Detection of the correlations in target volumes for primary tumor of non­small cell lung cancer based on FDG PET/CT and the end­expiration phase of 4D­CT

Abstract

Objective To investigate the correlations in target volumes based on positron emission tomography CT (PET/CT) and the end-expiration phase of four-dimensional CT (4D-CT) images for non-small cell lung cancer (NSCLC). Methods Seventeen patients with NSCLC sequentially underwent three-dimensional CT (3DCT), 4D-CT and 18F-FDG PET/CT thoracic simulation scans. The gross target volume (GTV) was contoured on the end-expiration phase (50%) of 4D-CT and defined as GTV50%. The internal gross target volumes (IGTV) based on PET/CT images (IGTVPET) were determined by the standardized uptake value (SUV) 2.0 (IGTVPET2.0) and 20% percentage of the maximal standardized uptake value (SUVmax) (IGTVPET20%). The following parameters were calculated to analyze the correlation between IGTVPET and GTV50% in volume ratio (VR) and conformity index (CI): maximum transverse diameter of GTV50%, volume of GTV50%, the displacement of GTV in the cranial-caudal direction and 3D Vector calculated from 4D-CT dataset as well as the SUVmax. Results There was no significant correlation between the VR of IGTVPET2.0 to GTV50% and the maximum transverse diameter of GTV50%, volume of GTV50%, the displacement of GTV in the cranial-caudal direction, 3D Vector and the SUVmax (P>0.05). The VR between IGTVPET20% and GTV50% inversely related to maximum transverse diameter of GTV50%, volume of GTV50% and SUVmax (r=-0.663, -0.669, -0.752, P<0.05). The CI between IGTVPET2.0 and GTV50% positively related to volume of GTV50% and maximum transverse diameter of GTV50% (r=0.613, 0.483, P<0.05). Conclusions 3D PET images provide a time-averaged image of the tumor during the numerous breathing cycle. They fail to include the full information of moving tumor. The target volumes based on 3D PET might not reflect the real IGTV of NSCLC. Key words: Non-small cell lung cancer; Fluorodeoxyglucose positron emission tomography; Four-dimensional computed tomography; Standardized uptake value; Internal gross target volume