Development of a novel, robotic prostate biopsy
(BX) and brachytherapy (BT) device. The CoBra MRI-guided robot aims to
perform adaptive BT under real-time (RT)-MRI, accounting for target changes
due to tissue deformation. The robot has 5 DoF, is actuated with
ultrasonic–motors in closed-loop feedback and is MRI-compatible. Patient
remains in-bore throughout. Curved needle insertion allows
avoidance of OARs or obstructions. A quick-lock mechanism allows easy exchange
of the BX or BT modules. Seed delivery adapts to the new target position during
the implant, with the aid of omnidirectional steerable needles and RT dose calculations.
Use of RT-MR guided BT, requires rapid creation of
accurate synthetic-CT (sCT) datasets from the live MR images. We use an
algorithm called augmented cycle Generative Adversarial Network
(AugCGAN). This is more robust with the variability of MR images than the
standard cycleGAN. This study included T2w MR and CT pelvic images of 38
patients from 5 centres. The AugCGAN was trained on 2D transverse slices of 19
patients from 3 different sites. The network was then used to generate sCT
images of 19 patients coming from two other sites. Mean Absolute Errors (MAE)
for each patient were evaluated between real and sCT.
The needle path planning algorithm is designed for
the MR-teerable needles used in the CoBra project. The algorithm receives
the seed plan and prostate contours from MRI as an input. It clusters the seeds
and creates candidate path plans to reach all seed positions, using a single
insertion point. Fig. 1 is an example of four path candidates.
Acceptable results are those that allow all seed positions to be reached, while
keeping a minimum, pre-set distance between the needle and the urethra. From
all candidates, the one that causes the least amount of tissue damage, is
chosen.
For robot testing, an active bio-inspired
prostate phantom (BIP), depicting the motion, deformation and inflammation of
the prostate seen clinically during needle insertion, has been developed. The
BIP is connected to SOFA (simulation open framework architecture) to estimate the prostate changes, thus
enabling tracking of target position interactively (fig. 2).
Fig. 1. Needle trajectory planning software
Fig. 2. BIP in MRI scanner with CoBra robot