An improvement for the scanning process in high accuracy head tracking

Optical tracking systems have become state-of-the-art in radiation therapy. Nevertheless, they still cannot cope with the properties of soft tissue. We are developing a non-invasive method to automatically detect the cranial bone’s sur-face using only infrared laser light. Here, we present simulations to describe the influence of increased incident an-gles of the laser ray on the forehead’s surface caused by replacing the original robotic setup by galvanometric scan-ning mirrors. We show that the usable area on the forehead (angles below 45°) will decrease, but that successful scanning is still possible when the scanning distance is increased from 300 to 500 mm. These results are confirmed when comparing optical scans acquired with the robotic setup and the scanning mirror assembly. Additionally, we could determine the needed depth of field for three subjects (based on high-resolution MRI scans). At a distance of 500 mm, it ranges from 37 to 86 mm.