1 Department of Radiology and Radiological Science, 96 Jonathan Lucas St, MSC 323, Medical University of South Carolina, Charleston, SC 29425-3230.
AJR Am J Roentgenol. 2015 May;204(5):1064-8. doi: 10.2214/AJR.14.13102.
The purpose of this study was to estimate absorbed thyroid dose and consequent cancer risks in adult patients undergoing neck CT examinations.
We used data from neck CT examinations of 68 consecutive adult patients to calculate the thyroid dose and estimate the corresponding cancer risk. Age and sex were recorded along with the volume CT dose index (CTDIvol) that was used to perform the examination. CTDIvol values were used to estimate thyroid doses in the mathematic phantom used in the ImPACT patient CT dosimetry calculator. Corresponding doses in patients were estimated by modeling each patient's neck as an equivalent cylinder of water and applying correction factors for varying neck size and scanning length and the variation of radiation intensity due to automatic exposure control.
The mean (± SD) adult patient age was 59 ± 16 years, and the mean equivalent water cylinder diameter used for modeling the patient neck was 19.4 ± 4.2 cm. The average adult patient neck size was about 3 cm larger than the mathematic anthropomorphic phantom (16.5 cm), decreasing the estimated thyroid doses by 15%. Thyroid doses were independent of age and sex, with an average of 50 ± 23 mGy. The average cancer risk for a 20-year-old woman was six times higher than the corresponding risk for a 20-year-old man. Increasing patient age of either sex from 40 to 60 years reduced the cancer risk by approximately an order of magnitude.
Patient sex and age are the most important factors in determining thyroid cancer risk, with the thyroid dose being secondary.
本研究旨在评估行颈部 CT 检查的成年患者甲状腺吸收剂量及相应的癌症风险。
我们利用 68 例行颈部 CT 检查的成年患者的数据，计算甲状腺剂量并估计相应的癌症风险。记录患者年龄和性别，以及用于检查的容积 CT 剂量指数（CTDIvol）。使用 ImPACT 患者 CT 剂量计算器中的数学体模，将 CTDIvol 值用于估计甲状腺剂量。通过将每位患者的颈部模拟为等效水圆柱，并应用颈部大小和扫描长度的校正因子以及由于自动曝光控制而导致的辐射强度变化，来估计患者的相应剂量。
成年患者的平均（± SD）年龄为 59 ± 16 岁，用于模拟患者颈部的等效水圆柱平均直径为 19.4 ± 4.2 cm。成年患者颈部平均尺寸比数学模拟人体模型大 3 cm 左右（16.5 cm），这使估计的甲状腺剂量减少了 15%。甲状腺剂量与年龄和性别无关，平均为 50 ± 23 mGy。20 岁女性的平均癌症风险比 20 岁男性高 6 倍。无论性别如何，患者年龄从 40 岁增加到 60 岁，癌症风险都会降低一个数量级左右。
患者性别和年龄是决定甲状腺癌风险的最重要因素，而甲状腺剂量是次要因素。
