Analysis of Effective Dose at Computed Tomography in a Modern 64 slice Multidetector CT System in an Irish Tertiary Care Centre with Local and International Reference Standards

BackgroundComputed tomography (CT), by its nature, imparts a high dose of ionising radiation to patients being imaged. Diagnostic Reference Levels (DRLs) are used extensively in research but are also used in practice to establish if local imaging protocols have been optimised. AimTo audit effective dose (ED) at CT for four commonly performed examinations performed with a modern multidectector 64 slice CT (MDCT) system at large tertiary care centre by comparison with current international reference standards Methods800 consecutive studies of CT brain, cervical spine, thorax and abdomen-pelvis were examined. All patients were imaged on 64-slice MDCT with study-specific protocols. Dose descriptors were extracted from image dose reports. ED was calculated using dose-length product conversion coefficients for all patients. Data was collated with Irish national and local DRLs, and published international point values. ResultsED range at CT abdomen-pelvis of 2.03-26.04 mSv (mean 8.041 mSv) was 28.5% above the national DRL (9 mSv) and 26% above the local DRL (9.75 mSv). ED at CT thorax of 2.46-10.09 mSv (5.061 mSv) was 3.5% greater than local DRL (8.4mSv) and 42.5% greater than the national DRL (5.46 mSv). ED at CT brain of 2.25-8.08 mSv (3.075 mSv) was 100% above both the local (1.98 mSv) and national (2.06 mSv) DRLs. CT cervical spine ED of 1.49-21.94 mSv (5.14 mSv) was 79% greater than the local (3.07 mSv) and 100% greater than the national DRL (1.42 mSv). ConclusionsAll studies exceed national DRLs. A significant optimisation potential is noted, in particular, for studies involving the head and cervical spine. A further review of study protocols is necessary to facilitate optimisation of total study radiation dose.