title: QCT versus DXA in 320 survivors of childhood cancer: association of BMD with fracture history.
abstract: OBJECTIVE
  To assess agreement on diagnosis of diminished bone mineral density (BMD) and correlation between BMD values obtained by dual-energy X-ray absorptiometry (DXA) and quantitative computed tomography (QCT) in childhood cancer survivors.
  
  
  METHODS
  We retrospectively reviewed lumbar spine QCT and DXA studies for BMD in patients who underwent both imaging studies within a 24-hr period. We determined correlation between BMD values and agreement on diagnosis of diminished BMD obtained by both modalities. Diminished BMD was defined as two or more SDs below mean for age- and gender-matched reference values. We evaluated the relationship of BMD values determined by each modality to self-reported fracture history in the 160 (50%) patients with available reports.
  
  
  RESULTS
  Of 320 patients, 56% (178) were male; 87% (277) were white. Median age was 16.4 (range, 5.1-36.0) years. Median BMD Z-score was -1.43 (range, -5.96 to 3.20) by QCT and -1.30 (range, -5.50 to 2.80) by DXA. Correlation between QCT- and DXA-determined BMD values was significant but low, and agreement on diminished BMD was fair (kappa = 0.32). There was no association between BMD measured by either QCT or DXA and self-reported traumatic fracture history. Male gender was associated with doubling the traumatic fracture risk (P = 0.0499).
  
  
  CONCLUSIONS
  Quantitative computed tomography and DXA may give discrepant results when used to assess bone health in childhood cancer survivors, especially in those of non-white race. This inconsistency in indicators of BMD deficiency may complicate clinical decision-making. Consecutive use of a single modality is recommended to provide reliable longitudinal information.
authors.affiliation: Department of Radiological Sciences, St. Jude Children's Research Hospital, Memphis, Tennessee 38105-2794, USA. sue.kaste@stjude.org
authors.forename: Sue C
authors.initials: SC
authors.lastname: Kaste
authors.forename: Xin
authors.initials: X
authors.lastname: Tong
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Hendrick
authors.forename: Evguenia J
authors.initials: EJ
authors.lastname: Karimova
authors.forename: Deo Kumar
authors.initials: DK
authors.lastname: Srivastava
authors.forename: Frances A
authors.initials: FA
authors.lastname: Tylavsky
authors.forename: Terry L
authors.initials: TL
authors.lastname: Snider
authors.forename: Laura D
authors.initials: LD
authors.lastname: Carbone
mesh_terms: D015502:Absorptiometry, Photon; D000293:Adolescent; D000328:Adult; D015519:Bone Density; D002648:Child; D002675:Child, Preschool; D005260:Female; D050723:Fractures, Bone / Q000209:etiology*; D006801:Humans; D008297:Male; D009369:Neoplasms / Q000150:complications*; D012189:Retrospective Studies; D017741:Survivors; D014057:Tomography, X-Ray Computed