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Image guided interventional procedures DRLs in more detail

Diagnostic reference levels (DRLs)

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

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.

More information on DRLs, how they are used, and the regulatory requirements for Australian imaging facilities, is provided on the NDRLs in more detail page.

Development of IGIP DRLs

Data collection to establish national DRLs for IGIP is ongoing and consideration of the data is in progress. DRLs for diagnostic coronary angiography were published on 31 March 2020. DRLs for other IGIP categories will be published when sufficient data have been collected.

IGIP procedures covered by the DRL survey

The procedures included in the IGIP DRL survey were revised for 2020 following consultation with a liaison panel comprising representatives from relevant professional bodies. These procedures may be added to, or modified, subject to future changes in practice and technology.

We are gathering data on the following procedures:

  • Diagnostic coronary angiogram (no significant disease)
  • Diagnostic cerebral angiogram
  • Barium swallow
  • Gastrografin swallow
  • Percutaneous coronary intervention (PCI, single lesion)
  • Endovascular aortic repair (EVAR)
  • Pelvic embolization
  • Tunnelled line insertion.

Comparing your facility’s IGIP doses

Facilities submit survey data for specific procedures to the NDRLS. In return, ARPANSA will provide a report summarising the submitted data, derive a facility reference level (FRL), and compare that FRL with the relevant national DRL. Where national DRLs are yet to be published, a representative value from the published scientific literature will be used for comparison.

Once sufficient data has been collected, the liaison panel will review the data and make recommendations for national DRLs. Until this occurs, there is no regulatory obligation for facilities to conduct comparisons, however doing so represents good practice and will aid ARPANSA in formulating DRLs representative of common practice.

If your FRLs exceed the DRLs

If your FRL is higher than the DRL, then ARPANSA suggests that you conduct an investigation following the recommendations in International Commission on Radiological Protection (ICRP) Publication 135. It is recommended that you seek help from a Qualified Medical Physicist (QMP) particularly if your investigation indicates dose optimisation is warranted.

A list of QMPs can be found from the Australasian College of Physical Scientists and Engineers in Medicine website.

Paediatric IGIP DRLs

ARPANSA is initially focusing on adult IGIP protocols. Once these have been established, then developing paediatric national diagnostic reference levels for IGIP will be considered.

Dose metrics used in NDRLS IGIP surveys

The dose metrics recommended by the ICRP for the purpose of IGIP surveys are the reference air kerma (Ka,r) and the kerma area product (KAP, also called DAP). Some imaging units do not provide an estimate of the reference air kerma, in which case the Ka,r column of the survey can be left blank.

In addition to these dose metrics, the ARPANSA IGIP survey requests other procedural metrics. The Diagnostic Imaging Accreditation Scheme (DIAS) requires logging of screening times for fluoroscopy equipment and the logging and review of dose metrics by a qualified person for angiography equipment.

Details of the ARPANSA IGIP survey metrics are available on our website.

Definition of reference air kerma

According to IEC 60601-1-3 Ed 2.1:2013, reference air kerma is defined as:

air kerma free in air in the primary X-ray beam measured under specific conditions and expressed at the patient entrance reference point.

Patient entrance reference point

According to IEC 60601-2-43 Ed 2.0:2010, the patient entrance reference point (previously known as the interventional reference point) is defined as:

1 cm above the patient support for interventional X-ray equipment with the X-ray source assembly below the patient support

30 cm above the patient support for interventional X-ray equipment with the X-ray source assembly above the patient support

15 cm from the isocentre in the direction of the focal spot for C-arm interventional X-ray equipment or

for C-arm interventional equipment without an isocentre, a point along the X-ray beam axis defined by the manufacturer as being representative of the point of intersection of the X-ray beam axis with the patient surface. In this case, the statement in the instruction for use shall include the rationale for the choice of position made by the manufacturer or

at the point representing the minimum focal spot to skin distance for C-arm interventional X-ray equipment with focal spot to image receptor distance less than 45 cm

for interventional X-ray equipment not listed above the patient entrance reference point shall be specified by the manufacturer.

Multiple values of kerma area product (KAP)

For biplane interventional equipment, the dose report typically will indicate the cumulative dose for each plane with a total of the cumulative doses. Since the intention of a diagnostic reference level is to provide an indication of the median dose indicator for a type of procedure, the total of the cumulative doses should be reported.

Reporting 3D rotational angiography procedures

Some facilities will perform 3D rotational angiography (3D-RA) as part of their cerebral angiogram procedures. The survey spreadsheet for cerebral angiogram includes a field to indicate the number of 3D rotational angiography acquisitions (spins) included in a procedure for a given patient. This data is being recorded to track the complexity of each procedure. When data is analysed to set DRLs, the impact of the number of 3D rotational acquisitions will be assessed and taken into consideration when the liaison panel makes recommendations.

Reporting the number of vessels examined in cerebral angiogram procedures

Some facilities may only do both vertebrals and both common carotids for their cerebral angiograms. This will give a 4-vessel angiogram. However, other facilities, particularly when looking for arterio-venous malformation (AVM) or arterio-venous fistula (AVF), will also include the internal and external carotid arteries. This will give a count of up to 6 vessels. The survey spreadsheet for cerebral angiogram includes a field to indicate the number of vessels examined in a procedure for a given patient. This data is being recorded to track the complexity of each procedure. When data is analysed to set DRLs, the impact of the number of vessels examined will be assessed and taken into consideration when the liaison panel makes recommendations.