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Ultrasound image and 3D finite element based tissue deformation simulator for prostate brachytherapy Goksel, Orcun

Abstract

Brachytherapy is a prostate cancer treatment where radioactive pellets (seeds) are implanted into prostate region through long flexible needles. Steering them to preplanned locations require the use of tip bevel deflection effect and a thorough comprehension of tissue deformation and needle flexibility. A simulator is proposed to help medical residents in acquiring these procedural skills. In prostate brachytherapy, two important feedback modalities during needle insertions are the transrectal ultrasound (TRUS) imaging and the kinesthetic feedback received through the needle base. Thus, these have been incorporated in the simulator, the subsystems of which are presented here. In this thesis, a needle-tissue interaction model from prior work which was based on finite element method is extended into 3D and adapted for custom meshes. The issues related to needle-tissue coupling are addressed. A meshing scheme which generates soft tissue models with small number of nodes for haptic implementation from contours on parallel slices is proposed. It is utilized to generate a prostate volume mesh which consists of well-conditioned elements for finite element analysis. A simulation interface is developed where a 3D rendering of the model deformation is displayed while the needle can be manipulated by entering target positions for its base. A method for B-mode TRUS image synthesis out of a deformed tissue volume for which the patient data was collected at the BC Cancer Agency is also presented. Some interpolation schemes for remotely spaced ultrasound data are compared on a sample case and a method for overlaying needle shaft reflection onto TRUS images is described.

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