Development of Accurate/Advanced Radiotherapy Treatment Planning and Quality Assurance System (ARTS)

A prototype of accurate/advanced radiotherapy treatment planning and quality assurance system (ARTS) is developed and key technical issues related to the improvement of the treatment accuracy is studied. After a brief introduction to the prototype of ARTS, the advanced development in key technical issues is presented, including image data processing and human body modeling, fast and accurate hybrid dose calculation, multi-objective optimization of inverse planning, intelligent patient positioning, and dose verification.     

模体大小对MC程序计算速度与精度的影响研究

蒙特卡罗程序的计算速度与计算模型的体积大小有一定关联。 通过改变模体的厚度， 发现除在尾部有限范围内会出现差异外， 薄模体与厚模体的结果差别很小， 然而却可以获得模拟效率的指数性提升。 通过改变模体的宽度， 发现窄模体与宽模体相比， 只要宽度比照射野半影大， 对模拟效率的影响都很小； 而当宽度与照射野半影区重合时， 效率就有一定程度的提高， 同时对剂量结果影响很小。 将此研究结果用于临床头部实例， 获得了计算速度的显著提升。     

Varian 2300C 直线加速器6 MV X线的蒙特卡罗模拟

摘要: 利用先进的蒙特卡罗治疗头模拟程序BEAMnrc, 依据商家提供的详细设计资料, 集成多项优化模拟参数, 对医用直线加速器射线束传输部分进行了模拟, 获得与测量数据一致的模拟结果。 对复杂多叶光栏模型进行了建模, 模拟了非规则野的剂量分布, 以用于后续研究工作。 Based on the detail head structure designing provided by the manufacture, the ray transmission of VARIAN Clinic 2300C 6 MV X beam was simulated by Monte Carlo code, BEAMnrc. To accelerate the simulation efficiency, multiple optimized parameters were optimized. The simulated and the measured data were well coincident. The dose distribution of a complicated irregular field formed by MLC (Multi Leaf Collimators) was simulated, which are the base for further research work.     

目标函数设置对放疗逆向计划多目标优化过程的影响

目前放疗逆向计划中常用的目标函数有两种:基于剂量分布的目标函数和基于剂量．体积直方图（DVH）的目标函数。实际系统都基于单目标优化算法进行,不考虑逆向计划的多目标性。在Pareto多目标优化理论的基础上,研究逆向计划的目标函数设置问题,比较基于剂量分布的目标函数和基于DVH的目标函数对多目标优化过程的影响,包括优化时间、收敛性和存在的问题等,为逆向计划过程中多目标优化目标函数的设置提供依据。There are two kinds of objective functions in radiotherapy inverse planning: dose distribution-based and Dose-Volume Histogram （DVH）-based functions. The treatment planning in our days is still a trial and error process because the multi-objective problem is solved by transforming it into a single objective problem using a specific set of weights for each object. This work investigates the problem of objective function setting based on Pareto multi-optimization theory, and compares the effect on multi-objective inverse planning of those two kinds of objective functions including calculation time, converge speed, etc. The basis of objective function setting on inverse planning is discussed.     

蒙特卡罗剂量分布去噪中三维高斯和Savitzky-Golay滤波器的改进与混合

对模拟粒子轨迹数较少模拟时间较短的蒙特卡罗粗糙剂量分布进行三维滤波,可以加速其收敛速度.结合蒙特卡罗剂量分布特征,改进三维高斯和Savitzky-Golay滤波器,建立三维混合滤波方法,并比较并联和级联两种基本混合方式.根据卷积性质,提出用等效卷积核简化混合滤波器结构的方法.结果表明,改进后的高斯和Savitzky-Golay滤波器的整体去噪效果得以增强,混合滤波器进一步降低滤波结果的局部误差,两种混合滤波器都能够大幅度抑制MC粗糙剂量分布中的噪声,级联混合滤波器降噪效果略优于并联混合滤波器.     

模体厚度对MC程序计算速度与效率的影响研究

基于蒙特卡罗(MC)程序MCNP4c, DOSXYZnrc, DOSRZnrc 和DPM, 考察了模体厚度变化对MC程序计算速度和MC效率的影响, 发现模体的厚度变化对不同MC程序速度提升的影响差异较大, 其中DOSXYZnrc 提升最多, DOSRZnrc提升最小。 从MC效率方面来讲, DPM和DOSRZnrc具有明显的优势。 就4个程序而言, 薄模体均表现出一定的MC 效率优势。 从MC 效率提升角度来看, MCNP4c, DOSXYZnrc和DOSRZnrc表现出一定的相似性, 而DPM相对低些。 也对DOSRZnrc异常的统计不确定性特征、 速度提升进行了研究, 发现其内部植入的光子强迫方差减小技巧在降低体元统计不确定性的同时, 也削弱了薄模体的速度优势。 但是由于显著影响了方差, 所以总体来讲, 仍然提高了DOSRZnrc薄模体的MC 模拟效率。     

Multi-objective optimization of inverse planning for accurate radiotherapy

The multi-objective optimization of inverse planning based on the Pareto solution set, according to the multi-objective character of inverse planning in accurate radiotherapy, was studied in this paper. Firstly, the clinical requirements of a treatment plan were transformed into a multi-objective optimization problem with multiple constraints. Then, the fast and elitist multi-objective Non-dominated Sorting Genetic Algorithm (NSGA-Ⅱ) was introduced to optimize the problem. A clinical example was tested using this method. The results show that an obtained set of non-dominated solutions were uniformly distributed and the corresponding dose distribution of each solution not only approached the expected dose distribution, but also met the dose-volume constraints. It was indicated that the clinical requirements were better satisfied using the method and the planner could select the optimal treatment plan from the non-dominated solution set.     

基于混合Batho修正的RBM剂量计算方法在仿真头模实验中的剂量学验证

基于混合Batho修正的规则束模型剂量计算方法可以根据放射治疗过程中加速器相关物理参数和从病人的医学影像数据中获取的人体组织非均匀信息计算出人体内的剂量场数据。在简要介绍该方法的基础上,通过将其计算结果与仿真头模的实测结果进行对比,初步证明了该方法可以作为一种较为可靠的快速剂量计算方法供临床治疗计划系统使用。The dose distribution can be calculated by the Regular Beam Model （RBM） dose engine based on the accelerator parameters and the inhomogeneity data of the patient for the radiotherapy planning. In this paper, the newly-developed mixed Batho correction based RBM is introduced, and then the calculation results are compared with the measured ones using the head phantom. The results demonstrate that the RBM dose engine can be used as a kind of reliable fast dose calculation tool in the clinical treatment planning system.