Purpose: To investigate the correlations in target volumes based on ¹⁸F-FDG PET/CT and four-dimensional CT (4DCT) to detect the feasibility of implementing PET in determining gross target volumes (GTV) for tumor motion for primary thoracic esophageal cancer (EC).
Methods: Thirty-three patients with EC sequentially underwent contrast-enhanced 3DCT, 4DCT, and ¹⁸F-FDG PET-CT thoracic simulation. The internal gross target volume (IGTV)₁₀ was obtained by combining the GTV from ten phases of 4DCT. The GTVs based on PET/CT images were defined by setting of different standardized uptake value thresholds and visual contouring. The difference in volume ratio, conformity index (CI), and degree of inclusion (DI) between IGTV₁₀ and GTV_PET was compared.
Results: The images from 20 patients were suitable for further analysis. The optimal volume ratio of 0.95±0.32, 1.06±0.50, 1.07±0.49 was at standardized uptake value (SUV)_2.5, SUV_20%, or manual contouring. The mean CIs were from 0.33 to 0.54. The best CI was at SUV_2.0 (0.51±0.11), SUV_2.5 (0.53±0.13), SUV_20% (0.53±0.12), and manual contouring (0.54±0.14). The mean DIs of GTV_PET in IGTV₁₀ were from 0.60 to 0.90, and the mean DI of IGTV₁₀ in GTV_PET ranged from 0.35 to 0.78. A negative correlation was found between the mean CI and different SUV (P =0.000).
Conclusion: None of the PET-based contours had both close spatial and volumetric approximation to the 4DCT IGTV₁₀. Further evaluation and optimization of PET as a tool for target identification are required.
Keywords: esophageal cancer, ¹⁸F-FDG PET/CT, four-dimensional computed tomography, contour, tumor motion