Dzyubak O, Kincaid R, Yorke E, Hertanto A, Hu Y, Rimner A, Zhang Q, Mageras G
Memorial Sloan-Kettering Cancer Center, New York, NY.
Med Phys. 2012 Jun;39(6Part7):3679-3680. doi: 10.1118/1.4734954.
Respiration-induced motion artifacts in cone-beam CT (CBCT) can be corrected using a model of patient motion obtained from respiration-correlated CT (RCCT). This approach assumes that respiration-induced organ deformations at simulation, when RCCT scans are normally acquired, are still valid at treatment. The purpose of this study is to compare lung tumor image quality in motion-corrected CBCT images derived from treatment-day RCCT(tx) to simulation-day RCCT(sim) patient images.
In an IRB-approved study, lung cancer patients receive an RCCT at simulation, and an RCCT, gated CBCT and 1-minute CBCT at one treatment session. CBCT projections from the 1-minute scan are sorted according to breathing amplitude from an external monitor and reconstructed and warped to obtain a motion-corrected MC-CBCT at end expiration. Motion correction uses a model adapted from either RCCT(tx) or RCCT(sim), thus obtaining MC-CBCT(tx) and MC-CBCT(sim) images respectively. A gated CBCT, in which gantry rotation and projection acquisition occur within a gate at end expiration, serves as ground truth for comparison. Quality of MC-CBCT images is evaluated from tumor-to-background contrast ratio (TBCR) values measured by delineating the tumor and annular volume around it on the gated CBCT then transferring the contours and aligning them to each MC-CBCT.
TBCR is found tobe lower in MC-CBCT(sim) images, relative to MC-CBCT(tx), in four out of five patients with mean 21% reduction in a range 9-39%. In the remaining case, where there was no change in TBCR, tumor motion observed in the RCCT was small (2mm). Tumor motion extent relative to diaphragm is observed to change between RCCT(tx) and RCCT(sim) scans.
Preliminary results indicate that deformation patterns in lung do change between simulation and treatment. Such variations may reduce the validity of using simulation data for motion-corrected CBCT at treatment. The findings require confirmation with larger numbers of patients. NIH/NCI award R01 CA126993, research grant from Varian Medical Systems.
锥形束CT（CBCT）中呼吸诱导的运动伪影可使用从呼吸相关CT（RCCT）获得的患者运动模型进行校正。这种方法假定，在通常获取RCCT扫描的模拟阶段，呼吸诱导的器官变形在治疗时仍然有效。本研究的目的是比较从治疗日RCCT（tx）和模拟日RCCT（sim）患者图像得出的运动校正CBCT图像中肺肿瘤的图像质量。
在一项经机构审查委员会批准的研究中，肺癌患者在模拟阶段接受一次RCCT扫描，并在一个治疗疗程中接受一次RCCT扫描、门控CBCT扫描和1分钟CBCT扫描。1分钟扫描的CBCT投影根据外部监测器的呼吸幅度进行分类，然后重建并变形，以获得呼气末的运动校正MC-CBCT。运动校正使用从RCCT（tx）或RCCT（sim）改编的模型，从而分别获得MC-CBCT（tx）和MC-CBCT（sim）图像。门控CBCT在呼气末的一个门控内进行机架旋转和投影采集，作为比较的基准。通过在门控CBCT上勾勒肿瘤及其周围的环形体积，然后转移轮廓并将其与每个MC-CBCT对齐，测量肿瘤与背景对比度（TBCR）值，来评估MC-CBCT图像的质量。
在五名患者中，有四名患者的MC-CBCT（sim）图像中的TBCR低于MC-CBCT（tx）图像，平均降低21%，降低范围为9%-39%。在其余病例中，TBCR没有变化，在RCCT中观察到的肿瘤运动较小（2mm）。观察到相对于膈肌的肿瘤运动范围在RCCT（tx）和RCCT（sim）扫描之间有所变化。
初步结果表明，肺的变形模式在模拟和治疗之间确实会发生变化。这种变化可能会降低在治疗时使用模拟数据进行运动校正CBCT的有效性。这些发现需要更多患者的研究来证实。美国国立卫生研究院/国立癌症研究所授予R01 CA126993，瓦里安医疗系统公司的研究资助。
