title: Monte Carlo dosimetry of high dose rate gynecologic interstitial brachytherapy.
abstract: OBJECTIVE
  To assess the dosimetric effects of the presence of the applicator, air pockets in clinical target volume (CTV) and OARs along with tissue heterogeneities using the Monte Carlo (MC) method in high dose rate (HDR) gynecologic interstitial brachytherapy with a Syed-Neblett template.
  
  
  METHODS
  The CT based dosimetry has been achieved with the Geant4 MC toolkit version 9.2. DICOM-RT files of 38 patients were imported into our own platform for MC simulations. The dose distributions were then compared to those obtained with a conventional TG-43 calculation.
  
  
  RESULTS
  Taking account of heterogeneities has effects of the order of 1% on the HDR gynecological dose distributions. However, the exclusion of air pockets and applicator from the DVH calculation can lower the CTV D90 and V100 by as much as 8.7% and 5.0% in comparison with TG-43. Rectum dosimetric indices can also be lowered by approximately 3% compared with TG-43 for most cases. Differences for urethra and bladder are for most cases below 1%.
  
  
  CONCLUSIONS
  Exclusion of non-biological material such as air pockets and applicator volume from the CTV is important for both TG-43 and MC calculations. It could be easily implemented and automated in treatment planning systems without affecting computation times.
authors.affiliation: Département de Radio-Oncologie et Centre de Recherche du CHU de Québec, CHU de Québec, Canada; Département de Physique, de Génie Physique et d'optique, et Centre de Recherche sur le Cancer, Université Laval, Canada.
authors.forename: Maxime
authors.initials: M
authors.lastname: Desbiens
authors.forename: Michel
authors.initials: M
authors.lastname: D'Amours
authors.forename: Hossein
authors.initials: H
authors.lastname: Afsharpour
authors.forename: Frank
authors.initials: F
authors.lastname: Verhaegen
authors.forename: Marie-Claude
authors.initials: MC
authors.lastname: Lavallée
authors.forename: Isabelle
authors.initials: I
authors.lastname: Thibault
authors.forename: Éric
authors.initials: É
authors.lastname: Vigneault
authors.forename: Luc
authors.initials: L
authors.lastname: Beaulieu
mesh_terms: D001918:Brachytherapy / Q000379:methods*; D005260:Female; D005833:Genital Neoplasms, Female / Q000532:radiotherapy*; D006801:Humans; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012189:Retrospective Studies
keywords: Brachytherapy; Dosimetry; Gynecologic; HDR; Monte Carlo