A contribution to the establishment of diagnostic reference levels in CT

CT has become the major source of population exposure to diagnostic X-rays. CT dose index (CTDI) and dose-length product (DLP) have been proposed as the appropriate dose quantities for the establishment of diagnostic reference levels for optimizing patient exposure. Dose measurements on 27 CT scanners in Northern Greece involving six routine CT examinations have been performed in order to compare their performance with the currently proposed European reference dose values and to produce a preliminary set of data for the establishment of local diagnostic reference levels. All measurements were performed using a pencil shaped ionization chamber introduced into polymethyl methacrylate cylindrical head and body phantoms. The results revealed significant discrepancies in dose values among the CT scanners, which can be mainly attributed to variations in the examination protocols and the different kinds of scanners. Significant overdosing compared with the European reference levels has not been observed, with the exception of the routine head examination, where 47% of the scanners exceeded the corresponding CTDIw value. CT scans in the trunk region result in the higher effective doses, which can reach estimated maximal values of the order of 15 mSv.