Witztum A, George B, Warren S, Partridge M, Hawkins M A
CRUK/MRC Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford OX3 7DQ, United Kingdom.
Med Phys. 2016 Nov;43(11):6009. doi: 10.1118/1.4964790.
Toxicity dose-response models describe the correlation between dose delivered to an organ and a given toxic endpoint. Duodenal toxicity is a dose limiting factor in the treatment of pancreatic cancer with radiation but the relationship between dose and toxicity in the duodenum is not well understood. While there have been limited studies into duodenal toxicity through investigations of the volume of the organ receiving dose over a specific threshold, both dose-volume and dose-surface histograms lack spatial information about the dose distribution, which may be important in determining normal tissue response. Due to the complex geometry of the duodenum, previous methods for unwrapping tubular organs for spatial modeling of toxicity are insufficient. A geometrically robust method for producing 2D dose surface maps (DSMs), specifically for the duodenum, has been developed and tested in order to characterize the spatial dose distribution.
The organ contour is defined using Delaunay triangulation. The user selects a start and end coordinate in the structure and a path is found by regulating both length and curvature. This path is discretized and rays are cast from each point on the plane normal to the vector between the previous and the next point on the path and the dose at the closest perimeter point recorded. These angular perimeter slices are "unwrapped" from the edge distal to the pancreas to ensure the high dose region (proximal to the tumor) falls in the centre of the dose map. Gamma analysis is used to quantify the robustness of this method and the effect of overlapping planes.
This method was used to extract DSMs for 15 duodena, with one esophagus case to illustrate the application to simpler geometries. Visual comparison indicates that a 30 × 30 map provides sufficient resolution to view gross spatial features of interest. A lookup table is created to store the area (cm) represented by each pixel in the DSMs in order to allow spatial descriptors in absolute size. The method described in this paper is robust, requires minimal human interaction, has been shown to be generalizable to simpler geometries, and uses readily available commercial software. The difference seen in DSMs due to overlapping planes is large and justifies the need for a solution that removes such planes.
This is the first time 2D dose surface maps have been produced for the duodenum and provide spatial dose distribution information which can be explored to create models that may improve toxicity prediction in treatments for locally advanced pancreatic cancer.
毒性剂量反应模型描述了给予器官的剂量与特定毒性终点之间的相关性。十二指肠毒性是胰腺癌放射治疗中的剂量限制因素，但十二指肠中剂量与毒性之间的关系尚未完全明确。虽然通过研究接受超过特定阈值剂量的器官体积对十二指肠毒性进行的研究有限，但剂量体积直方图和剂量表面直方图都缺乏关于剂量分布的空间信息，而这在确定正常组织反应中可能很重要。由于十二指肠的几何形状复杂，以前用于展开管状器官以进行毒性空间建模的方法并不充分。为了表征空间剂量分布，已经开发并测试了一种专门针对十二指肠生成二维剂量表面图（DSM）的几何稳健方法。
使用德劳内三角剖分定义器官轮廓。用户在结构中选择一个起始坐标和一个结束坐标，并通过调节长度和曲率找到一条路径。该路径被离散化，从垂直于路径上前后点之间向量的平面上的每个点投射光线，并记录最接近周边点处的剂量。这些角向周边切片从胰腺远端的边缘“展开”，以确保高剂量区域（靠近肿瘤）落在剂量图的中心。使用伽马分析来量化该方法的稳健性以及重叠平面的影响。
该方法用于提取15个十二指肠的DSM，用一个食管病例来说明该方法在更简单几何形状中的应用。视觉比较表明，30×30的图提供了足够的分辨率来查看感兴趣的总体空间特征。创建一个查找表来存储DSM中每个像素所代表的面积（平方厘米），以便以绝对大小表示空间描述符。本文所述方法稳健，需要最少的人工干预，已被证明可推广到更简单的几何形状，并且使用现成的商业软件。由于重叠平面导致的DSM差异很大，这证明了需要一种消除此类平面的解决方案。
这是首次为十二指肠生成二维剂量表面图，并提供了空间剂量分布信息，可利用这些信息创建模型，以改善局部晚期胰腺癌治疗中的毒性预测。
