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EM-tracked MR-US live fusion and needle location in gynecologic brachytherapy
Thomas R Niedermayr1, Elizabeth A Kidd1
1Department of Radiation Oncology, Stanford University, Stanford, CA.
Purpose:
We describe a novel system which enhances and clarifies the live transrectal US information during gynecological brachytherapy implants for improved needle guidance during insertion. It combines a freehand, stepper-less transrectal ultrasound (US) probe with an electro-magnetic tracking system to continuously fuse a preexisting MR and visualize the inserted needle.
Methods:
A BK Spekto with a biplanar 9048 US probe, was instrumented with a Northern Digital Inc. Electro-magnetic tracker, part of the 3D Guidance Trakstar system. Software was developed using the 3D Slicer toolkit to enable live and continuous fusion of a preacquired MR. Contours generated on the MR can displayed on the live US image. A custom tracked stylet be placed inside a needle to visualize its location on the live US image using an overlay.
Results:
The system was assessed on a CIRS 054 phantom before being deployed in clinical implants. Registration accuracy between the live US image and the MR/contours was assessed by comparing the phantom or patient anatomy on the live US with the overlaid contours. A similar method was use for the needle localization tool. An accuracy < 4 mm was measured for the US/MR fusion, and < 5 mm for the needle localization overlay.
Conclusions:
A novel system has been developed and clinically tested to enhance the capabilities of US imaging for gynecological brachytherapy procedures by incorporating MR information and needle recognition. These features can help guide the practitioner to a geometrically more robust implant with actionable feedback.
