SU-F-T-639: Use of a 6D Couch for Real-Time Motion Correction During Frameless Stereotactic Radiosurgery.

PURPOSE: High precision patient positioning is critical in stereotactic radiosurgery (SRS). A 6 Degree-of-freedom (6D) robotic serial couch has the potential to correct both translational and rotational target motion deviations during image-guided radiosurgery procedures. An inverse kinematics algorithm based on the structure of the couch is presented, and a feedback control algorithm is discussed. The feasibility of motion compensation with a 6D couch is demonstrated by simulation with prerecorded volunteer head motion data.

METHODS: The proposed 6D couch motion compensation system included a robotic 6D couch, an image tracking system, and a control computer. For the control, the desired couch top plane was computed based on coordinate frames transformation, and the actuator outputs were calculated by 6D couch inverse kinematics algorithm. During the control, the rotation and translation were coupled, leading to undesired coupling motion of the lesion. Although such coupling was eventually cancelled out, it nonetheless represented unnecessary displacements of the target. An optimal decoupling control algorithm was designed to resolve this problem. The lever effect of the distance of between the target and the pivot of 6D couch roll/pitch were also discussed.

RESULTS: The pre-recorded volunteer head motion data was used in a computer-based motion compensation simulation, by 6D couch motion compensation, the corrected target was within a 0.3 mm of translational errors and 0.1 degree in the rotational errors about 99.5% of time.

CONCLUSION: We presented an optimal decoupling control algorithm for motion compensation by using a robotic 6D couch. The simulation also showed that reducing the distance between the target and the pivot of roll/pitch of the couch can also improve the accuracy of the compensation. The simulation showed that the 6D robotic system can achieve submillimeter/subdegree position accuracies.