title: A novel method for accurate needle-tip identification in trans-rectal ultrasound-based high-dose-rate prostate brachytherapy.
abstract: OBJECTIVE
  In real-time trans-rectal ultrasound (TRUS)-based high-dose-rate prostate brachytherapy, the accurate identification of needle-tip position is critical for treatment planning and delivery. Currently, needle-tip identification on ultrasound images can be subject to large uncertainty and errors because of ultrasound image quality and imaging artifacts. To address this problem, we developed a method based on physical measurements with simple and practical implementation to improve the accuracy and robustness of needle-tip identification.
  
  
  METHODS
  Our method uses measurements of the residual needle length and an off-line pre-established coordinate transformation factor, to calculate the needle-tip position on the TRUS images. The transformation factor was established through a one-time systematic set of measurements of the probe and template holder positions, applicable to all patients. To compare the accuracy and robustness of the proposed method and the conventional method (ultrasound detection), based on the gold-standard X-ray fluoroscopy, extensive measurements were conducted in water and gel phantoms.
  
  
  RESULTS
  In water phantom, our method showed an average tip-detection accuracy of 0.7 mm compared with 1.6 mm of the conventional method. In gel phantom (more realistic and tissue-like), our method maintained its level of accuracy while the uncertainty of the conventional method was 3.4mm on average with maximum values of over 10mm because of imaging artifacts.
  
  
  CONCLUSIONS
  A novel method based on simple physical measurements was developed to accurately detect the needle-tip position for TRUS-based high-dose-rate prostate brachytherapy. The method demonstrated much improved accuracy and robustness over the conventional method.
authors.affiliation: Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA 23298, USA.
authors.forename: Dandan
authors.initials: D
authors.lastname: Zheng
authors.forename: Dorin A
authors.initials: DA
authors.lastname: Todor
mesh_terms: D000230:Adenocarcinoma / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D001918:Brachytherapy / Q000295:instrumentation*; D006801:Humans; D008297:Male; D008422:Materials Testing; D009339:Needles; D011467:Prostate / Q000000981:diagnostic imaging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012007:Rectum / Q000000981:diagnostic imaging; D015203:Reproducibility of Results; D014463:Ultrasonography / Q000379:methods