Automatic brachytherapy seed placement under MRI guidance

Abstract

The paper presents a robotic method of performing low dose rate prostate brachytherapy under magnetic resonance imaging (MRI) guidance. The design and operation of a fully automated MR compatible seed injector is presented. This is used with the MrBot robot for transperineal percutaneous prostate access. A new image-registration marker and algorithms are also presented. The system is integrated and tested with a 3T MRI scanner. Tests compare three different registration methods, assess the precision of performing automated seed deployment, and use the seeds to assess the accuracy of needle targeting under image guidance. Under the ideal conditions of the in vitro experiments, results show outstanding image-guided needle and seed placement accuracy.

Fig. 1

System Diagram.

Fig. 2

MR compatible automated brachytherapy system components.

Fig. 3

Seed injector diagram; a) Seed dispenser b) Seed placement end-effector b.1) case; b.2) MR compatible actuator (PneuStep); b.3) needle cylinder; b.4) stylet cylinder; b.5) needle piston; b.6) stylet piston; b.7) seed drawer and cylinder; b.8) seed in the drawer; b.9) needle; b.10) stylet; b.11) seed fiber optic sensor; b.12) retract fiber optic sensor.

Fig. 4

MR Registration marker attached to the seed injector; 1) Ellipse, 2) Line, 3) Control Points, 4) Needle.

Fig. 5

Registration Error.

Fig. 6

Seed placement setup.

Fig. 7

Seed error placement distribution (gel tests).