title: Use of cone-beam imaging to correct for catheter displacement in high dose-rate prostate brachytherapy.
abstract: OBJECTIVE
  To determine the magnitude of catheter displacement between time of planning and time of treatment delivery for patients undergoing high dose-rate (HDR) brachytherapy, the dosimetric impact of catheter displacement, and the ability to improve dosimetry by catheter readjustment.
  
  
  METHODS
  Twenty consecutive patients receiving single fraction HDR brachytherapy underwent kilovoltage cone-beam CT in the treatment room before treatment. If catheter displacement was apparent, catheters were adjusted and imaging repeated. Both sets of kilovoltage cone-beam CT image sets were coregistered off-line with the CT data set used for planning with rigid fusion of anatomy based on implanted fiducials. Catheter displacement was measured on both sets of images and dosimetry calculated.
  
  
  RESULTS
  Mean internal displacement of catheters was 11mm. This would have resulted in a decrease in mean volume receiving 100% of prescription dose (V(100)) from the planned 97.6% to 77.3% (p<0.001), a decrease of the mean dose to 90% of the prostate (D(90)) from 110.5% to 72.9% (p<0.001), and increase in dose to 10% of urethra (urethra D(10)) from 118% to 125% (p=0.0094). Each 1cm of catheter displacement resulted in a 20% decrease in V(100) and 36% decrease in D(90). Catheter readjustment resulted in a final treated mean V(100) of 90.2% and D(90) of 97.4%, both less than planned. Mean urethra D(10) remained higher at126% (p=0.0324).
  
  
  CONCLUSIONS
  Significantly, internal displacement of HDR catheters commonly occurs between time of CT planning and treatment delivery, even when only a single fraction is used. The adverse effects on dosimetry can be partly corrected by readjustment of catheter position.
authors.affiliation: Department of Medical Physics, Odette Cancer Centre, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Rick
authors.initials: R
authors.lastname: Holly
authors.forename: Gerard C
authors.initials: GC
authors.lastname: Morton
authors.forename: Raxa
authors.initials: R
authors.lastname: Sankreacha
authors.forename: Niki
authors.initials: N
authors.lastname: Law
authors.forename: Thomas
authors.initials: T
authors.lastname: Cisecki
authors.forename: D Andrew
authors.initials: DA
authors.lastname: Loblaw
authors.forename: Hans T
authors.initials: HT
authors.lastname: Chung
mesh_terms: D001918:Brachytherapy / Q000295:instrumentation*; D057785:Catheters; D054893:Cone-Beam Computed Tomography; D057918:Fiducial Markers; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000175:diagnosis / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D016896:Treatment Outcome