MRI-Guided Robotically Assisted Focal Laser Ablation of the Prostate Using Canine Cadavers

Abstract

Objective: a magnetic resonance imaging (MRI)-conditional needle guidance robot is developed to enhance MRI-guided focal laser ablation (FLA) therapy in patients with focal prostate cancer.

Methods: inspired by the workflow of the manual FLA therapy, we developed an MRI-conditional robot with two degrees of freedom to provide the guidance for laser ablation catheter. This robot is powered by pneumatic turbine motors and encoded with the custom-designed optical encoder. The needle could be inserted manually through the designed robotic system, which keeps the patients inside MRI bore throughout the procedure. The robot hardware is integrated with the custom ablation planning and monitoring software (OncoNav) to provide an iterative treatment plan to cover the whole ablation zone. Virtual tumors were selected in three canine cadavers as targets to validate the performance of the proposed hardware and software system.

Results: phantom studies show that the average targeting error is less than 2 mm and the workflow of the entire procedure lasts for 100 minutes. Canine cadaver experiment results show that all the targets were successfully ablated in no more than three administrations.

Significance: MRI-guided prostate FLA is feasible using the proposed hardware and software system, indicating potential utility in future human trials.

Fig. 1.

(A) Prostate robot assembly. The detailed parts can be listed as follows: (1) custom designed pneumatic motor; (2) air hose bundle; (3) fiducial markers; (4) movable template; (5) supporting rod. (b) Prostate robot and volunteer inside the MR scanner. MRI coordinate frame is also shown. (C) Prostate robot and manual insertion mechanism for the canine cadaver study inside the MRI room. (D) User manually inserts the needle toward the target.

Fig. 2.

Left: schematic diagram of the robot working principle. The red and blue lines indicate the timing belts on the motor output shaft. Right: assembly design of the proposed robotic hardware system mounted on a rotation bar that can be rotated manually in discrete angles ±7.5°, 15°.

Fig. 3.

Top: motor control block diagram. Bottom: unit set-point positioning test for the motor accuracy performance evaluation.

Fig. 4.

From left to right: fiducial marker positions with respect to the robot frame with the offset of 50 mm perpendicular to the transverse plane of the robot to eliminate the effect of brass rod. Green balls show the five fiducial markers; MR image of the robot frame. White arrows: five fiducial markers within the MR image; front view of the prostate CAD model with fiducial markers labeled on the transverse plane. Red arrows: fiducial marker positions on the robot frame; MR image overlaid on the robot CAD design.

Fig. 5.

(A) MR image reconstruction of the canine prostate using OncoNav: the left panel shows the function menu, and the right panel displays different views of the target organ. (B) Treatment planning with three ablation positions (circles) to cover the ablation zone.

Fig. 6.

(A) The experimental setup of the prostate robot in the MRI scanner room and control room. (B) Designed robotic FLA surgical workflow. ε is the predefined targeting error threshold based on the experience of our clinical collaborators; in this study, it was set to be 2 mm.

Fig. 7.

(A) and (B) Plastic seed distributed inside the prostate phantom. (C) MRI image of the seed.

Fig. 8.

(A) Sagittal view of the virtual tumor (the irregular red contour). (B) Multiple ablation regions (white ellipses) calculated by OncoNav. (C) Robot-assisted FLA based on the ablation plan. (D) Ablated area overlaid on top of the virtual tumor.

Fig. 9.

Pre-operative and post-operative MR image canine cadaver prostate. The white circle indicates the virtual tumor position.

Fig. 10.

(A) and (B) MR image of the canine prostate for visualization, target identification and insertion position selection respectively. (C) Intra-operative MR thermal image of the canine prostate. (D) MRI thermal image overlapped on the MRI image in OncoNav to enable the intra-operative evaluation of the ablation outcome.