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Applications of Electromagnetic Tracking Technology to High Dose Rate (HDR) Interstitial Brachytherapy


A Damato

A Damato*, A Mehrtash, T Kapur, A Viswanathan, R Cormack, Brigham and Women's Hospital, Boston, MA

SU-D-108-2 Sunday 2:05PM - 3:00PM Room: 108

Purpose:
HDR interstitial brachytherapy (IB) is a technique used for the treatment of gynecologic and prostate tumors that places multiple 6F catheters in the target region. Determining catheter location without transferring the patient to a scanner would enhance planning and treatment quality assurance (QA). We investigate the use of electromagnetic tracking technology (EM) for the localization of catheters used in IB.

Methods:
A phantom implanted with 12 plastic catheters inserted through a template with 5 registration points was fabricated and CT scanned to establish reference geometry. A non-ionizing EM tracking system with a 1.3-mm diameter sensor that could be inserted through the length of the interstitial catheters was used to measure the configuration of catheters. EM and CT coordinates were rigidly fused based on 5 template points and 1 catheter tip. Implant shape is described by a self-distance matrix, with the distance between any two catheters as elements. The absolute difference between the EM and CT self-distance matrix is the shape tracking error. The positional tracking error is the mean distance between dwell positions in two corresponding catheters in EM and CT, averaged over the 12 possible tips used for registration.

Results:
The maximum shape tracking error was 2.8 mm. The mean shape tracking error was 1.2±0.7 mm. The maximum positional tracking error was 3.9 mm. The mean positional tracking error was 2.2±0.7 mm.

Conclusion:
EM can be used to localize dwell positions with an average error <2.5 mm, which is comparable to the error associated with the manual digitization of catheters on CT. EM tracking provides a non-ionizing method to measure catheter configuration without the need to transfer the patient to a scanner and offers a means to QA catheter digitization and checking for catheter shift before each fraction.

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