title: A comparison of ICRU point doses and volumetric doses of organs at risk (OARs) in brachytherapy for cervical cancer.
abstract: BACKGROUND
  In brachytherapy for cervix cancer, doses to organs at risk (OARs) are traditionally calculated using the ICRU-38 point doses to rectum and bladder. Three-dimensional image-guided brachytherapy allows assessment of OAR dose with dose volume histograms (DVHs). The purpose of this study was to analyse the correlation between DVHs and ICRU point doses.
  
  
  METHODS
  Using the PLATO™ planning system, the bladder, rectum and sigmoid were retrospectively contoured on 62 CT datasets for 20 patients treated with definitive radiotherapy. The median external beam radiotherapy dose was 45 Gy. Brachytherapy was delivered using a CT-MRI compatible tandem and ovoids to a median dose of 24 Gy in three fractions. DVHs were calculated, and the minimum dose to 2 cc of tissue receiving the highest dose (D(2cc) ) was recorded and compared with the ICRU point doses (D(ICRU) ).
  
  
  RESULTS
  The mean rectal D(ICRU) was 4.01 Gy compared with D(2cc) of 4.28 Gy. The mean bladder D(ICRU) was 6.74 Gy compared with D(2cc) of 8.65 Gy. The mean sigmoid D(2cc) was 4.58 Gy. The mean dose ratios (D(2cc) /D(ICRU) ) were 1.08 for rectum and 1.39 for bladder. D(ICRU) correlated with D(2cc) for rectum (r = 0.76, P = 0.001) and for bladder (r = 0.78, P = 0.01).
  
  
  CONCLUSIONS
  OAR doses assessed by DVH criteria were higher than ICRU point doses. The significant correlation between D(2cc) and D(ICRU) has allowed us to set DVH dose constraints for CT-based brachytherapy and thus begin the transition from two-dimensional to three-dimensional image-guided brachytherapy planning.
authors.affiliation: Cancer Therapy Centre, Liverpool Hospital University of New South Wales Collaboration for Cancer Outcomes, Research and Evaluation (CCORE), Sydney, New South Wales, Australia. shalini.vinod@sswahs.nsw.gov.au
authors.forename: Shalini K
authors.initials: SK
authors.lastname: Vinod
authors.forename: Kate
authors.initials: K
authors.lastname: Caldwell
authors.forename: Annie
authors.initials: A
authors.lastname: Lau
authors.forename: Allan R
authors.initials: AR
authors.lastname: Fowler
mesh_terms: D000230:Adenocarcinoma / Q000532:radiotherapy; D000328:Adult; D000368:Aged; D001918:Brachytherapy; D002294:Carcinoma, Squamous Cell / Q000532:radiotherapy; D012809:Colon, Sigmoid / Q000528:radiation effects; D005260:Female; D006801:Humans; D008875:Middle Aged; D058958:Organs at Risk / Q000528:radiation effects*; D011829:Radiation Dosage; D011879:Radiotherapy Dosage; D012007:Rectum / Q000528:radiation effects; D001743:Urinary Bladder / Q000528:radiation effects; D002583:Uterine Cervical Neoplasms / Q000532:radiotherapy*