Huda Walter, Spampinato Maria V, Tipnis Sameer V, Magill Dennise
Department of Radiology and Radiological Science, MUSC, 96 Jonathan Lucas Street, MSC 323, Charleston, SC 29425-3230, USA.
Radiat Prot Dosimetry. 2013 Oct;156(4):436-44. doi: 10.1093/rpd/nct090. Epub 2013 Apr 11.
The aim of the study was to investigate how differences in patient anatomy and CT technical factors in neck CT impact on thyroid doses and the corresponding carcinogenic risks. The CTDIvol and dose-length product used in 11 consecutive neck CT studies, as well as data on automatic exposure control (AEC) tube current variation(s) from the image DICOM header, were recorded. For each CT image that included the thyroid, the mass equivalent water cylinder was estimated based on the patient cross-sectional area and average relative attenuation coefficient (Hounsfield unit, HU). Patient thyroid doses were estimated by accounting for radiation intensity at the location of the patient's thyroid, patient size and the scan length. Thyroid doses were used to estimate thyroid cancer risks as a function of patient demographics using risk factors in BEIR VII. The length of the thyroid glands ranged from 21 to 54 mm with an average length of 42 ± 12 mm. Water cylinder diameters corresponding to the central slice through the patient thyroid ranged from 18 to 32 cm with a mean of 25 ± 5 cm. The average CTDIvol (32-cm phantom) used to perform these scans was 26 ± 6 mGy, but the use of an AEC increased the tube current by an average of 44 % at the thyroid mid-point. Thyroid doses ranged from 29 to 80 mGy, with an average of 55 ± 19 mGy. A 20-y-old female receiving the highest thyroid dose of 80 mGy would have a thyroid cancer risk of nearly 0.1 %, but radiation risks decreased very rapidly with increasing patient age. The key factors that affect thyroid doses in neck CT examinations are the radiation intensity at the thyroid location and the size of the patient. The corresponding patient thyroid cancer risk is markedly influenced by patient sex and age.
本研究的目的是调查颈部CT中患者解剖结构和CT技术因素的差异如何影响甲状腺剂量以及相应的致癌风险。记录了连续11项颈部CT研究中使用的容积CT剂量指数（CTDIvol）和剂量长度乘积，以及来自图像DICOM头部的自动曝光控制（AEC）管电流变化数据。对于每张包含甲状腺的CT图像，根据患者的横截面积和平均相对衰减系数（亨氏单位，HU）估算等效水模体。通过考虑患者甲状腺位置的辐射强度、患者体型和扫描长度来估算患者的甲状腺剂量。利用BEIR VII中的风险因素，根据患者人口统计学特征，将甲状腺剂量用于估算甲状腺癌风险。甲状腺的长度范围为21至54毫米，平均长度为42±12毫米。穿过患者甲状腺中心层面的水模体直径范围为18至32厘米，平均为25±5厘米。用于进行这些扫描的平均CTDIvol（32厘米体模）为26±6毫西弗，但使用AEC后，甲状腺中点处的管电流平均增加了44%。甲状腺剂量范围为29至80毫西弗，平均为55±19毫西弗。一名20岁女性接受的最高甲状腺剂量为80毫西弗，其患甲状腺癌的风险接近0.1%，但随着患者年龄的增加，辐射风险迅速降低。颈部CT检查中影响甲状腺剂量的关键因素是甲状腺位置的辐射强度和患者体型。相应的患者甲状腺癌风险受患者性别和年龄的显著影响。
