Normalised Organ Doses for X Ray Computed Tomography Calculated Using Monte Carlo Techniques and a Mathematical Anthropomorphic Phantom

Computed tomography (CT) practice has grown steadily over the past 20 years, yet without full appreciation of the relatively high patient doses. A recent survey has established CT as a major source of exposure to diagnostic X rays for the UK population and an important topic in the radiation protection of patients. However, only 7% of users reported any type of periodic dose measurement as part of a quality assurance programme. The dosimetric methods of the survey conveniently allow estimates of typical patient doses from details of local practice using scanner specific normalised organ dose data from Monte Carlo calculations for an anthropomorphic phantom and measured values of free-in-air axial dose. Such evaluations of dose permit the assessment of performance against national practice as part of the optimisation of exposure from CT. In order to promote more widespread patient dosimetry, the normalised dose data are available on computer microdisc.