Radiation Field Modeling and Computerized Treatment Planning

开发了一种采用三维体素体积的基于硬件的融合算法，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其灵敏度和准确度。目前的软件允许同时融合多达4个多模态图像集，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导致精度优于通过使用采用三个正交2维视图的常规方法获得的精度，所述精度为上级。目前的计划是将这种方法用于4维治疗计划，使用时间依赖性图像集来改善靶边缘并最小化正常组织并发症。基于电子-γ簇射（EGS-4）的蒙特卡罗剂量计算引擎（DCE）已在Linux和Windows环境中完全实现。在Windows环境下，DCE已集成到一个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发展。每个相空间模型的确定需要大量的计算能力，我们正在以允许使用并行处理的方式移植代码，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，该系统正用于研究小野立体定向放射外科。由于减小的场尺寸，边缘效应变得重要，并且用于访问辐射输出的检测器的尺寸影响测量结果。这些输出测量的蒙特卡罗模拟将极大地有助于选择最合适的探测器系统。在一个相关的项目中，我们正在调整代数和蒙特卡罗DCE来预测从诊断CT扫描接收的器官剂量。在儿童国家医疗中心用于临床扫描的GE CT扫描仪的X射线束的表征已经完成。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。我们现在正在进行一系列的验证测量使用热释光剂量计（TLD），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.