Gu J, Bednarz B, Caracappa P F, Xu X G
Nuclear Engineering and Engineering Physics Program, Rensselaer Polytechnic Institute, Troy, NY 12180, USA.
Phys Med Biol. 2009 May 7;54(9):2699-717. doi: 10.1088/0031-9155/54/9/007. Epub 2009 Apr 8.
The latest multiple-detector technologies have further increased the popularity of x-ray CT as a diagnostic imaging modality. There is a continuing need to assess the potential radiation risk associated with such rapidly evolving multi-detector CT (MDCT) modalities and scanning protocols. This need can be met by the use of CT source models that are integrated with patient computational phantoms for organ dose calculations. Based on this purpose, this work developed and validated an MDCT scanner using the Monte Carlo method, and meanwhile the pregnant patient phantoms were integrated into the MDCT scanner model for assessment of the dose to the fetus as well as doses to the organs or tissues of the pregnant patient phantom. A Monte Carlo code, MCNPX, was used to simulate the x-ray source including the energy spectrum, filter and scan trajectory. Detailed CT scanner components were specified using an iterative trial-and-error procedure for a GE LightSpeed CT scanner. The scanner model was validated by comparing simulated results against measured CTDI values and dose profiles reported in the literature. The source movement along the helical trajectory was simulated using the pitch of 0.9375 and 1.375, respectively. The validated scanner model was then integrated with phantoms of a pregnant patient in three different gestational periods to calculate organ doses. It was found that the dose to the fetus of the 3 month pregnant patient phantom was 0.13 mGy/100 mAs and 0.57 mGy/100 mAs from the chest and kidney scan, respectively. For the chest scan of the 6 month patient phantom and the 9 month patient phantom, the fetal doses were 0.21 mGy/100 mAs and 0.26 mGy/100 mAs, respectively. The paper also discusses how these fetal dose values can be used to evaluate imaging procedures and to assess risk using recommendations of the report from AAPM Task Group 36. This work demonstrates the ability of modeling and validating an MDCT scanner by the Monte Carlo method, as well as assessing fetal and organ doses by combining the MDCT scanner model and the pregnant patient phantom.
最新的多探测器技术进一步提高了X射线计算机断层扫描（CT）作为一种诊断成像方式的普及程度。持续需要评估与这种快速发展的多探测器CT（MDCT）模式和扫描协议相关的潜在辐射风险。通过使用与患者计算体模集成以进行器官剂量计算的CT源模型，可以满足这一需求。基于此目的，本研究使用蒙特卡洛方法开发并验证了一台MDCT扫描仪，同时将孕妇体模集成到MDCT扫描仪模型中，以评估胎儿所受剂量以及孕妇体模各器官或组织所受剂量。使用蒙特卡洛代码MCNPX模拟X射线源，包括能谱、滤过器和扫描轨迹。针对GE LightSpeed CT扫描仪，通过反复试验的迭代过程详细指定了CT扫描仪组件。通过将模拟结果与文献中报道的测量CTDI值和剂量分布进行比较，对扫描仪模型进行了验证。分别使用螺距0.9375和1.375模拟源沿螺旋轨迹的移动。然后将经过验证的扫描仪模型与处于三个不同孕期的孕妇体模集成，以计算器官剂量。结果发现，怀孕3个月孕妇体模胸部和肾脏扫描时，胎儿所受剂量分别为0.13 mGy/100 mAs和0.57 mGy/100 mAs。对于怀孕6个月孕妇体模和怀孕9个月孕妇体模的胸部扫描，胎儿所受剂量分别为0.21 mGy/100 mAs和0.26 mGy/100 mAs。本文还讨论了如何利用这些胎儿剂量值，根据美国医学物理师协会（AAPM）任务组36报告中的建议来评估成像程序和风险。这项工作展示了通过蒙特卡洛方法对MDCT扫描仪进行建模和验证的能力，以及通过结合MDCT扫描仪模型和孕妇体模来评估胎儿和器官剂量的能力。
