Department of Biomedical Physics and Department of Radiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90024, USA.
Med Phys. 2011 Feb;38(2):820-9. doi: 10.1118/1.3533897.
A recent work has demonstrated the feasibility of estimating the dose to individual organs from multidetector CT exams using patient-specific, scanner-independent CTDIvol-to-organ-dose conversion coefficients. However, the previous study only investigated organ dose to a single patient model from a full-body helical CT scan. The purpose of this work was to extend the validity of this dose estimation technique to patients of any size undergoing a common clinical exam. This was done by determining the influence of patient size on organ dose conversion coefficients generated for typical abdominal CT exams.
Monte Carlo simulations of abdominal exams were performed using models of 64-slice MDCT scanners from each of the four major manufacturers to obtain dose to radiosensitive organs for eight patient models of varying size, age, and gender. The scanner-specific organ doses were normalized by corresponding CTDIvol values and averaged across scanners to obtain scanner-independent CTDIvol-to-organ-dose conversion coefficients for each patient model. In order to obtain a metric for patient size, the outer perimeter of each patient was measured at the central slice of the abdominal scan region. Then, the relationship between CTDIvol-to-organ-dose conversion coefficients and patient perimeter was investigated for organs that were directly irradiated by the abdominal scan. These included organs that were either completely ("fully irradiated") or partly ("partially irradiated") contained within the abdominal exam region. Finally, dose to organs that were not at all contained within the scan region ("nonirradiated") were compared to the doses delivered to fully irradiated organs.
CTDIvol-to-organ-dose conversion coefficients for fully irradiated abdominal organs had a strong exponential correlation with patient perimeter. Conversely, partially irradiated organs did not have a strong dependence on patient perimeter. In almost all cases, the doses delivered to nonirradiated organs were less than 5%, on average across patient models, of the mean dose of the fully irradiated organs.
This work demonstrates the feasibility of calculating patient-specific, scanner-independent CTDIvol-to-organ-dose conversion coefficients for fully irradiated organs in patients undergoing typical abdominal CT exams. A method to calculate patient-specific, scanner-specific, and exam-specific organ dose estimates that requires only knowledge of the CTDIvol for the scan protocol and the patient's perimeter is thus possible. This method will have to be extended in future studies to include organs that are partially irradiated. Finally, it was shown that, in most cases, the doses to nonirradiated organs were small compared to the dose to fully irradiated organs.
最近的一项工作已经证明，使用特定于患者的、与扫描仪无关的 CTDIvol 到器官剂量转换系数，可以从多排 CT 检查中估算单个器官的剂量是可行的。然而，之前的研究仅调查了来自全身螺旋 CT 扫描的单个患者模型的器官剂量。这项工作的目的是将这种剂量估算技术的有效性扩展到任何大小的患者进行常见临床检查。这是通过确定患者大小对为典型腹部 CT 检查生成的器官剂量转换系数的影响来实现的。
使用来自四个主要制造商的 64 层 MDCT 扫描仪的模型进行腹部检查的蒙特卡罗模拟，以获得八个不同大小、年龄和性别的患者模型的敏感器官剂量。将特定于扫描仪的器官剂量除以相应的 CTDIvol 值，并在扫描仪之间进行平均，以获得每个患者模型的与扫描仪无关的 CTDIvol 到器官剂量转换系数。为了获得患者大小的度量标准，在腹部扫描区域的中央切片处测量每个患者的外周长。然后，研究了与腹部扫描直接辐照的器官的 CTDIvol 到器官剂量转换系数与患者周长之间的关系。这些器官包括完全包含在腹部检查区域内的器官（“完全辐照”）或部分包含在该区域内的器官（“部分辐照”）。最后，将不包含在扫描区域内的器官的剂量（“非辐照”）与完全辐照器官的剂量进行比较。
完全辐照的腹部器官的 CTDIvol 到器官剂量转换系数与患者周长呈强烈的指数相关性。相反，部分辐照的器官与患者周长没有很强的依赖性。在几乎所有情况下，非辐照器官的剂量平均低于所有患者模型中完全辐照器官的平均剂量的 5%。
这项工作证明了在接受典型腹部 CT 检查的患者中计算特定于患者的、与扫描仪无关的 CTDIvol 到器官剂量转换系数的可行性。因此，有可能计算出仅需要了解扫描方案的 CTDIvol 和患者周长的特定于患者的、特定于扫描仪的和特定于检查的器官剂量估算。在未来的研究中，这种方法还必须扩展到包括部分辐照的器官。最后，结果表明，在大多数情况下，非辐照器官的剂量与完全辐照器官的剂量相比较小。
