Department of Radiology and Radiological Science, Medical University of South Carolina, 96 Jonathan Lucas Street, MSC 323, Charleston, SC 29425-3230, USA.
Phys Med Biol. 2010 Jul 7;55(13):3675-84. doi: 10.1088/0031-9155/55/13/007. Epub 2010 Jun 9.
We present a method of estimating effective doses in cardiac CT that accounts for selected techniques (kV mAs(-1)), anatomical location of the scan and patient size. A CT dosimetry spreadsheet (ImPACT CT Patient Dosimetry Calculator) was used to estimate effective doses (E) using ICRP 103 weighting factors for a 70 kg patient undergoing cardiac CT examinations. Using dose length product (DLP) for the same scans, we obtained values of E/DLP for three CT scanners used in cardiac imaging from two vendors. E/DLP ratios were obtained as a function of the anatomical location in the chest and for x-ray tube voltages ranging from 80 to 140 kV. We also computed the ratio of the average absorbed dose in a water cylinder modeling a patient weighing W kg to the corresponding average absorbed dose in a water cylinder equivalent to a 70 kg patient. The average E/DLP for a 16 cm cardiac heart CT scan was 26 microSv (mGy cm)(-1), which is about 70% higher than the current E/DLP values used for chest CT scans (i.e. 14-17 microSv (mGy cm)(-1)). Our cardiac E/DLP ratios are higher because the cardiac region is approximately 30% more radiosensitive than the chest, and use of the ICRP 103 tissue weighting factors increases cardiac CT effective doses by approximately 30%. Increasing the x-ray tube voltage from 80 to 140 kV increases the E/DLP conversion factor for cardiac CT by 17%. For the same incident radiation at 120 kV, doses in 45 kg adults were approximately 22% higher than those in 70 kg adults, whereas doses in 120 kg adults were approximately 28% lower. Accurate estimates of the patient effective dose in cardiac CT should use ICRP 103 tissue weighting factors, and account for a choice of scan techniques (kV mAs(-1)), exposed scan region, as well as patient size.
我们提出了一种估算心脏 CT 有效剂量的方法，该方法考虑了选定的技术（kV mAs(-1)）、扫描的解剖位置和患者体型。我们使用 CT 剂量学电子表格（ImPACT CT 患者剂量计算器），根据 ICRP 103 对体重为 70kg 的患者进行心脏 CT 检查时的权重因子来估算有效剂量（E）。使用相同扫描的剂量长度乘积（DLP），我们从两个供应商的三个用于心脏成像的 CT 扫描仪中获得了 E/DLP 值。我们还获得了 E/DLP 比值与胸部解剖位置以及从 80 到 140kV 的 X 射线管电压的关系。我们还计算了一个重 Wkg 的患者水箱的平均吸收剂量与一个相当于 70kg 患者的水箱的平均吸收剂量之比。16cm 心脏 CT 扫描的平均 E/DLP 为 26μSv（mGy cm）（-1），比当前用于胸部 CT 扫描的 E/DLP 值（即 14-17μSv（mGy cm）（-1））高约 70%。我们的心脏 E/DLP 比值较高，是因为心脏区域比胸部大约敏感 30%，而且使用 ICRP 103 组织权重因子使心脏 CT 有效剂量增加了约 30%。将 X 射线管电压从 80 增加到 140kV 会使心脏 CT 的 E/DLP 转换因子增加 17%。在 120kV 相同入射辐射下，45kg 成年人的剂量比 70kg 成年人高约 22%，而 120kg 成年人的剂量则低约 28%。心脏 CT 中患者有效剂量的准确估算应使用 ICRP 103 组织权重因子，并考虑扫描技术（kV mAs(-1)）、暴露扫描区域以及患者体型的选择。
