A practical approach to the first iteration in the optimization of radiation dose and image quality in CT: estimates of the collective dose savings achieved

CT is a diagnostic imaging modality giving higher patient dose in comparison with other radiological procedures. It contributed an estimated 20% to the collective effective dose to the UK population from medical X-rays in 1990, rising to an estimated 40% in 1999. Tremendous national effort has been expended in reducing patient doses from other radiological procedures with considerable success, but much of the collective dose reduction achieved has been offset by a corresponding increase in the collective dose from CT. Over a period of about 2 years, following the installation of a helical CT scanner, CT scan parameters in this hospital have been adjusted with the aim of working towards optimization of image quality and patient dose. A 33% reduction in annual collective effective dose has been achieved, from about 16.5 manSv to I I manSv. However, despite this dose reduction, the annual collective effective dose to our subpopulation is 2.8 times the value 9 years ago. The increase is almost entirely the result of an increased application of CT; 6149 examinations per annum. in 1999 compared with 2210 in 1991. The crucial importance of reducing patient doses from this modality is discussed. Indicative effective doses and image noise values are presented for examination protocols approaching optimization.