Needle control along desired tracks in robotic prostate brachytherapy

In prostate brachytherapy, multiple seeds are implanted during each needle insertion, and the locations of these seeds are dependent on the track of the needle shaft inside the tissue. Therefore, the track of needle shaft is as important as the placement of the needle tip on the outcome of this procedure and the effectiveness of therapy. In this study, the needle is rotated at particular locations during insertion in order to maintain the needle on a desired track. To define locations of rotation, a needle deflection model based on Euler-Bernoulli beam bending equations is proposed. This model estimates the reciprocal of the needle curvature and predicts the needle tip position based on real-time force/moment feedback prior to the first rotation. The needle tip position is then predicted based on needle motion on a circular segment. Tissue deformation resulting from needle deflection is also measured during insertions. In order to validate the performance of the proposed method, experimental results are presented for robot-assisted needle insertion in animal phantoms.