Wang L, Turaka A, Meyer J, Spoka D, Jin L, Fan J, Ma C
Fox Chase Cancer Center, Philsadelphia, PA.
Med Phys. 2012 Jun;39(6Part6):3657. doi: 10.1118/1.4734857.
To assess the reliability of soft tissue alignment by comparing pre- and post-treatment cone-beam CT (CBCT) for image guidance in stereotactic body radiotherapy (SBRT) of lung cancers.
Our lung SBRT procedures require all patients undergo 4D CT scan in order to obtain patient-specific target motion information through reconstructed 4D data using the maximum-intensity projection (MIP) algorithm. The internal target volume (ITV) was outlined directly from the MIP images and a 3-5 mm margin expansion was then applied to the ITV to create the PTV. Conformal treatment planning was performed on the helical images, to which the MIP images were fused. Prior to each treatment, CBCT was used for image guidance by comparing with the simulation CT and for patient relocalization based on the bony anatomy. Any displacement of the patient bony structure would be considered as setup errors and would be corrected by couch shifts. Theoretically, as the PTV definition included target internal motion, no further shifts other than setup corrections should be made. However, it is our practice to have treating physicians further check target localization within the PTV. Whenever the shifts based on the soft-tissue alignment (that is, target alignment) exceeded a certain value (e.g. 5 mm), a post-treatment CBCT was carried out to ensure that the tissue alignment is reliable by comparing between pre- and post-treatment CBCT.
Pre- and post-CBCT has been performed for 7 patients so far who had shifts beyond 5 mm despite bony alignment. For all patients, post CBCT confirmed that the visualized target position was kept in the same position as before treatment after adjusting for soft-tissue alignment.
For the patient population studied, it is shown that soft-tissue alignment is necessary and reliable in the lung SBRT for individual cases.
通过比较肺癌立体定向体部放疗（SBRT）治疗前和治疗后的锥形束CT（CBCT）来评估软组织配准的可靠性，以用于图像引导。
我们的肺部SBRT程序要求所有患者进行4D CT扫描，以便通过使用最大强度投影（MIP）算法重建的4D数据获得患者特异性的靶区运动信息。直接从MIP图像勾勒出内部靶区体积（ITV），然后对ITV应用3 - 5 mm的边界扩展以创建计划靶区体积（PTV）。在融合了MIP图像的螺旋图像上进行适形治疗计划。每次治疗前，通过与模拟CT比较，使用CBCT进行图像引导，并基于骨骼解剖结构对患者进行重新定位。患者骨骼结构的任何位移都将被视为摆位误差，并通过治疗床移动进行校正。理论上，由于PTV定义包括了靶区内的运动，除了摆位校正外不应进行进一步的移动。然而，我们的做法是让治疗医生进一步检查PTV内的靶区定位。每当基于软组织配准（即靶区配准）的移动超过一定值（例如5 mm）时，进行治疗后CBCT，通过比较治疗前和治疗后的CBCT来确保组织配准是可靠的。
到目前为止，对7例尽管骨骼配准但仍有超过5 mm移动的患者进行了治疗前和治疗后的CBCT。对于所有患者，治疗后CBCT证实，在调整软组织配准后，可视化的靶区位置与治疗前保持在同一位置。
对于所研究的患者群体，结果表明在肺部SBRT中，软组织配准对于个别病例是必要且可靠的。
