title: Novel assessment of renal motion in children as measured via four-dimensional computed tomography.
abstract: OBJECTIVE
  Abdominal intensity-modulated radiation therapy and proton therapy require quantification of target and organ motion to optimize localization and treatment. Although addressed in adults, there is no available literature on this issue in pediatric patients. We assessed physiologic renal motion in pediatric patients.
  
  
  METHODS
  Twenty free-breathing pediatric patients at a median age of 8 years (range, 2-18 years) with intra-abdominal tumors underwent computed tomography simulation and four-dimensional computed tomography acquisition (slice thickness, 3 mm). Kidneys and diaphragms were contoured during eight phases of respiration to estimate center-of-mass motion. We quantified center of kidney mass mobility vectors in three dimensions: anteroposterior (AP), mediolateral (ML), and superoinferior (SI).
  
  
  RESULTS
  Kidney motion decreases linearly with decreasing age and height. The 95% confidence interval for the averaged minima and maxima of renal motion in children younger than 9 years was 5-9 mm in the ML direction, 4-11 mm in the AP direction, and 12-25 mm in the SI dimension for both kidneys. In children older than 9 years, the same confidence interval reveals a widening range of motion that was 5-16 mm in the ML direction, 6-17 mm in the AP direction, and 21-52 mm in the SI direction. Although not statistically significant, renal motion correlated with diaphragm motion in older patients. The correlation between diaphragm motion and body mass index was borderline (r = 0.52, p = 0.0816) in younger patients.
  
  
  CONCLUSIONS
  Renal motion is age and height dependent. Measuring diaphragmatic motion alone does not reliably quantify pediatric renal motion. Renal motion in young children ranges from 5 to 25 mm in orientation-specific directions. The vectors of motion range from 5 to 52 mm in older children. These preliminary data represent novel analyses of pediatric intra-abdominal organ motion.
authors.affiliation: Department of Radiological Sciences, St. Jude Children's Research Hospital, Memphis, TN, USA. atmaram.pai-panandiker@stjude.org
authors.forename: Atmaram S
authors.initials: AS
authors.lastname: Pai Panandiker
authors.forename: Shelly
authors.initials: S
authors.lastname: Sharma
authors.forename: Mihir H
authors.initials: MH
authors.lastname: Naik
authors.forename: Shengjie
authors.initials: S
authors.lastname: Wu
authors.forename: Chiaho
authors.initials: C
authors.lastname: Hua
authors.forename: Chris
authors.initials: C
authors.lastname: Beltran
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Krasin
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Merchant
mesh_terms: D000008:Abdominal Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D000293:Adolescent; D000367:Age Factors; D001827:Body Height; D015992:Body Mass Index; D002648:Child; D002675:Child, Preschool; D016001:Confidence Intervals; D003964:Diaphragm / Q000000981:diagnostic imaging; D005260:Female; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D007668:Kidney / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D008297:Male; D009068:Movement; D058958:Organs at Risk / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012119:Respiration; D012189:Retrospective Studies