Trajectory planning and control of needle insertion in robotics-assisted prostate brachytherapy

Robot-assisted needle insertion has attracted considerable attention in recent years because of its promising applications in minimally invasive percutaneous procedures such as biopsies and brachytherapies. These procedures require accurate needle insertion into soft, inhomogeneous tissue. Two major problems during needle insertion are needle deflection and tissue deformation. This study is initiated to address these problems with particular reference to the prostate brachytherapy procedure. Prostate brachytherapy is a method of treatment for prostate cancer. The latter is the second leading cause of death from cancer in men in North America. This study presents a novel model for needle deflection in soft tissue. The model is based on flexible beam theory. The model is integrated into an online trajectory generation algorithm for robot-assisted needle insertion. The algorithm uses needle rotation to compensate for needle deflection during insertion. The effect of other insertion techniques such as needle spinning and transversal needle base motion on needle deflection and target displacement are also studied in this thesis. According to the experimental results, the proposed model-based trajectory that includes needle rotation through 180° at particular points, i.e., at specific depths inside the tissue, provides considerable improvement in performance with regard to needle deflection and tissue deformation. It is also found that compensating needle deflection by needle rotation is more effective than steering the needle by moving its base outside the tissue. In addition, a study is conducted to compare the performance of master-slave needle insertion with autonomous and semi-autonomous needle insertion. The results of this study show that incorporation of force feedback can improve teleoperated needle insertion. However, autonomous and semi-autonomous needle insertions, which use our proposed needle deflection model, provide significantly better performance.Keywords. Robot-assisted needle guidance, needle deflection, prostate brachytherapy, master-slave needle insertion.