National Diagnostic Reference Level Service in more detail

Diagnostic reference levels

A diagnostic reference level (DRL) is an indicative dose that is not expected to be exceeded under normal imaging conditions for a given diagnostic taski.

A DRL is not a regulatory limit, it is a benchmark that when exceeded triggers a review. Conducting a local dose audit and comparing the results to a DRL provides an imaging facility with a simple method of identifying situations where they are delivering an unusually high patient dose.

Modalities currently covered by Australian DRLs

ARPANSA has focussed on developing DRLs for the procedures with the highest dose burden on the Australian population. So far, DRLs have been published for:

  • Multi-detector computed tomography for adult and paediatric patients,
  • General nuclear medicine and PET for adult patients only, and
  • CT conducted as part of SPECT/CT and PET/CT procedures for adult patients only.

ARPANSA is also actively collecting data on image guided interventional procedures (IGIP). There are no Australian DRLs for planar radiography, dental X-ray, cone beam CT or mammography.

The purpose of a DRL and why it's important

The objective of a DRL is to help avoid excess radiation dose to patients for a specified imaging taskii.

A diagnostic reference level can be used to:

  • promote an optimum range of doses for specified medical imaging protocols
  • give you a common dose metric for the comparison of doses between facilities, protocols and modalities
  • prompt you to perform local dose audits (via regulatory requirements).

DRLs can only be effective if appropriate local review and action is undertaken when the doses observed are consistently outside the relevant diagnostic reference level.

How we determine DRLs

The International Commission on Radiological Protection (ICRP) recommends that DRLs should reflect common practice within a given geographical region. ARPANSA achieves this by determining DRLs based on the results of wide-scale surveys of imaging facilities.

Survey participants submit their protocol, patient, and dose information to us for a variety of procedures. We use this information to calculate the facility reference levels (FRLs) for those surveys. The DRLs are based on the 75th percentile (third quartile) of the resulting FRL distributions.

More information for particular imaging modalities can be found in the relevant modality pages.

Facility reference levels

A facility reference level (FRL) indicates the typical patient dose and is the quantity you compare against the DRL. It is the median dose delivered to a sample of patients undergoing a particular routine diagnostic imaging protocol at a given facility. In cases where the dose is dependent on the equipment used to perform the imaging (for example CT), the FRL is also equipment specific (i.e. a facility may have more than one FRL for a single procedure).

FRLs can be used to:

  • monitor your local facility doses for common procedures
  • compare doses between similar protocols
  • assess the dose impact of the introduction of new protocols
  • compare doses between facilities
  • compare with regional or national DRLs

The following diagram shows the relationship between an FRL for a particular scan and the national DRL for that scan (in this case for a CT scan).

 The relationship between an FRL for a particular scan and the national DRL for that scan

How you can calculate your FRLs

You should determine the median dose delivered to a representative sample of patients undergoing your common protocols. ARPANSA gives you a variety of tools to help with the calculation. To access these tools visit the relevant imaging modality pages.

If your FRLs exceed the DRLs

If your FRL exceeds the DRL for a particular protocol, it is an indication that you are delivering a higher dose than 75% of Australian imaging facilities for that procedure.

Section 3.1.8 b) of RPS 14 states that you should review your imaging protocols if the DRLs are consistently exceeded. In practice, this means that if your FRL exceeds the DRL, you’ll need to review your protocols and procedures. If the review shows that you need to optimise your scans, you should perform this in collaboration with a qualified medical physicist (QMP). A list of QMPs can be found on the Australasian College of Physical Scientists and Engineers in Medicine website.

What you need to do

Know your regulatory requirements

State and territory regulatory bodies require implementation of the ARPANSA Code of Practice (RPS 14) which requires the development and application of diagnostic reference levels. Section 3.1.8 of RPS 14 states that:

"the Responsible Person must establish a program to ensure that radiation doses administered to a patient for diagnostic purposes are:

  1. Periodically compared with diagnostic reference levels (DRLs) for diagnostic procedures for which DRLs have been established in Australia; and
  2. If DRLs are consistently exceeded, reviewed to determine whether radiation has been optimised."

The Department of Health Diagnostic Imaging Accreditation Scheme (DIAS), the Royal Australian & New Zealand College of Radiology (RANZCR) Quality and Accreditation Program and the Australian College on Healthcare Standards (ACHS) EQuIP 5 Accreditation Standards all require compliance with state and territory regulation, which in turn requires compliance with the ARPANSA Code of Practice.

Know your Diagnostic Imaging Accreditation Scheme requirements

The requirements of the Diagnostic Imaging Accreditation Scheme (DIAS) were amended in 2016 to include the following:

Your imaging practice must establish a program to ensure that radiation doses administered to a patient for diagnostic purposes are:

  1. annually compared with diagnostic reference levels (DRLs) for diagnostic procedures for which DRLs have been established in Australia
  2. if DRLs are consistently exceeded, reviewed to determine whether radiation protection has been optimised.

Read the DIAS user guides on their website.

Compare your FRLs to the DRLs at least once a year

As mentioned earlier, it depends on your state or territory regulator and DIAS auditors as to:

  • how often you need to compare your FRLs to the DRLs
  • what form that comparison takes.

However, it is ARPANSA's opinion that you should conduct a comparison annually and whenever new equipment or exposure parameters are introduced or if you notice something unusual. The exception is for general nuclear medicine procedures – see the nuclear medicine page for details.

Even if you scan infrequently, compare to the DRLs

It is beneficial to compare even the relatively few doses from rarely performed scans to their respective DRL. Just keep in mind that if you have a small sample size then the characteristics of patients within your cohort may be the reason for an unusually high or low dose.

NDRLS principal stakeholders

Contact us

If you have any further questions please contact us. We are available by telephone on 1800 033 972 between 9am and 4pm weekdays, or by email at

i European Commission. The Health Protection of Individuals Against the Dangers of Ionizing Radiation in Relation to Medical Exposure. Council Directive 97/43/Euratom,OJ L180 p22. Luxemburg, 1997

ii ICRP. The 2007 Recommendations of the International Commission on Radiological Protection. ICRP publication 103. Ann ICRP 2007; 37:1-332