TRUS-MRI Fusion for focal prostate therapy

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                  Integration of the TRUS-MRI fusion framework  with Variseed 9 (TM) dosimetry software

Focal therapy in low-risk prostate cancer may provide the best balance between cancer control and quality of life preservation. As a minimally invasive approach performed under TRUS guidance, brachytherapy is an appealing framework for focal therapy. However, the contrast in TRUS images is generally insufficient to distinguish the target lesion from normal prostate tissue. MRI usually offers a much better contrast between the lesion and surrounding tissues. Registration between TRUS and MRI may therefore significantly improve lesion targeting capability in focal prostate brachytherapy. We propose a deformable registration framework for the accurate fusion of TRUS and MRI prostate volumes under large deformations arising from dissimilarities in diameter, shape, and orientation between endorectal coils and TRUS probes.

Following pose correction by a RANSAC implementation of the ICP algorithm, TRUS and MRI Prostate contour points are represented by a 3-D extension of the shape-context descriptor and matched by the Hungarian algorithm. Eventually a smooth free-form warping is computed by fitting a 3-D B-spline mesh to the set of matched points.

Quantitative validation of  the registration accuracy is provided on a retrospective set of 10 real cases, using as landmarks either brachytherapy seeds (6 cases) or external beam radiotherapy fiducials (4 cases) implanted and visible in both modalities. The average registration error between the landmarks  was 2.49 mm and 3.20 mm, for the brachytherapy and external beam sets, respectively, that is less than the MRI voxels’ long axis length (=3.6 mm). The overall average registration error (for brachytherapy and external beam datasets together) was 2.56mm.

The proposed method provides a promising framework for TRUS-MRI registration in focal prostate brachytherapy.

 PIs: Prof. Zvi Symon, Dr. Arnaldo Mayer

Link to the IJCARS paper

 

  

                        Small field-of-view CT-MRI fusion for focused external beam radiotherapy of the prostate 

                                                                displayed on the planning system

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