title: Small bowel dose parameters predicting grade ≥ 3 acute toxicity in rectal cancer patients treated with neoadjuvant chemoradiation: an independent validation study comparing peritoneal space versus small bowel loop contouring techniques.
abstract: OBJECTIVE
  To determine whether volumes based on contours of the peritoneal space can be used instead of individual small bowel loops to predict for grade ≥3 acute small bowel toxicity in patients with rectal cancer treated with neoadjuvant chemoradiation therapy.
  
  
  METHODS
  A standardized contouring method was developed for the peritoneal space and retrospectively applied to the radiation treatment plans of 67 patients treated with neoadjuvant chemoradiation therapy for rectal cancer. Dose-volume histogram (DVH) data were extracted and analyzed against patient toxicity. Receiver operating characteristic analysis and logistic regression were carried out for both contouring methods.
  
  
  RESULTS
  Grade ≥3 small bowel toxicity occurred in 16% (11/67) of patients in the study. A highly significant dose-volume relationship between small bowel irradiation and acute small bowel toxicity was supported by the use of both small bowel loop and peritoneal space contouring techniques. Receiver operating characteristic analysis demonstrated that, for both contouring methods, the greatest sensitivity for predicting toxicity was associated with the volume receiving between 15 and 25 Gy.
  
  
  CONCLUSIONS
  DVH analysis of peritoneal space volumes accurately predicts grade ≥3 small bowel toxicity in patients with rectal cancer receiving neoadjuvant chemoradiation therapy, suggesting that the contours of the peritoneal space provide a reasonable surrogate for the contours of individual small bowel loops. The study finds that a small bowel V15 less than 275 cc and a peritoneal space V15 less than 830 cc are associated with a less than 10% risk of grade ≥3 acute toxicity.
authors.affiliation: Department of Radiation Oncology, Tom Baker Cancer Centre, University of Calgary, Calgary, Alberta, Canada. robynbanerjee@gmail.com
authors.forename: Robyn
authors.initials: R
authors.lastname: Banerjee
authors.forename: Santam
authors.initials: S
authors.lastname: Chakraborty
authors.forename: Ian
authors.initials: I
authors.lastname: Nygren
authors.forename: Richie
authors.initials: R
authors.lastname: Sinha
mesh_terms: D000964:Antimetabolites, Antineoplastic / Q000008:administration & dosage; D059186:Chemoradiotherapy, Adjuvant / Q000009:adverse effects* / Q000379:methods; D005260:Female; D005472:Fluorouracil / Q000008:administration & dosage; D006801:Humans; D007421:Intestine, Small / Q000000981:diagnostic imaging* / Q000528:radiation effects; D008297:Male; D008875:Middle Aged; D020360:Neoadjuvant Therapy / Q000009:adverse effects* / Q000379:methods; D058958:Organs at Risk / Q000000981:diagnostic imaging / Q000528:radiation effects; D010529:Peritoneal Cavity / Q000000981:diagnostic imaging* / Q000528:radiation effects; D012372:ROC Curve; D011832:Radiation Injuries / Q000473:pathology*; D011859:Radiography; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D012004:Rectal Neoplasms / Q000628:therapy*; D012044:Regression Analysis; D012189:Retrospective Studies; D012737:Sex Factors
chemical_list: D000964:Antimetabolites, Antineoplastic; D005472:Fluorouracil