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Effect of Robot Pose On Beam Blocking for Ultrasound Guided SBRT of the Prostate

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I Kuhlemann

S Gerlach1 , I Kuhlemann2*, F Ernst2 , C Fuerweger3 , A Schlaefer1 , (1) Hamburg University of Technology, Hamburg, GERMANY, (2) Universitaet zu Luebeck, Luebeck, GERMANY, (3) European Cyberknife Center Munich, Munich, GERMANY


SU-G-JeP3-3 (Sunday, July 31, 2016) 5:00 PM - 5:30 PM Room: ePoster Theater

Purpose: Ultrasound presents a fast, volumetric image modality for realtime tracking of abdominal organ motion. How-ever, ultrasound transducer placement during radiation therapy is challenging. Recently, approaches using robotic arms for intra-treatment ultrasound imaging have been proposed. Good and reliable imaging requires placing the transducer close to the PTV. We studied the effect of a seven degrees of freedom robot on the fea-sible beam directions.

Methods: For five CyberKnife prostate treatment plans we established viewports for the transducer, i.e., points on the patient surface with a soft tissue view towards the PTV. Choosing a feasible transducer pose and using the kinematic redundancy of the KUKA LBR iiwa robot, we considered three robot poses. Poses 1 to 3 had the elbow point anterior, superior, and inferior, respectively. For each pose and each beam starting point, the pro-jections of robot and PTV were computed. We added a 20 mm margin accounting for organ / beam motion. The number of nodes for which the PTV was partially of fully blocked were established. Moreover, the cumula-tive overlap for each of the poses and the minimum overlap over all poses were computed.

Results: The fully and partially blocked nodes ranged from 12% to 20% and 13% to 27%, respectively. Typically, pose 3 caused the fewest blocked nodes. The cumulative overlap ranged from 19% to 29%. Taking the minimum overlap, i.e., considering moving the robot’s elbow while maintaining the transducer pose, the cumulative over-lap was reduced to 16% to 18% and was 3% to 6% lower than for the best individual pose.

Conclusion: Our results indicate that it is possible to identify feasible ultrasound transducer poses and to use the kinematic redundancy of a 7 DOF robot to minimize the impact of the imaging subsystem on the feasible beam directions for ultrasound guided and motion compensated SBRT.

Funding Support, Disclosures, and Conflict of Interest: Research partially funded by DFG grants ER 817/1-1 and SCHL 1844/3-1.

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