Diagnostic reference levels in interventional radiology

Following the release of European Directive EU 97/43, radiodiagnostic facil ities within the European Union are required to implement a system of patie nt dose reviews based on comparisons with European. national and local diag nostic reference levels (DRLs). Establishing these levels for typical inter ventional radiology examinations presents a problem as definition of 'typic al' examinations can be difficult, patient numbers are limited and these pr ocedures are often performed at a FEW specialist centres. This paper uses dose-area product (DAP) gathered over a period of 3 years f rom 40 fluoroscopy rooms to investigate potential difficulties when it come s to Forming diagnostic reference levels for interventional radiology. Comp arison of DAP distributions with standard complex (fluoroscopy based) exami nations such as barium enema reveals considerably more variation For interv entional procedures. Two methods of forming a DRL are compared: pooled pati ent DAP distributions versus a distribution of DAP per room. The bootstrap resampling method is then applied to DAP distributions to form a confidence interval for the chosen DRL statistic. Potential error on a DRL formed at a local level from a limited number of patient dose readings and x-ray room s is significant. The results are reviewed in the wider context of DRLs in general radiology. For complex examinations, it is suggested that the funct ion of the DRL is best served by setting DRLs based on pooled size-correcte d patient DAP distributions rather than distributions of average DAP per ro om.