Lin Teh, Ma Chang-Ming Charlie
Department of Radiation Oncology Fox Chase Cancer Center, Temple University, Philadelphia, USA.
BJR Open. 2019 Mar 15;1(1):20190013. doi: 10.1259/bjro.20190013. eCollection 2019.
To investigate motion artifacts on kV CBCT and MV CBCT images with metal localization devices for image-guided radiation therapy.
The 8 μ pelvis CBCT template for the Siemens Artiste MVision and Pelvis template for the 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 markers. To magnify the artifacts, a 4 cm diameter metal ball was also implanted into the thoracic phantom to mimic the metal artifacts.
For MV CBCT, the CNR at a 4 sec breathing cycle with 1 cm 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 the kV CBCT. On the images, the kV CBCT showed symmetric streaking artifacts both in the transverse and longitudinal directions relative to the motion direction. The kV CBCT images predicted 89 % of the expected volume, while the MV CBCT images predicted 95 % of the expected volume. The simulated soft tissue observed in the MVCT could not be detected in the kV CBCT.
The MV CBCT images showed better volume prediction, less streaking effects and better CNRs of a moving metal target, . clips, BBs, gold seeds and metal balls than on the kV CBCT images. The MV CBCT was more advantageous compared to the kV CBCT with less motion artifacts for metal localization devices.
This study would benefit clinicians to prescribe MV CBCT as localization modality for radiation treatment with moving target when metal markers are implanted.
研究在图像引导放射治疗中使用金属定位装置时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）图像上的运动伪影。
本研究使用西门子Artiste MVision的8 μ骨盆CBCT模板和瓦里安IX机载精确臂kV上的骨盆模板来获取CBCT图像。在三个不同的视图平面上，对两种CBCT模态的图像进行对比度噪声比（CNR）、金属标志物绝对位置和图像体积畸变方面的比较。图像是在一个模拟呼吸的胸部体模上采集的，该体模中植入了几种典型的金属定位装置，包括用于乳腺患者的夹子和金属丝、用于前列腺患者的金种子以及作为皮肤标记物的铅弹。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。
对于MV CBCT，在呼吸幅度为1厘米、呼吸周期为4秒时，夹子、金种子和铅弹的CNR分别为5.0、3.4和4.6，而kV CBCT的相应值为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都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kV CBCT中无法检测到。
MV CBCT图像在体积预测方面表现更好，运动金属目标（夹子、铅弹、金种子和金属球）的条纹效应更少且CNR更高，与kV CBCT图像相比，MV CBCT在金属定位装置的运动伪影方面更具优势。
本研究将有助于临床医生在植入金属标记物时，将MV CBCT作为移动靶放射治疗的定位方式。
