Department of Clinical Physics and Bioengineering, University of Glasgow, Gartnavel Royal Hospital, Glasgow G12 0XH, United Kingdom.
King Abdulaziz City for Science and Technology (KACST), Riyadh, Saudi Arabia.
J Radiol Prot. 2021 Nov 3;41(4). doi: 10.1088/1361-6498/abecf5.
The dose quantities displayed routinely on CT scanners, the volume averaged CT dose index (CTDI) and dose length product, provide measures of doses calculated for standard phantoms. The American Association of Medical Physics has published conversion factors for the adjustment of CTDIto take account of variations in patient size, the results being termed size-specific dose estimate (SSDE). However, CTDIand SSDE, while useful in comparing and optimising doses from a set procedure, do not provide risk-related information that takes account of the organs and tissues irradiated and associated cancer risks. A derivative of effective dose that takes account of differences in body and organ sizes and masses, referred to here as size-specific effective dose (SED), can provide such information. Data on organ doses from NCICT software that is based on Monte Carlo simulations of CT scans for 193 adult phantoms have been used to compute values of SED for CT examinations of the trunk and results compared with corresponding values of SSDE. Relationships within ±8% were observed between SED and SSDE for scans extending over similar regions for phantoms with a wide range of sizes. Coefficients have been derived from fits of the data to estimate SED values from SSDEs for different regions of the body for scans of standard lengths based on patient height. A method developed to take account of differences in scan length gave SED results within ±5% of values calculated using the NCI phantom library. This approach could potentially be used to estimate SED from SSDE values, allowing their display at the time a CT scan is performed.
CT 扫描仪上常规显示的剂量量、体积平均 CT 剂量指数 (CTDI) 和剂量长度乘积，提供了针对标准体模计算的剂量的度量。美国医学物理协会已发布了 CTDI 的转换因子，以考虑患者体型的变化，其结果被称为体型特异性剂量估计 (SSDE)。然而，CTDI 和 SSDE 虽然在比较和优化一组程序的剂量时很有用，但它们并未提供考虑受照射器官和组织以及相关癌症风险的风险相关信息。有效剂量的一种衍生量，考虑到身体和器官大小和质量的差异，这里称为体型特异性有效剂量 (SED)，可以提供此类信息。基于对 193 个成人体模 CT 扫描的蒙特卡罗模拟的 NCICT 软件中的器官剂量数据已被用于计算躯干 CT 检查的 SED 值，并将其与相应的 SSDE 值进行比较。对于在大小范围广泛的体模中扫描相似区域的情况，SED 和 SSDE 之间观察到了在 ±8%以内的关系。基于患者身高，针对不同身体区域的标准长度扫描，已从数据拟合中推导出了系数，以从 SSDE 估计 SED 值。为考虑扫描长度差异而开发的方法使 SED 结果与使用 NCI 体模库计算的值相差在 ±5%以内。这种方法有可能用于从 SSDE 值估计 SED，允许在进行 CT 扫描时显示其值。
