四维CT影像中不同方法勾画肺内病灶作为照射靶区的体积差异

Target Volume Variation of Intrapulmonary Lesions Delineated in Four-dimensional CT Imaging

目的分别在常规三维CT（3DCT）的自由呼吸下任意时相（FCT0）和四维CT（4DCT）影像上分别勾画肺内孤立性结节作为靶区并分析其体积差别。方法 8例患者（17个原发性肺内结节）和4例患者（转移性结节）分别接受FCT和4DCT扫描,4DCT分别按2、3、4、5、10个等间隔时相、最大密度投影（MIP）重建。对同一个肺结节分别在FCT（FCT0）和4CDT中的不同时相勾画肿瘤大体体积（GTVx0,x=0,1,2,3,4,5,6,7,8,9）。在3DCT中的FCT0均匀外放1、2、3、4和5 mm形成获得FCTx（x=1,2,3,4,5）,分别用2、3、4、5、10个时相上勾画的GTV求并集获得合成GTV即ITVx（x=2,3,4,5,10）。用配对t检验分别比较FCT0、MIP与GTVx0、FCTx0、ITVx的差异。结果与FCT0相比,4DCT中GTVx0（x=0,1,2,3,4,5,6）减小21%32%,GTVx0（x=7,8,9）减少7%-13%（P<0.05）。在FCT0基础上外放边界每增加1 mm,FCTx的绝对体积增加69 cm3,增加16%31%;当外放边界分别为1、2,3、4和5 mm时,FCT1、FCT2、FCT3、FCT4和FCT5的体积分别较FCT0增加27%、68%、96%、141%、198%倍。所有ITVx体积均大于MIP体积,与MIP相比,ITVx的体积增加24%-54%;ITV2、ITV3均与MIP的体积无明显差别（P>0.05）,ITV4、ITV5、ITV10与MIP有明显差别（P<0.05）。结论同一个肺内病灶通过不同CT影像手段获得的靶区体积有明显差别,在肺癌放疗（特别是立体定向放疗）计划设计时需考虑该差异。

Objective To compare the volumetric variations of target volume including gross tumor volume(GTV) and internal target volume(ITV) those were delineated in 3-dimensional(3D) and 4-Dimensional(4D) CT imaging. Methods Eight primary non-small cell lung cancer patients with 17 intrapulmonary solitary lesions and 4 patients with metastatic nodes received free-phase CT(FCT_0)at random respiratory phase and 4DCT scanning. 4DCT was reconstructed with 2-,3-,4-,5-,10- phase and maximal intensity projection(MIP). For a single lesion, GTV was delineated in FCT_0 and various phases(GTV_x0, x=0, 1, 2, 3, 4, 5, 6,7, 8, 9)in 4DCTs. FCT_x(x=0, 1, 2, 3, 4, 5)was expanded for the GTV in FCT with a margin of 1, 2, 3, 4, 5 mm. ITV_2(x=2, 3, 4, 5, 10)was composed of 2, 3, 4, 5 and 10 phases. The difference among the FCT_x, ITV_xand MIP was compared by paired t-test. Results Compared with the GTV in FCT, GTV_x0(x=0, 1, 2, 3, 4, 5, 6) in 4DCT was decreased by 21%-32% and GTV_x0(x=7, 8, 9) by 7%-13%(P<0.05). The absolute and relative volume of FCT- x(x=0, 1, 2 3, 4, 5) was increased by 6-9 cm3 and 16%-31% respectively. As the additional margin were 1, 2,3, 4 and 5 mm, the GTV of FCT_1, FCT_2, FCT_3, FCT_4 and FCT_5 were increased 27%,68%,96%,141% and 198% respectively when comparing with that in GTV in FCT-0. ITV_x were signifi cantly larger than MIP(P<0.05). When compared with MIP, the ITV was increased by 24%-54%. ITV-2and ITV-3 were not signifi cantly different to the MIP(P>0.05). ITV-4, ITV-5, and ITV-10, were signifi cantly different to the MIP(P<0.05). Conclusion For a single intrapulmonary lesion, the target volume was signifi cantly different in FCT and 4DCT which should be carefully taken into account during the design of radiation planning, especially in the stereotactic body radiotherapy.