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Guidage robotisé d'une aiguille flexible sous échographie 3D pour la curiethérapie de prostate. (Guidance and control of a flexible needle for robotized prostate brachytherapy)

In France in 2012, 25% to 30% of the 40,000 prostate cancer cases were treated with brachytherapy. During this procedure, the clinician inserts manually about thirty needles into the prostate through the perineum using ultrasound images to locate the prostate and the needles. Radioactive seeds are released into the prostate at specific pre-planned locations using needle’s cannula. The success of this operation is closely related to the distribution and homogeneity of the radioactive dose distribution in the prostate, therefore the precision with which the seeds are positioned. This accuracy is affected by prostate motions and deformations due to the insertion of the needles and their bending during insertion. This work aims at increasing the precision, reliability, and efficiency of the needle tip positioning. To achieve this objective, our approach is based on a robotic transperineum needle insertion device called PROSPER and developed at TIMC-IMAG Laboratory. Positioning inaccuracy due to tissue deformations will be corrected using natural bevel-tip needle bending during insertion. In that purpose, a control strategy, using regular update of the needle path planning, will be set in closed-loop. This approach was born in LIRMM laboratory and is greatly optimized to satisfy the specifications of our system. However, this control is based on a regular feedback of needle position and bending. We choose 3D ultrasound imaging for its availability in clinic, its low cost and its compactness. However, needle detection is very challenging in this modality due to a complexity of the images. This work introduces a robust method to track a needle in a stream of 3D ultrasound volumes using a Random Sample Consensus algorithm and a precise region of interest. This region is determined using a predictive model of needle deformation and increases drastically the robustness of our tracking. The needle steering system is validated using PVC and paraffin phantoms with a precision of 1 to 2 mm. Finally, the design and the use of echogenic needles allow to increase their visibility under 3D ultrasound, which was the most challenging obstacle for needle steering in ex-vivo tissue. Thanks to these echogenic needles, our system has been validated on ex-vivo animal tissues and it achieves a precision of 2 to 4 mm. This robotized needle steering system using flexible bevel-tip needle under 3D ultrasound is a first step toward a clinical application, especially because of the use of brachytherapy robotic device. This approach might be adapted for other percutaneous clinical procedure in the future, and could increase their precision and success.