Department of Diagnostic Imaging and Radiology and the Children’s Research Institute, Children’s National Medical Center, Washington, DC, USA.
J Appl Clin Med Phys. 2011 Nov 15;12(4):3589. doi: 10.1120/jacmp.v12i4.3589.
Current estimation of radiation dose from computed tomography (CT) scans on patients has relied on the measurement of Computed Tomography Dose Index (CTDI) in standard cylindrical phantoms, and calculations based on mathematical representations of "standard man". Radiation dose to both adult and pediatric patients from a CT scan has been a concern, as noted in recent reports. The purpose of this study was to investigate the feasibility of adapting a radiation treatment planning system (RTPS) to provide patient-specific CT dosimetry. A radiation treatment planning system was modified to calculate patient-specific CT dose distributions, which can be represented by dose at specific points within an organ of interest, as well as organ dose-volumes (after image segmentation) for a GE Light Speed Ultra Plus CT scanner. The RTPS calculation algorithm is based on a semi-empirical, measured correction-based algorithm, which has been well established in the radiotherapy community. Digital representations of the physical phantoms (virtual phantom) were acquired with the GE CT scanner in axial mode. Thermoluminescent dosimeter (TLDs) measurements in pediatric anthropomorphic phantoms were utilized to validate the dose at specific points within organs of interest relative to RTPS calculations and Monte Carlo simulations of the same virtual phantoms (digital representation). Congruence of the calculated and measured point doses for the same physical anthropomorphic phantom geometry was used to verify the feasibility of the method. The RTPS algorithm can be extended to calculate the organ dose by calculating a dose distribution point-by-point for a designated volume. Electron Gamma Shower (EGSnrc) codes for radiation transport calculations developed by National Research Council of Canada (NRCC) were utilized to perform the Monte Carlo (MC) simulation. In general, the RTPS and MC dose calculations are within 10% of the TLD measurements for the infant and child chest scans. With respect to the dose comparisons for the head, the RTPS dose calculations are slightly higher (10%-20%) than the TLD measurements, while the MC results were within 10% of the TLD measurements. The advantage of the algebraic dose calculation engine of the RTPS is a substantially reduced computation time (minutes vs. days) relative to Monte Carlo calculations, as well as providing patient-specific dose estimation. It also provides the basis for a more elaborate reporting of dosimetric results, such as patient specific organ dose volumes after image segmentation.
目前，对患者进行计算机断层扫描（CT）检查的辐射剂量估算依赖于在标准圆柱形体模中测量的 CT 剂量指数（CTDI），并基于“标准人”的数学表示进行计算。最近的报告指出，成人和儿科患者的 CT 扫描辐射剂量一直是人们关注的问题。本研究旨在探讨将放射治疗计划系统（RTPS）适应于提供患者特定 CT 剂量测定的可行性。修改了放射治疗计划系统以计算患者特定的 CT 剂量分布，这些分布可以通过特定感兴趣器官内的点剂量来表示，也可以通过图像分割后的器官剂量体积来表示，适用于 GE Light Speed Ultra Plus CT 扫描仪。RTPS 计算算法基于一种半经验的、基于测量校正的算法，该算法在放射治疗领域已经得到了很好的建立。使用 GE CT 扫描仪在轴向模式下获取物理体模（虚拟体模）的数字表示。在儿科人体模型中使用热释光剂量计（TLD）测量来验证相对于 RTPS 计算和相同虚拟体模（数字表示）的蒙特卡罗模拟的特定感兴趣器官内的点剂量。相同物理人体模型几何形状的计算和测量点剂量的一致性用于验证该方法的可行性。RTPS 算法可以通过为指定体积逐个点计算剂量分布来扩展到计算器官剂量。加拿大国家研究委员会（NRCC）开发的用于辐射传输计算的电子伽马淋浴（EGSnrc）代码用于执行蒙特卡罗（MC）模拟。一般来说，对于婴儿和儿童胸部扫描，RTPS 和 MC 剂量计算与 TLD 测量值的差值在 10%以内。对于头部的剂量比较，RTPS 剂量计算值略高于 TLD 测量值（10%-20%），而 MC 结果与 TLD 测量值的差值在 10%以内。RTPS 的代数剂量计算引擎的优点是与蒙特卡罗计算相比，计算时间大大减少（分钟与天），同时提供患者特定的剂量估计。它还为更详细的剂量学结果报告提供了基础，例如图像分割后的患者特定器官剂量体积。
