title: Measuring skin dose in CT examinations under complex geometries: Instruments, methods and considerations.
abstract: OBJECTIVE
  To investigate skin dose in Computed Tomography (CT) and its dependence on scanning geometry.
  
  
  METHODS
  Measurements of entrance surface air kerma (ESAK) in free air and entrance skin dose (ESD) on an anthropomorphic phantom were performed in a 64-slice CT scanner, using two different instruments: the Dose Profiler (DP) and the QED skin diode (QEDSD). Using DP and QEDSD, the ESAK rate profiles at the isocenter and at different distances from it, were measured using axial scans. Using DP and helical scans the ESAK rate profile in the Z-axis was acquired. The same profile was acquired with the QEDSD also, using many axial scans and manual table translation. ESD measurements were performed with the DP and QEDSD, in axial and helical scan mode.
  
  
  RESULTS
  ESAK measurements with DP and QEDSD were in good agreement, for both point dose and profile measurements. The agreement was also good for ESD measurements but not for helical scans, due to variable X-ray beam overlapping and different tube angular positions at each scan start. It was observed that the ESD values at different Y-axis offsets were comparable to the respective ESAK values recorded at the same Y-axis offset distances without the phantom.
  
  
  CONCLUSIONS
  Both DP and QEDSD were proven suitable for performing point ESD measurements. However, calculating the skin dose distribution in CT examinations is a very challenging task. A practical approach would be for CT scanners to provide a conservative estimate of the peak skin dose using the isocenter ESAK value.
authors.affiliation: Medical Physics Department, Agios Savvas Hospital, 171 Alexandras Av, 115 22, Athens, Greece. Electronic address: j_tsalas@hotmail.com.
authors.forename: I A
authors.initials: IA
authors.lastname: Tsalafoutas
authors.affiliation: Medical Physics Department, Agios Savvas Hospital, 171 Alexandras Av, 115 22, Athens, Greece.
authors.forename: A
authors.initials: A
authors.lastname: Epistatou
authors.affiliation: Raymed & Co LTD, Maroussi, Athens 15125, Greece.
authors.forename: S
authors.initials: S
authors.lastname: Nikoletopoulos
authors.affiliation: Medical Physics Unit, Konstantopoulio Hospital, Nea Ionia, Athens 142 33, Greece.
authors.forename: V
authors.initials: V
authors.lastname: Tsapaki
mesh_terms: D000388:Air; D006801:Humans; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011874:Radiometry / Q000295:instrumentation / Q000379:methods*; D012867:Skin / Q000528:radiation effects*; D013499:Surface Properties; D014057:Tomography, X-Ray Computed
keywords: CT; ESD; Interventional; Skin dose