Fig. 3

Examples of both inaccurate and accurate structures matching. Left: pre-treatment CT. Right: post-treatment CT. a Inaccurate structures matching. Although the skull, the jaw, and the top of the spinal cord are aligned, the tongue of the patient appears in a different position between the two scans, leading to a misalignment of pertinent structures for tumor recurrence analysis. b Accurate structures matching. The skull, jaw and spinal cord are aligned and no anatomical differences between the soft tissues were found nearby the tumor. Blue: pre-treatment tumor. Red: post-treatment tumor