title: Seed misplacement and stabilizing needles in transperineal permanent prostate implants.
abstract: OBJECTIVE
  Seed misplacement occurring in transperineal permanent implants contributes to the degradation in dose coverage. It has been suggested that needles could be used to immobilize the prostate and help reduce misplacement. This study investigates the effects of parallel stabilizing needles on seed misplacement.
  
  
  METHODS
  A group of ten patients implanted with stabilizing needles was compared with a group of 20 patients implanted without stabilization. Measurements were performed on the displacement of individual seeds and needles. The needle measurements are: insertion angle, the ratio of post-implant over pre-implant lengths and the clustering tendency, a measure of relative misplacement among the seeds of the same needle.
  
  
  RESULTS
  No difference was observed in seed misplacement. No difference was observed in needle insertion angle, a measure which was expected to improve with the use of stabilizing needles.
  
  
  CONCLUSIONS
  None of the expected effects from the use of parallel stabilizing needles have been observed. This method of prostate contention appears to be without benefits. Seed misplacement is most pronounced along the insertion axis and is caused by friction between prostatic tissues and implantation needles. Reducing friction could be a promising alternative to prostate contention in trying to reduce misplacement.
authors.affiliation: Département de Radio-Oncologie, Centre de Recherche en Cancérologie de l'Université Laval, Centre Hospitalier Universitaire de Québec (CHUQ), Pavilion l'Hôtel-Dieu de Québec, 11 Côte du Palais, Québec, Canada.
authors.forename: R
authors.initials: R
authors.lastname: Taschereau
authors.forename: J
authors.initials: J
authors.lastname: Pouliot
authors.forename: J
authors.initials: J
authors.lastname: Roy
authors.forename: D
authors.initials: D
authors.lastname: Tremblay
mesh_terms: D000465:Algorithms; D001918:Brachytherapy / Q000295:instrumentation*; D017276:Friction; D006801:Humans; D008297:Male; D009339:Needles; D010502:Perineum; D011467:Prostate / Q000528:radiation effects; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D012399:Rotation; D018709:Statistics, Nonparametric