调强放射治疗子野权重优化方法研究

由于子野分割带来的误差, 使得调强放疗(Intensity Modulated Radiation Therapy, 简称IMRT)计划系统所制作的计划往往不能满足临床要求。 本研究将采用基于共轭梯度法的子野权重优化方法来减小此误差, 提高制作计划的效率和效果。 采用共轭梯度法优化子野权重和微调子野形状, 最终使得子野分割前后强度误差最小。 在精确放疗系统中对常见的临床病例（鼻咽癌和周围性肺癌）进行测试, 通过对比靶区和危及器官的剂量体积直方图以及CT片上的等剂量线, 发现子野权重优化后靶区的平均剂量分别从87.0%提高到100.2%和从90.0%提高到98.4%, 更好地满足临床要求。     

Preliminary study on CAD-based method of characteristics for neutron transport calculation

Our new method makes use of a CAD-based automatic modeling tool, MCAM, for geometry modeling and ray tracing of particle transport in method of characteristics (MOC). It was found that it could considerably enhance the capability of MOC to deal with more complicated models for neutron transport calculation. In our study, the diamond-difference scheme was applied to MOC to reduce the spatial discretization errors of the flat flux approximation. Based on MCAM and MOC, a new 2D MOC code was developed and integrated into the SuperMC system, which is a Super Multi-function Computational system for neutronics and radiation simulation. The numerical results demonstrated the feasibility and effectiveness of the new method for neutron transport calculation in MOC.     

Preliminary study on CAD-based method of characteristics for neutron transport calculation

Our new method makes use of a CAD-based automatic modeling tool, MCAM, for geometry modeling and ray tracing of particle transport in method of characteristics （MOC）. It was found that it could considerably enhance the capability of MOC to deal with more complicated models for neutron transport calculation. In our study, the diamond-difference scheme was applied to MOC to reduce the spatial discretization errors of the fiat flux approximation. Based on MCAM and MOC, a new 2D MOC code was developed and integrated into the SuperMC system, which is a Super Multi-function Computational system for neutronics and radiation simulation. The numerical results demonstrated the feasibility and effectiveness of the new method for neutron transport calculation in MOC.     

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.     

基于共轭梯度法的调强放疗射束强度分布优化

针对逆向调强放疗中强度分布优化涉及的参数多, 且临床上对其优化速度要求高的特点, 将医生期望的靶区剂量和周围正常组织剂量限制转化为二次函数形式的目标函数, 然后利用共轭梯度法对该目标函数进行优化。 最后采用一例C形靶区紧密包围危及器官的模拟病例和一例临床常用的前列腺实例, 在PC机（CPU E7200@2.53GHz, 2.00GB内存, Windows XP）上对强度分布优化效果进行测试, 对模拟病例10 s便找到最优解; 而对前列腺病例20 s便可以找到最优解; 且两个测试病例优化所得强度分布对应的剂量分布均满足要求。 测试结果表明, 采用共轭梯度法优化强度分布具有快速和效果好的优点, 因此可以将其应用在精确放疗系统中。 The beam intensity map optimization of Intensity Modulated Radiation Treatment(IMRT) is a large scale optimization problem because of thousands of parameters involved. A fast and efficient approach was studied in the paper according to the clinical requirement for high speed and good results. Firstly, the clinical prescribed dose of Planning Target Volume(PTV) and dose volume constraints of Normal Tissue and Organ at Risk(OAR) were transformed into a quadratic objective function. And then Conjugate Gradient(CG) was adopted to optimize the objective function. At last, a simulated case and a clinical case were used to test the approach. The results showed that the optimization process need 40 s while satisfied results could be obtained in 10 s for simulated case and the optimization process need 1 min and 20 s while optimized results could be obtained in 20 s for the clinical prostate case. So it can be found that the approach of proposed in this paper is valid and efficient, and can be used to the accurate radiation therapy system.     

精确放射治疗中改进的楔形挡板剂量修正算法

在精确放射治疗中,精确计算楔形挡板的楔形因子是精确修正加入楔形挡板后剂量值的关键。提出了基于衰减系数法思想的改进楔形野剂量修正算法,首先计算了楔形挡板材料的线性衰减系数,再根据楔形挡板的实际剖面尺寸,建立了线性拟合公式计算射线束穿过楔形挡板的实际厚度,精确计算楔形因子,并以AAPM55号报告提供的45°楔形挡板进行了验证。该方法在保证计算精度的同时减少了大量离轴测量数据,减轻了物理师的负担,可以作为一种有效的楔形挡板修正算法应用于放射治疗计划系统中。