Comparative evaluation of CT-based and PET/4DCT-based planning target volumes in the radiation of primary esophageal cancer.

PURPOSE To compare planning target volume (PTV) defined by PET combined with 4DCT to 3DCT and 4DCT. METHODS Eighteen (18/30) esophageal cancer patients who underwent 3DCT, 4DCT and (18)F-FDG PET-CT thoracic simulation with SUVmax≥2.0 of the primary volume were enrolled. CTV3D was formed on 3DCT by adding a margin of 30 mm in cranial-caudal direction and 5 mm in transversal direction. PTV3D was defined using a 10 mm margin to CTV3D and CTV4D was obtained by fusion of CTV from ten phases of 4DCT. A 5 mm margin for setup errors to CTV4D was to form PTV4D. BTVPET was generated with the assumption that motion was captured in PET images using a thresholding methods: 20% SUVmax. CTV(PET) 4DCT was calculated by the union of BTVPET and CTV4D, and a 5 mm margin to CTV(PET) 4DCT was used to form PTV(PET) 4DCT. The geometrical differences of the targets were evaluated. RESULTS Statistically significant differences were observed among CTV3D, CTV4D and CTV(PET) 4DCT (CTV(PET) 4DCT>CTV4D>CTV3D, P=0.000-0.038). PTV3D, PTV4D, and PTV(PET) 4DCT also differed significantly from each other (PTV(PET) 4DCT>PTV4D>PTV3D, P=0.000-0.048). The DI of PTV3D in PTV(PET) 4DCT was significantly larger than that of PTV3D in PTV 4D (P=0.042). There were no significant differences between the DI of PTV4D in PTV3D and PTV(PET) 4DCT in PTV3D (P=0.118). CONCLUSIONS As demonstrated by the assessment of the geometrical differences in PET/4DCT-based and 3DCT-based PTV, PET/4DCT could affect not only the volume of PTV but also its shape.