title: Interfractional renal and diaphragmatic position variation during radiotherapy in children and adults: is there a difference?
abstract: BACKGROUND
  Pediatric safety margins are generally based on data from adult studies; however, adult-based margins might be too large for children. The aim of this study was to quantify and compare interfractional organ position variation in children and adults.
  
  
  METHODS
  For 35 children and 35 adults treated with thoracic/abdominal irradiation, 850 (range 5-30 per patient) retrospectively collected cone beam CT images were registered to the reference CT that was used for radiation treatment planning purposes. Renal position variation was assessed in three orthogonal directions and summarized as 3D vector lengths. Diaphragmatic position variation was assessed in the cranio-caudal (CC) direction only. We calculated means and SDs to estimate group systematic (Σ) and random errors (σ) of organ position variation. Finally, we investigated possible correlations between organ position variation and patients' height.
  
  
  RESULTS
  Interfractional organ position variation was different in children and adults. Median 3D right and left kidney vector lengths were significantly smaller in children than in adults (2.8, 2.9 mm vs. 5.6, 5.2 mm, respectively; p < .05). Generally, the pediatric Σ and σ were significantly smaller than in adults (p < .007). Overall and within both subgroups, organ position variation and patients' height were only negligibly correlated.
  
  
  CONCLUSIONS
  Interfractional renal and diaphragmatic position variation in children is smaller than in adults indicating that pediatric margins should be defined differently from adult margins. Underlying mechanisms and other components of geometrical uncertainties need further investigation to explain differences and to appropriately define pediatric safety margins.
authors.affiliation: a Department of Radiation Oncology , Academic Medical Center, University of Amsterdam , Amsterdam , The Netherlands.
authors.forename: Irma W E M
authors.initials: IWEM
authors.lastname: van Dijk
authors.affiliation: a Department of Radiation Oncology , Academic Medical Center, University of Amsterdam , Amsterdam , The Netherlands.
authors.forename: Sophie C
authors.initials: SC
authors.lastname: Huijskens
authors.affiliation: a Department of Radiation Oncology , Academic Medical Center, University of Amsterdam , Amsterdam , The Netherlands.
authors.forename: Rianne
authors.initials: R
authors.lastname: de Jong
authors.affiliation: a Department of Radiation Oncology , Academic Medical Center, University of Amsterdam , Amsterdam , The Netherlands.
authors.forename: Jorrit
authors.initials: J
authors.lastname: Visser
authors.affiliation: a Department of Radiation Oncology , Academic Medical Center, University of Amsterdam , Amsterdam , The Netherlands.
authors.forename: Raquel Dávila
authors.initials: RD
authors.lastname: Fajardo
authors.affiliation: a Department of Radiation Oncology , Academic Medical Center, University of Amsterdam , Amsterdam , The Netherlands.
authors.forename: Coen R N
authors.initials: CRN
authors.lastname: Rasch
authors.affiliation: a Department of Radiation Oncology , Academic Medical Center, University of Amsterdam , Amsterdam , The Netherlands.
authors.forename: Tanja
authors.initials: T
authors.lastname: Alderliesten
authors.affiliation: a Department of Radiation Oncology , Academic Medical Center, University of Amsterdam , Amsterdam , The Netherlands.
authors.forename: Arjan
authors.initials: A
authors.lastname: Bel
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D003964:Diaphragm / Q000528:radiation effects*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D007223:Infant; D007231:Infant, Newborn; D007668:Kidney / Q000528:radiation effects*; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000532:radiotherapy*; D058958:Organs at Risk / Q000528:radiation effects*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods; D055815:Young Adult