Pokhrel Damodar, Mallory Richard, Bernard Mark E
Department of Radiation Medicine, University of Kentucky, Lexington, KY 40536, USA.
Department of Radiation Medicine, University of Kentucky, Lexington, KY 40536, USA.
Med Dosim. 2023;48(3):170-175. doi: 10.1016/j.meddos.2023.03.005. Epub 2023 Apr 13.
Stereotactic body radiotherapy (SBRT) treatment of oligometastatic lesions via single-isocenter/multi-target (SIMT) plan is more efficient than using multi-isocenter/multitarget SBRT. This study quantifies the spatial positioning accuracy of 2 commercially available LINAC systems for SIMT treatment pertaining to the potential amplification of error as a function of the target's distance-to-isocenter. We compare the Ring-Gantry Halcyon LINAC equipped with the fast iterative conebeam-CT (iCBCT) for image-guided SIMT treatment, and the SBRT-dedicated C-Arm TrueBeam with standard pretreatment CBCT imaging. For both systems, Sun Nuclear's MultiMet Winston-Lutz Cube phantom with 6 metallic BBs distributed at different planes up to 7 cm away from the isocenter was used. The phantom was aligned and imaged via CBCT, and then couch corrections were applied. To treat all 6 BBs, an Eclipse 10-field 3D-conformal Field-in-Field (2×2 cm MLC field to each BB) plan for varying gantry, collimator, and couch (TrueBeam only) positions was developed for both machines with 6MV-FFF beam. The plan was delivered through ARIA once a week. The EPID images were analyzed via Sun Nuclear's software for spatial positioning accuracy. On TrueBeam, the treatment plan was delivered twice: once with 3DoF translational corrections and once with PerfectPitch 6DoF couch corrections. The average 3D spatial positioning accuracy was 0.55 ± 0.30 mm, 0.54 ± 0.24 mm, and 0.56 ± 0.28 mm at isocenter, and 0.59 ± 0.30 mm, 0.69 ± 0.30 mm, and 0.70 ± 0.35 mm at 7 cm distance-to-isocenter for Halcyon, TrueBeam 3DoF, and TrueBeam 6DoF, respectively. This suggests there are no clinically significant deviations of spatial uncertainty between the platforms with the distance-to-isocenter. On both platforms, our weekly independent measurements demonstrated the reproducibility for less than 1.0 mm positional accuracy of off-axis targets up to 7 cm from the isocenter. Due to this, no additional PTV-margin is suggested for lesions within 7 cm of isocenter. This study confirms that Halcyon can deliver similar positional accuracy to SBRT-dedicated TrueBeam to off-axis targets up to 7 cm from isocenter. These results further benchmark the spatial uncertainty of our extensively used SBRT-dedicated TrueBeam LINAC for SIMT SBRT treatments.
通过单等中心/多靶点（SIMT）计划进行立体定向体部放疗（SBRT）治疗寡转移病灶比使用多等中心/多靶点SBRT更有效。本研究量化了2种商用直线加速器系统在SIMT治疗中的空间定位精度，该精度与靶点到等中心距离所导致的误差潜在放大有关。我们比较了配备快速迭代锥形束CT（iCBCT）用于图像引导SIMT治疗的环形机架Halcyon直线加速器，以及采用标准预处理CBCT成像的SBRT专用C形臂TrueBeam直线加速器。对于这两种系统，均使用了Sun Nuclear公司的MultiMet Winston-Lutz体模，其带有6个金属BB，分布在距等中心最远7 cm的不同平面上。通过CBCT对体模进行对齐和成像，然后进行治疗床校正。为了治疗所有6个BB，针对两台机器均制定了Eclipse 10野3D适形野中野（每个BB采用2×2 cm多叶准直器野）计划，用于改变机架、准直器和治疗床（仅TrueBeam）的位置，采用6MV-FFF束。该计划每周通过ARIA执行一次。通过Sun Nuclear公司的软件分析EPID图像的空间定位精度。在TrueBeam上，治疗计划执行两次：一次采用3自由度平移校正，一次采用PerfectPitch 6自由度治疗床校正。在等中心处，Halcyon、TrueBeam 3自由度和TrueBeam 6自由度的平均三维空间定位精度分别为0.55±0.30 mm、0.5
