Spatial and temporal performance of 3D optical surface imaging for real-time head position tracking

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Image-Guided Therapy

Background:

• Frameless stereotactic radiosurgery (SRS) requires precise patient head positioning.
• Accurate real-time head motion tracking is essential for effective SRS delivery.
• 3D optical surface imaging offers a potential non-invasive solution for head tracking.

Purpose of the Study:

• To evaluate the spatial and temporal tracking performance of a commercial 3D optical surface imaging system.
• To assess its suitability for frameless stereotactic radiosurgery head tracking.
• To compare 3D surface tracking with infrared (IR) marker tracking.

Main Methods:

• Simultaneous 3D surface and IR marker tracking were performed on a head phantom and human subjects.
• Phantom studies utilized an XYZ motion stage for controlled movements.
• Human subjects had tracking on the facial region (3D surface) and dental plate/forehead (IR markers).

Main Results:

• 3D surface tracking achieved a root mean squared error (RMSE) of ~0.30 mm on phantoms with >1000 vertices.
• Tracking accuracy was independent of region-of-interest (ROI) size if features were sufficient.
• On human subjects, RMSE between 3D surface and IR tracking was sub-millimeter across all axes (e.g., 0.22 mm L-R, 0.44 mm S-I, 0.27 mm A-P) and sub-degree for rotations.

Conclusions:

• 3D optical surface imaging demonstrates potential for submillimeter head motion tracking in SRS.
• High accuracy is achievable with precise camera-to-LINAC calibration.
• Sufficient ROI size and distinct surface features are critical for reliable registration and tracking.