宫颈癌PET-CT图像放疗靶区四种勾画方法的初步研究

目的 通过比较4种勾画方法在宫颈癌FDG PET-CT图像上大体肿瘤体积(GTV)差异,寻找适合临床应用的方法。方法 16例行FDG PET-CT放疗前定位的28个宫颈癌病灶的PET图像,分别用视觉勾画法(GTV_vis)、SUV=2.5为边界勾画法(GTV_2.5)、40%阈值边界勾画法(GTV₄₀)、拟合公式勾画法(GTV_公式)对GTV勾画,其差异比较采用成组t检验。结果 GTV_vis、GTV_2.5 、GTV₄₀、GTV_公式勾画的平均体积分别为63.41、53.20、41.33、61.84 cm³,除GTV₄₀vis外(t=2.32,P=0.029),GTV_2.5、GTV_公式与GTV_vis均相似(t=1.05、0.91,P=0.305、0.370)。最大SUV值>6或<6、靶本底比值>3∶1或<3∶1对GTV₄₀和GTV_公式与GTV_vis差值均无影响(t=0.00、－0.34、0.92、0.35,P=1.000、0.746、0.374、0.737),但对GTV_2.5与GTV_vis差值有影响(t=－3.87、3.16,P=0.002、0.016)。结论 在GTV_2.5、GTV_公式能勾画出靶区情况下,GTV_公式、GTV_2.5和GTV_vis均相似且可用于临床,GTV_公式与GTV_vis最为接近;但GTV₄₀vis,应用时应谨慎;GTV_2.5明显受病灶SUV_max值及靶本底比值影响。

Comparison of four methods for delineation of gross tumor volume on FDG PET/CT for patients with cervical cancer

Objective To compare the differences in 4 sets of gross tumor volumes (GTVs) generated from FDG PET/CT in cervical cancer,and determine the optimal method for target volume delineation of cervical cancer.Methods Sixteen cervical cancer patients with 28 primary or metastatic lesions underwent FDG PET/CT.CT and PET images were coregistered,and transferred to Pinnacle therapy planning workstation.Four sets of GTVs were defined.The first set ( GTVvis ) was manually contoured using a visual method on PET images.The second set ( GTV40 ) was autocontoured using a threshold of 40％ of the maximum intensity level for PET images.The third set ( GTV2.5 ) used an autocontour of standardized uptake value (SUV) of 2.5 around the tumor.By phantom measurements we determined an algorithm ( threshold =(mean target concentration + 2.623)/1.975),GTVfunction was defined using this method as the fourth approach.The volumes of 4 sets of GTVs were compared with group t-test.Results The average volumes of GTVvis,GTV2.5,GTV40,and GTVfunction were 63.41,53.20,41.33,and 61.84 cm3. There was no significant difference between GTVfunctoon,GTV2.5 and GTVvis ( t =1.05,0.91,P =0.305,0.37 ),but GTV40were smaller than GTVvis.The SUVmax and target to background value had no significant influence on the differences between GTV40 and GTVfunction or GTVvis ( t =0.00,- 0.34,0.92,0.35,P =1.000,0.746,0.374,0.737),but they had significant influence on the difference between GTV2.5 and GTVvis (t =- 3.87,3.16,P =0.002,0.016).Conclusions GTVvis,GTV2.5 and GTVfunction all could be used for target delineation if the method can define the GTV.The difference between the GTVfunction and GTVvis was the smallest;GTV40 was smaller than GTVvis. GTV2.5 was significantly influenced by SUVmax and target to background value of the legions.