Radiation Field Modeling and Computerized Treatment Planning

我们使用的是一家商业视频处理器板供应商(NVIDIA)，它们的价格都比上一代定制的批量渲染板便宜得多，而且在性能方面有更大的增长潜力。该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(CUDA)，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。我们的研究开发了一种利用躯干外部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。我们扩大了我们的研究范围，将传统的CT剂量学方法与新的CTD方法进行了直接比较，以突出个性化剂量学的优势，并演示特定器官的剂量描述。我们的下一个目标是使用小的点剂量计进行螺旋扇束CT扫描仪的调试，而不是传统的诊断放射学中使用的CTDI测量。希望该系统将为流行病学剂量-反应研究的患者群体提供更完整的剂量评估框架。此外，我们还使用上述蒙特卡罗剂量测量系统模拟了能谱与标准校准条件不同的低能X射线场的剂量学行为。这种剂量-反应图对于正确校准广泛用于放射生物学实验的柜式X射线装置的X射线场是必不可少的。我们目前的结果包括误差幅度在+/-5%以下。虽然这比制造商+/-20%的精度有所提高，但文希望将不确定度降低到+/-2%以下。

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 have expanded our research to include 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. Our next goal is to 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 have modeled the dosimetric behavior of low energy x-ray fields which have energy spectra different from standardized 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 experiments. Our current results include a margin of error of under +/- 5%. Although this is an improvement on the manufacturers accuracy of +/- 20%, wen hope to reduce the uncertainty to less than +/-2%.