Patient doses in multi-slice CT and the importance of optimisation.

Substantive surveys of patient doses arising from CT examinations have been conducted in our Hospital. In the first instance doses were measured on a single-slice Siemens Plus 4 scanner. A similar survey was conducted initially following commissioning of a Siemens multi-slice Sensation scanner and subsequently after some effort was made to optimise scanning protocols. Doses are reported in terms of dose-length products (DLPs) and as effective doses. The optimisation process on the multi-slice scanner resulted in a reduction in DLP values by between 14% and 58%. With two exceptions, significantly lower or comparable DLP values were obtained when meaningful comparisons were made with results previously obtained with the single-slice scanner. Specific results for the multi-slice scanner in terms of the median DLP in mGy.cm (and median effective dose in mSv) are: routine brain, 660 (1.5); routine chest, 195 (4.0); chest with portal liver phase, 370 (7.2); routine chest with high resolution component, 250 (5.1); chest/abdomen/pelvis with contrast, 560 (11.0); routine abdomen without contrast, 145 (2.4); routine abdomen with contrast 215 (3.6); routine abdomen/pelvis without contrast, 230 (4.4); routine abdomen/pelvis with contrast, 345 (6.3); abdomen/pelvis triple phase, 715 (13.3); renal scan, 260 (4.6); lumbar spine, 445 (7.2); cerebral angiography, 240 (0.58); pulmonary angiography, 165 (3.4); aortic angiography, 305 (5.7). Based on the survey findings possible values for CT examination local diagnostic reference levels (LDRLs) are suggested.