PET与四维CT图像结合构建胸段食管癌计划靶体积研究

Comparison of planning target volumes based on combination of ^(18)F-FDG PET-CT and 4DCT in thoracic esophageal cancer

目的比较基于三维CT(three-dimensional CT,3DCT)、四维CT(4DCT)与基于正电子发射计算机断层显像(positron emission tomograpay CT,PET-CT)结合4DCT所构建胸段食管癌原发肿瘤计划靶体积(planning target volume,PTV)位置及体积的差异性。方法选取2012-12-01-2014-02-28在山东省肿瘤医院放疗科序贯完成3DCT、4DCT和脱氧葡萄糖(fluorodeoxyglucose,FDG)PET-CT胸部定位扫描,且PET图像原发肿瘤最大标准化摄取值(maximum standardized uptake value,SUVmax)≥2.0的18例胸段食管癌患者。将3DCT图像所得大体肿瘤体积(gross tumor volume,GTV)上下方向外扩30mm,横向方向外扩5mm得到临床靶体积(clinical target volume,CTV3D);CTV3D各方向外扩10mm得到计划靶体积(planning target volume,PTV3D);内肿瘤靶体积(internal target volume,ITV4D)通过4DCT 10个时相CTV获得;将ITV4D各方向外扩5mm得到PTV4D;基于SUV≥20%SUVmax得到内生物靶体积(internal biological target volume,IBTVPET20%),将ITV4D与IBTVPET20%通过布尔逻辑运算得到ITVPET4DCT;将ITVPET4DCT各方向外扩5mm得到PTVPET4DCT。结果 PTV3D显著大于PTV4D和PTVPET4DCT,P值分别为<0.001和0.044;PTVPET4DCT显著大于PTV4D,P=0.048。PTV3D对PTVPET4DCT的包含度(degree of inclusion,DI;0.70±0.05)显著大于PTV3D对PTV4D的DI(0.69±0.06),P=0.042;PTV4D对PTV3D的DI(0.96±0.03)与PTVPET4DCT对PTV3D的DI(0.95±0.03)间差异无统计学意义,P=0.118。结论在构建胸段食管癌靶区时,利用PET与4DCT图像结合不仅改变了肿瘤PTV的大小,而且改变了空间位置及其形状。将二者结合,也许能够为食管癌放疗靶区构建提供借鉴。

[ABSTRACT~ OBJECTIVE This study aims to compare planning target volume （PTV） defined on PET combined with 4DCT to PTV based on 3DCT and 4DCT. METHODS 32 patients sequentially underwent 3DCT, 4DCT and FDG PET-CT thoracic simulation, and those （18/30） with SUVm,x^2.0 of the primary tumor volume were enrolled. CTVaD was formed on GTV3D contoured on 3DCT by adding a margin of 30ram in cranial-caudal direction and 5ram in transversal direction. PTV3D was defined using a 10 mm margin to CTV3D ; ITV4D was obtained by fusion of CTV from ten phases of 4DCT. A 5 mm margin for setup errors to CTV4D was to form PTV4D. IBTVPET was generated with the assumption that ITV4~zwas calculated by the union of motion was captured in PET images using a thresholding methods： 20 % SUV PET PTV4DcT. The geometrical differences of the tar- IBTVPET and ITV4D, and a 5 mm margin to ITV4DCT PETwas used to form PET PTV4DCT and was much gets were evaluated. RESULTS PTV3D was significantly larger than both PTV4D and PET DTVPET , X4DCT bigger than PTV4D （P〈0. 001, 0. 048）. The DI of PTV3D in PTV4DCT PET（0.70±0.05）was significantly larger than that of PTV3D in PTV40 （0. 69 ± 0.06, P = 0. 042）. There were no significant differences between the DI of PTV4D in PTV3D（0.96±0.03） andPTV4DCT PET in PTV3D（0.95±0.03,P=0. 118）. CONCLUSIONS As demonstrated by the assessment of the geometrical differences in PET/4DCT-based and 3DCT-based PTV, PET/4DCT could affect not only the volume of PTV but also its shape. PET/CT combined with 4DCT may be useful for defining target volumes.