TU‐F‐BRF‐02: MR‐US Prostate Registration Using Patient‐Specific Tissue Elasticity Property Prior for MR‐Targeted, TRUS‐Guided HDR Brachytherapy

Abstract

Purpose:High‐dose‐rate (HDR) brachytherapy has become a popular treatment modality for prostate cancer. Conventional transrectal ultrasound (TRUS)‐guided prostate HDR brachytherapy could benefit significantly from MR‐targeted, TRUS‐guided procedure where the tumor locations, acquired from the multiparametric MRI, are incorporated into the treatment planning. In order to enable this integration, we have developed a MR‐TRUS registration with a patient‐specific biomechanical elasticity prior.Methods:The proposed method used a biomechanical elasticity prior to guide the prostate volumetric B‐spline deformation in the MRI and TRUS registration. The patient‐specific biomechanical elasticity prior was generated using ultrasound elastography, where two 3D TRUS prostate images were acquired under different probe‐induced pressures during the HDR procedure, which takes 2‐4 minutes. These two 3D TRUS images were used to calculate the local displacement (elasticity map) of two prostate volumes. The B‐spline transformation was calculated by minimizing the Euclidean distance between the normalized attribute vectors of the prostate surface landmarks on the MR and TRUS. This technique was evaluated through two studies: a prostate‐phantom study and a pilot study with 5 patients undergoing prostate HDR treatment. The accuracy of our approach was assessed through the locations of several landmarks in the post‐registration and TRUS images; our registration results were compared with the surface‐based method.Results:For the phantom study, the mean landmark displacement of the proposed method was 1.29±0.11 mm. For the 5 patients, the mean landmark displacement of the surface‐based method was 3.25±0.51 mm; our method, 1.71±0.25 mm. Therefore, our proposed method of prostate registration outperformed the surfaced‐based registration significantly.Conclusion:We have developed a novel MR‐TRUS prostate registration approach based on patient‐specific biomechanical elasticity prior. Successful integration of multi‐parametric MR and TRUS prostate images provides a prostate‐cancer map for treatment planning, enables accurate dose planning and delivery, and potentially enhances prostate HDR treatment outcome.