J Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL, 32611-6131, USA.
Department of Medical Physics, Memorial Sloan Kettering Cancer Center, 1275 York Avenue, New York, NY, 10065, USA.
Med Phys. 2017 Oct;44(10):5423-5432. doi: 10.1002/mp.12461. Epub 2017 Sep 22.
To physically validate the accuracy of a Monte Carlo-based, phantom-derived methodology for computed tomography (CT) dosimetry that utilizes organ doses from precomputed axial scans and that accounts for tube current modulation (TCM).
The output of a Toshiba Aquilion ONE CT scanner was modeled, based on physical measurement, in the Monte Carlo radiation transport code MCNPX (v2.70). CT examinations were taken of two anthropomorphic phantoms representing pediatric and adult patients (15-yr-old female and adult male) at various energies, in which physical organ dose measurements were made using optically stimulated luminescence dosimeters (OSLDs). These exams (chest-abdomen-pelvis) were modeled using organ dose data obtained from the computationally equivalent phantom of each anthropomorphic phantom. TCM was accounted for by weighting all organ dose contributions by both the relative attenuation of the phantom and the image-derived mA value (from the DICOM header) at the same z-extent (cranial-caudal direction) of the axial dose data.
The root mean squares of percent difference in organ dose when comparing the physical organ dose measurements to the computational estimates were 21.2, 12.1, and 15.1% for the uniform (no attenuation weighting), weighted (computationally derived), and image-based methodologies, respectively.
Overall, these data suggest that the Monte Carlo-based dosimetry presented in this work is viable for CT dosimetry. Additionally, for CT exams with TCM, local attenuation weighting of organ dose contributions from precomputed axial dosimetry libraries increases organ dose accuracy.
通过物理验证，证明一种基于蒙特卡罗的、利用预计算轴向扫描的器官剂量并考虑管电流调制（TCM）的 CT 剂量学计算方法的准确性。
根据物理测量，在蒙特卡罗辐射输运代码 MCNPX（v2.70）中对东芝 Aquilion ONE CT 扫描仪的输出进行建模。对两个代表儿科和成人患者（15 岁女性和成年男性）的人体模型进行 CT 检查，在不同能量下进行，使用光激励发光剂量计（OSLD）进行物理器官剂量测量。使用每个人体模型的计算等效体模中的器官剂量数据对这些检查（胸部-腹部-骨盆）进行建模。通过相对衰减和图像衍生的 mA 值（来自 DICOM 标题）在轴向剂量数据的相同 z 范围（颅尾方向）对所有器官剂量贡献进行加权，以考虑 TCM。
当将物理器官剂量测量值与计算估计值进行比较时，器官剂量的均方根百分比差异分别为 21.2%、12.1%和 15.1%，用于均匀（无衰减加权）、加权（计算得出）和基于图像的方法。
总体而言，这些数据表明，本工作中提出的基于蒙特卡罗的剂量学方法适用于 CT 剂量学。此外，对于具有 TCM 的 CT 检查，对预计算轴向剂量学库中的器官剂量贡献进行局部衰减加权可提高器官剂量的准确性。
