title: Peak skin and eye lens radiation dose from brain perfusion CT based on Monte Carlo simulation.
abstract: OBJECTIVE
  The purpose of our study was to accurately estimate the radiation dose to skin and the eye lens from clinical CT brain perfusion studies, investigate how well scanner output (expressed as volume CT dose index [CTDI(vol)]) matches these estimated doses, and investigate the efficacy of eye lens dose reduction techniques.
  
  
  METHODS
  Peak skin dose and eye lens dose were estimated using Monte Carlo simulation methods on a voxelized patient model and 64-MDCT scanners from four major manufacturers. A range of clinical protocols was evaluated. CTDI(vol) for each scanner was obtained from the scanner console. Dose reduction to the eye lens was evaluated for various gantry tilt angles as well as scan locations.
  
  
  RESULTS
  Peak skin dose and eye lens dose ranged from 81 mGy to 348 mGy, depending on the scanner and protocol used. Peak skin dose and eye lens dose were observed to be 66-79% and 59-63%, respectively, of the CTDI(vol) values reported by the scanners. The eye lens dose was significantly reduced when the eye lenses were not directly irradiated.
  
  
  CONCLUSIONS
  CTDI(vol) should not be interpreted as patient dose; this study has shown it to overestimate dose to the skin or eye lens. These results may be used to provide more accurate estimates of actual dose to ensure that protocols are operated safely below thresholds. Tilting the gantry or moving the scanning region further away from the eyes are effective for reducing lens dose in clinical practice. These actions should be considered when they are consistent with the clinical task and patient anatomy.
authors.affiliation: Department of Radiological Sciences, UCLA David Geffen School of Medicine, Los Angeles, CA, USA. skintchenzhang@gmail.com
authors.forename: Di
authors.initials: D
authors.lastname: Zhang
authors.forename: Chris H
authors.initials: CH
authors.lastname: Cagnon
authors.forename: J Pablo
authors.initials: JP
authors.lastname: Villablanca
authors.forename: Cynthia H
authors.initials: CH
authors.lastname: McCollough
authors.forename: Dianna D
authors.initials: DD
authors.lastname: Cody
authors.forename: Donna M
authors.initials: DM
authors.lastname: Stevens
authors.forename: Maria
authors.initials: M
authors.lastname: Zankl
authors.forename: John J
authors.initials: JJ
authors.lastname: Demarco
authors.forename: Adam C
authors.initials: AC
authors.lastname: Turner
authors.forename: Maryam
authors.initials: M
authors.lastname: Khatonabadi
authors.forename: Michael F
authors.initials: MF
authors.lastname: McNitt-Gray
mesh_terms: D001921:Brain / Q000000981:diagnostic imaging*; D002985:Clinical Protocols; D006801:Humans; D007908:Lens, Crystalline / Q000528:radiation effects*; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011832:Radiation Injuries / Q000517:prevention & control; D011874:Radiometry / Q000379:methods; D012867:Skin / Q000528:radiation effects*; D014057:Tomography, X-Ray Computed / Q000379:methods*