Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia, 23298, USA.
Med Phys. 2011 Jan;38(1):343-53. doi: 10.1118/1.3528201.
This article presents a general procedural framework to assess the point-by-point precision in mapped dose associated with the intrinsic uncertainty of a deformable image registration (DIR) for any arbitrary patient.
Dose uncertainty is obtained via a three-step process. In the first step, for each voxel in an imaging pair, a cluster of points is obtained by an iterative DIR procedure. In the second step, the dispersion of the points due to the imprecision of the DIR method is used to compute the spatial uncertainty. Two different ways to quantify the spatial uncertainty are presented in this work. Method A consists of a one-dimensional analysis of the modules of the position vectors, whereas method B performs a more detailed 3D analysis of the coordinates of the points. In the third step, the resulting spatial uncertainty estimates are used in combination with the mapped dose distribution to compute the point-by-point dose standard deviation. The process is demonstrated to estimate the dose uncertainty induced by mapping a 62.6 Gy dose delivered on maximum exhale to maximum inhale of a ten-phase four-dimensional lung CT.
For the demonstration lung image pair, the standard deviation of inconsistency vectors is found to be up to 9.2 mm with a mean sigma of 1.3 mm. This uncertainty results in a maximum estimated dose uncertainty of 29.65 Gy if method A is used and 21.81 Gy for method B. The calculated volume with dose uncertainty above 10.00 Gy is 602 cm3 for method A and 1422 cm3 for method B.
This procedure represents a useful tool to evaluate the precision of a mapped dose distribution due to the intrinsic DIR uncertainty in a patient. The procedure is flexible, allowing incorporation of alternative intrinsic error models.
本文提出了一种通用的程序框架，用于评估与任意患者的变形图像配准（DIR）固有不确定性相关的映射剂量的逐点精度。
通过三步过程获得剂量不确定性。在第一步中，对于成像对中的每个体素，通过迭代 DIR 过程获得一组点。在第二步中，使用 DIR 方法的不精确性来计算空间不确定性的点的离散度。在这项工作中提出了两种量化空间不确定性的方法。方法 A 由位置向量的模块的一维分析组成，而方法 B 对点的坐标进行更详细的 3D 分析。在第三步中，将得到的空间不确定性估计与映射剂量分布结合使用，以计算逐点剂量标准偏差。该过程用于估计将 62.6Gy 剂量映射到十相四维肺 CT 的最大呼气和最大吸气时引起的剂量不确定性。
对于演示用的肺图像对，发现不一致向量的标准偏差高达 9.2mm，平均 sigma 为 1.3mm。如果使用方法 A，则这种不确定性会导致最大估计剂量不确定性为 29.65Gy，如果使用方法 B，则最大估计剂量不确定性为 21.81Gy。如果使用方法 A，则计算出的剂量不确定性超过 10.00Gy 的体积为 602cm3，如果使用方法 B，则计算出的剂量不确定性超过 10.00Gy 的体积为 1422cm3。
该程序代表了一种有用的工具，可用于评估由于患者内在 DIR 不确定性导致的映射剂量分布的精度。该程序具有灵活性，允许纳入替代的内在误差模型。
