title: Brachytherapy in endometrial cancer: quantification of air gaps around a vaginal cylinder.
abstract: OBJECTIVE
  Vaginal vault brachytherapy, prescribed to 0.5 cm, is used in endometrial cancer postoperatively to reduce the risk of vault recurrence. However, it is unknown if the vaginal mucosa is closely opposed to the vaginal cylinder, or if air gaps lift the mucosa from the cylinder. The aim of this study was to quantify the extent, magnitude, and effect on dose of any air gaps around the vaginal cylinder using CT-scan images.
  
  
  METHODS
  Twenty-five patients treated between January and December 2005 were included in the study. The brachytherapy was prescribed to 0.5 cm with a reference volume length (RVL) of 4 cm. Pelvic CT scans taken before the first treatment with cylinder in situ were examined for presence of air gaps around the cylinder within the RVL.
  
  
  RESULTS
  The median number of air gaps was 1 (range, 0-5) with a mean average area of 0.20 cm2 (range, 0.02-1.65). This resulted in an average of 0.86% (range, 0-6.3) of the vaginal surface within the RVL being raised from the surface of the cylinder. Over the air gaps, the dose the mucosa received at 0.5 cm was on average 86.7% (range, 54.7-97.3) of that which it would have received if there was no air gap. Overall, the dose at 0.5 cm of the whole vaginal mucosa within the RVL was 99.6% (range, 100-96.0) of that prescribed.
  
  
  CONCLUSIONS
  Most postoperative patients with endometrial cancer do not have any clinically significant air gaps around the vaginal cylinder used to administer brachytherapy to the vaginal vault.
authors.affiliation: Department of Oncology, Bristol Haematology Oncology Centre, Bristol, UK. Alison.cameron@UHbristol.nhs.uk
authors.forename: Alison L
authors.initials: AL
authors.lastname: Cameron
authors.forename: Paul
authors.initials: P
authors.lastname: Cornes
authors.forename: Hoda
authors.initials: H
authors.lastname: Al-Booz
mesh_terms: D001918:Brachytherapy / Q000379:methods*; D015331:Cohort Studies; D003131:Combined Modality Therapy; D016889:Endometrial Neoplasms / Q000532:radiotherapy* / Q000601:surgery; D005260:Female; D006801:Humans; D007044:Hysterectomy; D008198:Lymph Nodes / Q000528:radiation effects*; D015182:Lymphatic Irradiation / Q000379:methods*; D014057:Tomography, X-Ray Computed; D014621:Vagina / Q000000981:diagnostic imaging / Q000528:radiation effects