Zhang Tiezhi, Orton Nigel P, Tomé Wolfgang A
Department of Human Oncology, University of Wisconsin, Madison, Wisconsin 53792, USA.
Med Phys. 2005 Nov;32(11):3493-502. doi: 10.1118/1.2106448.
Stereotactic body radiotherapy (SBRT) can be used to treat small lesions in the chest. A vacuum-based immobilization system is used in our clinic for SBRT, and a motion envelope is used in treatment planning. The purpose of this study is to automatically derive motion envelopes using deformable image registration of 4D-CT images, and to assess the effect of abdominal pressure on the motion envelopes. 4D-CT scans at ten phases were acquired prior to treatment for both free and restricted breathing using a vacuum-based immobilization system that includes an abdominal pressure pillow. To study the stability of the motion envelope over the course of treatment, a mid-treatment 4D-CT scan was obtained after delivery of the third fraction for two patients. The planning target volume excluding breathing motion (PTV(ex)) was defined on the image set at full exhalation phase and transformed into all other phases using displacement maps from deformable image registration. The motion envelope was obtained as the union of PTV(ex) masks of all phases. The ratios of the motion envelope to PTV(ex) volume ranged from 1.3 to 2.5. When pressure was applied, the ratios were reduced by as much as 29% compared to free breathing for some patients, but increased by up to 9% for others. The abdominal pressure pillow has more motion restriction effects on the anterior/inferior region of the lung. For one of the two patients for whom the 4D-CT scan was repeated at mid-treatment, the motion envelope was reproducible. However, for the other patient the tumor location and lung motion pattern significantly changed due to changes in the anatomy surrounding the tumor during the course of treatment, indicating that an image-guided approach to SBRT may increase the efficacy of this treatment.
立体定向体部放射治疗（SBRT）可用于治疗胸部的小病灶。我们诊所使用基于真空的固定系统进行SBRT，并在治疗计划中使用运动包络。本研究的目的是利用4D-CT图像的可变形图像配准自动得出运动包络，并评估腹部压力对运动包络的影响。在治疗前，使用包括腹部压力垫的基于真空的固定系统，对自由呼吸和受限呼吸状态下的患者进行了十个时相的4D-CT扫描。为研究运动包络在治疗过程中的稳定性，对两名患者在第三次分次放疗后进行了一次治疗中期的4D-CT扫描。在全呼气期图像集上定义排除呼吸运动的计划靶区（PTV(ex)），并使用可变形图像配准的位移图将其转换到所有其他时相。运动包络通过所有时相的PTV(ex)掩码的并集获得。运动包络与PTV(ex)体积的比值范围为1.3至2.5。施加压力时，部分患者的比值与自由呼吸相比降低了多达29%，但其他患者则增加了多达9%。腹部压力垫对肺的前/下区域有更大的运动限制作用。对于在治疗中期重复进行4D-CT扫描的两名患者中的一名，运动包络是可重复的。然而，对于另一名患者，由于治疗过程中肿瘤周围解剖结构的变化，肿瘤位置和肺运动模式发生了显著改变，这表明SBRT的图像引导方法可能会提高这种治疗的疗效。
