Robot-assisted 3D-TRUS guided prostate brachytherapy: System integration and validation

Abstract

Current transperineal prostate brachytherapy uses transrectal ultrasound (TRUS) guidance and a template at a fixed position to guide needles along parallel trajectories. However, pubic arch interference (PAI) with the implant path obstructs part of the prostate from being targeted by the brachytherapy needles along parallel trajectories. To solve the PAI problem, some investigators have explored other insertion trajectories than parallel, i.e., oblique. However, parallel trajectory constraints in current brachytherapy procedure do not allow oblique insertion. In this paper, we describe a robot-assisted, three-dimensional (3D) TRUS guided approach to solve this problem. Our prototype consists of a commercial robot, and a 3D TRUS imaging system including an ultrasound machine, image acquisition apparatus and 3D TRUS image reconstruction, and display software. In our approach, we use the robot as a movable needle guide, i.e., the robot positions the needle before insertion, but the physician inserts the needle into the patient's prostate. In a later phase of our work, we will include robot insertion. By unifying the robot, ultrasound transducer, and the 3D TRUS image coordinate systems, the position of the template hole can be accurately related to 3D TRUS image coordinate system, allowing accurate and consistent insertion of the needle via the template hole into the targeted position in the prostate. The unification of the various coordinate systems includes two steps, i.e., 3D image calibration and robot calibration. Our testing of the system showed that the needle placement accuracy of the robot system at the "patient's" skin position was 0.15 mm+/-0.06 mm, and the mean needle angulation error was 0.07 degrees. The fiducial localization error (FLE) in localizing the intersections of the nylon strings for image calibration was 0.13 mm, and the FLE in localizing the divots for robot calibration was 0.37 mm. The fiducial registration error for image calibration was 0.12 mm and 0.52 mm for robot calibration. The target registration error for image calibration was 0.23 mm, and 0.68 mm for robot calibration. Evaluation of the complete system showed that needles can be used to target positions in agar phantoms with a mean error of 0.79 mm+/-0.32 mm.

Robotic assistance for ultrasound-guided prostate brachytherapy

“…Fenster and colleagues have made major strides toward a more clinically feasible TRUSguided robotic prostate brachytherapy system (Wei et al, 2004). They adopted an industrial serial-link robot for needle manipulation while motorizing a conventional TRUS probe to produce a smooth sagittal sweep in the rectum.…”

Robotic Systems for Radiation Therapy

“…With this mode of therapy, a high radiation dose can be delivered locally to the tumor with rapid dose falloff in the surrounding normal tissue. Recently, several research groups have reported the investigation and development of the robotic systems for the prostate seeds implants, (Stoianovici et al, 2003), (Wei et al, 2004), (Fichtinger et al, 2006), , (Meltsner, 2007), , (Stoianovici et al, 2007), , (Salcudean et al, 2008), (Lin et al, 2008), (Moerland et al, 2008). The potential advantages of the robotic seed implants include improving the accuracy of the needle placement and seed delivery, as well as improving the consistency of the seed implant.…”

On the Use of a Hexapod Table to Improve Tumour Targeting in Radiation Therapy

“…In brachytherapy, the radioactive sources are guided into or near the tumour through needles. A number of groups are currently working on prototypes and have demonstrated the feasibility of using robots as a moveable needle guide (Dimaio et al, 2007;Wei et al, 2004) leaving the actual insertion of the needle into the target organ to the physician. Other groups are working on placing radioactive seeds directly into the lesion, e.g.…”