Four-Dimensional Monte Carlo Dose Calculation

描述(由申请人提供)：为了研究依赖时间的几何图形中的剂量学效应，通常将单独的三维(3D)计算的结果相加或统计组合。如果几何形状复杂，如果设想高时间分辨率(例如，考虑剂量率)，或者如果作为时间函数的微观体积位移是未知的，则这是困难的。此外，很难研究双动力学系统来研究随时间变化的束流传输(多叶准直器中的移动叶片)对运动靶中的剂量沉积(器官运动或变形)的影响。这里需要的是4D而不是多个3D计算。蒙特卡罗(MC)模拟被认为是最准确的剂量计算工具，并可能在密度变化较大的地区产生最大影响，例如用于肺癌治疗。有趣的是，这也是我们可以预期器官运动对剂量分布影响最大的区域。MC方法非常适合于高精度地研究运动的剂量学效应。然而，到目前为止，与解析剂量计算技术一样，几何信息在模拟过程中不能被修改。这将应用程序限制为多个3D而不是真正的4D。利用面向对象的C编程技术，我们提出了真正的4D MC剂量计算。当射束结构和器官几何形状连续改变时，将计算患者体内的局部剂量沉积，根据叶排序文件，MLC叶位置将在模拟过程中改变。在可变形图像配准的基础上，我们将在剂量计算过程中根据患者的CT来跟踪微观区域。4D剂量计算将允许使用基于临床经验或患者特定的4D CT信息的预设移动模式。基于治疗头变化和患者呼吸模式研究任意时间尺度下双动力系统中随时间变化的几何关系和相互作用的能力，将把MC剂量计算提高到一个新的水平，达到4D治疗模拟的水平。

DESCRIPTION (provided by applicant): To study dosimetric effects in time-dependent geometries the results of individual three-dimensional (3D) calculations are usually added or statistically combined. This is cumbersome if the geometry is complex, if high time resolution is envisaged (e.g. considering dose rate), or if the microscopic volume displacement as a function of time is not known. Furthermore, it is difficult to study double-dynamic systems to investigate the influence of time-dependent beam delivery (moving leafs in a multi-leaf collimator) on the dose deposition in a moving target (organ motion or deformation). Here, 4D instead of multiple 3D calculations are required. Monte Carlo (MC) simulations are believed to be the most accurate tool for dose calculation and wiII presumably have the biggest impact in areas of large density variations, e.g. for lung cancer treatments. Interestingly, this is also the area where we might expect the biggest impact of organ motion on the dose distribution. The MC method is well suited to study dosimetric effects of motion with high accuracy. However, until now, like for analytical dose calculation techniques, the geometric information cannot be modified during the simulation. This limits applications to multiple 3D instead of true 4D. In taking advantage of objejctoriented C++ programming techniques we are proposing true 4D MC dose calculation. Local dose deposition in the patient will be calculated while beam configuration and organ geometry are changed continuously MLC leaf positions will be changing during the simulation according to leaf sequencing files. Based on deformable image registration we will track microscopic areas based on the patient's CT during the dose calculation. 4D dose calculation will allow the usage of a preset moving pattern based on clinical experience or patient specific 4D CT information. The capability of studying time dependent geometries and the interplay in double-dynamic systems for any time scale based on treatment head variations and patient's breathing pattern will take MC dose calculation to a new level, to the level of 4D treatment simulation.