SU‐D‐9A‐06: 3D Localization of Neurovascular Bundles Through MR‐TRUS Registration in Prostate Radiotherapy

Abstract

Purpose:Erectile dysfunction (ED) is the most common complication of prostate‐cancer radiotherapy (RT) and the major mechanism is radiation‐induced neurovascular bundle (NVB) damage. However, the localization of the NVB remains challenging. This study's purpose is to accurately localize 3D NVB by integrating MR and transrectal ultrasound (TRUS) images through MR‐TRUS fusion.Methods:T1 and T2‐weighted MR prostate images were acquired using a Philips 1.5T MR scanner and a pelvic phase‐array coil. The 3D TRUS images were captured with a clinical scanner and a 7.5 MHz biplane probe. The TRUS probe was attached to a stepper; the B‐mode images were captured from the prostate base to apex at a 1‐mm step and the Doppler images were acquired in a 5‐mm step. The registration method modeled the prostate tissue as an elastic material, and jointly estimated the boundary condition (surface deformation) and the volumetric deformations under elastic constraint. This technique was validated with a clinical study of 7 patients undergoing RT treatment for prostate cancer. The accuracy of our approach was assessed through the locations of landmarks, as well as previous ultrasound Doppler images of patients.Results:MR‐TRUS registration was successfully performed for all patients. The mean displacement of the landmarks between the post‐registration MR and TRUS images was 1.37±0.42 mm, which demonstrated the precision of the registration based on the biomechanical model; and the NVB volume Dice Overlap Coefficient was 92.1±3.2%, which demonstrated the accuracy of the NVB localization.Conclusion:We have developed a novel approach to improve 3D NVB localization through MR‐TRUS fusion for prostate RT, demonstrated its clinical feasibility, and validated its accuracy with ultrasound Doppler data. This technique could be a useful tool as we try to spare the NVB in prostate RT, monitor NBV response to RT, and potentially improve post‐RT potency outcomes.