FIGURE 6. Application of software registration in radiotherapy. (A) Stand-alone whole-body ¹⁸F-FDG PET and thoracic CT images are registered using mutual information method. Both emission (top left) and transmission maps (bottom left) were used by computer algorithm. Note flat shape of bed used for simulation CT. Similar flat-bed configuration was simulated on PET scanner using styrofoam insert. Patient was positioned with arms up during both scans. Simulation CT scan was acquired during normal breathing. 3D orthogonal slices are shown (right) demonstrating volume of tumor in right lung as smaller on PET than on CT, probably because of necrosis. (B) Subsequently, radiotherapy planning was performed with coregistered PET and CT. Coregistered images were transferred via DICOM protocol to treatment planning workstation, and tumor volume was delineated using both scans. PET data allowed reduction of treatment volume. Patient data acquired at London Regional Cancer Center and Hamilton Health Sciences Center, Ontario, Canada.