title: Electromagnetic tracking for catheter reconstruction in ultrasound-guided high-dose-rate brachytherapy of the prostate.
abstract: OBJECTIVE
  The accurate delivery of high-dose-rate brachytherapy is dependent on the correct identification of the position and shape of the treatment catheters. In many brachytherapy clinics, transrectal ultrasound (TRUS) imaging is used to identify the catheters. However, manual catheter identification on TRUS images can be time consuming, subjective, and operator dependent because of calcifications and distal shadowing artifacts. We report the use of electromagnetic (EM) tracking technology to map the position and shape of catheters inserted in a tissue-mimicking phantom.
  
  
  METHODS
  The accuracy of the EM system was comprehensively quantified using a three-axis robotic system. In addition, EM tracks acquired from catheters in a phantom were compared with catheter positions determined from TRUS and CT images to compare EM system performance to standard clinical imaging modalities. The tracking experiments were performed in a controlled laboratory environment and also in a typical brachytherapy operating room to test for potential EM distortions.
  
  
  RESULTS
  The robotic validation of the EM system yielded a mean accuracy of <0.5 mm for a clinically acceptable field of view in a nondistorting environment. The EM-tracked catheter representations were found to have an accuracy of <1 mm when compared with TRUS- and CT-identified positions, both in the laboratory environment and in the brachytherapy operating room. The achievable accuracy depends to a large extent on the calibration of the TRUS probe, geometry of the tracked devices relative to the EM field generator, and locations of surrounding clinical equipment. To address the issue of variable accuracy, a robust calibration algorithm has been developed and integrated into the workflow. The proposed mapping technique was also found to improve the workflow efficiency of catheter identification.
  
  
  CONCLUSIONS
  The high baseline accuracy of the EM system, the consistent agreement between EM-tracked, TRUS- and CT-identified catheters, and the improved workflow efficiency illustrate the potential value of using EM tracking for catheter mapping in high-dose-rate brachytherapy.
authors.affiliation: Department of Ultrasound Imaging and Interventions, Philips Research North America, Briarcliff Manor, NY. Electronic address: sbharat@uwalumni.com.
authors.forename: Shyam
authors.initials: S
authors.lastname: Bharat
authors.affiliation: Department of Ultrasound Imaging and Interventions, Philips Research North America, Briarcliff Manor, NY.
authors.forename: Cynthia
authors.initials: C
authors.lastname: Kung
authors.affiliation: Department of Ultrasound Imaging and Interventions, Philips Research North America, Briarcliff Manor, NY.
authors.forename: Ehsan
authors.initials: E
authors.lastname: Dehghan
authors.affiliation: Department of Radiation Oncology, Sunnybrook Health Sciences Center, Toronto, ON, Canada.
authors.forename: Ananth
authors.initials: A
authors.lastname: Ravi
authors.affiliation: Department of Radiation Oncology, Sunnybrook Health Sciences Center, Toronto, ON, Canada.
authors.forename: Niranjan
authors.initials: N
authors.lastname: Venugopal
authors.affiliation: Department of Ultrasound Imaging and Interventions, Philips Research North America, Briarcliff Manor, NY.
authors.forename: Antonio
authors.initials: A
authors.lastname: Bonillas
authors.affiliation: Department of Ultrasound Imaging and Interventions, Philips Research North America, Briarcliff Manor, NY.
authors.forename: Doug
authors.initials: D
authors.lastname: Stanton
authors.affiliation: Department of Ultrasound Imaging and Interventions, Philips Research North America, Briarcliff Manor, NY.
authors.forename: Jochen
authors.initials: J
authors.lastname: Kruecker
mesh_terms: D000465:Algorithms; D001918:Brachytherapy / Q000379:methods*; D002138:Calibration; D057785:Catheters; D055590:Electromagnetic Phenomena; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D019047:Phantoms, Imaging; D011467:Prostate / Q000000981:diagnostic imaging*; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D012371:Robotics; D014463:Ultrasonography
keywords: Catheter mapping; Electromagnetic tracking; High-dose-rate brachytherapy; Treatment planning