Postoperative evaluation of prostate brachytherapy is typically
performed using CT, which does not have sufficient
soft tissue contrast for accurate anatomy delineation. MR-CT
fusion enables more accurate localization of both anatomy
and implanted radioactive seeds, and hence, improves the
accuracy of postoperative dosimetry. We propose a method
for automatic registration of MR and CT images without a
need for manual initialization. Our registration method employs
a point-to-volume registration scheme during which
localized seeds in the CT images, produced by commercial
treatment planning systems as part of the standard of care,
are rigidly registered to preprocessed MRI images. We tested
our algorithm on ten patient data sets and achieved an overall
registration error of 1.6 ± 0.8mm with a running time of less
than 20s. With high registration accuracy and computational
speed, and no need for manual intervention, our method has
the potential to be employed in clinical applications.