Comparison of primary target volumes delineated on four-dimensional CT and 18?F-FDG PET/CT of non-small-cell lung cancer

摘要

Background To determine the optimal threshold of 18?F-fluorodexyglucose (18?F-FDG) positron emission tomography CT (PET/CT) images that generates the best volumetric match to internal gross target volume (IGTV) based on four-dimensional CT (4DCT) images. Methods Twenty patients with non-small cell lung cancer (NSCLC) underwent enhanced three-dimensional CT (3DCT) scan followed by enhanced 4DCT scan of the thorax under normal free breathing with the administration of intravenous contrast agents. A total of 100?ml of ioversol was injected intravenously, 2?ml/s for 3DCT and 1?ml/s for 4DCT. Then 18?F-FDG PET/CT scan was performed based on the same positioning parameters (the same immobilization devices and identical position verified by laser localizer as well as skin marks). Gross target volumes (GTVs) of the primary tumor were contoured on the ten phases images of 4DCT to generate IGTV₁₀. GTV_PET were determined with eight different threshold using an auto-contouring function. The differences in the position, volume, concordance index (CI) and degree of inclusion (DI) of the targets between GTV_PET and IGTV₁₀ were compared. Results The images from seventeen patients were suitable for further analysis. Significant differences between the centric coordinate positions of GTV_PET (excluding GTV_PET15%) and IGTV₁₀ were observed only in z axes (P?PET15%, GTV_PET25% and GTV_PET2.0 were not statistically different from IGTV₁₀ (P?PET15% approximated closely to IGTV₁₀ with median percentage volume changes of 4.86%. The best CI was between IGTV₁₀ and GTV_PET15% (0.57). The best DI of IGTV₁₀ in GTV_PET was IGTV₁₀ in GTV_PET15% (0.80). Conclusion None of the PET-based contours had both close spatial and volumetric approximation to the 4DCT IGTV₁₀. At present 3D-PET/CT should not be used for IGTV generation.