The two basic principles of radiation protection for medical exposures as recommended by ICRP are justification of practice and optimisation of protection, including the consideration of diagnostic reference levels (1, 2, 3). The emphasis is to keep dose to the patient as low as reasonably achievable (ALARA), consistent with clinical requirements. These principles are largely translated into a legal framework by the Council Directive (4).
Justification is the first step in radiation protection and no diagnostic exposure is justifiable without a valid clinical indication. Every examination must result in a net benefit for the patient. This will be the case when it can be anticipated that the examination will influence the efficacy of clinical decisions made with respect to the following:
Justification for computed tomography (CT) also implies that the required result cannot be achieved by other methods which are associated with lower risks for the patient. Ultrasound and MRI offer alternatives to CT in many areas of application.
The magnitude of the absorbed dose in CT means that particular care is required for the examination of pregnant women, children, and particularly sensitive organs or tissues. Criteria for approving clinical requests in these circumstances need to be particularly stringent.
As a corollary, justification requires that the imaging procedure is acceptably reliable, i.e. its results are reproducible and have sufficient predictive value with respect to the particular clinical question.
Justification also necessitates that a suitably qualified person (as recognised by the competent authority), usually a radiologist, approves the need for CT and takes overall clinical responsibility for the examination. This person should work in close contact with the referring physician in order to establish the investigation procedure most appropriate to patient management. The person responsible may authorize an appropriately qualified operator (eg radiographer or medical radiation technologist) to perform the examination.
In respect of radiological examinations, ICRP draws attention to the use of diagnostic reference levels as an aid to optimisation of protection in medical exposure. Once the diagnostic examination has been clinically justified, the subsequent imaging process must be optimised. The optimal use of ionising radiation involves the interplay of three important aspects of the imaging process:
This document provides guidance on all three of these aspects for a number of selected CT examinations, as an example of an achievable standard of day-to-day practice. The Quality Criteria presented define a level of performance considered necessary to produce images of standard quality for a particular anatomical region.
For comparability, the aim has been to establish Guidelines on Quality Criteria for CT in accordance with the structure of the existing "European Guidelines for Diagnostic Radiographic Images" for adult and paediatric patients in conventional radiology (5, 6).