Optimization of Patient Protection in Diagnostic Radiology by Application of Guidance Levels

INTRODUCTION It is well recognized that, apart from natural background, medical exposures are at present by far the largest source of exposure to ionizing radiation of the population and that several radiation protection measures should be taken by each country to prevent unnecessary or unproductive medical radiation exposure. The main tools generally to achieve this aim are justification of practices, optimization of protection and the use of dose limits. As dose limits do not apply to medical exposures, individual justification (good clinical indication) and optimisation are even more important than in other practices using ionising radiation. According to ICRP Publication 60 (1), optimisation means keeping the dose « as low as reasonably achievable, economic and social factors being taken into account ». For diagnostic medical exposures this is interpreted as being a dose as low as possible, which is consistent with the required image quality (2) and necessary for obtaining the desired diagnostic information. In the context of optimisation of patient protection in diagnostic radiology, an important step was the introduction of Diagnostic Guidance Levels (DGLs), following the recommendation of the ICRP in its Publication 73 (3). According to the definition, in X-ray diagnosis, a Diagnostic Guidance Level (DGL) is a dose level set for standard procedures and for groups of standard-sized patients or a standard phantom (4,5): -entrance surface dose per radiograph, for diagnostic radiography; -entrance surface dose rate, for fluoroscopy; -average glandular dose per cranio-caudal projection, for mammography; -multiple scan average dose, for computed tomography. DGLs practically should assist in the optimisation of the patient protection, by helping to avoid unnecessarily high doses to the patient. The system for using DGLs includes: -estimation of patient doses, as part of a regular quality assurance programme ; -comparison of obtained doses with the internationally recommended guidance levels ; -corrective actions whenever guidance levels are consistently exceeded. Since the beginnings of 1990 (6,7), the Institute of Public Health-Bucharest participated to the research coordinated programme on Radiation Doses in Diagnostic Radiology and Methods for Dose Reduction (8), initiated by the International Atomic Energy Agency, in co-operation with European Commission. Some of the recent results are presented below.