DeMarco J J, Cagnon C H, Cody D D, Stevens D M, McCollough C H, Zankl M, Angel E, McNitt-Gray M F
David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.
Phys Med Biol. 2007 May 7;52(9):2583-97. doi: 10.1088/0031-9155/52/9/017. Epub 2007 Apr 17.
The purpose of this work is to examine the effects of patient size on radiation dose from CT scans. To perform these investigations, we used Monte Carlo simulation methods with detailed models of both patients and multidetector computed tomography (MDCT) scanners. A family of three-dimensional, voxelized patient models previously developed and validated by the GSF was implemented as input files using the Monte Carlo code MCNPX. These patient models represent a range of patient sizes and ages (8 weeks to 48 years) and have all radiosensitive organs previously identified and segmented, allowing the estimation of dose to any individual organ and calculation of patient effective dose. To estimate radiation dose, every voxel in each patient model was assigned both a specific organ index number and an elemental composition and mass density. Simulated CT scans of each voxelized patient model were performed using a previously developed MDCT source model that includes scanner specific spectra, including bowtie filter, scanner geometry and helical source path. The scan simulations in this work include a whole-body scan protocol and a thoracic CT scan protocol, each performed with fixed tube current. The whole-body scan simulation yielded a predictable decrease in effective dose as a function of increasing patient weight. Results from analysis of individual organs demonstrated similar trends, but with some individual variations. A comparison with a conventional dose estimation method using the ImPACT spreadsheet yielded an effective dose of 0.14 mSv mAs(-1) for the whole-body scan. This result is lower than the simulations on the voxelized model designated 'Irene' (0.15 mSv mAs(-1)) and higher than the models 'Donna' and 'Golem' (0.12 mSv mAs(-1)). For the thoracic scan protocol, the ImPACT spreadsheet estimates an effective dose of 0.037 mSv mAs(-1), which falls between the calculated values for Irene (0.042 mSv mAs(-1)) and Donna (0.031 mSv mAs(-1)) and is higher relative to Golem (0.025 mSv mAs(-1)). This work demonstrates the ability to estimate both individual organ and effective doses from any arbitrary CT scan protocol on individual patient-based models and to provide estimates of the effect of patient size on these dose metrics.
这项工作的目的是研究患者体型对CT扫描辐射剂量的影响。为了进行这些研究，我们使用了蒙特卡罗模拟方法以及患者和多探测器计算机断层扫描（MDCT）扫描仪的详细模型。GSF之前开发并验证的一系列三维体素化患者模型被用作输入文件，使用蒙特卡罗代码MCNPX。这些患者模型代表了一系列患者体型和年龄（8周至48岁），并且所有先前已识别和分割的放射敏感器官都包含在内，从而可以估计任何单个器官的剂量并计算患者的有效剂量。为了估计辐射剂量，每个患者模型中的每个体素都被赋予了一个特定的器官索引号以及元素组成和质量密度。使用先前开发的MDCT源模型对每个体素化患者模型进行模拟CT扫描，该模型包括扫描仪特定的光谱，包括蝴蝶结滤波器、扫描仪几何形状和螺旋源路径。这项工作中的扫描模拟包括全身扫描协议和胸部CT扫描协议，每个协议均以固定管电流进行。全身扫描模拟显示，随着患者体重增加，有效剂量可预测地降低。对各个器官的分析结果显示出类似趋势，但存在一些个体差异。与使用ImPACT电子表格的传统剂量估计方法进行比较，全身扫描的有效剂量为0.14 mSv mAs⁻¹。该结果低于指定为“Irene”的体素化模型的模拟结果（0.15 mSv mAs⁻¹），高于“Donna”和“Golem”模型（0.12 mSv mAs⁻¹）。对于胸部扫描协议，ImPACT电子表格估计的有效剂量为0.037 mSv mAs⁻¹，介于Irene（0.042 mSv mAs⁻¹）和Donna（0.031 mSv mAs⁻¹）的计算值之间，相对于Golem（0.025 mSv mAs⁻¹）更高。这项工作证明了能够在基于个体患者的模型上根据任何任意CT扫描协议估计单个器官剂量和有效剂量，并能够提供患者体型对这些剂量指标影响的估计。
