RESUMEN
Objective:To investigate the application value of 18F-FDG PET-CT combined with MRI in the radiotherapy for esophageal carcinoma by comparing the differences in the gross target volume (GTV), position length delineated on the end expiratory (EE) phase of 4DCT, PET-CT and T 2-weighted MRI (T 2W-MRI). Methods:Twenty-six patients with thoracic esophageal cancer scheduled to receive concurrent chemoradiotherapy sequentially underwent 3DCT, 4DCT, PET-CT and enhanced MRI for thoracic localization. All images were fused with the 3DCT images by deformable registration. GTV CT, GTV 50% GTV PET2.5, GTV MRI and GTV DWI were delineated on 3DCT, the EE phase of 4DCT images, PET-CT with the thresholds of SUV≥2.5, T 2W-MRI and diffusion-weighted images, respectively. Results:GTV PET2.5 was significantly larger than GTV 50% and GTV MRI ( P<0.001 and P=0.008), whereas the volume of GTV MRI was similar to that of GTV 50%( P=0.439). Significant differences were observed between the CI of GTV MRI to GTV 50% and GTV PET2.5 to GTV 50%( P=0.004). The conformity indexes (CIs) of GTV MRI to GTV CT and GTV PET2.5 to GTV CT were statistically significant ( P=0.004 and P=0.039). The CI of GTV MRI to GTV PET2.5 was significantly smaller than that of GTV MRI to GTV 50%, GTV MRI to GTV CT, GTV PET2.5 to GTV 50% and GTV PET2.5 to GTV CT ( P=0.000-0.021). The length of gastroscopy was similar to those of GTV PET2.5 and GTV DWI (both P>0.05), and there was no significant difference in the length between GTV PET2.5 and GTV DWI ( P=0.072). Conclusion:GTV MRI yields significantly different volume and poor spatial matching compared with GTV PET2.5. The application of PET-CT combined with MRI under respiratory gating system in the delineation of GTV should be used with caution in thoracic squamous esophageal cancer. MRI-DWI can replace PET-CT to help determine the upper and lower boundaries of GTV based on CT images.