Lin T, Ma C
Fox Chase Cancer Center, Philadelphia, PA.
Med Phys. 2012 Jun;39(6Part6):3652. doi: 10.1118/1.4734835.
To investigate motion artifacts of kV CBCT and MV CBCT images on metal localization devices for image guided radiation therapy.
8 MU pelvis CBCT template for Siemens Artiste MVision and Pelvis template for Varian IX on-board Exact Arms kV were used to acquire CBCT images in this study. Images from both CBCT modalities were compared in CNRs, metal landmark absolute positions, and image volume distortion on three different planes of view. The images were taken on a breathing-simulated thoracic phantom in which several typical metal localization devices were implanted, including clips and wires for breast patients, gold seeds for prostate patients, and BBs as skin marks. To magnify the artifacts, a 4cm diameter metal ball was also implanted in the thoracic phantom to mimic the metal artifacts. The amplitude of the sinusoidal breathing was 1cm, and the period varies from 2sec, 4sec to 8sec.
For MV CBCT, the CNR at 4sec breathing cycle with 1cm breathing amplitude was 5.0, 3.4 and 4.6 for clips, gold seeds and BBs, respectively while it was 1.5, 2.0 and 1.6 for kV CBCT. On the images, kV CBCT showed symmetric streaking artifacts both in the transverse and longitudinal directions relative to the motion direction. kV CBCT images predicted 89% of the expected volume, while MV CBCT images predicted 95% of the expected volume. Simulated soft tissue observed in MVCT cannot be detected in kVCT.
MV CBCT images showed better volume prediction, less streaking effects and better CNRs of a moving metal target, i.e. clips, BBs, gold seeds and metal balls than kV CBCT images. MV CBCT was more advantageous compared to kV CBCT with less motion artifacts for metal localization devices.
研究千伏锥形束计算机断层扫描（kV CBCT）和兆伏锥形束计算机断层扫描（MV CBCT）图像在图像引导放射治疗的金属定位装置上的运动伪影。
本研究使用西门子Artiste MVision的8 MU骨盆CBCT模板和Varian IX机载Exact Arms kV的骨盆模板来获取CBCT图像。在三个不同的视图平面上，比较了两种CBCT模式图像的对比噪声比（CNR）、金属标记物的绝对位置和图像体积畸变。图像采集于一个模拟呼吸的胸部体模，其中植入了几种典型的金属定位装置，包括用于乳腺癌患者的夹子和导线、用于前列腺癌患者的金种子以及作为皮肤标记的铅丸。为了放大伪影，还在胸部体模中植入了一个直径4厘米的金属球以模拟金属伪影。正弦呼吸的幅度为1厘米，周期从2秒、4秒到8秒不等。
对于MV CBCT，在呼吸幅度为1厘米、呼吸周期为4秒时，夹子、金种子和铅丸的CNR分别为5.0、3.4和4.6，而kV CBCT的相应值分别为1.5、2.0和1.6。在图像上，kV CBCT在相对于运动方向的横向和纵向均显示出对称的条纹伪影。kV CBCT图像预测的体积为预期体积的89%，而MV CBCT图像预测的体积为预期体积的95%。在MVCT中观察到的模拟软组织在kVCT中无法检测到。
与kV CBCT图像相比，MV CBCT图像在移动金属目标（即夹子、铅丸、金种子和金属球）的体积预测方面表现更好，条纹效应更少，CNR更高。对于金属定位装置，MV CBCT相比kV CBCT具有更少的运动伪影，更具优势。
