An automatic seed identification technique for interstitial implants using three isocentric radiographs

Abstract

A technique for the automatic reconstruction of the spatial coordinates of seeds in an interstitial implant has been developed. Seed coordinates from three isocentric radiographs, an anterior-posterior film, and an orthogonal pair of films taken at gantry angles of +/- 45 degrees from the anterior-posterior direction are digitized and recorded in a random sequence. From this, the three-dimensional coordinates of the seeds in the implant are computed by matching the values of common coordinates along the axis of rotation. This rotate and match technique leads to an accurate and consistent identification and reconstruction of seeds with 90% of them within 2 mm of their actual location. These new computer routines have been added to an existing treatment planning system (AECL TP-11 treatment planning system, version 5A). We present our algorithm and technique along with clinical examples.

Clinical application and validation of an iterative forward projection matching algorithm for permanent brachytherapy seed localization from conebeam‐CT x‐ray projections

“…Also, it avoids the intraobserver and interobserver variability of seed finding that is often observed when using three-film methods. [5][6][7][8][9][10][11] It can correct for errors in the measured imaging geometry by iteratively adjusting the imaging gantry positions used in the iterative projection process. Current clinical practice relies on reconstructed 3D CT images for reconstructing seed positions.…”

“…Also, intraoperative FBCT installations in brachytherapy suites are uncommon. A more common approach to seed localization is backprojection of seed positions in 2D x-ray projections using two-film 5 and three-film [6][7][8][9][10][11] techniques. The reconstructed implant geometry is then fused to intraoperatively acquired ultrasound images, upon which dose planning can be performed.…”

Intra-operative dosimetry of trans-rectal ultrasound guided 125I prostate implants using C-arm fluoroscopic images

“…Use of interventional MRI has also been reported for real-time dosimetry of prostate implants,[4] but this technology is not commonly available in brachytherapy procedure rooms. A few authors have used radiotherapy simulators[56] that are isocentrically mounted to obtain the seed positions accurately with radiographic images taken at AP and two oblique angles. In this study, we have investigated the use of a C-arm fluoroscopy unit for intra-operative dosimetry of prostate implants.…”

Three-dimensional seed reconstruction from an incomplete data set for prostate brachytherapy

“…This can potentially lead to mismatches in the reconstruction if, for example, two views have one undetected seed each but do not correspond to the same 3D seed. Other projection x-ray-based seed reconstruction algorithms (Amols and Rosen 1981, Altschuler et al 1983, Jackson 1983, Rosenthal and Nath 1983, Tubic et al 2001, Narayanan et al 2002, Todor et al 2003 do not address the problem of undetected seeds. It is usually assumed that this problem does not occur or is rare.…”