title: Dose reduction to anterior surfaces with organ-based tube-current modulation: evaluation of performance in a phantom study.
abstract: OBJECTIVE
  The purpose of this study was to evaluate in phantoms the dose reduction to anterior surfaces and image quality with organ-based tube-current modulation in head and thoracic CT.
  
  
  METHODS
  Organ-based tube-current modulation is designed to reduce radiation dose to superficial radiosensitive organs, such as the lens of the eye, thyroid, and breast, by decreasing the tube current when the tube passes closest to these organs. Dose and image quality were evaluated in phantoms for clinical head and thorax examination protocols with and without organ-based tube-current modulation. Surface dose reduction as a function of position was measured using a 32-cm CT dose index (CTDI) phantom, an anthropomorphic adult phantom, and ion chambers. Surface dose reduction as a function of patient size was investigated using three semianthropomorphic phantoms with posteroanterior dimensions of 14, 25, and 31 cm. Image noise (the SD of CT numbers in regions of interest) was evaluated for the anthropomorphic and the semianthropomorphic phantoms.
  
  
  RESULTS
  For equivalent scanner output (volume CTDI), the dose to the midline of the anterior surface was reduced by 27-50%, depending on the anatomic region (head or thorax) and phantom size, and the dose to the posterior surface was correspondingly increased. Image noise was not significantly different between scans with and without organ-based tube-current modulation (p = 0.85).
  
  
  CONCLUSIONS
  Organ-based tube-current modulation can reduce the dose to the anterior surface of patients without increasing image noise by commensurately increasing the dose to the posterior surface. This technique can reduce the dose to anterior radiosensitive organs for head and thoracic CT scans.
authors.affiliation: Department of Radiology, CT Clinical Innovation Center, Mayo Clinic, 200 First St SW, Rochester, MN 55905, USA.
authors.forename: Xinhui
authors.initials: X
authors.lastname: Duan
authors.forename: Jia
authors.initials: J
authors.lastname: Wang
authors.forename: Jodie A
authors.initials: JA
authors.lastname: Christner
authors.forename: Shuai
authors.initials: S
authors.lastname: Leng
authors.forename: Katharine L
authors.initials: KL
authors.lastname: Grant
authors.forename: Cynthia H
authors.initials: CH
authors.lastname: McCollough
mesh_terms: D006257:Head / Q000528:radiation effects; D006801:Humans; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011835:Radiation Protection / Q000379:methods*; D011874:Radiometry / Q000379:methods; D013909:Thorax / Q000528:radiation effects; D014057:Tomography, X-Ray Computed / Q000295:instrumentation*