Radiation Field Modeling and Computerized Treatment Planning

今年的主要变化是摆脱了我们与体积渲染硬件供应商的长期合作关系，转而选择了一家高性能视频图形加速器的商业供应商。这些单元提供了与老板相当的性能，但都大大降低了成本，并具有更大的业绩增长潜力。商业供应商还提供了利用电路板进行蒙特卡罗计算的软件，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。我们的研究已经建立了三维躯干外部体积的时间运动与内部器官的时间运动之间的基本关系，尤其是肺。这可以作为验证依赖外部基准点的剂量门控或剂量跟踪方法的基础。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。目前，该系统主要用于小视野立体定向放射外科的研究。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。蒙特卡罗算法与实验测量结果吻合得很好，小到5 mm。在一个相关的项目中，我们采用了代数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。

The major change this year was to move away from our long association with a vendor of volume rendering hardware and select instead a commercial vendor of high performance video graphics accelerators. These units offer comparable performance to the old boards, but are both substantially less expensive and have a greater potential for growth in performance. The commercial vendor also provides software 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. This can serve as the basis for the validation of dose gating or dose tracking methodologies that rely on external fiducials. 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.