Radiation Field Modeling and Computerized Treatment Planning

开发了一种使用三维体素体积的硬件融合算法，并通过融合磁共振成像(MRI-T1，MRI-T2)、正电子发射断层扫描(PET)和X射线计算机断层扫描(CT)图像的配对组合，测试了算法的灵敏度和准确性。目前的软件允许同时融合多达4个多模式图像集，使用完整的器官体积作为配准标志。将器官表面用于融合标志，其精度优于使用三个正交二维视图的传统方法。目前的计划是将这种方法应用于四维治疗计划，使用依赖时间的图像集来提高靶区范围并将正常组织并发症降至最低。基于电子伽马簇射(EGS-4)的蒙特卡罗剂量计算引擎(DCE)已经在Linux和Windows环境下完全实现。在Windows环境中，DCE已集成到功能齐全的治疗计划系统中。现在的工作集中在相空间源模型的开发上。确定每个相空间模型需要大量的计算能力，我们移植代码的方式将允许使用并行处理，希望将测试模型参数所需的计算时间从3-4周减少到1天以下。目前，该系统正被用于研究小视野立体定向放射外科。由于减小了场大小，边缘效应变得重要，用于访问辐射输出的探测器的大小影响测量结果。对这些输出测量的蒙特卡罗模拟将极大地帮助选择最合适的探测器系统。在一个相关的项目中，我们正在采用代数DCES和蒙特卡罗DCES来预测从诊断CT扫描中接收到的器官剂量。来自GE CT扫描仪的X射线束在国家儿童医学中心用于临床扫描的特征已经完成。我们还完成了绝对剂量测量，将计算机断层扫描剂量指数(CTDI)的标准诊断测量与实际吸收剂量联系起来。我们现在开始使用热释光剂量计(TLD)进行一系列验证测量，以确认该模型。

A hardware-based fusion algorithm which employs 3-dimensional voxel volumes has been developed and tested for sensitivity and accuracy by fusing paired combinations of Magnetic Resonance Imaging (MRI-T1, MRI-T2), Positron Emission Tomography (PET) and x-ray Computed Tomography (CT) images. Current software allows for the simultaneous fusion of as many as 4 muti-modality image sets using the full organ volumes asregistration landmarks. The use of organ surfaces for the fusion landmarks results in an accuracy which is superior to that obtained by using the conventional method which employs three orthogonal 2-dimensional views. Current plans are to adapt this methodology for 4-dimensional treatment planning, using time-dependent image sets to improve target margins and minimize normal tisseu complications. The Electron-Gamma Shower (EGS-4)-based Monte Carlo Dose Calculation Engine (DCE) has been fully implemented in both a LINUX and Windows environment. In the Windows environment, the DCE has been integrated into a full featured treatment planning system. Work is now centered on the development of phase-space source models. The determination of each phase-space model requires substantial computing power and we are porting the code in a manner that will permit the use of parallel processing that, hopefully, will reduce the calculation time required to test model parameters from 3-4 weeks to under 1 day. Currently, this system is being used to investigate small field stereotactic radiosurgery. Due to the reduced field size, edge effects become important and the size of detectors used to access the radiation output affect the measurement results. Monte Carlo simulation of these output measurements will greatly assist in the selection of the detector system that is most suitable. In a related project, we are adapting both algebraic and Monte Carlo DCEs to predict organ doses received from diagnostic CT scans. The characterization of the x-ray beam from a GE CT Scanner used for clinical scanning at Children's National Medical Center is complete. We have also completed absolute dosimetry measurements linking the standard diagnostic measurement of Computer Tomography Dose Index (CTDI) to actual absorbed dose. We are now embarking on a series of verification measurements usilg Thermolumeniscent Dosimeters (TLDs) to confirm the model.