A technique for the quantitative evaluation of dose distributions
A technique for the quantitative evaluation of dose distributions
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DOI：
10.1118/1.598248
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发表时间：
1998-05-01
期刊：
影响因子：
3.8
通讯作者：
Purdy, JA
中科院分区：
文献类型：
--
作者：
Low, DA;Harms, WB;Purdy, JA
三维治疗计划系统的调试需要比较测量的和计算的剂量分布。技术已经开发，以促进定量比较，包括叠加等剂量，剂量差异，和距离协议（DTA）的分布。可接受的计算性能的标准通常被定义为分别在低剂量梯度和高剂量梯度区域中的剂量和DTA的公差。剂量差和DTA分布在它们的有用区域中相互补充。最近开发了一种复合分布，该分布呈现了未通过剂量差异和DTA比较标准的区域中的剂量差异。虽然复合分布标识了计算未通过预选标准的位置，但不提供数字质量度量以供显示或分析。开发了一种使用验收标准统一剂量分布比较的技术。可接受性的度量是剂量和物理距离中测量点和计算点之间的多维距离，按验收标准的分数缩放。在由剂量和空间坐标组成的空间中，验收标准形成一个椭圆面，其长轴尺度由各个验收标准确定，其中心位于所讨论的测量点。当计算的剂量分布面通过椭球体时，计算通过测量点的验收测试。测量点和计算点之间的最小径向距离（表示为剂量-距离空间中的表面）称为伽马指数。gamma > 1的区域对应于计算不符合验收标准的位置。整个测量剂量分布中的伽马测定提供了定量指示计算准确度的表示。使用6 MV射束半影的示例来说明伽马指数。(C)1998年美国医学物理学家协会。
The commissioning of a three-dimensional treatment planning system requires comparisons of measured and calculated dose distributions. Techniques have been developed to facilitate quantitative comparisons, including superimposed isodoses, dose-difference, and distance-to-agreement (DTA) distributions. The criterion for acceptable calculation performance is generally defined as a tolerance of the dose and DTA in regions of low and high dose gradients, respectively. The dose difference and DTA distributions complement each other in their useful regions. A composite distribution has recently been developed that presents the dose difference in regions that fail both dose-difference and DTA comparison criteria. Although the composite distribution identifies locations where the calculation fails the preselected criteria, no numerical quality measure is provided for display or analysis. A technique is developed to unify dose distribution comparisons using the acceptance criteria. The measure of acceptability is the multidimensional distance between the measurement and calculation points in both the dose and the physical distance, scaled as a fraction of the acceptance criteria. In a space composed of dose and spatial coordinates, the acceptance criteria form an ellipsoid surface, the major axis scales of which are determined by individual acceptance criteria and the center of which is located at the measurement point in question. When the calculated dose distribution surface passes through the ellipsoid, the calculation passes the acceptance test for the measurement point. The minimum radial distance between the measurement point and the calculation points (expressed as a surface in the dose-distance space) is termed the gamma index. Regions where gamma > 1 correspond to locations where the calculation does not meet the acceptance criteria. The determination of gamma throughout the measured dose distribution provides a presentation that quantitatively indicates the calculation accuracy. Examples of a 6 MV beam penumbra are used to illustrate the gamma index. (C) 1998 American Association of Physicists in Medicine.