Received for publication June 30, 2020; and accepted for publication, after revision, August 18, 2020. From the Department of Medical Physics, School of Medicine, University of Crete, Crete, Greece.
Invest Radiol. 2021 Jan;56(1):62-68. doi: 10.1097/RLI.0000000000000727.
Radiation dose in computed tomography (CT) has become a hot topic due to an upward trend in the number of CT procedures worldwide and the relatively high doses associated with these procedures. The main aim of this review article is to provide an overview of the most frequently used metrics for CT radiation dose characterization, discuss their strengths and limitations, and present patient dose assessment methods. Computed tomography dosimetry is still based on a CT dose index (CTDI) measured using 100-mm-long pencil ionization chambers and standard dosimetry phantoms (CTDI100). This dose index is easily measured but has important limitations. Computed tomography dose index underestimates the dose generated by modern CT scanners with wide beam collimation. Manufacturers should report corrected CTDI values in the consoles of CT systems. The size-specific dose estimate has been proposed to provide an estimate of the average dose at the center of the scan volume along the z-axis of a CT scan. Size-specific dose estimate is based on CTDI and conversion factors and, therefore, its calculation incorporates uncertainties associated with the measurement of CTDI. Moreover, the calculation of size-specific dose estimate is straightforward only when the tube current modulation is not activated and when the patient body diameter does not change considerably along the z-axis of the scan. Effective dose can be used to provide typical patient dose values from CT examinations, compare dose between modalities, and communicate radiogenic risks. In practice, effective dose has been used incorrectly, for example, to characterize a CT procedure as a low-dose examination. Organ or tissue doses, not effective doses, are required for assessing the probability of cancer induction in exposed individuals. Monte Carlo simulation is a powerful technique to estimate organ and tissue dose from CT. However, vendors should make available to the research community the required information to model the imaging process of their CT scanners. Personalized dosimetry based on Monte Carlo simulation and patient models allows accurate organ dose estimation. However, it is not user friendly and fast enough to be applied routinely. Future research efforts should involve the development of advanced artificial intelligence algorithms to overcome drawbacks associated with the current equipment-specific and patient-specific dosimetry.
由于全球 CT 检查数量呈上升趋势，且这些检查的辐射剂量相对较高，因此 CT 中的辐射剂量已成为一个热门话题。本文的主要目的是概述 CT 辐射剂量特征的最常用指标，讨论其优缺点，并介绍患者剂量评估方法。CT 剂量学仍然基于使用 100mm 长铅笔电离室和标准剂量体模（CTDI100）测量的 CT 剂量指数（CTDI）。该剂量指数易于测量，但存在重要的局限性。CTDI 低估了具有宽束准直的现代 CT 扫描仪产生的剂量。制造商应在 CT 系统控制台中报告校正后的 CTDI 值。提出了基于体模的剂量指数，以提供沿 CT 扫描的 z 轴在扫描体积中心处的平均剂量估计值。基于体模的剂量指数基于 CTDI 和转换系数，因此其计算包含与 CTDI 测量相关的不确定性。此外，只有当管电流调制未激活且患者身体直径在扫描的 z 轴上没有明显变化时，基于体模的剂量指数的计算才简单。有效剂量可用于提供 CT 检查的典型患者剂量值，比较不同模态之间的剂量，并传达放射风险。在实践中，有效剂量被错误地用于将 CT 程序描述为低剂量检查。为了评估暴露个体中癌症诱导的概率，需要器官或组织剂量而不是有效剂量。蒙特卡罗模拟是一种从 CT 估算器官和组织剂量的强大技术。然而，供应商应向研究界提供建模其 CT 扫描仪成像过程所需的信息。基于蒙特卡罗模拟和患者模型的个性化剂量学可实现准确的器官剂量估算。然而，它不够用户友好且不够快速，无法常规应用。未来的研究工作应涉及开发先进的人工智能算法，以克服与当前特定于设备和特定于患者的剂量学相关的缺点。
