Multimodality images of many radiation therapy patients could be correlated/fused using software tools provided in treatment planning software. We have developed a phantom and a registration method for evaluation and verification of the fusion process and fusion software. Image registration was verified by contouring spheres and rods on the primary CT scan and observing contour locations on the second CT scan, MRI, or PET images which have been resampled in the plan of the primary CT scan . When properly registered, the contours of spheres and rods from the primary CT scan are expected to match images of these features in the other modalities. All contours were within 2 mm from their expected locations on the second CT scan, MRI, and PET scans. Proper registration was also verified by observing locations of fiducial markers, which were also within 2 mm from their expected locations. Again, the fiducial markers were outlined on the primary CT scan and their location observed on other scans.