True three-dimensional dose computations for megavoltage x-ray therapy: a role for the superposition principle.
True three-dimensional dose computations for megavoltage x-ray therapy: a role for the superposition principle.
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兆伏 X 射线治疗的真实三维剂量计算：叠加原理的作用。
DOI：
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发表时间：
1992
期刊：
影响因子：
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通讯作者：
Sharpe Mb
中科院分区：
文献类型：
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作者：
Battista Jj;Sharpe Mb
：放射治疗的目的是将规定的放射剂量准确地集中在患者的目标体积内。成像技术的重大进步极大地提高了我们在三维 (3D) 上规划放射治疗和几何验证治疗的能力，但同时也需要提高剂量测定的准确性。建议在靶区和辐射敏感的正常组织中以 3% 的精度计算辐射剂量。我们回顾了这一建议背后的基本原理，并描述了能够实现这一目标的新一代 3D 剂量算法。真正的 3D 剂量计算可跟踪 3D 空间中的初级辐射和散射辐射，同时考虑组织不均匀性。过去，剂量分布是在二维横向切片中计算的，假设患者的解剖结构在附近切片中不会突然变化。我们证明了正确计算 3D 散射对光子和电子剂量的贡献的重要性，并显示了使用传统 2D 方法引起的剂量误差的大小。蒙特卡罗技术是最通用和最严格的方法，因为模拟了单独的初级和次级粒子轨迹。然而，这种方法对于临床治疗计划来说太耗时。我们回顾了一种基于叠加原理的方法，该方法在计算速度和剂量精度之间实现了合理的折衷。在这种方法中，剂量沉积分为两个步骤。首先，计算吸收体中相互作用的入射光子的衰减，以确定材料中释放的总能量（TERMA）。该量被视为每个照射点的脉冲。其次，散射光子和电子的能量传输由点剂量扩散核描述。剂量分布是内核的叠加，由所有相互作用位点的 TERMA 脉冲大小加权。在这篇综述中，我们展示了叠加方法的功能，特别是对于带电粒子不平衡的情况，并且我们报告了几个研究小组在将该方法应用于临床治疗计划方面所取得的进展。未来，叠加方法将在适形照射技术的剂量优化中发挥重要作用，因为它与滤波反投影图像重建密切相关。
: The objective of radiation therapy is to concentrate a prescribed radiation dose accurately within a target volume in the patient. Major advances in imaging technology have greatly improved our ability to plan radiation treatments in three dimensions (3D) and to verify the treatment geometrically, but there is a concomitant need to improve dosimetric accuracy. It has been recommended that radiation doses should be computed with an accuracy of 3% within the target volume and in radiosensitive normal tissues. We review the rationale behind this recommendation, and describe a new generation of 3D dose algorithms which are capable of achieving this goal. A true 3D dose calculation tracks primary and scattered radiations in 3D space while accounting for tissue inhomogeneities. In the past, dose distributions have been computed in a 2D transverse slice with the assumption that the anatomy of the patient dose not change abruptly in nearby slices. We demonstrate the importance of computing 3D scatter contributions to dose from photons and electrons correctly, and show the magnitude of dose errors caused by using traditional 2D methods. The Monte Carlo technique is the most general and rigorous approach since individual primary and secondary particle tracks are simulated. However, this approach is too time-consuming for clinical treatment planning. We review an approach that is based on the superposition principle and achieves a reasonable compromise between the speed of computation and accuracy in dose. In this approach, dose deposition is separated into two steps. Firstly, the attenuation of incident photons interacting in the absorber is computed to determine the total energy released in the material (TERMA). This quantity is treated as an impulse at each irradiated point. Secondly, the transport of energy by scattered photons and electrons is described by a point dose spread kernel. The dose distribution is the superposition of the kernels, weighted by the magnitude of the TERMA impulse for all interaction sites. In this review, we demonstrate the capabilities of the superposition method, particularly for situations of charged particle disequilibrium, and we report on the progress made by several research groups in adapting this method to clinical treatment planning. In the future, the superposition method will have a significant role in dose optimization for conformal irradiation techniques because of its close correspondence to image reconstruction by filtered back-projection.