Room: AAPM ePoster Library
Purpose: Feasibility evaluation of electromagnetic (EM) tracking of catheter paths in trans-rectal ultrasound (TRUS) guided prostate HDR brachytherapy for different imaging and treatment environments.
Methods: Under TRUS guidance, fifteen brachytherapy catheters were implanted in a tissue-equivalent prostate phantom (Model-053G, CIRS, Norfolk, VA) embedded inside a pelvic phantom. Subsequently, EM tracking of the catheter paths was performed in five different environments: a brachytherapy operating room (OR) with the TRUS probe inside (ProbeIN-OR) and withdrawn from (ProbeOUT-OR) the phantom rectum; on a CT simulator with the probe inside (ProbeIN-CT) and withdrawn from the phantom rectum (ProbeOUT-CT), and in a perturbation free environment (ProbeOUT-GT). An EM sensor (Model-55) was threaded sequentially into catheters for tracking measurements. A driveBAY field generator and a reference sensor (Model-800) were used (Ascension, Shelburne, VT). Plus (www.plustoolkit.org) and SlicerIGT (www.SlicerIGT.org) softwares were used for data collection and processing. EM tracked catheter paths were smoothed with least squares polynomial regression, and the tracking accuracy was evaluated using maximum, average and best 95% Hausdorff distance displacements compared to catheters tracked on CT, considered as the ground truth.
Results: Reconstruction errors for EM tracking with TRUS probe inside (ProbeIN) were significantly higher than for probe withdrawn (ProbeOUT) from the rectum. EM field perturbations by the TRUS probe caused significant warping of EM tracks near the probe. The average displacement errors for ProbeIN-OR, ProbeIN-CT, ProbeOUT-OR, ProbeOUT-CT and ProbeOUT-GT scenarios were 4.14mm, 3.98mm, 1.00mm, 1.55mm and 1.31mm, respectively; manual corrections for systematic errors improved the error estimates to 3.94mm, 3.73mm, 0.35mm, 0.49mm, and 0.37mm, respectively. Smoothing catheter paths reduced displacement errors compared to raw data (p <0.001), except for ProbeIN-CT (p=0.023).
Conclusion: EM tracking based spatial reconstruction of catheters is a viable option for catheter tracking in prostate HDR brachytherapy workflows not requiring TRUS probe inside the rectum at the time of treatment.
Funding Support, Disclosures, and Conflict of Interest: Thanks to the Ride For Dad, Prostate Cancer Fight Foundation Grant (Kingston-Quinte) (2013) for their funding support, and Harold E. Johns Studentship (2014, 2015) towards Stephen MacGregor and Nikhil Seth for their technical contributions during the preliminary work for this project.