Smith A, Shah G A, Kron T
Faculty of Medicine and Health Sciences, University of Newcastle, New South Wales, Australia.
Br J Radiol. 1998 Dec;71(852):1296-301. doi: 10.1259/bjr.71.852.10319004.
CT dose varies with both equipment related and operator dependent factors. Thermoluminescence dosimetry (TLD) was employed in two phantoms to investigate the variation in absorbed dose for head CT scans, using a cylindrical head CT dose phantom. Dose profiles were plotted and the computed tomography dose index (CTDI) calculated for a single 10 mm thick slice on 14 CT scanners. An anthropomorphic head phantom was also scanned from the base-of-skull to the vertex using 10/10 mm slices. The absorbed dose measured at the centre of the scan series is reported (Dmid). The mean CTDIw for the 14 scanners was 60.0 mGy, while the mean Dmid was 45.8 mGy. Dmid better represents the absorbed dose in human tissues. The CTDIw and Dmid normalized to mAs varied by up to a factor of 2.2 for the different scanners. Equipment related factors contribute to such variations. However, variations due to operator dependent factors such as the choice of exposure factors, scanning protocol and positioning technique must also be considered. When such factors are taken into account the absorbed dose received by the patient can vary considerably, by as much as 16.2 for lens dose. Increased awareness of the factors influencing CT dose and the standardization of scanning protocols is recommended.
CT剂量随设备相关因素和操作人员相关因素而变化。使用圆柱形头部CT剂量体模，通过热释光剂量测定法（TLD）在两个体模中研究头部CT扫描时吸收剂量的变化。绘制了剂量分布图，并计算了14台CT扫描仪上单个10毫米厚切片的计算机断层扫描剂量指数（CTDI）。还使用10/10毫米切片从颅底到头顶对一个仿真人体头部模型进行了扫描。报告了在扫描系列中心测得的吸收剂量（Dmid）。14台扫描仪的平均加权CTDI为60.0毫戈瑞，而平均Dmid为45.8毫戈瑞。Dmid能更好地代表人体组织中的吸收剂量。不同扫描仪的CTDIw和归一化为毫安秒的Dmid变化高达2.2倍。设备相关因素导致了这种变化。然而，也必须考虑操作人员相关因素导致的变化，如曝光因素的选择、扫描方案和定位技术。考虑到这些因素时，患者接受的吸收剂量可能会有很大差异，晶状体剂量差异高达16.2倍。建议提高对影响CT剂量因素的认识并规范扫描方案。
