Department of Physiology and Biophysics, University at Buffalo, NY, Buffalo, 14214-3005, USA.
Department of Radiation Medicine, Roswell Park Cancer Institute, NY, Buffalo, 14293, USA.
Radiat Oncol. 2017 Nov 3;12(1):166. doi: 10.1186/s13014-017-0907-8.
The "gold standard" approach for defining an internal target volume (ITV) is using 10 gross tumor volume (GTV) phases delineated over the course of one respiratory cycle. However, different sites have adopted several alternative techniques which compress all temporal information into one CT image set to optimize work flow efficiency. The purpose of this study is to evaluate alternative target segmentation strategies with respect to the 10 phase gold standard.
A Quasar respiratory motion phantom was employed to simulate lung tumor movement. Utilizing 4DCT imaging, a gold standard ITV was created by merging 10 GTV time resolved image sets. Four alternative planed ITV's were compared using free breathing (FB), average intensity projection (AIP), maximum image projection (MIP), and an augmented FB (FB-Aug) set where the ITV included structures from FB plus max-inhale/exhale image sets. Statistical analysis was performed using the Dice similarity coefficient (DSC). Seventeen patients previously treated for lung SBRT were also included in this retroactive study.
PTV's derived from the FB image set are the least comparable with the 10 phase benchmark (DSC = 0.740-0.408). For phantom target motion greater than 1 cm, FB and AIP ITV delineation exceeded the 10 phase benchmark by 2% or greater, whereas MIP target segmentation was found to be consistently within 2% agreement with the gold standard (DSC > 0.878). Clinically, however, the FB-Aug method proved to be most favorable for tumor movement up to 2 cm (DSC = 0.881 ± 0.056).
Our results indicate the range of tumor motion dictates the accuracy of the defined PTV with respect to the gold standard. When considering delineation efficiency relative to the 10 phase benchmark, the FB-Aug technique presents a potentially proficient and viable clinical alternative. Among various techniques used for image segmentation, a judicious balance between accuracy and efficiency is inherently required to account for tumor trajectory, range and rate of mobility.
定义内部靶区（ITV）的“金标准”方法是使用在一个呼吸周期内勾画的 10 个大体肿瘤靶区（GTV）相位。然而，不同的机构已经采用了几种替代技术，将所有时间信息压缩到一个 CT 图像集中，以优化工作流程效率。本研究的目的是评估替代靶区分割策略与 10 相位金标准的关系。
使用 Quasar 呼吸运动体模模拟肺肿瘤运动。利用 4DCT 成像，通过合并 10 个 GTV 时分辨图像集创建金标准 ITV。使用自由呼吸（FB）、平均强度投影（AIP）、最大图像投影（MIP）和增强 FB（FB-Aug）集比较了四个替代计划的 ITV，其中 ITV 包括 FB 加最大吸气/呼气图像集的结构。使用 Dice 相似系数（DSC）进行统计学分析。17 例先前接受肺部 SBRT 治疗的患者也被纳入本回顾性研究。
从 FB 图像集获得的 PTV 与 10 相位基准最不相似（DSC=0.740-0.408）。对于大于 1cm 的体模靶区运动，FB 和 AIP ITV 勾画超过 10 相位基准 2%，而 MIP 靶区分割始终与金标准相差 2%以内（DSC>0.878）。然而，在临床上，FB-Aug 方法对于 2cm 以内的肿瘤运动最为有利（DSC=0.881±0.056）。
我们的结果表明，肿瘤运动范围决定了定义的 PTV 相对于金标准的准确性。考虑到与 10 相位基准的勾画效率，FB-Aug 技术为一种潜在的高效且可行的临床替代方案。在用于图像分割的各种技术中，需要在准确性和效率之间取得平衡，以考虑肿瘤轨迹、范围和移动速度。
