Jiang Steve B, Sharp Greg C, Neicu Toni, Berbeco Ross I, Flampouri Stella, Bortfeld Thomas
Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA.
Phys Med Biol. 2006 Feb 21;51(4):759-76. doi: 10.1088/0031-9155/51/4/001. Epub 2006 Jan 25.
In radiotherapy practice, one often needs to compare two dose distributions. Especially with the wide clinical implementation of intensity-modulated radiation therapy, software tools for quantitative dose (or fluence) distribution comparison are required for patient-specific quality assurance. Dose distribution comparison is not a trivial task since it has to be performed in both dose and spatial domains in order to be clinically relevant. Each of the existing comparison methods has its own strengths and weaknesses and there is room for improvement. In this work, we developed a general framework for comparing dose distributions. Using a new concept called maximum allowed dose difference (MADD), the comparison in both dose and spatial domains can be performed entirely in the dose domain. Formulae for calculating MADD values for various comparison methods, such as composite analysis and gamma index, have been derived. For convenience in clinical practice, a new measure called normalized dose difference (NDD) has also been proposed, which is the dose difference at a point scaled by the ratio of MADD to the predetermined dose acceptance tolerance. Unlike the simple dose difference test, NDD works in both low and high dose gradient regions because it considers both dose and spatial acceptance tolerances through MADD. The new method has been applied to a test case and a clinical example. It was found that the new method combines the merits of the existing methods (accurate, simple, clinically intuitive and insensitive to dose grid size) and can easily be implemented into any dose/intensity comparison tool.
在放射治疗实践中，人们常常需要比较两种剂量分布。特别是随着调强放射治疗在临床上的广泛应用，针对患者的质量保证需要用于定量剂量（或注量）分布比较的软件工具。剂量分布比较并非易事，因为为了具有临床相关性，必须在剂量域和空间域中进行。现有的每种比较方法都有其优缺点，仍有改进的空间。在这项工作中，我们开发了一个用于比较剂量分布的通用框架。使用一种称为最大允许剂量差异（MADD）的新概念，可以在剂量域中完全进行剂量域和空间域的比较。已经推导了用于各种比较方法（如综合分析和伽马指数）的MADD值的计算公式。为方便临床实践，还提出了一种称为归一化剂量差异（NDD）的新度量，它是通过MADD与预定剂量接受容差的比值缩放的某一点处的剂量差异。与简单的剂量差异测试不同，NDD在低剂量梯度区域和高剂量梯度区域均有效，因为它通过MADD同时考虑了剂量和空间接受容差。该新方法已应用于一个测试案例和一个临床实例。结果发现，该新方法结合了现有方法的优点（准确、简单、临床直观且对剂量网格大小不敏感），并且可以轻松地应用于任何剂量/强度比较工具中。
