title: CT dosimetry considerations in non typical conditions: the effect of scan field of view and table height selection.
abstract: OBJECTIVE
  To experimentally investigate the effect of the scan field of view (SFOV) selection and table height settings on the Computed Tomography Dose Index (CTDI) and the implications concerning patient effective and skin dose.
  
  
  METHODS
  Air-kerma length product (AKLP) measurements were carried out in a helical CT scanner using a pencil type dosimeter positioned in air and inside the holes of a head and a body phantom, using all available SFOV selections and different table height settings. Furthermore, using radiotherapy verification films placed on the CT table surface, the entrance surface air kerma (ESAK) profiles were derived with different SFOV and table height selections, both with and without a phantom on top of the films.
  
  
  RESULTS
  The AKLP is strongly dependent on the SFOV selection and the table height settings. Different SFOV selections correspond to the selection of different bowtie filters that shape the X-ray beam intensity, resulting in different ESAK values at the isocenter and at the other points within the scanning plane. With the off-center positioning the calculated CTDI values within the center and the periphery of the phantom change also, as a result of the different intensity and width of the X-ray beam to which are exposed to.
  
  
  CONCLUSIONS
  The existing protocols for calculating effective dose are limited to only two patient anatomy-SFOV combinations and cannot account for off-center positioning. Therefore, more work will be required to estimate the effective and skin dose for non-standard SFOV-patient anatomy combinations and off-center patient positioning.
authors: Medical Physics Department, Agios Savvas Hospital, 171 Alexandras Avenue, 115 22 Athens, Greece. j_tsalas@hotmail.com
authors: Ioannis A
authors: IA
authors: Tsalafoutas
authors: Paraskevi
authors: P
authors: Georgolopoulou
authors: Ioannis
authors: I
authors: Abatzoglou
mesh_terms: D016477:Artifacts; D005373:Film Dosimetry; D011829:Radiation Dosage; D014057:Tomography, X-Ray Computed / Q000295:instrumentation*