| Objective To compare volume, conformity index (CI), degree of inclusion (DI) of internal gross target volumes (IGTV) delineated on 4DCT and PET-CT images for primary esophageal cancer. Meanwhile, to investigate the correlations in target volumes based on 18F-FDG PET/CT and the end-expiration phase (T50) of 4DCT to explore the characteristics of internal gross target volume (IGTV) deriving from 18F-FDG PET/CT for primary esophageal cancer.Methods The patients enrolled in this study with thoracic esophageal cancer sequentially performed 3DCT,4DCT and PET-CT simulation. The 3DCT,4DCT and PET, CT images were imported into MEVI software (MTM,6.1.0). The CT images of PET-CT sets were firstly registered and fused with the 3DCT images using Maximum Mutual Information (MMI) method. The MIP images of 4DCT and the PET images of PET-CT were automatically registered to the same coordinate system. And then further adjusted manually referring to the bony anatomic landmarks such as the sternum or the front edge of vertebral bony. The target volume size, the coordinates in LR, AP, and CC directions of the COM from 3DCT,4DCT, PET, CT dataset could be generated by using the Statistics Viewer in MEVI software. The maximum transversal diameter was measured and estimated by the gross target volume contoured on the end expiration phase of 4DCT dataset.The gross target volumes (GTVs) of ten phases of 4DCT were contoured, and IGTV10 was obtained by combining the ten GTVs. IGTVMIP was obtained by contouring on 4DCT maximum intensity projection (MIP). The PET contours were determined with different standardized uptake value (SUV) threshold methods and manual contouring:SUV>2.0,2.5, 3.0,3.5; or≥20%,25%,30%,35%,40% of the maximal tumor SUVmax, and were defined as IGTVPET2.0, IGTVPET2.5, IGTVPET3.0, IGTVPET3.5, IGTVPET20%, IGTVPET25%, IGTVPET30%, IGTVPET35%, IGTVPET40%, IGTVPETMAN, respectively. The differences in volume, CI, DI of target volumes were compared, and the correlations in target volumes based on FDG PET/CT and the end-expiration phase (T50) of 4DCT were investigated.Results The volume ratios of IGTVPET2.5 to IGTV10, IGTVPET20% to IGTV10 were 0.92(P=0.985),1.08(P=0.886), respectively. The CIs of IGTVPET2.0 vs IGTV10, IGTVPET2.5 vs IGTV10, IGTVPET20% vs IGTV10 were 0.53(P=0.432),0.52(P=1.000),0.53(P=0.414), respectively. The CIs of IGTVPET2.0 vs IGTV10, IGTVPET2.5 vs IGTV10, IGTVPET20% vs IGTV10 were bigger than other IGTVPET vs IGTV10 (0.33-0.50,P=0.000-0.047)The volume ratios (VR) of IGTVPET2.5 to IGTVMIp, IGTVPET20% to IGTVMIP, IGTVPETMAN to IGTVMIP were 0.86,0.88,1.06, respectively, which approached closest to 1. The CIs of IGTVPET2.0、IGTVPET2.5、IGTVPET20%、IGTVPETMAN and IGTVMIP were 0.55, 0.56,0.56,0.54,0.55, respectively (P>0.05).There was no significant correlation between the VR of IGTVPET (IGTVPET2.0, IGTVPET20%) to GTV50% and maximum transverse diameter of GTV50%, volume of GTV50%, the displacement of COM in CC direction and 3D Vector (P=0.055-0.932). The CIs between IGTVPET (IGTVPET2.0, IGTVPET20%) and GTV50% statistically correlated to maximum transverse diameter of GTV50%, volume of GTV50%,the displacement of COM in CC direction and 3D Vector(P=0.005-0.033). The VR and CI of IGTVPET20%to GTV50% correlated well with SUVmax (P=0.001,0.016).Conclusions The IGTV contoured by SUV threshold settings of≥2.5 or≥20% of SUVmax corresponded better with the IGTV which was combined by GTVs contoured on ten phases of 4DCT, and achieved relatively better spatial matching degree.The targets delineated based on SUV threshold setting of≥2.5,20% of the SUVmax and manual contours on PET images correspond better with the target delineated on maximum intensity projection of 4DCT images than other SUV thresholding methods.IGTVPET could not reflect up real tumor motion. The extent of tumor motion may be better quantified by using 4DCT as a guide for PET. |
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