Assessment of residual error for online cone-beam CT-guided treatment of prostate cancer patients
Assessment of residual error for online cone-beam CT-guided treatment of prostate cancer patients
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DOI：
10.1016/j.ijrobp.2005.03.035
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发表时间：
2005-07-15
影响因子：
7
通讯作者：
Wong, J
中科院分区：
文献类型：
--
作者：
Létourneau, D;Martinez, AA;Wong, J
目的：在医学加速器上实现的千压锥束CT （CBCT）可用于临床图像引导应用。这项工作的目的是评估与CBCT在线引导前列腺癌患者设置相关的剩余设置误差的大小和稳定性。残余误差涉及图像配准的不确定性、有限的机械精度以及成像和处理过程中的屈光内运动。方法和材料：CBCT在线引导校正的残余误差首先在一个幻影研究中确定。在线校正后，通过将每隔90秒采集的巨压门静脉图像与相应的数字重建x线照片进行比较，确定残差。在临床研究中，8例前列腺癌患者植入了三种高缠绕线圈制成的不透射线标记物。在使用皮肤标记定位患者后，获得CBCT扫描，并通过融合CBCT上的线圈和计划CT扫描来确定安装误差。然后通过相应地移动沙发来纠正患者的设置。校正后立即进行第二次CBCT扫描，以评估残余目标设置误差。通过跟踪线圈和两次CBCT扫描之间每30秒获得的千伏x线片上的骨标记来评估屈光运动。通过对齐规划CT和CBCT图像上定义的前列腺轮廓，离线评估基于软组织配准的校正。结果：对于理想的刚性幻影，CBCT图像引导治疗通常可达到1 mm或更高的设置精度。对于患者来说，经过CBCT校正后，几乎所有病例的靶位设置误差都减小了，一般在+/- 1.5 mm以内。图像引导过程花费23-35分钟，由计算机速度和网络配置决定。折射内运动对残余设置误差的贡献很小，标准差为+/- 0.9 mm。线圈和软组织配准获得的设置校正之间的平均差异在上位方向上最大，等于-1.1 +/- 2.9 mm。结论：基于剩余设置误差测量，本研究中纳入的患者在线CBCT校正后所需的余量约为3mm，由于观察到较小的屈光内运动，这被认为是下限。使用线圈或软组织进行注册所获得的设置校正之间的差异可能部分是由于线圈缺乏完整的三维信息或前列腺描绘困难，需要进一步研究。(c) 2005爱思唯尔公司
Purpose: Kilovoltage cone-beam CT (CBCT) implemented on board a medical accelerator is available for image-guidance applications in our clinic. The objective of this work was to assess the magnitude and stability of the residual setup error associated with CBCT online-guided prostate cancer patient setup. Residual error pertains to the uncertainty in image registration, the limited mechanical accuracy, and the intrafraction motion during imaging and treatment.Methods and Materials: The residual error for CBCT online-guided correction was first determined in a phantom study. After online correction, the phantom residual error was determined by comparing megavoltage portal images acquired every 90 to the corresponding digitally reconstructed radiographs. In the clinical study, 8 prostate cancer patients were implanted with three radiopaque markers made of high-winding coils. After positioning the patient using the skin marks, a CBCT scan was acquired and the setup error determined by fusing the coils on the CBCT and planning CT scans. The patient setup was then corrected by moving the couch accordingly. A second CBCT scan was acquired immediately after the correction to evaluate the residual target setup error. Intrafraction motion was evaluated by tracking the coils and the bony landmarks on kilovoltage radiographs acquired every 30 s between the two CBCT scans. Corrections based on soft-tissue registration were evaluated offline by aligning the prostate contours defined on both planning CT and CBCT images.Results: For ideal rigid phantoms, CBCT image-guided treatment can usually achieve setup accuracy of 1 mm or better. For the patients, after CBCT correction, the target setup error was reduced in almost all cases and was generally within +/- 1.5 mm. The image guidance process took 23-35 min, dictated by the computer speed and network configuration. The contribution of the intrafraction motion to the residual setup error was small, with a standard deviation of +/- 0.9 mm. The average difference between the setup corrections obtained with coil and soft-tissue registration was greatest in the superoinferior direction and was equal to -1.1 +/- 2.9 mm.Conclusion: On the basis of the residual setup error measurements, the margin required after online CBCT correction for the patients enrolled in this study would be approximatively 3 mm and is considered to be a lower limit owing to the small intrafraction motion observed. The discrepancy between setup corrections derived from registration using coils or soft tissue can be due in part to the lack of complete three-dimensional information with the coils or to the difficulty in prostate delineation and requires further study. (c) 2005 Elsevier Inc.