Feng Christine H, Gerry Emily, Chmura Steven J, Hasan Yasmin, Al-Hallaq Hania A
Department of Radiation and Cellular Oncology, The University of Chicago, Chicago, Illinois.
Department of Radiation and Cellular Oncology, The University of Chicago, Chicago, Illinois.
Int J Radiat Oncol Biol Phys. 2015 Jan 1;91(1):58-64. doi: 10.1016/j.ijrobp.2014.09.007. Epub 2014 Oct 22.
To calculate planning target volume (PTV) margins for chest wall and regional nodal targets using daily orthogonal kilovolt (kV) imaging and to study residual setup error after kV alignment using volumetric cone-beam computed tomography (CBCT).
Twenty-one postmastectomy patients were treated with intensity modulated radiation therapy with 7-mm PTV margins. Population-based PTV margins were calculated from translational shifts after daily kV positioning and/or weekly CBCT data for each of 8 patients, whose surgical clips were used as surrogates for target volumes. Errors from kV and CBCT data were mathematically combined to generate PTV margins for 3 simulated alignment workflows: (1) skin marks alone; (2) weekly kV imaging; and (3) daily kV imaging.
The kV data from 613 treatment fractions indicated that a 7-mm uniform margin would account for 95% of daily shifts if patients were positioned using only skin marks. Total setup errors incorporating both kV and CBCT data were larger than those from kV alone, yielding PTV expansions of 7 mm anterior-posterior, 9 mm left-right, and 9 mm superior-inferior. Required PTV margins after weekly kV imaging were similar in magnitude as alignment to skin marks, but rotational adjustments of patients were required in 32% ± 17% of treatments. These rotations would have remained uncorrected without the use of daily kV imaging. Despite the use of daily kV imaging, CBCT data taken at the treatment position indicate that an anisotropic PTV margin of 6 mm anterior-posterior, 4 mm left-right, and 8 mm superior-inferior must be retained to account for residual errors.
Cone-beam CT provides additional information on 3-dimensional reproducibility of treatment setup for chest wall targets. Three-dimensional data indicate that a uniform 7-mm PTV margin is insufficient in the absence of daily IGRT. Interfraction movement is greater than suggested by 2-dimensional imaging, thus a margin of at least 4 to 8 mm must be retained despite the use of daily IGRT.
利用每日正交千伏（kV）成像计算胸壁和区域淋巴结靶区的计划靶体积（PTV）边界，并使用容积锥形束计算机断层扫描（CBCT）研究kV校准后的残余摆位误差。
21例乳房切除术后患者接受调强放射治疗，PTV边界为7 mm。基于群体的PTV边界是根据8例患者中每例患者每日kV定位后和/或每周CBCT数据的平移位移计算得出的，这些患者的手术夹被用作靶区体积的替代物。将kV和CBCT数据的误差进行数学合并，以生成3种模拟校准工作流程的PTV边界：（1）仅使用皮肤标记；（2）每周kV成像；（3）每日kV成像。
来自613个治疗分次的kV数据表明，如果仅使用皮肤标记对患者进行定位，7 mm的均匀边界将涵盖95%的每日位移。结合kV和CBCT数据的总摆位误差大于仅来自kV的误差，导致PTV在前后方向扩展7 mm，左右方向扩展9 mm，上下方向扩展9 mm。每周kV成像后的所需PTV边界在大小上与校准到皮肤标记相似，但在32%±17%的治疗中需要对患者进行旋转调整。如果不使用每日kV成像，这些旋转将无法得到校正。尽管使用了每日kV成像，但在治疗位置采集的CBCT数据表明，必须保留前后方向6 mm、左右方向4 mm和上下方向8 mm的各向异性PTV边界，以考虑残余误差。
锥形束CT提供了关于胸壁靶区治疗摆位三维可重复性的额外信息。三维数据表明，在没有每日影像引导放射治疗（IGRT）的情况下，7 mm的均匀PTV边界是不够的。分次间运动大于二维成像所显示的，因此尽管使用了每日IGRT，仍必须保留至少4至8 mm的边界。
