title: Dosimetric effect of small bowel oral contrast on conventional radiation therapy, linear accelerator-based intensity modulated radiation therapy, and helical tomotherapy plans for rectal cancer.
abstract: OBJECTIVE
  This study evaluated the dosimetric effect of small bowel oral contrast on conventional radiation therapy, linear accelerator-based intensity modulated radiation therapy (IMRT), and helical tomotherapy (HT) treatment plans.
  
  
  METHODS
  Thirteen patients with rectal cancer underwent computed tomography (CT) simulation with oral contrast (CCT) in preparation for chemoradiation therapy. The contrast in the small bowel was contoured, and a noncontrast CT scan (NCCT) was simulated by reassigning a CT number of 0 Hounsfield units to the contrast volume. Conventional, IMRT, and HT plans were generated with the CCT. The plan generated on the CCT was then recalculated on the NCCT, maintaining the same number of monitor units for each field, and the plans were not renormalized. Dosimetric parameters representing coverage of the planning target volume with 45 Gy (D98%, D95%, D50%, and D2%) and sparing of the bladder and peritoneal cavity (D50%, D30%, and D10%) were recorded. The ratio of dose calculated in the presence of contrast to dose with contrast edited out was recorded for each parameter. A paired Student t test was used for comparison of plans.
  
  
  RESULTS
  For conventional plans, there was <0.1% variance in the dose ratio for all volumes of interest. For IMRT plans, there was a 1% decrease in the mean dose ratio, and the range of dose ratios for all volumes was greater than that for HT or conventional plans. For HT plans, for all volumes of interest, the mean dose ratio was <0.2%, and the range for all patients was <1%. For all IMRT dosimetric parameters, the difference was in the order of 1% of the mean dose (P < .05). The dose difference was not statistically significant for the conventional or HT plans.
  
  
  CONCLUSIONS
  The use of CCT during CT simulation has no clinically significant effect on dose calculations for conventional, IMRT, and HT treatment plans and may not require replacement of the contrast with a CT number of 0 Hounsfield units.
authors.affiliation: Division of Radiation Oncology, Department of Oncology, University of Alberta, and Cross Cancer Institute, Edmonton, Alberta, Canada. Electronic address: kurian.joseph@albertahealthservices.ca.
authors.forename: Kurian
authors.initials: K
authors.lastname: Joseph
authors.affiliation: Division of Medical Physics, Department of Oncology, University of Alberta, and Cross Cancer Institute, Edmonton, Alberta, Canada.
authors.forename: Derek
authors.initials: D
authors.lastname: Liu
authors.affiliation: Division of Radiation Oncology, Department of Oncology, University of Alberta, and Cross Cancer Institute, Edmonton, Alberta, Canada.
authors.forename: Diane
authors.initials: D
authors.lastname: Severin
authors.affiliation: Department of Medical Physics, Cross Cancer Institute, Edmonton, Alberta, Canada.
authors.forename: Mike
authors.initials: M
authors.lastname: Dickey
authors.affiliation: Department of Medical Physics, Cross Cancer Institute, Edmonton, Alberta, Canada.
authors.forename: Lee-Anne
authors.initials: LA
authors.lastname: Polkosnik
authors.affiliation: Division of Medical Physics, Department of Oncology, University of Alberta, and Cross Cancer Institute, Edmonton, Alberta, Canada.
authors.forename: Heather
authors.initials: H
authors.lastname: Warkentin
authors.affiliation: Division of Radiation Oncology, UPMC Beacon Hospital, Dublin, Ireland.
authors.forename: Alina
authors.initials: A
authors.lastname: Mihai
authors.affiliation: Division of Medical Oncology, Department of Oncology, University of Alberta, and Cross Cancer Institute, Edmonton, Alberta, Canada.
authors.forename: Sunita
authors.initials: S
authors.lastname: Ghosh
authors.affiliation: Division of Medical Physics, Department of Oncology, University of Alberta, and Cross Cancer Institute, Edmonton, Alberta, Canada.
authors.forename: Colin
authors.initials: C
authors.lastname: Field
mesh_terms: D000284:Administration, Oral; D003287:Contrast Media; D006801:Humans; D007421:Intestine, Small / Q000033:anatomy & histology*; D010315:Particle Accelerators; D011874:Radiometry / Q000295:instrumentation / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012004:Rectal Neoplasms / Q000532:radiotherapy*; D036542:Tomography, Spiral Computed / Q000295:instrumentation / Q000379:methods
chemical_list: D003287:Contrast Media