Purpose
To assess retrospectively the clinical accuracy of an magnetic
resonance imaging-guided robotic prostate biopsy system that has been used
in the US National Cancer Institute for over 6 years.
Methods
Series of 2D transverse volumetric MR image slices of the prostate
both pre (high-resolution T2-weighted)-and post (low-resolution)-needle
insertions were used to evaluate biopsy accuracy. A three-stage registration
algorithm consisting of an initial two-step rigid registration followed by a
B-spline deformable alignment was developed to capture prostate motion
during biopsy. The target displacement (distance between planned and actual
biopsy target), needle placement error (distance from planned biopsy target
to needle trajectory), and biopsy error (distance from actual biopsy target
to needle trajectory) were calculated as accuracy assessment.
Results
A total of 90 biopsies from 24 patients were studied. The
registrations were validated by checking prostate contour alignment using
image overlay, and the results were accurate to within 2 mm. The mean target
displacement, needle placement error, and clinical biopsy error were 5.2,
2.5, and 4.3 mm, respectively.
Conclusion
The biopsy error reported suggests that quantitative imaging
techniques for prostate registration and motion compensation may improve
prostate biopsy targeting accuracy.