A Monte Carlo based method to estimate radiation dose from multidetector CT (MDCT): cylindrical and anthropomorphic phantoms
A Monte Carlo based method to estimate radiation dose from multidetector CT (MDCT): cylindrical and anthropomorphic phantoms
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DOI：
10.1088/0031-9155/50/17/005
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发表时间：
2005-09-07
影响因子：
3.5
通讯作者：
McNitt-Gray, MF
中科院分区：
文献类型：
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作者：
DeMarco, JJ;Cagnon, CH;McNitt-Gray, MF
这项工作的目的是扩展基于蒙特卡罗方法的验证，用于估计计算机断层扫描（CT）检查中的辐射剂量，超出单CT扫描仪到多探测器CT（MDCT）扫描仪，并从圆柱形CTDI体模测量到圆柱形和物理拟人体模。圆柱形和物理拟人模型在特定条件下在MDCT上扫描。铅笔电离室用于记录圆柱体模的暴露量，而MOSFET（金属氧化物半导体场效应晶体管）探测器用于记录拟人体模表面的暴露量。在指定条件下，使用铅笔电离室在等中心的空气中进行参考测量。为MDCT扫描仪开发了详细的蒙特卡罗模型，以描述X射线源（光谱、蝴蝶结滤波器等）和几何因素（从焦点到等中心的距离、轴向或螺旋扫描引起的源移动等）。圆柱形（CTDI）体模的模型可从以前的工作。对于拟人化体模，CT图像数据用于创建体模几何形状的详细体素化模型。拟人体模材料成分由制造商提供。使用扫描仪、体模和指定扫描参数的数学模型进行物理扫描的模拟。在对应于MOSFET物理测量的特定体素位置处记录计数。进行空气扫描的模拟，以获得归一化因子，将结果转换为绝对剂量值。对于CTDI体模（32 cm），所有条件下的测量和模拟结果均在3.5%范围内。对于拟人体模，连续轴向扫描测得的表面剂量值显示出显著变化，范围为8 mGy/100 mAs至16 mGy/100 mAs。重叠螺距（0.9375）和扩展螺距（1.375）螺旋扫描的结果也得到了。MOSFET的测量值和绝对剂量值之间的比较来自Monte Carlo模拟证明协议的绝对剂量值以及空间变化的特性。这项工作证明了扩展模型的能力，从一个单一的探测器扫描仪使用圆柱体的MDCT扫描仪使用圆柱体和拟人体。未来的工作将扩展到不同尺寸的体素化患者模型和其他MDCT扫描仪。
The purpose of this work was to extend the verification of Monte Carlo based methods for estimating radiation dose in computed tomography (CT) exams beyond a single CT scanner to a multidetector CT (MDCT) scanner, and from cylindrical CTDI phantom measurements to both cylindrical and physical anthropomorphic phantoms. Both cylindrical and physical anthropomorphic phantoms were scanned on an MDCT under the specified conditions. A pencil ionization chamber was used to record exposure for the cylindrical phantom, while MOSFET (metal oxide semiconductor field effect transistor) detectors were used to record exposure at the surface of the anthropomorphic phantom. Reference measurements were made in air at isocentre using the pencil ionization chamber under the specified conditions. Detailed Monte Carlo models were developed for the MDCT scanner to describe the x-ray source (spectra, bowtie filter, etc) and geometry factors (distance from focal spot to isocentre, source movement due to axial or helical scanning, etc). Models for the cylindrical (CTDI) phantoms were available from the previous work. For the anthropomorphic phantom, CT image data were used to create a detailed voxelized model of the phantom's geometry. Anthropomorphic phantom material compositions were provided by the manufacturer. A simulation of the physical scan was performed using the mathematical models of the scanner, phantom and specified scan parameters. Tallies were recorded at specific voxel locations corresponding to the MOSFET physical measurements. Simulations of air scans were performed to obtain normalization factors to convert results to absolute dose values. For the CTDI body (32 cm) phantom, measurements and simulation results agreed to within 3.5% across all conditions. For the anthropomorphic phantom, measured surface dose values from a contiguous axial scan showed significant variation and ranged from 8 mGy/100 mAs to 16 mGy/100 mAs. Results from helical scans of overlapping pitch (0.9375) and extended pitch (1.375) were also obtained. Comparisons between the MOSFET measurements and the absolute dose value derived from the Monte Carlo simulations demonstrate agreement in terms of absolute dose values as well as the spatially varying characteristics. This work demonstrates the ability to extend models from a single detector scanner using cylindrical phantoms to an MDCT scanner using both cylindrical and anthropomorphic phantoms. Future work will be extended to voxelized patient models of different sizes and to other MDCT scanners.