Seed Localization in MRI-guided Prostate Brachytherapy using Inversion-Recovery With ON-Resonant Water Suppression (IRON)

Introduction: Prostate brachytherapy is a common treatment for low-risk prostate cancer involving the insertion of needles in precise locations of the prostate to implant rice-like radioactive sources known as seeds. Seed localization in relation to the prostate is one of the major current limitations of intraoperative treatment planning for prostate brachytherapy [1]. This issue limits the effectiveness of real-time dosimetry and therefore leads to suboptimal prostate cancer treatment. While transrectal ultrasound and X-ray have been the traditional means of image guidance, MRI is a promising modality for guiding brachytherapy, having been validated in over 500 patients using the GE Signa SP 0.5T open-bore scanner [2] and now progressing toward closed-bore scanners through the aid of robotics [3,4]. Previous studies assessing MR pulse sequences in imaging brachytherapy seeds [5,6] have shown that localization is problematic because the seeds generally appear as diffuse, dark voids. Nonetheless, recent developments in pulse sequences that image local changes in susceptibility provide a new opportunity to revisit this topic. We therefore provide an initial demonstration of the potential to image and localize brachytherapy seeds using Inversion-Recovery with ON-resonant water suppression (IRON) [7].