CT standard protocols are of limited value in assessing actual patient dose

In the last 10 years the use of computed tomography in radiodiagnosis has increased markedly and CT scanners are now present in most district general hospitals. Modern CT scanners are versatile in their operation and offer the operator a wide choice in exposure parameters which affect the doses received by the patients. As CT is a major contributor to medical radiation doses, the National Radiological Protection Board (NRPB) recommends that an estimate of typical patient dose should be made for commonly used local scanning protocols. A survey has been undertaken in the Anglia and Oxford region covering 12 CT scanners. Common procedures were chosen, concentrating on those most frequently carried out and giving higher effective doses. These included routine heads, routine chests, high resolution chests and abdomen/pelvis examinations. Questionnaires were sent out to each CT centre to collect data on standard protocols and to record the procedure used for five actual patients for each examination type thus enabling a comparison of the two methodologies. This study has shown that many examinations are tailored to the individual patient size and clinical indications, particularly in the chest/abdomen/pelvis. Thus, assessing doses based on collecting standard protocols may not give a true indication of the effective doses being received by particular patients.