基于3D-CT和4D-CT的肺癌放射治疗靶区勾画方法的研究

Study of Internal Tumor Volume for Radiation Treatment of Non-small Cell Lung Cancer on 3D-CT and 4D-CT

[目的]以3D-CT和4D-CT模拟定位,比较非小细胞肺癌放疗靶区的不同勾画方法。[方法]患者处于平静呼吸状态,依次做3D-CT扫描、4D-CT扫描,然后根据采集到的图像,按下列不同方式勾画出内靶区(ITV):(1)将4D-CT构建的10个呼吸相中的肿瘤靶区(GTV)全部勾画,然后融合至全10相形成ITV10相;(2)以4D-CT的0%和50%相作为2个极限呼吸相,分别勾画GTV再融合至0~50相,形成ITV2相;(3)构建4D-CT的最高密度投影(MIP)图像,直接在MIP图像勾画ITVMIP;(4)在4D-CT图像上,测量头-脚、腹-背和左-右方向GTV的位移,计算95%位移值,用于3D-CT的GTV的外放依据,形成ITV3DCT。上述4种ITV,再在三维方向扩大5mm的处理,得到与之相对应的计划靶区(PTV)。从几何容积和形状匹配度两方面对上述4种ITV和PTV进行对比。[结果]在头-脚、腹-背、左-右方向上,GTV的位移值分别为(3.2±4.1)mm、(2.1±3.0)mm、(0.7±0.7)mm。两两比对提示,肿瘤的位移更多体现在头-脚和腹-背方向(P值均<0.0001)。基于此数据,以GTV3DCT的头-脚、腹-背、左-右三个方向进行外放5mm、3mm、1mm生成ITV3DCT。ITV10相、ITV2相、ITVMIP、ITV3DCT中位容积分别为12.98cm^3、11.55cm^3、12.95cm^3、16.54cm^3,PTV10相、PTV2相、PTVMIP、PTV3DCT中位容积分别为31.22cm^3、28.64cm^3、31.18cm^3、37.51cm^3。与ITV10相和PTV10相比较,ITV2相、ITVMIP、ITV3DCT和PTV2相、PTVMIP和PTV3DCT的MI均值分别为0.83、0.95、0.7和0.88、0.94和0.74。[结论]ITVMIP和PTVMIP与ITV10相和PTV10相的差距最小,合适病例可用MIP勾画靶区以保证精准、提高效率。由于容积差异较大、匹配度较低,不建议用ITV2相或ITV3DCT直接替代ITV10相设计计划。

[Objective]To analyze the difference between internal tumor volumes(ITVs)based on three-dimensional computed tomography(3D-CT)and four-dimensional(4 D-CT)images in radiotherapy for non-small cell lung cancer(NSCLC).[Methods]Eligible patients diagnosed as NSCLC received both 3D-CT and 4D-CT scans before radiotherapy.There were four different ITV delineation methods as:(1)Fusing all of 10 tumor target volumes(GTVs)form 10 respiratory phases created by 4D-CT and forming ITV10 phases;(2)Defining 0% and 50% phases from 4D-CT image as two extreme phases,and combining GTVs from these two phases as ITV2 phases;(3)Contouring GTV on maximum intensity projection(MIP)created after 4D-CT directly and forming ITVMIP;(4)Calculating 95%of GTV centroid displacement values in each direction measured by 4D-CT and then enlarging GTV from 3D-CT to form ITV3DCT.An isotropic margin of 5 mm from each ITVs were generated to from plan target volumes(PTVs),respectively.The volume and matching index(MI)was analyzed to study the difference between ITVs and PTVs,and MI was defined as the ratio of ITV10 phasesand PTV10 phases.[Results]In the superior-inferior(S-I),anterior-posterior(A-P)and left-right(L-R)directions,the motion of GTV centroid was(3.2±4.1)mm,(2.1±3.0)mm and(0.7±0.7)mm,respectively.A-P and S-I directions showed greater displacement of GTV centroid compared with L-R direction(P<0.01).According to the displacement values on each direction,ITV3DCTwere created by adding certain margins 1,3 and 5 mm in L-R,A-P and S-I directions to GTV based on 3D-CT,respectively.The median volumes of ITV10 Phasesand PTV10 Phaseswere 12.98 cm^3 and31.22 cm^3;the median volumes of ITV32 Phasesand PTV2 Phaseswere 11.55 cm^3 and 28.64 cm;the median volumes of ITVMIPand PTVMIPwere 12.95 cm^3 and 31.18 cm^3;the median volumes of ITV3DCTand PTV3 DCTwere 16.54 cm^3 and 37.51 cm^3.In comparisons with ITV10 Phasesand PTV10 Phases,the MI values of ITV2 Phases,ITVMIP,ITV3DCT,PTV2 Phases,PTVMIPand PTV3 DCTwere 0.83,0.95,0.78,0.88,0.94 and 0.74,respectively.[Conclusion]A method of contouring ITV on MIP image based on 4D-CT might have a potential to be optimal ITV10 Phasesfor NSCLC.However,neither ITV2 phasesnor ITV3DCTshowed appropriateness in replacing ITV10 phasesdirectly,according to greater difference between volume and form in comparison with ITV10 phases.