Yeo Seung-Gu, Kim Eun Seog
Department of Radiation Oncology, Soonchunhyang University College of Medicine, Cheonan, Korea.
Radiat Oncol J. 2013 Dec;31(4):247-51. doi: 10.3857/roj.2013.31.4.247. Epub 2013 Dec 31.
This study aimed to investigate efficient approaches for determining internal target volume (ITV) from four-dimensional computed tomography (4D CT) images used in stereotactic body radiotherapy (SBRT) for patients with early-stage non-small cell lung cancer (NSCLC).
4D CT images were analyzed for 15 patients who received SBRT for stage I NSCLC. Three different ITVs were determined as follows: combining clinical target volume (CTV) from all 10 respiratory phases (ITV10Phases); combining CTV from four respiratory phases, including two extreme phases (0% and 50%) plus two intermediate phases (20% and 70%) (ITV4Phases); and combining CTV from two extreme phases (ITV2Phases). The matching index (MI) of ITV4Phases and ITV2Phases was defined as the ratio of ITV4Phases and ITV2Phases, respectively, to the ITV10Phases. The tumor motion index (TMI) was defined as the ratio of ITV10Phases to CTVmean, which was the mean of 10 CTVs delineated on 10 respiratory phases.
The ITVs were significantly different in the order of ITV10Phases, ITV4Phases, and ITV2Phases (all p < 0.05). The MI of ITV4Phases was significantly higher than that of ITV2Phases (p < 0.001). The MI of ITV4Phases was inversely related to TMI (r = -0.569, p = 0.034). In a subgroup with low TMI (n = 7), ITV4Phases was not statistically different from ITV10Phases (p = 0.192) and its MI was significantly higher than that of ITV2Phases (p = 0.016).
The ITV4Phases may be an efficient approach alternative to optimal ITV10Phases in SBRT for early-stage NSCLC with less tumor motion.
本研究旨在探讨从用于早期非小细胞肺癌（NSCLC）患者立体定向体部放疗（SBRT）的四维计算机断层扫描（4D CT）图像中确定内部靶区（ITV）的有效方法。
对15例接受I期NSCLC的SBRT治疗的患者的4D CT图像进行分析。确定了三种不同的ITV，如下所示：合并所有10个呼吸时相的临床靶区（CTV）（ITV10时相）；合并四个呼吸时相的CTV，包括两个极端时相（0%和50%）加上两个中间时相（20%和70%）（ITV4时相）；以及合并两个极端时相的CTV（ITV2时相）。ITV4时相和ITV2时相的匹配指数（MI）分别定义为ITV4时相和ITV2时相对于ITV10时相的比值。肿瘤运动指数（TMI）定义为ITV10时相与CTV均值的比值，CTV均值是在10个呼吸时相上勾画的10个CTV的平均值。
ITV在ITV10时相、ITV4时相和ITV2时相的顺序上有显著差异（所有p < 0.05）。ITV4时相的MI显著高于ITV2时相（p < 0.001）。ITV4时相的MI与TMI呈负相关（r = -0.569，p = 0.034）。在TMI较低的亚组（n = 7）中，ITV4时相与ITV10时相无统计学差异（p = 0.192），其MI显著高于ITV2时相（p = 0.016）。
对于肿瘤运动较小的早期NSCLC患者，在SBRT中，ITV4时相可能是替代最佳ITV10时相的有效方法。
