Comparison of gross target volumes based on four‐dimensional CT, positron emission tomography‐computed tomography, and magnetic resonance imaging in thoracic esophageal cancer

PURPOSE: The application value of (18)F‐FDG PET‐CT combined with MRI in the radiotherapy of esophageal carcinoma was discussed by comparing the differences in position, volume, and the length of GTVs delineated on the end‐expiration (EE) phase of 4DCT, (18)F‐FDG PET‐CT, and T(2)W‐MRI. METHODS: A total of 26 patients with thoracic esophageal cancer sequentially performed 3DCT, 4DCT, (18)F‐FDG PET‐CT, and MRI simulation for thoracic localization. All images were fused with the 3DCT images by deformable registration. GTV(CT) and GTV(50%) were delineated on 3DCT and the EE phase of 4DCT images, respectively. The GTV based on PET‐CT images was determined by thresholds of SUV ≥ 2.5 and designated as GTV(PET2.5). The images of T(2)‐weighted sequence and diffusion‐weighted sequence were referred as GTV(MRI) and GTV(DWI), respectively. The length of the abnormality seen on the 4DCT, PET‐CT, and DWI was compared. RESULTS: GTV(PET2.5) was significantly larger than GTV(50%) and GTV(MRI) (P = .000 and 0.008, respectively), and the volume of GTV(MRI) was similar to that of GTV(50%) (P = .439). Significant differences were observed between the CI of GTV(MRI) to GTV(50%) and GTV(PET2.5) to GTV(50%) (P = .004). The CI of GTV(MRI) to GTV(CT) and GTV(PET2.5) to GTV(CT) were statistically significant (P = .039). The CI of GTV(MRI) to GTV(PET2.5) was significantly lower 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 = .000‐0.021). Tumor length measurements by endoscopy were similar to the tumor length as measured by PET and DWI scan (P > .05), and there was no significant difference between the longitudinal length of GTV(PET2.5) and GTV(DWI) (P = .072). CONCLUSION: The volumes of GTV(MRI) and GTV(50%) were similar. However, GTV(MRI) has different volumes and poor spatial matching compared with GTV(PET2.5).The MRI imaging could not include entire respiration. It may be a good choice to guide target delineation and construction of esophageal carcinoma by combining 4DCT with MRI imaging. Utilization of DWI in treatment planning for esophageal cancer may provide further information to assist with target delineation. Further studies are needed to determine if this technology will translate into meaningful differences in clinical outcome.