Comparison of 4D-CT and PET-CT based internal gross tumor volumes delineation for non-small-cell lung cancer

Abstract

Objective To compare the positional and volumetric differences of internal gross target volumes (IGTVs) delineation based on four-dimensional CT (4D-CT) images and different standardized uptake values of 18F-fluorodeoxyglucose positron emission tomography CT (PET-CT) for the primary non-small cell lung cancer (NSCLC).Methods Ten NSCLC patients underwent enhanced three-dimensional CT scan followed by enhanced 4D-CT scan of the thorax under normal free breathing and then 18F-FDG PET-CT scan was performed based on the same position and positioning parameters.The gross target volumes (GTVs) of 10 phases of 4D-CT were contoured and IGTV10 was obtained by fusion of the 10 GTVs.IGTVPET were determined with nine different threshold methods using the auto-contouring function and manual contouring.The differences of position,volume,degree of inclusion (DI) and conformity index (CI) between IGTVPET and IGTV10 were compared.Results For superior-inferior (SI) directions,there were statistically significant differences between the centric coordinate parameters of IGTVPET(excluding IGTVPET1.5) and IGTV10 (Z =-2.703--2.293,P ＜ 0.05).In volume terms,IGTVPET2.0 was approximated close to IGTV10 with median volume ratios of 0.90,followed by IGTVPET20％ to IGTV10 with median volume ratios of 0.84,but there was no significant difference between them.The DI of IGTVPET1.5 in IGTV10 was higher than the DIs of other IGTVPET in IGTV10 (Z =-2.803--2.429,P ＜ 0.05).The CI of IGTVPE2.0 and IGTV10 was superior than the CIs of IGTVPET35％ and IGTV10,IGTVPET40％ and IGTV10,IGTVPET2.5 and IGTV10,IGTVPET3.0 and IGTV10 (Z =-2.803--2.191,P ＜ 0.05).Conclusions The IGTVPET contoured by SUV≥2.0 or 20％ of the maximal SUV are approximate close to IGTV10 in target size,but the extent of spatial mismatch is relatively obvious between them.So neither IGTVPET20％ nor IGTVPET2.0 could replace IGTV10. Key words: Non-small cell lung cancer; Fluorodeoxyglucose positron emission tomography computed tomography; Four-dimensional computed tomography; Internal gross target volume; Standardized uptake value