Department of Radiation Oncology, School of Medicine, The University of Texas Health Science Center at San Antonio, San Antonio, TX, USA.
J Appl Clin Med Phys. 2021 Jul;22(7):198-207. doi: 10.1002/acm2.13310. Epub 2021 Jun 3.
For mobile lung tumors, four-dimensional computer tomography (4D CT) is often used for simulation and treatment planning. Localization accuracy remains a challenge in lung stereotactic body radiation therapy (SBRT) treatments. An attractive image guidance method to increase localization accuracy is 4D cone-beam CT (CBCT) as it allows for visualization of tumor motion with reduced motion artifacts. However, acquisition and reconstruction of 4D CBCT differ from that of 4D CT. This study evaluates the discrepancies between the reconstructed motion of 4D CBCT and 4D CT imaging over a wide range of sine target motion parameters and patient waveforms.
A thorax motion phantom was used to examine 24 sine motions with varying amplitudes and cycle times and seven patient waveforms. Each programmed motion was imaged using 4D CT and 4D CBCT. The images were processed to auto segment the target. For sine motion, the target centroid at each phase was fitted to a sinusoidal curve to evaluate equivalence in amplitude between the two imaging modalities. The patient waveform motion was evaluated based on the average 4D data sets.
The mean difference and root-mean-square-error between the two modalities for sine motion were -0.35 ± 0.22 and 0.60 mm, respectively, with 4D CBCT slightly overestimating amplitude compared with 4D CT. The two imaging methods were determined to be significantly equivalent within ±1 mm based on two one-sided t tests (p < 0.001). For patient-specific motion, the mean difference was 1.5 ± 2.1 (0.8 ± 0.6 without outlier), 0.4 ± 0.3, and 0.8 ± 0.6 mm for superior/inferior (SI), anterior/posterior (AP), and left/right (LR), respectively.
In cases where 4D CT is used to image mobile tumors, 4D CBCT is an attractive localization method due to its assessment of motion with respect to 4D CT, particularly for lung SBRT treatments where accuracy is paramount.
对于移动肺部肿瘤，通常使用四维计算机断层扫描（4D CT）进行模拟和治疗计划。在肺部立体定向体放射治疗（SBRT）治疗中，定位准确性仍然是一个挑战。一种增加定位准确性的有吸引力的图像引导方法是四维锥形束 CT（4D CBCT），因为它可以减少运动伪影，实现肿瘤运动的可视化。然而，4D CBCT 的采集和重建与 4D CT 不同。本研究评估了在广泛的正弦目标运动参数和患者波形范围内，4D CBCT 与 4D CT 成像重建的运动之间的差异。
使用胸部运动体模检查了 24 个具有不同幅度和周期时间的正弦运动和 7 个患者波形。每个编程运动都使用 4D CT 和 4D CBCT 进行成像。对图像进行处理以自动分割目标。对于正弦运动，将目标质心在每个相位拟合到正弦曲线，以评估两种成像方式的幅度等效性。根据平均 4D 数据集评估患者波形运动。
两种模式的正弦运动的平均差值和均方根误差分别为-0.35±0.22 和 0.60mm，4D CBCT 略高于 4D CT 对幅度的估计。根据两个单边 t 检验（p<0.001），两种成像方法在±1mm 内被确定为显著等效。对于特定于患者的运动，平均差值分别为 1.5±2.1（无异常值时为 0.8±0.6）、0.4±0.3 和 0.8±0.6mm，用于上下（SI）、前后（AP）和左右（LR）。
在使用 4D CT 对移动肿瘤进行成像的情况下，4D CBCT 是一种有吸引力的定位方法，因为它可以根据 4D CT 评估运动，特别是在需要高精度的肺部 SBRT 治疗中。
