Robot-guided sheaths consisting of pre-curved tubes and steerable needles are proposed to provide surgical access to locations deep within the body. In comparison to current minimally invasive surgical robotic instruments, these sheaths are thinner, can move along more highly curved paths, and are potentially less expensive. This paper presents the patient-specific design of the pre-curved tube portion of a robot-guided sheath for access to a kidney stone; such a device could be used for delivery of an endoscope to fragment and remove the stone in a pediatric patient. First, feasible two-dimensional paths were determined considering workspace limitations, including avoidance of the ribs and lung, and minimizing collateral damage to surrounding tissue by leveraging the curvatures of the sheaths. Second, building on prior work in concentric-tube robot mechanics, the mechanical interaction of a two-element sheath was modeled and the resulting kinematics was demonstrated to achieve a feasible path in simulation. In addition, as a first step toward three-dimensional planning, patient-specific CT data was used to reconstruct a three-dimensional model of the area of interest.
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