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。 该商业供应商还提供软件（CUDA），用于利用板进行Monte Carlo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了一个体积的图像跟踪方法，使用外部躯干体积的变化，已申请专利。电子伽马簇射（EGS-4）为基础的蒙特卡罗剂量计算引擎（DCE）已完全实现在Linux和Windows环境。 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相联系的绝对剂量测量。我们的第一篇关于CT剂量测量系统（CTDS）的论文已经发表，并获得了应用临床医学物理杂志颁发的2011年最佳成像论文奖。 进一步的研究将是传统的CT剂量测定方法与新的CTDS的直接比较，以突出个性化剂量测定的优势，并展示器官特异性剂量描述。 我们的下一个目标是进行调试的螺旋扇形束CT扫描仪使用一个小的点剂量计，而不是传统的测量CTDI诊断放射学。 新的、最先进的三维扫描水模型的获得将极大地促进必要的测量。 希望该系统将为流行病学剂量反应研究提供对患者人群进行更完整剂量评估的框架。 此外，我们已经开始使用上述Monte Carlo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。

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.Our first manuscript on the CT Dosimetry System (CTDS) has been published and has received an award for Best Imaging Paper of 2011 from the Journal of Applied Clinical Medical Physics. 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. 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. The acquisition of a new, state-of-the-art 3-dimensional scanning water phantom will greatly facilitate the necessary measurements. 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 begun to model 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.