title: Contouring and constraining bowel on a full-bladder computed tomography scan may not reflect treatment bowel position and dose certainty in gynecologic external beam radiation therapy.
abstract: OBJECTIVE
  To evaluate, in a gynecologic cancer setting, changes in bowel position, dose-volume parameters, and biological indices that arise between full-bladder (FB) and empty-bladder (EB) treatment situations; and to evaluate, using cone beam computed tomography (CT), the validity of FB treatment presumption.
  
  
  METHODS
  Seventeen gynecologic cancer patients were retrospectively analyzed. Empty-bladder and FB CTs were obtained. Full-bladder CTs were used for planning and dose optimization. Patients were given FB instructions for treatment. For the study purpose, bowel was contoured on the EB CTs for all patients. Bowel position and volume changes between FB and EB states were determined. Full-bladder plans were applied on EB CTs for determining bowel dose-volume changes in EB state. Biological indices (generalized equivalent uniform dose and normal tissue complication probability) were calculated and compared between FB and EB. Weekly cone beam CT data were available in 6 patients to assess bladder volume at treatment.
  
  
  RESULTS
  Average (±SD) planned bladder volume was 299.7 ± 68.5 cm(3). Median bowel shift in the craniocaudal direction between FB and EB was 12.5 mm (range, 3-30 mm), and corresponding increase in exposed bowel volume was 151.3 cm(3) (range, 74.3-251.4 cm(3)). Absolute bowel volumes receiving 45 Gy were higher for EB compared with FB (mean 328.0 ± 174.8 vs 176.0 ± 87.5 cm(3); P=.0038). Bowel normal tissue complication probability increased 1.5× to 23.5× when FB planned treatments were applied in the EB state. For the study, the mean percentage value of relative bladder volume at treatment was 32%.
  
  
  CONCLUSIONS
  Full-bladder planning does not necessarily translate into FB treatments, with a patient tendency toward EB. Given the uncertainty in daily control over bladder volume for treatment, we strongly recommend a "planning-at-risk volume bowel" (PRV_Bowel) concept to account for bowel motion between FB and EB that can be tailored for the individual patient.
authors.affiliation: Department of Radiation Oncology, Montefiore Medical Center and the Albert Einstein College of Medicine, Bronx, New York. Electronic address: ryaparpa@montefiore.org.
authors.forename: Ravindra
authors.initials: R
authors.lastname: Yaparpalvi
authors.affiliation: Department of Radiation Oncology, Montefiore Medical Center and the Albert Einstein College of Medicine, Bronx, New York.
authors.forename: Keyur J
authors.initials: KJ
authors.lastname: Mehta
authors.affiliation: Department of Radiation Oncology, Montefiore Medical Center and the Albert Einstein College of Medicine, Bronx, New York.
authors.forename: Michael B
authors.initials: MB
authors.lastname: Bernstein
authors.affiliation: Department of Radiation Oncology, Montefiore Medical Center and the Albert Einstein College of Medicine, Bronx, New York.
authors.forename: Rafi
authors.initials: R
authors.lastname: Kabarriti
authors.affiliation: Department of Radiation Oncology, Montefiore Medical Center and the Albert Einstein College of Medicine, Bronx, New York.
authors.forename: Linda X
authors.initials: LX
authors.lastname: Hong
authors.affiliation: Department of Radiation Oncology, Montefiore Medical Center and the Albert Einstein College of Medicine, Bronx, New York.
authors.forename: Madhur K
authors.initials: MK
authors.lastname: Garg
authors.affiliation: Department of Radiation Oncology, Montefiore Medical Center and the Albert Einstein College of Medicine, Bronx, New York.
authors.forename: Chandan
authors.initials: C
authors.lastname: Guha
authors.affiliation: Department of Radiation Oncology, Montefiore Medical Center and the Albert Einstein College of Medicine, Bronx, New York.
authors.forename: Shalom
authors.initials: S
authors.lastname: Kalnicki
authors.affiliation: Department of Radiation Oncology, Montefiore Medical Center and the Albert Einstein College of Medicine, Bronx, New York.
authors.forename: Wolfgang A
authors.initials: WA
authors.lastname: Tomé
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D016889:Endometrial Neoplasms / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D007422:Intestines / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D008875:Middle Aged; D009929:Organ Size; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods*; D012189:Retrospective Studies; D001743:Urinary Bladder / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D002583:Uterine Cervical Neoplasms / Q000532:radiotherapy*