Dabin Jérémie, Mencarelli Alessandra, McMillan Dayton, Romanyukha Anna, Struelens Lara, Lee Choonsik
Department of Radiation Protection Dosimetry and Calibration, Belgian Nuclear Research Centre, Mol 2400, Belgium.
Phys Med Biol. 2016 Jun 7;61(11):4168-82. doi: 10.1088/0031-9155/61/11/4168. Epub 2016 May 18.
Many organ dose calculation tools for computed tomography (CT) scans rely on the assumptions: (1) organ doses estimated for one CT scanner can be converted into organ doses for another CT scanner using the ratio of the Computed Tomography Dose Index (CTDI) between two CT scanners; and (2) helical scans can be approximated as the summation of axial slices covering the same scan range. The current study aims to validate experimentally these two assumptions. We performed organ dose measurements in a 5 year-old physical anthropomorphic phantom for five different CT scanners from four manufacturers. Absorbed doses to 22 organs were measured using thermoluminescent dosimeters for head-to-torso scans. We then compared the measured organ doses with the values calculated from the National Cancer Institute dosimetry system for CT (NCICT) computer program, developed at the National Cancer Institute. Whereas the measured organ doses showed significant variability (coefficient of variation (CoV) up to 53% at 80 kV) across different scanner models, the CoV of organ doses normalised to CTDIvol substantially decreased (12% CoV on average at 80 kV). For most organs, the difference between measured and simulated organ doses was within ±20% except for the bone marrow, breasts and ovaries. The discrepancies were further explained by additional Monte Carlo calculations of organ doses using a voxel phantom developed from CT images of the physical phantom. The results demonstrate that organ doses calculated for one CT scanner can be used to assess organ doses from other CT scanners with 20% uncertainty (k = 1), for the scan settings considered in the study.
许多用于计算机断层扫描（CT）的器官剂量计算工具基于以下假设：（1）使用两台CT扫描仪之间的计算机断层扫描剂量指数（CTDI）之比，可将为一台CT扫描仪估算的器官剂量转换为另一台CT扫描仪的器官剂量；（2）螺旋扫描可近似为覆盖相同扫描范围的轴向切片之和。本研究旨在通过实验验证这两个假设。我们在一个5岁的物理人体模型中，对来自四个制造商的五台不同CT扫描仪进行了器官剂量测量。使用热释光剂量计对头至躯干扫描测量了22个器官的吸收剂量。然后，我们将测量的器官剂量与美国国立癌症研究所开发的CT（NCICT）计算机程序的美国国立癌症研究所剂量测定系统计算的值进行了比较。尽管不同扫描仪型号之间测量的器官剂量显示出显著差异（在80 kV时变异系数（CoV）高达53%），但归一化为CTDIvol的器官剂量的CoV大幅下降（在80 kV时平均CoV为12%）。对于大多数器官，测量和模拟的器官剂量之间的差异在±20%以内，但骨髓、乳房和卵巢除外。使用从物理模型的CT图像开发的体素模型对器官剂量进行的额外蒙特卡罗计算进一步解释了这些差异。结果表明，对于本研究中考虑的扫描设置，为一台CT扫描仪计算的器官剂量可用于评估其他CT扫描仪的器官剂量，不确定性为20%（k = 1）。
