  Purpose: We report what is to our knowledge the initial experience with a new
3-dimensional ultrasound robotic system for prostate brachytherapy assistance,
focal therapy and prostate biopsies. Its ability to track prostate motion
intraoperatively allows it to manage motions and guide needles to predefined
targets. Materials and Methods: A robotic system was created for transrectal
ultrasound guided needle implantation combined with intraoperative prostate
tracking. Experiments were done on 90 targets embedded in a total of 9 mobile,
deformable, synthetic prostate phantoms. Experiments involved trying to insert
glass beads as close as possible to targets in multimodal anthropomorphic
imaging phantoms. Results were measured by segmenting the inserted beads in
computerized tomography volumes of the phantoms. Results: The robot reached the
chosen targets in phantoms with a median accuracy of 2.73 mm and a median
prostate motion of 5.46 mm. Accuracy was better at the apex than at the base
(2.28 vs 3.83 mm, p <0.001), and similar for horizontal and angled needle
inclinations (2.7 vs 2.82 mm, p = 0.18). Conclusions: To our knowledge this
robot for prostate focal therapy, brachytherapy and targeted prostate biopsies
is the first system to use intraoperative prostate motion tracking to guide
needles into the prostate. Preliminary experiments show its ability to reach
targets despite prostate motion.
