Badal Andreu, Kyprianou Iacovos, Badano Aldo, Sempau Josep
Institut de Tècniques Energètiques, Universitat Politècnica de Catalunya, Spain.
Radiother Oncol. 2008 Jan;86(1):99-103. doi: 10.1016/j.radonc.2007.11.009. Epub 2007 Dec 3.
Monte Carlo codes can simulate the transport of radiation within matter with high accuracy and can be used to study medical applications of ionising radiations. The aim of our work was to develop a Monte Carlo code capable of generating projection images of the human body. In order to obtain clinically realistic images a detailed anthropomorphic phantom was prepared. These two simulation tools are intended to study the multiple applications of imaging in radiotherapy, from image guided treatments to portal imaging.
We adapted the general-purpose code PENELOPE 2006 to simulate a radiation source, an ideal digital detector, and a realistic model of the patient anatomy. The anthropomorphic phantom was developed using computer-aided design tools, and is based on the NCAT phantom. The surface of each organ is modelled using a closed triangle mesh, and the full phantom contains 330 organs and more than 5 million triangles. A novel object-oriented geometry package, which includes an octree structure to sort the triangles, has been developed to use this complex geometry with PENELOPE.
As an example of the capabilities of the new code, projection images of the human pelvis region were simulated. Radioactive seeds were included inside the phantom's prostate. Therefore, the resulting simulated images resemble what would be obtained in a clinical procedure to assess the positioning of the seeds in a prostate brachytherapy treatment.
The new code can produce projection images of the human body that are comparable to those obtained by a real imaging system (within the limitations of the anatomical phantom and the detector model). The simulated images can be used to study and optimise an imaging task (i.e., maximise the object detectability, minimise the delivered dose, find the optimum beam energy, etc.). Since PENELOPE can simulate radiation from 50 eV to 1 GeV, the code can also be used to simulate radiotherapy treatments and portal imaging. Using the octree data structure, the new geometry model does not significantly increase the computing time when compared to the simulation of a much simpler quadric geometry. In conclusion, we have shown that it is feasible to use PENELOPE and a complex triangle mesh geometry to simulate real medical physics applications.
蒙特卡罗代码能够高精度地模拟辐射在物质中的传输，可用于研究电离辐射的医学应用。我们工作的目的是开发一种能够生成人体投影图像的蒙特卡罗代码。为了获得临床真实感图像，制备了一个详细的人体模型。这两种模拟工具旨在研究成像在放射治疗中的多种应用，从图像引导治疗到射野成像。
我们对通用代码PENELOPE 2006进行了改编，以模拟辐射源、理想数字探测器和患者解剖结构的真实模型。人体模型是使用计算机辅助设计工具开发的，基于NCAT模型。每个器官的表面使用封闭三角形网格建模，完整的模型包含330个器官和超过500万个三角形。已经开发了一个新颖的面向对象几何包，其中包括一个用于对三角形进行排序的八叉树结构，以便在PENELOPE中使用这种复杂的几何结构。
作为新代码功能的一个示例，模拟了人体骨盆区域的投影图像。人体模型的前列腺内包含放射性粒子。因此，生成的模拟图像类似于在临床程序中评估前列腺近距离治疗中粒子定位时获得的图像。
新代码可以生成与真实成像系统获得的图像相当的人体投影图像（在解剖模型和探测器模型的限制范围内）。模拟图像可用于研究和优化成像任务（即最大化物体可检测性、最小化所输送的剂量、找到最佳束能量等）。由于PENELOPE可以模拟50 eV至1 GeV的辐射，该代码还可用于模拟放射治疗和射野成像。使用八叉树数据结构，与模拟简单得多的二次几何结构相比，新的几何模型不会显著增加计算时间。总之，我们已经表明使用PENELOPE和复杂的三角形网格几何结构来模拟实际医学物理应用是可行的。
