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.
Keywords: 18F-FDG PET-CT; Esophageal cancer; four-dimensional computed tomography; planning target volume.