title: Defining bowel dose volume constraints for bladder radiotherapy treatment planning.
abstract: OBJECTIVE
  Increases to radiotherapy dose are constrained by normal tissue effects. The relationship between bowel dose volume data and late bowel toxicity in patients with muscle-invasive bladder cancer treated with radical radiotherapy was assessed.
  
  
  METHODS
  The bowel was contoured retrospectively on radiotherapy plans of 47 patients recruited to the BC2001 trial (CRUK/01/004). The relationship between bowel volume at various dose levels and prospectively collected late bowel toxicity was explored.
  
  
  RESULTS
  Fifteen per cent and 6% of patients experienced grade 1 and grade 2 or more late bowel toxicity, respectively. The mean bowel volume was significantly less at doses ≥50 Gy in those treated with reduced high dose volume radiotherapy compared with standard radiotherapy. The probability of late bowel toxicity increased as bowel volume increased (P ≤ 0.05 for dose levels 30-50 Gy). No grade 2 or more late bowel toxicity was observed in patients with bowel volumes under the thresholds given in the model that predict for 25% probability of late bowel toxicity.
  
  
  CONCLUSIONS
  There is a dose volume effect for late bowel toxicity in radical bladder radiotherapy. We have modelled the probability of late bowel toxicity from absolute bowel volumes to guide clinicians in assessing radical bladder radiotherapy plans. Thresholds predicting for a 25% probability of late bowel toxicity are proposed as dose volume constraints.
authors.affiliation: Academic Radiotherapy Unit, Institute of Cancer Research, London, UK; The Royal Marsden NHS Foundation Trust, Sutton, Surrey, UK.
authors.forename: F
authors.initials: F
authors.lastname: McDonald
authors.affiliation: Clinical Trials and Statistics Unit, Institute of Cancer Research, London, UK.
authors.forename: R
authors.initials: R
authors.lastname: Waters
authors.affiliation: Joint Department of Physics, Institute of Cancer Research and Royal Marsden NHS Foundation Trust, Sutton, Surrey, UK.
authors.forename: S
authors.initials: S
authors.lastname: Gulliford
authors.affiliation: Clinical Trials and Statistics Unit, Institute of Cancer Research, London, UK.
authors.forename: E
authors.initials: E
authors.lastname: Hall
authors.affiliation: Clinical Trials Unit Gibbet Hill Campus, University of Warwick, Coventry, UK.
authors.forename: N
authors.initials: N
authors.lastname: James
authors.affiliation: Academic Radiotherapy Unit, Institute of Cancer Research, London, UK; The Royal Marsden NHS Foundation Trust, Sutton, Surrey, UK. Electronic address: Robert.Huddart@icr.ac.uk.
authors.forename: R A
authors.initials: RA
authors.lastname: Huddart
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007422:Intestines / Q000528:radiation effects*; D008297:Male; D008875:Middle Aged; D011832:Radiation Injuries / Q000209:etiology / Q000517:prevention & control; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000009:adverse effects / Q000379:methods; D012189:Retrospective Studies; D001749:Urinary Bladder Neoplasms / Q000532:radiotherapy*
keywords: Bladder radiotherapy; bowel constraints; dose escalation; radiotherapy planning