Automatic image registration of diagnostic and radiotherapy treatment planning CT head images

PURPOSE: Accurate image registration is an essential step to integrate information from diagnostic and radiotherapy treatment planning (RTP) CT images. In this paper a fully automatic algorithm is presented to quickly register such diagnostic and RTP CT head scans. METHODS AND MATERIALS: The registration algorithm, which regards one image as the moved version of the other, was applied to seven clinically obtained diagnostic and RTP CT data set pairs. During the RTP scan patients were in treatment position and wearing mold masks. Hence, patient position differed strongly in both image sets. Registrations were inspected visually and compared with results obtained minimizing the sum-of-square difference. RESULTS: Registrations were accurate upon visual inspection. Differences between the two algorithms were at subvoxel level. All cases were successfully registered, using several different starting points. Registration calculations took 1-2 minutes. Minimization of the sum-of-square difference took 1-1.5 hours. CONCLUSIONS: The results show that a fast and accurate image registration is achieved without prior segmentation or feature extraction and that the algorithm is robust, which makes it clinically applicable.