Barreto Izabella L, Gress Dustin A, Leon Stephanie M, Schwarz Bryan C, Kobistek Robert J, Mahesh M, Tomlinson James A, Dillon Chad M
University of Florida College of Medicine, Gainesville, Florida, USA.
American College of Radiology, Reston, Virginia, USA.
Med Phys. 2025 Mar;52(3):1823-1832. doi: 10.1002/mp.17543. Epub 2024 Dec 11.
While many clinical computed tomography (CT) protocols use helical scanning, the traditional method for measuring the volume CT Dose Index (CTDI) requires modifying the helical protocol to perform a single axial rotation. This modification can present challenges and mismatched settings across various scanner models.
This study investigates the generalizability of a helical methodology for estimating CTDI across a diverse range of participants, CT scanner models, and protocol parameters.
A web-based platform collected axial and helical CTDI measurements from 24 medical physicists who submitted 569 data sets obtained using four CT protocols on scanners from seven CT manufacturers. Various parameters were tested for tube voltage (70-140 kVp), rotation time (0.25-1.50 s), beam width (8-80 mm), and pitch (0.29-3.0) settings. Measurements from the two methodologies were assessed for reproducibility using three repeated exposures and then compared to each other and to the scanner-displayed CTDI. Agreement between the methodologies was assessed using Bland-Altman analysis, linear regression, paired t-tests, and a paired two one-sided tests (TOST) procedure with equivalence margins of 5% of the mean protocol CTDI. The impact of beam width and pitch on measurement accuracy was assessed using linear regression analysis and an independent t-test.
This study demonstrated better measurement reproducibility with the helical method (p < 0.05) and excellent concordance between helical and axial measurements (CCC > 0.99), with an average difference of -0.61 mGy (limits of agreement: -4.54 and 3.32). The TOST analysis confirmed that the measurement methods were statistically equivalent within the defined equivalence margins. The number of measurements that differed from the displayed CTDI by more than ± 20% was 10 for the axial method and 22 for the helical method. We did not identify a linear correlation between measurement accuracy and beam width or pitch (R< 0.06). However, differences between axial and helical methods were significant for protocols with beam widths up to 40 mm versus those greater than 40 mm, as well as for protocols with pitch factors up to 1.0 compared to those greater than 1.0 (p < 0.001).
Utilizing the same equipment currently used for measuring CTDI and a simple measurement setup, the helical method offers an alternative measurement methodology that can be seamlessly implemented by medical physicists and adopted by regulatory and accrediting bodies for routine quality control of CT scanners.
虽然许多临床计算机断层扫描（CT）协议使用螺旋扫描，但传统的容积CT剂量指数（CTDI）测量方法需要修改螺旋协议以进行单次轴向旋转。这种修改在各种扫描仪型号上可能带来挑战且设置不匹配。
本研究调查了一种螺旋方法在不同参与者、CT扫描仪型号和协议参数范围内估计CTDI的通用性。
一个基于网络的平台收集了24名医学物理学家的轴向和螺旋CTDI测量值，他们提交了使用来自7家CT制造商的扫描仪上的4种CT协议获得的569个数据集。对管电压（70 - 140 kVp）、旋转时间（0.25 - 1.50 s）、束宽（8 - 80 mm）和螺距（0.29 - 3.0）设置等各种参数进行了测试。使用三次重复曝光评估两种方法测量的可重复性，然后相互比较并与扫描仪显示的CTDI进行比较。使用Bland - Altman分析、线性回归、配对t检验和配对双侧单侧检验（TOST）程序评估两种方法之间的一致性，等效界限为协议平均CTDI的5%。使用线性回归分析和独立t检验评估束宽和螺距对测量准确性的影响。
本研究表明螺旋方法具有更好的测量可重复性（p < 0.05），并且螺旋测量与轴向测量之间具有极好的一致性（CCC > 0.99），平均差异为 - 0.61 mGy（一致性界限：- 4.54和3.32）。TOST分析证实，在定义的等效界限内，测量方法在统计学上是等效的。轴向方法中与显示的CTDI相差超过±20%的测量次数为10次，螺旋方法为22次。我们未发现测量准确性与束宽或螺距之间存在线性相关性（R < 0.06）。然而，对于束宽高达40 mm与大于40 mm的协议，以及螺距因子高达1.0与大于1.0的协议，轴向和螺旋方法之间的差异是显著的（p < 0.001）。
利用目前用于测量CTDI的相同设备和简单的测量设置，螺旋方法提供了一种替代测量方法，医学物理学家可以无缝实施，监管和认证机构也可采用其进行CT扫描仪的常规质量控制。
