Evaluation of the cone beam CT for internal target volume localization in lung stereotactic radiotherapy in comparison with 4D MIP images
Evaluation of the cone beam CT for internal target volume localization in lung stereotactic radiotherapy in comparison with 4D MIP images
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DOI：
10.1118/1.4823785
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发表时间：
2013-11-01
期刊：
影响因子：
3.8
通讯作者：
Ma, Charlie M.
中科院分区：
文献类型：
--
作者：
Wang, Lu;Chen, Xiaoming;Ma, Charlie M.
目的：探讨三维锥形束CT（CBCT）在图像引导肺立体定向放射治疗中用于内部靶体积（ITV）定位的临床等效性是否与四维计算机断层扫描（4DCT）最大强度投影（MIP）重建图像等同。将具有已知体积的内置立方体、球体和圆锥体的球形聚苯乙烯体模连接到电机驱动平台，其模拟具有可变运动幅度和频率的正弦运动。在患者体内模拟上下（S-I）方向的靶运动，具有3个运动周期和2 cm峰-峰振幅。使用Varian机载Exact-Arms kV CBCT系统和GE LightSpeed四层CT（集成了位置管理4DCT扫描仪）扫描移动体模。从4DCT图像生成MIP图像。通过比较沿运动方向沿着移动物体的极端位置、ITV的质心位置和由Velocity自动绘制轮廓或使用成像梯度方法计算的ITV体积，评价了两组图像的临床等效性。作者比较了由上述方法确定的ITV体积与通过考虑物理对象尺寸和运动幅度而理论预测的ITV体积。通过梯度法沿穿过物体中心的S-I轴沿着确定极限位置。质心位置由自动中心函数确定。结果：两种成像模式所确定的物体的极端位置基本一致，且两种成像模式所确定的物体的极端位置基本一致。它们不受运动周期的影响。两种模态在极端位置的平均差异分别为立方体0.68%、球体1.35%和圆锥体0.5%。对于研究的所有运动周期，两种模式之间圆柱体、球体和圆锥体的质心位置的最大差异小于1.4 mm。对于ITV体积评价，作者发现基于MIP和基于CBCT的ITV均随运动周期的增加而增加。此外，基于MIP的ITV体积通常大于CBCT图像确定的ITV体积，球体、圆柱体和圆锥体的自动轮廓体积差异分别为2.57%、1.66%和1.82%，而使用梯度法时，上述对象的这些差异增加到9.57%、3.52%和8.71%。作者发现，自动轮廓法是足够准确的预测ITV的实际值的绝对差异小于2.4%的理论预测value.Conclusions相比：极端位置和质心位置的目标之间的两种图像模式，当呼吸运动是正弦的相互同意。虽然从两种图像模式描绘的ITV体积随运动周期而变化，但当使用优化的窗位时，两种模式之间的ITV差异最小。作者的结果表明，CBCT和MIP图像在确定ITV的位置在研究的条件下是等效的。CBCT足以为肺癌治疗提供影像学指导。(C)2013年美国医学物理学家协会。
Purpose: To investigate whether the three-dimensional cone-beam CT (CBCT) is clinically equivalent to the four-dimensional computed tomography (4DCT) maximum intensity projection (MIP) reconstructed images for internal target volume (ITV) localization in image-guided lung stereotactic radiotherapy.Methods: A ball-shaped polystyrene phantom with built-in cube, sphere, and cone of known volumes was attached to a motor-driven platform, which simulates a sinusoidal movement with changeable motion amplitude and frequency. Target motion was simulated in the patient in a superior-inferior (S-I) direction with three motion periods and 2 cm peak-to-peak amplitudes. The Varian onboard Exact-Arms kV CBCT system and the GE LightSpeed four-slice CT integrated with the respiratory-position-management 4DCT scanner were used to scan the moving phantom. MIP images were generated from the 4DCT images. The clinical equivalence of the two sets of images was evaluated by comparing the extreme locations of the moving objects along the motion direction, the centroid position of the ITV, and the ITV volumes that were contoured automatically by Velocity or calculated with an imaging gradient method. The authors compared the ITV volumes determined by the above methods with those theoretically predicted by taking into account the physical object dimensions and the motion amplitudes. The extreme locations were determined by the gradient method along the S-I axis through the center of the object. The centroid positions were determined by autocenter functions. The effect of motion period on the volume sizes was also studied.Results: It was found that the extreme locations of the objects determined from the two image modalities agreed with each other satisfactorily. They were not affected by the motion period. The average difference between the two modalities in the extreme locations was 0.68% for the cube, 1.35% for the sphere, and 0.5% for the cone, respectively. The maximum difference in the centroid position of the cylinder, sphere, and cone was less than 1.4 mm between the two modalities for all motion periods studied. For the ITV volume evaluation, the authors found that both MIP-based and CBCT-based ITVs increased with increases of motion period. Furthermore, the MIP-based ITV volumes were generally larger than those determined from the CBCT images, with the difference in autocontoured volumes being 2.57%, 1.66%, and 1.82% for the sphere, cylinder, and cone, respectively, while these differences increased to 9.57%, 3.52%, 8.71% for the above objects when the gradient method was used. The authors found that the autocontour method was accurate enough to predict the actual ITV values with the absolute differences less than 2.4% comparing to the theoretically predicted values.Conclusions: The extreme location and the centroid position of the objects agree with each other between the two image modalities when the breathing motion is sinusoidal. Although the ITV volumes delineated from both image modalities changed with the motion period, the differences in ITV between the two modalities were minimal when an optimized window level was used. The authors' results suggest that CBCT and MIP images are equivalent in determining an ITV's position in the conditions studied. The CBCT is adequate in providing imaging-guidance for lung cancer treatment. (C) 2013 American Association of Physicists in Medicine.