Radiation Field Modeling and Computerized Treatment Planning

我们使用的是一个商业视频处理器板（NVidia），它比上一代的自定义体积渲染板便宜得多，而且在性能上有更大的增长潜力。商业供应商还提供软件（CUDA），用于利用板进行蒙特卡罗计算，这进一步支持了我们的研究目标。我们已经从三维图像融合过渡到探索四维放射成像。我们的研究建立了三维躯干外部体积的时间运动与内部器官，特别是肺的时间运动之间的基本关系。我们的研究开发了一种使用外部躯干体积变化进行图像跟踪的体积方法，该方法已申请专利。基于电子伽马阵雨（EGS-4）的蒙特卡罗剂量计算引擎（DCE）已经在LINUX和Windows环境中完全实现。在Windows环境中，DCE已经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开发上。目前，该系统用于小视野立体定向放射外科的研究。由于场尺寸减小，边缘效应变得重要，用于访问辐射输出的探测器的尺寸影响测量结果。这些输出测量的蒙特卡罗模拟极大地有助于选择最适合这些测量的探测器系统。蒙特卡罗算法提供了良好的协议与实验测量小至5毫米的涂抹器。在一个相关的项目中，我们已经采用了代数和蒙特卡罗dce来预测从诊断性CT扫描中接受的器官剂量。在儿童国家医疗中心的临床扫描中使用的GE CT扫描仪的x射线束的表征是完整的。我们还完成了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的绝对剂量学测量。我们正在等待CT剂量测定系统（CTDS）的审稿。进一步的研究将是直接比较传统的CT剂量学方法与新的CTDS，以突出个体化剂量学的优势，并证明器官特异性剂量描述。我们还将使用小型点剂量计进行螺旋扇束CT扫描仪的调试，而不是在诊断放射学中使用传统的CTDI测量。希望这一系统将为流行病学剂量反应研究提供对患者群体进行更完整剂量评估的框架。此外，我们正在开始一项研究，以模拟低能x射线场的剂量学行为，这与使用上述蒙特卡罗剂量学系统的可用校准条件不同。这种剂量反应映射对于从广泛用于放射生物学的柜式x射线装置正确校准x射线场是必不可少的

We are using a commercial vendor of video processor boards (NVidia) which are both substantially less expensive than the previous generation of custom volume rendering boards as well as haveing a greater potential for growth in performance. The commercial vendor also provides software (CUDA) for utilizing the boards for Monte Carlo calculations, which further supports our research objectives. We have transitioned from 3-dimensional image fusion to exploring 4-dimensional radiotherapy imaging. Our research has established a fundamental relationship between the temporal motion of the 3-dimensional external torso volume and those of internal organs, especially the lungs. Our research has developed a volumetric methodology for image tracking using external torso volume change for which a patent has been applied for. 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. Currently, this system is 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 greatly assisted in the selection of the detector system that is most suitable for these measurements. The Monte Carlo algorithm provided good agreement with experimental measurements down to applicators as small as 5mm. In a related project, we have adapted 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 awaiting review of our manuscript on the CT Dosimetry System (CTDS). Further research will be a direct comparison of traditional CT dosimetry methodology versus the new CTDS to highlight the advantages of individualized dosimetry and demonstrate organ-specific dose descriptions. We shall also undertake the commissioning of a helical fan-beam CT scanner using a small point-dosimeter, as opposed to the traditional measurement of CTDI employed in diagnostic radiology. It is hoped that this system will provide the framework for a more complete dose assessment of patient populations for epidemiological dose-response studies. Additionally, we are starting a study to model the dosimetric behavior of low energy x-ray fields which are different than available calibration conditions using the Monte Carlo dosimetry system described above. This mapping of dose-response is essential for the proper calibration of x-ray fields from cabinet x-ray units which are widely utilized for radiobiological