Estimation of error sources for optical head tracking in cranial radiation therapy

There is a growing demand for high-accuracy and frameless solutions for cranial radiation therapy. Among different approaches for intra-fractional head tracking using X-Ray or MV imaging or Cone Beam CT, optical head tracking in particular promises high spatial and temporal resolution with a minimum of system latency and no additional dose exposition. It may therefore be ideal for motion-compensated or high-accuracy cranial radiation therapy. Nevertheless, up to now optical systems lack accuracy and are therefore only found in prototypes or test setups. Using a consumer-grade optical rangefinder, we have built a test setup to systematically quantify critical error sources for tracking systems based on triangulation. Subsequently, we present and discuss potential solutions to minimize the error.