About Diagnostic Reference Levels (DRLs)

Frequently asked questions by the health professionals

» What is the purpose of DRLs? 
» How to set DRLs? 
» Who is responsible for setting and updating DRLs? 
» Do DRLs apply to individual patients? 
» What is the difference between national DRLs (NDRLs) and local DRLs (LDRLs)? 
» Are DRLs effective in improving patient radiation protection?

» What is the purpose of DRLs?

DRLs should be set for representative examinations or procedures performed in the local area, country or region where they are applied. 

National DRLs (NDRLs) should be set on the basis of wide scale surveys of the median doses representing typical practice for a patient group (e.g. adults or children of different sizes) at a range of representative healthcare facilities for a specific type of examination or procedure. NDRLs are commonly set at the third quartile values (the values that splits off the highest 25% of data from the remaining 75%) of these national distributions. As such, NDRLs are not optimum doses, but nevertheless they are helpful in identifying potentially unusual practice (healthcare facilities where median doses are among the highest 25% of the national dose distribution). DRLs can be also established for a region within the country or, in some cases, regions of several countries. They can also be used to set updated values for new technologies that may allow lower dose levels to be achieved. Where no national or regional DRLs are available, DRLs can be set based on local dosimetry or practice data, or can be based on published values that are appropriate for the local circumstances.

» How to set DRLs?

DRLs should be set for representative examinations or procedures performed in the local area, country or region where they are applied. 

National DRLs (NDRLs) should be set on the basis of wide scale surveys of the median doses representing typical practice for a patient group (e.g. adults or children of different sizes) at a range of representative healthcare facilities for a specific type of examination or procedure. NDRLs are commonly set at the third quartile values (the values that splits off the highest 25% of data from the remaining 75%) of these national distributions. As such, NDRLs are not optimum doses, but nevertheless they are helpful in identifying potentially unusual practice (healthcare facilities where median doses are among the highest 25% of the national dose distribution). DRLs can be also established for a region within the country or, in some cases, regions of several countries. They can also be used to set updated values for new technologies that may allow lower dose levels to be achieved. Where no national or regional DRLs are available, DRLs can be set based on local dosimetry or practice data, or can be based on published values that are appropriate for the local circumstances.

» Who is responsible for setting and updating DRLs?

The government has a responsibility to ensure that DRLs are established for the country, as per requirement 34 in International Basic Safety Standards.

The processes and steps towards establishing DRLs are likely to involve many players, including the imaging facilities, the health authority, the professional bodies, and the regulatory body. In particular there should be collective ‘ownership’ of the DRLs in deciding on what procedures and what size groups will be used, how the data will be collected, who will manage the data, and when the DRLs should be reviewed and updated. 

In some countries, a national governmental body administers the national patient dose database that underpins the establishing of DRLs. In other countries, this role may be taken by the regulatory body or a professional body. There is no preferred custodian: what is important is that a patient dose database (for DRLs) is established and maintained, DRL values are set, these are promulgated through the regulatory processes, and a process for periodic review is established. It may be more appropriate to take a regional rather than a national approach to DRLs.

» Do DRLs apply to individual patients?

No. 

DRLs are general guideline for clinical operations and do not apply directly to individual patients and examinations. 

DRLs relate to typical practice for a specific examination or procedure and to some extent to clinical conditions (e.g., CT of brain in relation to acute stroke) and patient group (e.g., by age or weight, especially for children), as summarized by median doses observed for a sample of patients. Values of the dose quantities for specific examinations or procedures on individual patients can be expected to vary somewhat according to patient physique and clinical needs, and so these individual doses should not be compared directly with relevant DRLs, whose purpose is to promote general improvements in overall practice for the examination or procedure. However, an investigation could be considered when doses for a group of individuals are consistently exceeding a DRL, with a view to reviewing and as necessary revising examination or procedure technique for optimized patient protection.

» What is the difference between national DRLs (NDRLs) and local DRLs (LDRLs)?

NDRL for each examination or procedure and patient group are set on the basis of distributions of the typical (median) doses observed in wide scale (national) surveys, commonly by adopting the third quartile value to provide investigation levels for unusual practice (doses in top 25%). 

LDRLs represent the typical local practice at a single large centre or group of healthcare facilities, set as the third quartile of the median doses determined from samples of patients in the different healthcare facilities of the group.

» Are DRLs effective in improving patient radiation protection?

Yes. 

DRLs have already proved useful as a tool in support of dose audit and practice review for promoting improvements in patient protection. 
Their application since 1989 in the UK within a coherent framework for managing patient dose has been instrumental in promoting increased awareness of dose and helping to reduce unnecessary x-ray exposure. UK national DRLs for conventional X-ray examinations on adult patients, for example, have typically fallen by a factor of two over the last 20 years owing to improvements in imaging practice.