Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Med Phys. 2010 Mar;37(3):1254-60. doi: 10.1118/1.3298007.
To estimate the position and volume errors in 4D-CT caused by irregular breathing.
A virtual 4D-CT scanner was designed to reproduce axial mode scans with retrospective resorting. This virtual scanner creates an artificial spherical tumor based on the specifications of the user, and recreates images that might be produced by a 4D-CT scanner using a patient breathing waveform. 155 respiratory waveforms of patients were used to test the variability of 4D-CT scans. Each breathing waveform was normalized and scaled to 1, 2, and 3 cm peak-to-peak motion, and artificial tumors with 2 and 4 cm radius were simulated for each scaled waveform. The center of mass and volume of resorted 4D-CT images were calculated and compared to the expected values of center of mass and volume for the artificial tumor. Intrasubject variability was investigated by running the virtual scanner over different subintervals of each patient's breathing waveform.
The average error in the center of mass location of an artificial tumor was less than 2 mm standard deviation for 2 cm motion. The corresponding average error in volume was less than 4%. In the worst-case scenarios, a center of mass error of 1.0 cm standard deviation and volume errors of 30%-60% at inhale were found. Systematic errors were observed in a subset of patients due to irregular breathing, and these errors were more pronounced when the tumor volume is smaller.
Irregular breathing during 4D-CT simulation causes systematic errors in volume and center of mass measurements. These errors are small but depend on the tumor size, motion amplitude, and degree of breathing irregularity.
估计不规则呼吸引起的 4D-CT 位置和体积误差。
设计了一个虚拟的 4D-CT 扫描仪，用于通过回顾性重排来模拟轴向模式扫描。该虚拟扫描仪基于用户规格创建一个人工球形肿瘤，并使用患者呼吸波形来重建可能由 4D-CT 扫描仪产生的图像。使用 155 个患者呼吸波形来测试 4D-CT 扫描的可变性。每个呼吸波形都经过归一化和缩放，以达到 1、2 和 3cm 峰到峰运动，并针对每个缩放波形模拟具有 2 和 4cm 半径的人工肿瘤。计算重排 4D-CT 图像的质心和体积，并将其与人工肿瘤的质心和体积预期值进行比较。通过在每个患者呼吸波形的不同子间隔上运行虚拟扫描仪来研究个体内变异性。
对于 2cm 运动，人工肿瘤质心位置的平均误差小于 2mm 标准差。相应的体积平均误差小于 4%。在最坏情况下，发现质心误差为 1.0cm 标准差，吸入时体积误差为 30%-60%。由于不规则呼吸，在一部分患者中观察到系统误差，并且当肿瘤体积较小时，这些误差更为明显。
4D-CT 模拟过程中的不规则呼吸会导致体积和质心测量的系统误差。这些误差虽然较小，但取决于肿瘤大小、运动幅度和呼吸不规则程度。
