title: Sigmoid colon is an unexpected organ at risk in brachytherapy for cervix cancer.
abstract: OBJECTIVE
  To identify organs at risk (OAR) and analyze the dose volume histograms (DVHs) for intracavitary brachytherapy in cancer of the cervix. Late toxicities are our concern in treatment of cancer cervix especially as it is presenting in younger age population.
  
  
  METHODS
  Patients with cancer of the cervix were treated using CT and MRI compatible, high dose rate, (HDR) applicators. CT images were acquired with the intra-uterine tube and colpostats in place and subsequently imported into Varian Brachyvision planning software. We identified the gross tumour volume (GTV) and organs at risk (OARs) and analyzed the dose distribution using dose volume histograms (DVHs). Doses were calculated according to ICRU 38. Critical tissue DVHs were analysed following the American Brachytherapy Society rules. Dose points are recorded as the dose encompassed by the greatest contiguous 1 cm3, 2 cm3, and 5 cm3 volumes in the plan.
  
  
  RESULTS
  We found the sigmoid colon to be a relatively immobile structure that repeatedly received doses in excess of 70% of the intended point A dose. The only solution in order to bring sigmoid DVHs within 5% toxicity limits was to reduce the dose to point A. Planning images and DVHs for the OARs are shown as an example of our work.
  
  
  CONCLUSIONS
  The recto-sigmoid colon is identified as an unexpected OAR in a majority of cervix brachytherapy plans. A new consensus on the DVH limit of this structure will be needed in the era of CT planned brachytherapy, if arbitrary dose reductions to point A are to be the solution to the problem of sigmoid DVHs that exceed conventional tolerance limits.
authors.affiliation: The Department of Clinical Oncology, Bristol Haematology and Oncology Centre, Bristol, United Kingdom. hodabooz@doctors,org.uk
authors.forename: Hoda
authors.initials: H
authors.lastname: Al-Booz
authors.forename: Ion
authors.initials: I
authors.lastname: Boiangiu
authors.forename: Helen
authors.initials: H
authors.lastname: Appleby
authors.forename: Chris
authors.initials: C
authors.lastname: French
authors.forename: Helen
authors.initials: H
authors.lastname: Coomber
authors.forename: Pauline
authors.initials: P
authors.lastname: Humphery
authors.forename: Paul
authors.initials: P
authors.lastname: Cornes
mesh_terms: D000328:Adult; D000368:Aged; D001918:Brachytherapy / Q000009:adverse effects*; D012809:Colon, Sigmoid / Q000528:radiation effects*; D005260:Female; D006801:Humans; D008875:Middle Aged; D011879:Radiotherapy Dosage; D002583:Uterine Cervical Neoplasms / Q000532:radiotherapy*