EMVision: An electromagnetic tracking guidance system for accurate placement of interstitial brachytherapy applicators

To design, construct, and evaluate a system for image-guided placement of brachytherapy applicators using electromagnetic tracking (EMT) technology for improved procedure quality and efficiency. The system, named EMVision, provides a three-dimensional display of planned needle sites, visibility of the anatomy and needle position during placement, and reference tracking to account for generator or target anatomy shifts. The EMVision EMT guidance system registers CT and EMT reference frames using an automated point-based algorithm according to tandem/ovoid locations. Subsequent needle placement and digitization is guided with an intraluminal EMT sensor and user interface that displays the needle's location in axial, coronal, sagittal, and 3D-volumetric CT views. The interface can overlay contours, preplanned needles, and provide 6DOF compensation for tandem movement during needle placement/manipulation. EMVision accuracy was evaluated in phantom and human cadaver by comparing EMVision's DICOM needle positions with a ground-truth, postimplant CT. Proof of concept was demonstrated for EMT-assisted placement of brachytherapy needles. EMVision accuracy in phantom (mean ± standard deviation) on a brachysuite CT table was 0.76 ± 0.13 mm for needle tips placed up to 75 mm from the tandem/ovoids and 0.52 ± 0.27 mm for needle shafts at distances up to 100 mm from the tandem/ovoids. Performance in human cadaver was similar, with tip and shaft accuracies of 0.77 ± 0.14 mm and 0.40 ± 0.21 mm, respectively. EMVision provides sub-millimeter accuracy for the placement of brachytherapy needles without repeated or continuous imaging. The technology can be used to reduce brachytherapy procedure times, improve the correspondence between intended and actual needle positions, or decrease the trainee learning curve.