2018 update of multi detector computed tomography adult diagnostic reference levels

ARPANSA updated the diagnostic reference levels (DRLs) for adult multi-detector computed tomography (MDCT) procedures on 1 July 2018. Facility dose audits should be compared against these new MDCT DRLs.

One of the aims when establishing a diagnostic reference level program is to have the DRLs reflect current practice, which requires monitoring and periodic updates to the DRLs. In Australia, ARPANSA is responsible for DRL monitoring, which it does through data collection via the National Diagnostic Reference Level Service (NDRLS). A liaison panel, made up of members representing relevant professional organisations, reviews the data from the NDRLS MDCT survey to set updated DRLs.

DRL review process

The MDCT DRLs for adult patients went through this review and update process in late 2017 and early 2018. The issues considered by the liaison panel, and their subsequent decisions, are summarised below:

  1. Separation of DRLs based on reconstruction technique.
    The panel decided not to separate the DRLs based on reconstruction technique. This decision was made for simplicity and because filtered back projection is becoming less prevalent. The panel also decided that the DRLs should be set for the imaging task, rather than the specifics of the imaging technique. However, the panel decided to provide the information regarding the dose distributions for the data categorised by reconstruction technique.
  2. Narrowed example clinical indications
    The panel decided there should be more guidance on clinical indications. The panel decided that by providing a tighter range of example clinical indications for each scan region, the scans included in each facility survey would use a more comparable or equivalent acquisition technique. Providing more guidance on clinical indications is expected to result in DRLs which are more reflective of common practice.
  3. Revised scan regions
    Three new scan regions were introduced. The neck scan region was removed and replaced with soft-tissue neck and cervical spine. The panel also added the kidney-ureter-bladder scan region.
  4. Additional signifiers of the facility reference level (FRL) distribution
    The panel agreed that it would be beneficial to provide imaging facilities with the 25th and 50th percentiles of the FRL distribution, in addition to the DRL, which is set at the 75th percentile. The panel believed that the additional context would increase the value to facilities of conducting a DRL comparison.

The liaison panel used data submitted to the NDRLS MDCT survey in 2017 to develop the updated DRLs. A summary of the data analysis performed is on the MDCT statistics page.

Transitioning to the updated DRLs

The ARPANSA National Diagnostic Reference Level Service MDCT portal was updated on 2 July 2018 to enable surveys to be compared against the new MDCT DRLs. Any surveys for head, chest, abdomen-pelvis, lumbar spine and chest-abdomen-pelvis scan regions started before 2 July 2018 but completed after the portal update will be compared against the new DRLs. Neck surveys started before 2 July 2018 will be compared against the existing neck DRL.

Accreditors for the Diagnostic Imaging Accreditation Scheme (DIAS) have been advised to accept facility dose comparisons conducted against the existing DRLs until 31 December 2018. From 1 January 2019, as part of an application for accreditation (including re-accreditation), accreditors will require evidence that policies for undertaking a DRL comparison have been updated to include the new MDCT DRLs, and that audits conducted after 1 January 2019 have been compared against the new MDCT DRLs.

State and territory radiation regulatory authorities have also been briefed on the changes through discussions within ARPANSA’s Radiation Health Committee. The radiation regulatory authorities have also agreed to accept dose comparisons conducted against the existing DRLs until 31 December 2018 and will require that audits conducted after 1 January 2019 be compared against the new DRLs.