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

ARPANSA is in the process of developing DRLs for IGIP. Data collection to establish national DRLs for IGIP is ongoing and consideration of the data is in progress. It is anticipated that formal publication of DRLs for IGIP will occur in the near future.

IGIP procedures covered by the DRL survey

ARPANSA identified the most common interventional procedures as the basis for implementing national diagnostic reference levels (DRLs) in IGIP. These seven procedures may be added to, or modified, subject to changes in practice and technology.

We are gathering data on the following seven procedures:

  1. 'Normal’ coronary angiogram
  2. Cerebral angiogram (1-3 vessels)
  3. Cerebral angiogram (1-3 vessels) with RA
  4. Cerebral angiogram (4+ vessels)
  5. Cerebral angiogram (4+ vessels) with RA
  6. Abdominal angiogram
  7. Endoscopic retrograde cholangiopancreatography (ERCP)

Comparing your facility’s IGIP doses

While national DRLs are yet to be finalised, facilities can submit surveys 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 draft DRLs. The draft DRLs came from the following sources:

  1. 'Normal’ coronary angiogram:
    The draft DRL is based on data submitted to the Image Guided Interventional Procedures Survey during 2015-2016.
  2. Cerebral Angiogram:
    The four draft DRLs are based on data reported by Erskine et al. (Australas Phys Eng Sci Med (2014) 37:75-82). They are indicative only.
  3. Abdominal angiogram:
    As above, the DRLs are based on data reported by Erskine et al. (Australas Phys Eng Sci Med (2014) 37:75-82). It is indicative only.
  4. ERCP: The Draft DRL is based on data reported by the DoseDataMed2 project in Europe.

Once sufficient data has been collected, these draft DRLs will be superseded. 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 draft DRLs

If your FRL is higher than the draft DRL, then ARPANSA suggests that you conduct an investigation following the recommendations in 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 the most common adult IGIP protocols. Once these have been established, then developing paediatric national diagnostic reference levels (DRLs) for IGIP will be considered.

Dose metrics used in NDRLS IGIP surveys

The dose metrics recommended by the International Commission on Radiological Protection (ICRP) for the purpose of IGIP surveys are the reference air kerma (Ka,r) and the kerma area product (KAP). 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. 1 cm above the patient support for interventional X-ray equipment with the X-ray source assembly below the patient support
  2. 30 cm above the patient support for interventional X-ray equipment with the X-ray source assembly above the patient support
  3. 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 bema 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 less than 45 cm
  1. 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.

Separating diagnostic and interventional components

Any interventional component must be excluded from the data you submit to the survey. Our survey is assessing the patient doses from the diagnostic component of a procedure only.

Reporting 3D rotational angiography procedures

Some facilities will perform 3D rotational angiography (3D-RA) as part of their cerebral angiogram procedures. We have decided to create separate spreadsheets for cerebral angiography including rotational angiography. If your facility mostly includes 3D-RA in cerebral angiography procedures then use the “with RA” spreadsheet and exclude patients where 3D-RA is not used. Alternatively, if your facility mostly doesn’t include 3D-RA in cerebral angiography procedures then use the regular spreadsheet and exclude patients where 3D-RA is used. If your facility performs enough studies of both these classifications then you may submit surveys for each type, recording the patients that do get 3D-RA on the “with RA” sheet and those that don’t on the regular spreadsheet. The 3D-RA component should be counted as part of the Digital Acquisition component when recording exposure time, number of frames and frame rate.

Reporting 4- vessel and 4+ vessel 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 4+ vessel count.