Optimizing Configurations for 7-DoF Robotic Ultrasound Guidance in Radiotherapy of the Prostate

Robotic ultrasound guidance is promising for tracking of organ motion during radiotherapy treatments, but the radio-opaque robot and probe interfere with beam delivery. The effect on treatment plan quality can be mitigated by the use of a robot arm with kinematic redundancy, such that the robot is able to elude delivered beams during treatment by changing its configuration. However, these changes require robot motion close to the patient, lead to an increased treatment time, and require coordination with the beam delivery. We propose an optimization workflow which integrates the problem of selecting suitable robot configurations into a linear-programming-based workflow for treatment plan optimization. Starting with a large set of candidate configurations, a minimal subset is determined which provides equivalent plan quality. Our results show that, typically, six configurations are sufficient for this purpose. Furthermore, we show that optimal configurations can be reused for dose planning of subsequent patients.