MULTIPLE SCATTERING THEORY APPLIED TO ELECTRON DOSIMETRY

电子束越来越多地用于辐射 治疗癌症，因为它们的快速剂量下降最小化 治疗后关键健康组织的辐照 音量. 不幸的是，对于治疗计划而言， 还可以常规计算吸收剂量分布 确切地说，特别是在存在组织不均匀性的情况下， 和身体弯曲。 在穿透人体的过程中，高能电子 遭受了许多碰撞，并遵循曲折，虽然 主要是前进，路径。直到最近， 研究人员已经开始应用费米-艾格斯多重散射 理论对电子剂量计算问题的认识， 这个理论将电子束的行为描述为 合理的第一近似，至少在均匀或 水平分层介质 然而费米-艾格斯理论 不能直接用于计算电子剂量 具有局部不均匀性的配置的分布， 某种近似的梁-梁求和方法必须 使用这种配置，如果费米-Eyges理论是要 采用 这个正在进行的研究项目的目标是开发一种电子 剂量计算算法，其在 预期在临床上遇到的最复杂的情况， 然而，在能够以一种 计算机化治疗计划系统（足够短的计算 时间）。 产生这样一个算法需要从我们的 广义高斯多次散射理论及其发展 一个比费米-艾格斯更精确的理论 理论，并提供剂量的即时计算 直接从（三维）CT扫描数据，即使对于任意 局部不均匀性的配置。 除了多重 散射过程中，各种次级效应将被 加入到计算算法中。 广泛的蒙特 卡洛计算机工作是设想在发展和 算法验证。

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.