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A uniform approach to setting and using DRLs?

The term diagnostic reference level (more commonly heard in its shortened form, DRL) is now regularly discussed in diagnostic radiology departments in the UK, thanks to the European Union's Medical Exposure Directive [1] and its subsequent translation into UK legislation as the Ionising Radiation (Medical Exposure) Regulations 2000 (IRMER) [2]. The idea of DRLs developed from the UK concept of setting dose reference levels at a national level, which was introduced in 1990 in the Royal College of Radiologists (RCR)/National Radiological Protection Board (NRPB) publication "Patient dose reduction in diagnostic radiology" [3]. However, this relatively simple idea of having national benchmarks for comparison purposes has developed over the past 10 years or so into a very clear, legally backed requirement placed on each radiology department in the UK to take ownership of patient dose and to set, monitor and use their own DRLs as an aid to patient dose optimization.

Of all the IRMER requirements, the need to set and use DRLs has probably been the one that most departments, and their medical physics experts, have put off longest in the hope that some national consensus on exactly what should be done would emerge. After an initial promising start with a meeting held at the Department of Health in early 2000, this consensus has been slow in coming. The recent Institute of Physics and Engineering in Medicine (IPEM) publication "Guidance on the establishment and use of diagnostic reference levels for medical X-ray examinations" [4] represents a major step forward.

This new guidance is a result of deliberations by representatives of all the professional groups who have an interest in patient dose quantification and optimization (namely IPEM, British Institute of Radiology (BIR), College of Radiographers (CoR), NRPB and RCR). Most importantly, it provides a pragmatic methodology for setting local DRLs for procedures carried out by radiology department staff. In addition, it explains the difference between the setting and use of local DRLs as opposed to national DRLs, makes proposals for a somewhat different approach for procedures carried out by non-radiology staff (e.g. in theatre), outlines how to act when local DRLs are consistently exceeded and provides a summary of data that can be used for setting national DRLs.

This has been a large undertaking and it is not surprising that a few of the suggestions have caused some dissension. There is still some criticism (mainly from within the medical physics community) of the approach of basing local DRLs on the mean value of measurements performed in the different rooms in an organization such as an NHS Trust and the validity of the statistical test suggested to determine when local DRLs have been exceeded. However, there is considerable benefit to be gained from a unified national approach so that we all understand the same thing by local DRL (without having to guess whether it is a mean value, an upper quartile value or some other local variant) and we are all using DRLs in the same way to optimize patient dose. The basic methodology provided in this report should be put into routine use in radiology departments throughout the UK as soon as possible to achieve this aim.

At UKRC in 2003, a long session on DRLs introduced the basic concepts of the guidance and explained the thinking behind their development. This coming year at UKRC 2004, it is hoped that the DRL session will be able to concentrate on the experiences of departments in implementing these concepts and early reports on their effectiveness in monitoring and optimizing patient dose.

References

1. European Communities. Council Directive 97/43/Euratom of 30 June 1997 on health protection of individuals against the dangers of ionising radiation in relation to medical exposure. Official Journal of the European Communities No L 180/22, 1997.
2. Ionising Radiation (Medical Exposure) Regulations 2000 (SI 2000 No. 1059). London: HMSO, 2000.
3. Royal College of Radiologists/National Radiological Protection Board. Patient dose reduction in diagnostic radiology. Documents of the NRPB 1990;1(3).
4. Guidance on the establishment and use of diagnostic reference levels for medical X-ray examinations. Joint Working Party Report 88. London: IPEM, 2004.

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