Investigation of Precise Needle Insertion for Prostate Brachytherapy.

Abstract

This research investigates needle insertion through soft tissue, enabling the development and validation of force models and insertion techniques for accurate needle tip placement. During needle insertion into the prostate, the needle deflects en route to the target which leads to seed misplacement and suboptimal dose to cancerous cells. Many researchers have studied slow needle insertion speed and axial - needle insertion direction - force distribution and components. However, little work has been performed on stiffer needle material properties, tissue deformation with needle deflection, and normal - perpendicular to needle insertion direction - force distribution. This lack of knowledge have led to tissue deformation, needle deflection, and misplaced target when performing needle insertion procedures. This research aims to quantify the impact of an optimized needle grid, insertion techniques, and needle-tissue force interaction leading to needle deflection and phantom deformation. First, an improved grid used to guide the needle was investigated and inserted via different hand insertion techniques to acquire needle deflection. To measure needle deflection, a measurement apparatus with acceptable gauge repeatability and reproducibility (GR&R) and documented accuracy was introduced. Next, stiffer needle properties were explored and inserted at much faster speed via a high-speed device, when compared to hand insertion or current robotic devices. Finally, finite element analysis (FEA) models were developed to predict relative needle-phantom motion using measured force data, while simultaneously obtaining experimental needle deflection and phantom deformation. The needle and phantom FEA models and the normal force distribution on the needle shaft were validated with separate experimental results. Findings from this dissertation include a 40% decrease in average needle deflection with the improved grid (and the same fast hand insertion technique), in addition to a 60% decrease in average needle deflection with the stiffer needle at the faster speed (compared to the less stiff needle and slow speed). Also, the needle and phantom FEA models are reasonably accurate to the experimental data, having a difference of 7% and 18%, respectively. These findings can be used to improve needle insertion techniques, while understanding force distribution effect on needle bending and compensate during the insertion path.