Phantom Study on Radiotherapy Planning Using PET/CT - Delineation of GTV by Evaluating SUV -

PET/CT/ 18 F-FDG/Radiotherapy planning/Target delineation/Standardized uptake value. We assessed the usefulness of PET/CT images to determine the target volume in radiotherapy planning by evaluating the standardized uptake value (SUV ). We evaluated the imaging conditions and imagereconstruction conditions of PET/CT useful for treatment planning by collecting 18 F-FDG images of acrylic spheres (10–48 mm in diameter) in a phantom. The 18 F-FDG concentration in the spheres was 10fold higher than that of the phantom. The contours were delineated according to the SUV by the threshold and regions of interest (ROI) methods. Comparisons of two- and three-dimensional (2D and 3D) acquisition images indicated that the sharpness and quantitative qualities of the sphere boundaries were better in the f ormer than in the latter. In the extraction of outlines using the SUV, outlines obtained at an SUV of 40–50% of the maximum agreed well with the actual acrylic sphere size. 2D acquisition images are more suitable for delineating target volume contours, although 3D acquisition images are more popular in diagnostic imaging. An SUV of 40–50% of the maximum is suggested to be appropriate for GTV contouring of sphere tumors with homogenously distributed 18 F-FDG.