A Hybrid Concentric Tube Robot for Cholesteatoma Laser Surgery

This letter presents a hybrid concentric tube robot which covers the middle ear volume for exhaustive ablation of residual cholesteatoma. The proposed robotic system combines a concentric tube robot and a wrist at the distal end, actuated by a tendon. We first introduce the surgical protocol through two access points (ear canal and few millimeters size hole through the mastoid), then derive the anatomical constraints and specify the robot tasks. Based on the robot model enriched with the optical fiber stiffness and on anatomical constraints, the robot parameters are determined as the ones among discretized sets that provide the maximal volume coverage. Experiments are conducted with a benchtop prototype on a 3D printed middle ear phantom to validate the wrist model with the optical fiber and the robot repeatability assessment. The wrist model achieved an root mean square error (RMSE) of $1.33^{\circ }$ and $R^2 = 96.8\%$ . The robot repeatability has an RMSE of 0.7 mm for distance errors and $1.34^{\circ }$ - $2.42^{\circ }$ - $3.11^{\circ }$ for the angular ones. We finally demonstrated the ablation of cholesteatoma by the embedded optical fiber on the hybrid concentric tube robot prototype.