Stepanek J, Blattmann H, Laissue J A, Lyubimova N, Di Michiel M, Slatkin D N
Institute of Pathology, University of Bern, Switzerland.
Med Phys. 2000 Jul;27(7):1664-75. doi: 10.1118/1.599034.
Microbeam radiation therapy (MRT) is a currently experimental method of radiotherapy which is mediated by an array of parallel microbeams of synchrotron-wiggler-generated x-rays. Suitably selected, nominally supralethal doses of x-rays delivered to parallel microslices of tumor-bearing tissues in rats can be either palliative or curative while causing little or no serious damage to contiguous normal tissues. Although the pathogenesis of MRT-mediated tumor regression is not understood, as in all radiotherapy such understanding will be based ultimately on our understanding of the relationships among the following three factors: (1) microdosimetry, (2) damage to normal tissues, and (3) therapeutic efficacy. Although physical microdosimetry is feasible, published information on MRT microdosimetry to date is computational. This report describes Monte Carlo-based computational MRT microdosimetry using photon and/or electron scattering and photoionization cross-section data in the 1 eV through 100 GeV range distributed publicly by the U.S. Lawrence Livermore National Laboratory (LLNL) in the 1990s. These are compared with Monte Carlo-based microdosimetric computations using a code and physical data available in the 1980s. With the aim of using the PSI-version of GEANT Monte Carlo code for future macro- and micro/nano-dosimetric studies of Microbeam Radiation Therapy (MRT) a comparison of this code is made with the INHOM(EGS4) (version 1990), Dilmanian-CPE and Persliden-CPE Monte Carlo photon-electron codes (both version 1990) with which the absorbed dose distributions were calculated in 1990 and 1991 considering, (a) a single cylindrical microbeam, (b) multiple cylindrical microbeams in an orthogonal square bundle, and (c) multiple planar microbeams. It is shown that the PSI-version of GEANT can potentially deliver more accurate results (a) using presently the most advanced atomic data, and especially (b) employing "Single-collision" electron transport instead of only the "Condensed-history" electron transport as in code INHOM(EGS4). In contrast Dilmanian-CPE and Persliden-CPE codes deposit the electron energy locally instead of transporting it to the correct position.
微束放射治疗（MRT）是一种目前仍处于实验阶段的放射治疗方法，它由同步加速器摆动器产生的X射线的一系列平行微束介导。适当选择后，以名义上的超致死剂量将X射线传递给大鼠体内携带肿瘤组织的平行微切片，既可以起到姑息作用，也可以达到治愈效果，同时对相邻的正常组织几乎不造成或不造成严重损害。尽管MRT介导的肿瘤消退的发病机制尚不清楚，但与所有放射治疗一样，这种理解最终将基于我们对以下三个因素之间关系的理解：（1）微剂量学，（2）对正常组织的损伤，以及（3）治疗效果。虽然物理微剂量学是可行的，但迄今为止关于MRT微剂量学的已发表信息都是计算性的。本报告描述了基于蒙特卡罗的计算MRT微剂量学，使用了美国劳伦斯利弗莫尔国家实验室（LLNL）在20世纪90年代公开发布的1eV至100GeV范围内的光子和/或电子散射以及光电离截面数据。将这些数据与使用20世纪80年代可用的代码和物理数据进行的基于蒙特卡罗的微剂量学计算进行了比较。为了在未来对微束放射治疗（MRT）进行宏观和微观/纳米剂量学研究时使用GEANT蒙特卡罗代码的PSI版本，将该代码与INHOM（EGS4）（1990版）、Dilmanian-CPE和Persliden-CPE蒙特卡罗光子-电子代码（均为1990版）进行了比较，在1990年和1991年使用这些代码计算了吸收剂量分布，考虑了：（a）单个圆柱形微束，（b）正交方形束中的多个圆柱形微束，以及（c）多个平面微束。结果表明，GEANT的PSI版本可能会提供更准确的结果，（a）目前使用最先进的原子数据，特别是（b）采用“单碰撞”电子传输，而不是像INHOM（EGS4）代码那样仅采用“凝聚历史”电子传输。相比之下，Dilmanian-CPE和Persliden-CPE代码将电子能量局部沉积，而不是将其传输到正确位置。
