三维运动模体的4DCBCT与4DCT图像配准

目的 研究4DCT与4DCBCT对三维运动模体的成像和配准精度。方法 对CIRS008A模体进行4DCT和4DCBCT扫描。用直径1、2 cm小球模拟不同大小肿瘤,设置小球在三维方向作正弦运动(上下、前后和左右方向振幅分别为±1.0、±0.4、±0.2 cm),运动周期为4 s。勾画图像中的10个时相靶区、IGTV、MIP及平均密度投影(MeanIP)的靶区并测量体积。对4DCT与4DCBCT图像靶体积与小球静止体积V_S及运动体积V_D相比较;刚性配准后分析4DCT与4DCBCT图像靶区的匹配度(MI)。结果 图像中各时相的靶体积均>V_S。小体积小球的4DCT与4DCBCT图像各时相体积均值相对于V_S的变化(35.03%和32.62%)大于大体积小球 22.66%和17%)。ITV和MIP靶区体积略>V_D,MeanIP靶区体积D。小体积小球各时相靶区的平均MI (66.76%)小于大体积小球MI (82.21%);同时IGTV、MIP、MeanIP的MI (77.39%、75.90%、74.47%)也小于大体积小球的IGTV、MIP、MeanIP (90.29%、89.28%、82.74%)。结论 在肿瘤体积较小、运动幅度较大的情况下,谨慎使用4DCT与4DCBCT进行相互间配准比较。

Image registration of a three-dimensional dynamic phantom in four-dimensional cone-beam computed tomography and four-dimensional computed tomography

Objective To evaluate the image quality and registration accuracy of a three-dimensional (3D) dynamic phantom in four-dimensional computed tomography (4DCT) and four-dimensional cone-beam computed tomography (4DCBCT). Methods The Computerized Imaging Reference Systems Dynamic Thorax Phantom Model 008A was scanned to get 4DCT and 4DCBCT images. Two balls with different diameters (= 1 cm and = 2 cm) were used to simulate tumors with different sizes. The motion mode of the balls was 3D sinusoidal motion at 0.25 Hz (the amplitudes along the x, y, and z axes were ±1.0 cm, ±0.4 cm, and ±0.2 cm, respectively). Gross target volumes (GTVs) from 10-phase bins, internal gross target volumes (IGTV), and target volumes on maximum intensity projection (MIP) and mean intensity projection (MeanIP) images were contoured and calculated. Target volumes on 4DCT or 4DCBCT images were compared with the static and dynamic volumes of the balls (V_S and V_D). The matching index (MI) of target volumes between the 4DCT and 4DCBCT images was analyzed after rigid image registration. Results The GTV in each phase of the image was larger than V_S. The difference between the average GTV derived from 10 phases of 4DCT or 4DCBCT images and Vs of the small ball was larger than that of the large ball (35.03% vs. 22.66%;32.62% vs. 17.00%). All the IGTVs and target volumes on MIP images were slightly larger than V_D, but target volumes on MeanIP images were smaller than V_D. The average MI of 10-phase bins of the small ball was smaller than that of the large ball (66.76% vs. 82.21%). Moreover, MIs of IGTV,MIP, and MeanIP of the small ball were also smaller than those of the large ball (77.39% vs. 90.29%;75.90% vs. 89.28%;74.47% vs. 82.74%). Conclusions In the case of a relatively small tumor volume and a relatively large motion amplitude, 4DCT and 4DCBCT should be used with caution for comparison of image registration.