Closed-Loop Control of a Tendon-Driven Active Needle for Tip Tracking at Desired Bending Angle inside a Water Medium using Ultrasound or EM Tracker Feedback for High-Dose-Rate Prostate Brachytherapy

Abstract

Prostate cancer is the second most common malignancy in American men. High-dose-rate brachytherapy is a popular treatment technique in which a large, localized radiation dose is used to kill cancer. Utilization of curvilinear catheter implantation inside the prostate gland to provide access channels to host the radiation source is under investigation by our group. To this aim, we have introduced an active needle to curve inside the prostate conformal to the patient’s specific anatomical relationship for improved dose distribution to the prostate and reduced toxicity to the organs at risk (OARs). This work presents closed-loop control of our tendon-driven active needle in water medium and air using the position feedback of the tip obtained in real time from an ultrasound (US) or an electromagnetic (EM) tracking sensor, respectively. The active needle consists of a flexure compliant section to realize bending in two directions via actuation of two internal tendons. The actuation system is developed using two Maxon motors programmed to pull the two tendons at certain displacements. An US or EM tracker sensor is used to track the tip of the robotic tool in real time and provide position feedback to the controller. Tracking errors using US and EM tracker are estimated and compared. Results show that the bending angle of the active needle could be controlled using position feedback of the US or the EM tracking system with a bending angle error of less than 1.00 degree. It is concluded that the actuation system and controller, presented in this work, are able to realize a desired bending angle at the active needle tip with reasonable accuracy.