title: Small bowel protection in IMRT for rectal cancer : A dosimetric study on supine vs. prone position.
abstract: BACKGROUND
  This treatment planning study analyzes dose coverage and dose to organs at risk (OAR) in intensity-modulated radiotherapy (IMRT) of rectal cancer and compares prone vs. supine positioning as well as the effect of dose optimization for the small bowel (SB) by additional dose constraints in the inverse planning process.
  
  
  METHODS
  Based on the CT datasets of ten male patients in both prone and supine position, a total of four different IMRT plans were created for each patient. OAR were defined as the SB, bladder, and femoral heads. In half of the plans, two additional SB cost functions were used in the inverse planning process.
  
  
  RESULTS
  There was a statistically significant dose reduction for the SB in prone position of up to 41% in the high and intermediate dose region, compared with the supine position. Furthermore, the femoral heads showed a significant dose reduction in prone position in the low dose region. Regarding the additional active SB constraints, the dose in the high dose region of the SB was significantly reduced by up to 14% with the additional cost functions. There were no significant differences in the dose distribution of the planning target volume (PTV) and the bladder.
  
  
  CONCLUSIONS
  Prone positioning can significantly reduce dose to the SB in IMRT for rectal cancer and therefore should not only be used in 3D conformal radiotherapy but also in IMRT of rectal cancer. Further protection of the SB can be achieved by additional dose constraints in inverse planning without jeopardizing the homogeneity of the PTV.
authors.affiliation: Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Theodor-Kutzer-Ufer 1-3, 68135, Mannheim, Germany. julia_koeck@gmx.net.
authors.forename: Julia
authors.identifier: http://orcid.org/0000-0003-0510-8574
authors.initials: J
authors.lastname: Koeck
authors.affiliation: Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Theodor-Kutzer-Ufer 1-3, 68135, Mannheim, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Kromer
authors.affiliation: Unita Operativa di Radioterapia, Dipartimento di Oncologia, Az. Ospedaliero-Universitaria di Modena, Modena, Italy.
authors.forename: Frank
authors.initials: F
authors.lastname: Lohr
authors.affiliation: Department of Internal Medicine, GRN Clinic Weinheim, Weinheim, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Baack
authors.affiliation: Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Theodor-Kutzer-Ufer 1-3, 68135, Mannheim, Germany.
authors.forename: Kerstin
authors.initials: K
authors.lastname: Siebenlist
authors.affiliation: Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Theodor-Kutzer-Ufer 1-3, 68135, Mannheim, Germany.
authors.forename: Sabine
authors.initials: S
authors.lastname: Mai
authors.affiliation: Department of Biomathematics and Medical Statistics, University Medical Center Mannheim, University of Heidelberg, Mannheim, Germany.
authors.forename: Sylvia
authors.initials: S
authors.lastname: Büttner
authors.affiliation: Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Theodor-Kutzer-Ufer 1-3, 68135, Mannheim, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Fleckenstein
authors.affiliation: Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Theodor-Kutzer-Ufer 1-3, 68135, Mannheim, Germany.
authors.forename: Frederik
authors.initials: F
authors.lastname: Wenz
mesh_terms: D015179:Colorectal Neoplasms / Q000532:radiotherapy*; D005270:Femur Head / Q000528:radiation effects; D006801:Humans; D007421:Intestine, Small / Q000528:radiation effects*; D008297:Male; D058958:Organs at Risk / Q000528:radiation effects; D056888:Patient Positioning; D016684:Prone Position; D011832:Radiation Injuries / Q000209:etiology* / Q000517:prevention & control*; D011835:Radiation Protection; D011874:Radiometry; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects* / Q000379:methods*; D016683:Supine Position; D001743:Urinary Bladder / Q000528:radiation effects
keywords: Intensity-modulated therapy; Inverse planning; Prone position; Rectal cancer; Small intestine