Ultrasound–fluoroscopy registration for prostate brachytherapy dosimetry

Abstract

Prostate brachytherapy is a treatment for prostate cancer using radioactive seeds that are permanently implanted in the prostate. The treatment success depends on adequate coverage of the target gland with a therapeutic dose, while sparing the surrounding tissue. Since seed implantation is performed under transrectal ultrasound (TRUS) imaging, intraoperative localization of the seeds in ultrasound can provide physicians with dynamic dose assessment and plan modification. However, since all seeds cannot be seen in the ultrasound images, registration between ultrasound and fluoroscopy is a practical solution for intraoperative dosimetry. In this manuscript, we introduce a new image-based nonrigid registration method that obviates the need for manual seed segmentation in TRUS images and compensates for the prostate displacement and deformation due to TRUS probe pressure. First, we filter the ultrasound images for subsequent registration using thresholding and Gaussian blurring. Second, a computationally efficient point-to-volume similarity metric, an affine transformation and an evolutionary optimizer are used in the registration loop. A phantom study showed final registration errors of 0.84 ± 0.45 mm compared to ground truth. In a study on data from 10 patients, the registration algorithm showed overall seed-to-seed errors of 1.7 ± 1.0 mm and 1.5 ± 0.9 mm for rigid and nonrigid registration methods, respectively, performed in approximately 30 seconds per patient.

An image‐guidance system for dynamic dose calculation in prostate brachytherapy using ultrasound and fluoroscopy

“…This resulted in an overall mean registration error of 1.3 mm with 0.4, 0.5, and 0.9 mm errors along the x, y, and z axes, respectively. This agrees closely to the overall mean registration error of 1.5 mm reported by Dehghan et al 28 with 0.5, 0.5, and 1.1 mm errors along the x, y, and z axes, respectively. Overall, this demonstrates that the seed reconstruction using the marker-based fiducial does not affect the performance of the registration algorithm.…”

“…The prostate contour outlined during planning is used as a volume of interest (VOI), but if it is unavailable, a VOI may be manually selected. We use an image-based pointto-volume registration method published by Dehghan et al 28 that affinely registers the reconstructed seeds to the bright hyperechoic regions of the TRUS volume.…”

“…29 The optimization is initialized by centering the reconstruction within the provided prostate contour or manual VOI. We refer readers to Dehghan et al 28 for more details.…”

Intraoperative Registered Ultrasound and Fluoroscopy (iRUF) for dose calculation during prostate brachytherapy: Improved accuracy compared to standard ultrasound-based dosimetry

“…A brief description of each component and the workflow follows. Full details have been described in our prior publications [13]– [17]. …”

CT and MRI fusion for postimplant prostate brachytherapy evaluation

“…We employ a similarity metric and optimizer previously used by Dehghan et al [10]. The salient feature of our registration approach lays in image processing step, where we apply a series of morphological filters, in order to enhance the visibility of seeds in the MR images.…”