title: Effect of patient size on radiation dose for abdominal MDCT with automatic tube current modulation: phantom study.
abstract: OBJECTIVE
  The purpose of this study was to evaluate in a phantom study the effect of patient size on radiation dose for abdominal MDCT with automatic tube current modulation.
  
  
  METHODS
  One or two 4-cm-thick circumferential layers of fat-equivalent material were added to the abdomen of an anthropomorphic phantom to simulate patients of three sizes: small (cross-sectional dimensions, 18 x 22 cm), average size (26 x 30 cm), and oversize (34 x 38 cm). Imaging was performed with a 64-MDCT scanner with combined z-axis and xy-axis tube current modulation according to two protocols: protocol A had a noise index of 12.5 H, and protocol B, 15.0 H. Radiation doses to three abdominal organs and the skin were assessed. Image noise also was measured.
  
  
  RESULTS
  Despite increasing patient size, the image noise measured was similar for protocol A (range, 11.7-12.2 H) and protocol B (range, 13.9-14.8 H) (p > 0.05). With the two protocols, in comparison with the dose of the small patient, the abdominal organ doses of the average-sized patient and the oversized patient increased 161.5-190.6%and 426.9-528.1%, respectively (p < 0.001). The skin dose increased as much as 268.6% for the average-sized patient and 816.3% for the oversized patient compared with the small patient (p < 0.001).
  
  
  CONCLUSIONS
  Oversized patients undergoing abdominal MDCT with tube current modulation receive significantly higher doses than do small patients. The noise index needs to be adjusted to the body habitus to ensure dose efficiency.
authors.affiliation: Department of Diagnostic Radiology, University Hospital of Bern, Bern, Switzerland.
authors.forename: Sebastian T
authors.initials: ST
authors.lastname: Schindera
authors.forename: Rendon C
authors.initials: RC
authors.lastname: Nelson
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Toth
authors.forename: Giao T
authors.initials: GT
authors.lastname: Nguyen
authors.forename: Greta I
authors.initials: GI
authors.lastname: Toncheva
authors.forename: David M
authors.initials: DM
authors.lastname: DeLong
authors.forename: Terry T
authors.initials: TT
authors.lastname: Yoshizumi
mesh_terms: D001822:Body Burden; D049628:Body Size; D006801:Humans; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011860:Radiography, Abdominal / Q000379:methods*; D011874:Radiometry / Q000379:methods*; D012062:Relative Biological Effectiveness; D013223:Statistics as Topic; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods*