Livermore National Laboratory, Materials Engineering Division/Non-destructive Evaluation Group, Livermore, CA, 94550, USA.
Department of Radiology, David Geffen School of Medicine, University of California, Los Angeles, Livermore, CA, 90024, USA.
Med Phys. 2021 Jan;48(1):523-532. doi: 10.1002/mp.14573. Epub 2020 Nov 28.
Task Group Report 195 of the American Association of Physicists in Medicine contains reference datasets for the direct comparison of results among different Monte Carlo (MC) simulation tools for various aspects of imaging research that employs ionizing radiation. While useful for comparing and validating MC codes, that effort did not provide the information needed to compare absolute dose estimates from CT exams. Therefore, the purpose of this work is to extend those efforts by providing a reference dataset for benchmarking fetal dose derived from MC simulations of clinical CT exams.
The reference dataset contains the four necessary elements for validating MC engines for CT dosimetry: (a) physical characteristics of the CT scanner, (b) patient information, (c) exam specifications, and (d) fetal dose results from previously validated and published MC simulations methods in tabular form. Scanner characteristics include non-proprietary descriptions of equivalent source cumulative distribution function (CDF) spectra and bowtie filtration profiles, as well as scanner geometry information. Additionally, for the MCNPX MC engine, normalization factors are provided to convert raw simulation results to absolute dose in mGy. The patient information is based on a set of publicly available fetal dose models and includes de-identified image data; voxelized MC input files with fetus, uterus, and gestational sac identified; and patient size metrics in the form of water equivalent diameter (D ) z-axis distributions from a simulated topogram (D ) and from the image data (D ). Exam characteristics include CT scan start and stop angles and table and patient locations, helical pitch, nominal collimation and measured beam width, and gantry rotation time for each simulation. For simulations involving estimating doses from exams using tube current modulation (TCM), a realistic TCM scheme is presented that is estimated based upon a validated method. (d) Absolute and CTDI -normalized fetal dose results for both TCM and FTC simulations are given for each patient model under each scan scenario.
Equivalent source CDFs and bowtie filtration profiles are available in text files. Image data are available in DICOM format. Voxelized models are represented by a header followed by a list of integers in a text file representing a three-dimensional model of the patient. Size distribution metrics are also given in text files. Results of absolute and normalized fetal dose with associated MC error estimates are presented in tabular form in an Excel spreadsheet. All data are stored on Zenodo and are publicly accessible using the following link: https://zenodo.org/record/3959512.
Similar to the work of AAPM Report 195, this work provides a set of reference data for benchmarking fetal dose estimates from clinical CT exams. This provides researchers with an opportunity to compare MC simulation results to a set of published reference data as part of their efforts to validate absolute and normalized fetal dose estimates. This could also be used as a basis for comparison to other non-MC approaches, such as deterministic approaches, or to commercial packages that provide estimates of fetal doses from clinical CT exams.
美国医学物理学家协会任务组报告 195 包含了用于比较不同蒙特卡罗（MC）模拟工具在各种成像研究方面结果的参考数据集，这些研究都涉及到电离辐射。虽然这对于比较和验证 MC 代码很有用，但该工作并没有提供比较 CT 检查绝对剂量估计所需的信息。因此，这项工作的目的是通过提供用于基准测试临床 CT 检查中 MC 模拟得出的胎儿剂量的参考数据集来扩展这些工作。
该参考数据集包含了验证 CT 剂量学 MC 引擎所需的四个必要元素：（a）CT 扫描仪的物理特性，（b）患者信息，（c）检查规范，以及（d）以表格形式呈现的先前经过验证和发布的 MC 模拟方法得出的胎儿剂量结果。扫描仪特性包括等效源累积分布函数（CDF）谱和 Bowtie 滤波轮廓的非专有描述，以及扫描仪几何信息。此外，对于 MCNPX MC 引擎，提供了归一化因子，可将原始模拟结果转换为 mGy 的绝对剂量。患者信息基于一组公开的胎儿剂量模型，包括去标识的图像数据；带有胎儿、子宫和妊娠囊的体素化 MC 输入文件；以及以模拟顶视图（D z -axis）和图像数据（D ）中的水等效直径（D ）分布形式呈现的患者尺寸度量。检查特征包括 CT 扫描的起始和停止角度以及表和患者位置、螺旋桨螺距、标称准直和测量的射束宽度，以及每个模拟的机架旋转时间。对于涉及使用管电流调制（TCM）估计检查剂量的模拟，提出了一种基于已验证方法的现实 TCM 方案。（d）为每个扫描场景下的每个患者模型提供了 TCM 和 FTC 模拟的绝对和 CTDI 归一化胎儿剂量结果。
等效源 CDF 和 Bowtie 滤波轮廓可在文本文件中获得。图像数据以 DICOM 格式提供。体素化模型由一个标题后跟一个文本文件中的整数列表表示，该列表代表患者的三维模型。尺寸分布度量也以文本文件的形式给出。以表格形式呈现绝对和归一化胎儿剂量及其相关 MC 误差估计的结果，保存在 Excel 电子表格中。所有数据都存储在 Zenodo 上，并可通过以下链接公开访问：https://zenodo.org/record/3959512。
与 AAPM 报告 195 的工作类似，这项工作为基准测试临床 CT 检查中的胎儿剂量估计提供了一组参考数据。这为研究人员提供了一个机会，使他们可以将 MC 模拟结果与一组已发布的参考数据进行比较，作为验证绝对和归一化胎儿剂量估计的一部分。这也可以用作与其他非 MC 方法（如确定性方法）或提供临床 CT 检查中胎儿剂量估计的商业软件包进行比较的基础。
