4D-CT在立体定向放射治疗中对内靶区体积和剂量的影响

Volumetric and dosimetric effects of 4D-CT on internal target areas in stereotactic body radiotherapy

目的:探究肺癌在三维立体定向放射治疗(SBRT)中利用4D-CT测量的肿瘤运动对内靶区(ITV)的体积和剂量影响。方法:在6例肺癌患者中共探究了两种ITV的定义方法。第一种是将10个呼吸时相的4D-CT序列的所有肿瘤区(GTV)进行合并所得到的区域(ITVall);第二种是在自由呼吸CT中的GTV加上从4D-CT测量到的肿瘤在前后(AP)、左右(LR)和颅尾(CC)方向上的运动距离所得的区域(ITVmotion)。最后分析了两种ITV在靶区体积和剂量上的区别。结果:在体积上,ITVmotion对ITVall的平均比值为2.36;对于这两种不同的ITV,它们的PTV覆盖非常接近。肺平均剂量(Dmean)随着ITV的减小而减小,ITVall的Dmean比ITVmotion少77.4 cGy。结论:由于SBRT治疗的肿瘤尺寸相对较小,因此两种ITV的剂量学差异不显著。考虑到产生ITVall所需的工作量和时间,ITVmotion会是一个不错的选择。

Objective To investigate the volumetric and dosimetric effects on internal target volume(ITV)delineations based on the tumor motions measured by four-dimensional computed tomography(4D-CT)in the stereotactic body radiotherapy(SBRT)of lung cancers.Methods Two ITV definition methods for 6 lung cancer patients were investigated.One of the definition is the ITVall combining all gross tumor volumes(GTV)in the 4D-CT sequences of 10 respiratory phases;and the other was ITVmotion which was obtained by adding the measured tumor motions in anterior-posterior,left-right and cranialcaudal directions from 4D-CT to the GTV in free-breathing CT.The volumes and dosimetric differences resulted from different ITV definitions were analyzed.Results In the term of volume,the average ratios of ITVmotion to ITVall were 2.36,and the two ITV definitions had similar PTV coverage.The lung mean dose(Dmean)was decreased as the TIV decreased,and the Dmean of ITVall was 77.4 cGy less than that of ITVmotion.Conclusion Due to the relative small tumor size for SBRT,no significant dosimetric differences were observed between two ITV definitions.Considering the workload and time required to generate ITVall,ITVmotion may be a preferred option.