Department of Medical Physics, University Hospital of Heraklion, Crete, Greece.
Invest Radiol. 2011 Oct;46(10):654-62. doi: 10.1097/RLI.0b013e3182213c55.
: The purpose of this study was (i) to measure absorbed dose to radiosensitive organs and estimate the effective dose associated with fixed tube current and automatic exposure control (AEC)-activated standard computed tomography (CT) examinations, and (ii) to investigate the relationship between the average reduction of tube current achieved by AEC and the reduction in organ and effective dose.
: Four physical anthropomorphic phantoms that represent the average individual as neonate, 1-year-old, 5-year-old, 10-year-old child, and the Rando phantom that simulates the average adult individual were employed. The phantoms were subjected to standard head and neck, thorax, and abdomen and pelvis scans using a 16-slice CT system. The scans were performed both with fixed tube current and with AEC. Dose measurements were performed for each scan using thermoluminescent dosimeters placed at internal locations in the phantoms and on the phantoms' surface. Dose measurements were performed for all radiosensitive organs according to the 2007 recommendations of the International Commission on Radiologic Protection. Effective dose was estimated on the basis of weighted sum of measured organ absorbed doses (EDMEAS). Percent reduction of organ absorbed dose and effective dose were compared with the mean percent reduction of the tube current.
: The percent organ dose reduction achieved when AEC was activated in standard head and neck CT scans ranged from 26.6% to 42% for neonate, 8.1% to 63.8% for 1-year-old, -2.9% to 22.5% for 5-year-old, -8.7% to 44.9% for 10-year-old, and 16.3% to 50.1% for an adult. The corresponding values for thorax scans were found to range from -26.1% to 9.9% for neonate, -2.5% to 37.7% for 1-year-old, -20.8% to 15.4% for 5-year-old, -61.9% to 9.3% for 10-year-old, and 5.6% to 42.2% for an adult, whereas the corresponding values for abdomen and pelvis scans were found to range from -12.1% to 29.1% for neonate, -4.9% to 26.6% for 1-year-old, -11.7% to 38.9% for 5-year-old, -62.4% to -17.3% for 10-year-old, and 31.0% to 56.8% for an adult. In neonate, the EDMEAS values ranged from 1.18 to 3.23 mSv for fixed tube current and 1.31 to 1.73 mSv for AEC scans. In 1-year-old phantom, the EDMEAS values ranged from 1.71 to 2.82 mSv for fixed tube current and 0.99 to 2.38 mSv for AEC scans. In 5-year-old phantom, the EDMEAS values ranged from 2.03 to 3.72 mSv for fixed tube current and 1.57 to 3.35 mSv for AEC scans. In 10-year-old phantom, the EDMEAS values ranged from 1.56 to 2.88 mSv for fixed tube current and 1.63 to 3.14 mSv for AEC scans. In adult phantom, the EDMEAS values ranged from 3.39 to 8.06 mSv for fixed tube current and 2.28 to 3.83 mSv for AEC scans. Mean mAs reduction is linearly related to the EDMEAS reduction (r = 0.807, P < 0.0001). The absolute percent difference between percent tube current and %EDMEAS reduction was in most cases higher than 15%.
: The reduction in the modulated tube current achieved by AEC should not be used to estimate the reduction in the absorbed dose to exposed radiosensitive organs. Moreover, the reduction in the modulated tube current may only be considered as a rough approximation of the corresponding effective dose reduction.
本研究的目的是：(i) 测量敏感器官的吸收剂量，并估算与固定管电流和自动曝光控制 (AEC) 激活的标准计算机断层扫描 (CT) 检查相关的有效剂量，以及 (ii) 研究 AEC 实现的管电流平均降低量与器官和有效剂量降低之间的关系。
使用四个代表新生儿、1 岁、5 岁、10 岁儿童和模拟成年个体的平均成年人的物理人体模型进行研究。对这些模型进行了 16 层 CT 系统的标准头颈部、胸部和腹部和骨盆扫描。使用放置在模型内部位置和模型表面的热释光剂量计对每次扫描进行剂量测量。根据国际放射防护委员会 2007 年的建议，对所有敏感器官进行剂量测量。基于测量的器官吸收剂量的加权总和来估计有效剂量 (EDMEAS)。将器官吸收剂量和有效剂量的百分比降低与管电流的平均百分比降低进行比较。
当 AEC 在标准头颈部 CT 扫描中激活时，新生儿的器官剂量降低百分比范围为 26.6%至 42%，1 岁的为 8.1%至 63.8%，5 岁的为 -2.9%至 22.5%，10 岁的为 -8.7%至 44.9%，成年人为 16.3%至 50.1%。胸部扫描的相应值为新生儿为 -26.1%至 9.9%，1 岁为 -2.5%至 37.7%，5 岁为 -20.8%至 15.4%，10 岁为 -61.9%至 9.3%，成年人为 5.6%至 42.2%。腹部和骨盆扫描的相应值为新生儿为 -12.1%至 29.1%，1 岁为 -4.9%至 26.6%，5 岁为 -11.7%至 38.9%，10 岁为 -62.4%至 -17.3%，成年人为 31.0%至 56.8%。在新生儿中，固定管电流的 EDMEAS 值范围为 1.18 至 3.23 mSv，AEC 扫描的 EDMEAS 值范围为 1.31 至 1.73 mSv。在 1 岁的模型中，固定管电流的 EDMEAS 值范围为 1.71 至 2.82 mSv，AEC 扫描的 EDMEAS 值范围为 0.99 至 2.38 mSv。在 5 岁的模型中，固定管电流的 EDMEAS 值范围为 2.03 至 3.72 mSv，AEC 扫描的 EDMEAS 值范围为 1.57 至 3.35 mSv。在 10 岁的模型中，固定管电流的 EDMEAS 值范围为 1.56 至 2.88 mSv，AEC 扫描的 EDMEAS 值范围为 1.63 至 3.14 mSv。在成年模型中，固定管电流的 EDMEAS 值范围为 3.39 至 8.06 mSv，AEC 扫描的 EDMEAS 值范围为 2.28 至 3.83 mSv。平均 mAs 降低与 EDMEAS 降低呈线性相关（r = 0.807，P < 0.0001）。在大多数情况下，管电流百分比与 %EDMEAS 降低百分比之间的绝对差值大于 15%。
AEC 实现的调制管电流降低不应用于估计暴露敏感器官的吸收剂量降低。此外，调制管电流的降低只能被认为是有效剂量降低的大致近似值。
