Seed-based ultrasound and fluoroscopy registration using iterative optimal assignment for intraoperative prostate brachytherapy dosimetry

Abstract

Prostate brachytherapy involves permanent implantation of radioactive sources into the prostate gland. Since fluoroscopy and transrectal ultrasound (TRUS) imaging modalities currently complement each other by providing good visualization of seeds and soft tissue, respectively, the registration of these two imaging modalities could lead to the intraoperative dosimetry analysis of brachytherapy procedures, thus improving patient outcome and reducing costs. Although it is desirable to register TRUS and fluoroscopy images by using the implanted seeds as fiducial markers, an operator, based on our experience, can locate only a small fraction of implanted seeds in axial TRUS images. Therefore, to perform TRUS-fluoroscopy registration in a clinical setting, there is a need for (1) a new method that can reliably perform registration at low seed detection rates and (2) a new imaging technique to enhance the seed visibility. We previously developed iterative optimal assignment (IOA), which can perform registration at seed detection rates below 20%, to address the former. In this paper, we present a new TRUS acquisition method where we acquire images of the prostate by rotating the longitudinal transducer of a biplanar probe in the clockwise/counter-clockwise direction. We acquired post-implant fluoroscopy and TRUS images from 35 patients who underwent a seed implant procedure. The results show that the combined use of IOA and rotational images makes TRUS-fluoroscopy registration possible and practical, thus our goal of intraoperative dosimetry can be realized.