进行的研究项目的目标是开发一种电子 具有足够精度的剂量计算算法 临床上预计会遇到的最复杂的情况， 但实际情况是能够在 计算机化治疗计划系统(足够短的计算 时间)。生成这样的算法需要从我们的 广义高斯多次散射理论及其发展 比费米-艾格斯理论更准确的适当理论 理论，它提供了立即计算剂量的方法 直接从(三维)CT扫描数据，即使是任意的 局部化不均匀的组态。除了多个 散射过程中，各种次要效应都会被 被合并到计算算法中。广泛的蒙特 卡洛计算机工作是在开发和设想中进行的 对算法进行了验证。

Electron beams are increasingly coming into use in the radiation treatment of cancer because their rapid dose falloff minimizes irradiation of critical healthy tissues beyond the treatment volume. Unfortunately, for treatment planning purposed it is not yet possible to routinely calculate the absorbed dose distribution precisely, particularly in the presence of tissue inhomogeneities and body curvature. In penetrating the body, high-energy electrons suffer a great many collisions and follow a tortuous, although mainly forward, path. It has only been recently that a number of investigators have begun to apply Fermi-Eyges multiple scattering theory to the problem of electron dose calculation, recognizing that this theory describes the behavior of the electron beam as a reasonable first approximation, at least in a homogeneous or horizontally layered medium. However, the Fermi-Eyges theory cannot be applied directly to calculating electron dose distributions for configurations with localized inhomogeneities, and some sort of approximate pencil-beam summation method must be use for such configurations if the Fermi-Eyges theory is to be used. The goal of this ongoing research project is to develop an electron dose calculation algorithm which is sufficiently accurate in the most complicated situations expected to be encountered clinically, yet practical in the sense of being able to be implemented in a computerized treatment planning system (short enough calculation time). Producing such an algorithm entails starting with our general Gaussian multiple-scattering theory and developing from it appropriate theory which is more accurate than the Fermi-Eyges theory, and which provides the immediate calculation of dose directly from (three-dimensional) CT scan data, even for arbitrary configurations of localized inhomogeneities. Besides the multiple scattering process, various secondary effects are to be incorporated into the computational algorithm. Extensive Monte Carlo computer work is envisioned in the development and verification of the algorithm.