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），它比上一代定制体绘制板便宜得多，而且性能增长潜力更大。商业供应商还提供软件（CUDA），用于使用蒙特卡洛计算板，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治疗成像。我们的研究已经建立了一个基本的三维外部躯干体积和内部器官，特别是肺的时间运动之间的关系。我们的研究已经开发出一种体积的方法，图像跟踪使用外部躯干体积变化，已申请专利。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。目前，该系统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Monte Carlo模拟极大地有助于选择最适合这些测量的探测器系统。Monte Carlo算法提供了良好的协议与实验测量小到5毫米的喷头。在一个相关的项目中，我们已经适应了代数和蒙特卡罗DCE来预测从诊断CT扫描收到的器官剂量。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。我们已经扩大了我们的研究，包括传统的CT剂量测定方法与新的CTDS的直接比较，突出个性化剂量测定的优势，并证明器官特异性剂量的描述。我们的下一个目标是进行委托的螺旋扇形束CT扫描仪使用一个小的点剂量计，而不是传统的测量CTDI在诊断放射学。希望这个系统将提供一个更完整的剂量评估的框架，流行病学剂量反应研究的患者人群。此外，我们已经使用上述蒙特卡罗剂量测定系统对具有不同于标准化校准条件的能谱的低能X射线场的剂量测定行为进行了建模。这种剂量-响应的映射对于正确校准广泛用于放射生物学实验的箱式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低于+/-5%的误差幅度。虽然这比制造商的精度提高了+/-20%，但我们希望将不确定性降低到+/-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%.