Update of multi detector computed tomography adult diagnostic reference levels - July 2025

ARPANSA will update the diagnostic reference levels (DRLs) for adult and paediatric multi-detector computed tomography (MDCT) procedures on 1 July 2025. From this date, facility dose audits should be compared against these updated MDCT DRLs.

DRL review process

A key objective of the diagnostic reference level program is to ensure that the DRLs reflect current practice, which requires ongoing monitoring and periodic updates. In Australia, ARPANSA oversees DRL monitoring through data collection via the National Diagnostic Reference Level Service (NDRLS). A liaison panel, consisting of members from relevant professional organisations, reviews data from the NDRLS MDCT survey to set updated DRLs.

The MDCT DRLs went through this review process in late 2024 and early 2025. The issues considered by the liaison panel, and their subsequent decisions, are summarised below:

Addition or removal of scan types from the list of National DRLs

The panel decided to retain all 8 existing scan types for adults and incorporate 2 additional ones: paranasal sinuses and low-dose CT (LDCT) chest. This is to ensure comprehensive data collection from CT scan types that involve the highest radiation exposure to the population. Medicare claims for all scan types were considered in setting the list of National DRLs. It was resolved to limit the number of scan types included to a maximum of 10 due to the administrative burden associated with conducting DRL comparisons.

Update of the Australian Adult CT DRLs

The updated adult CT DRLs are shown in Table 1. The panel decided to update the adult DRLs based on the data collected from over 600 facilities in the 2023 calendar year. The data collected through the NDRLS MDCT portal showed a significant reduction in radiation dose metrics used to perform diagnostic scans for all scan types for which data was collected. The panel also decided on DRLs for the two new scan types. The DRLs for paranasal sinuses are based on published DRLs from the UK which best aligned with clinical practice in Australia. The DRLs for low-dose CT (LDCT) chest are based on published information for the National Lung Cancer Screening Program (NLCSP) beginning in July 2025 and the AAPM Lung Cancer Screening CT Protocols Version 6.0.

Table 1: Multi detector computed tomography diagnostic reference levels for adults

Notes:

1. Diagrams of the scan regions and additional protocol information are available from the before you enter data page.
2. The scans included in a dose comparison do not necessarily have to be for the listed phase/indication; however, the exposure parameters of the included scans must match what would be used for the listed phase/indication.
3. Dose indices for the Head and Paranasal Sinuses regions are based on the 16 cm reference phantom. Dose indices for all other scan regions are based on the 32 cm reference phantom.
4. DRLs for the new scan categories will be reviewed once sufficient Australian data is collected.

Update of the Australian Paediatric CT DRLs

The panel has resolved to update the paediatric DRLs in accordance with the recommendations outlined in ICRP Publication 135. Paediatric DRLs will now be established for multiple age bands for head scans, while DRLs for body CT scans will be categorised by various weight bands. The updated paediatric CT DRLs are shown in Tables 2-4. This adjustment represents a considerable shift from the previous DRL age groupings of 0-4 years and 5-14 years, as instituted by ARPANSA in 2012.  Adoption of this more detailed approach to the paediatric DRLs will better represent the scanned patient cohort, and the impact of technique parameters based on patient size.

The updated paediatric DRLs have been established based on data gathered by the NDRLS, supplemented by published international DRLs where the NDRLS data was scarce.

Table 2: Australian Paediatric DRLs for Head CT Scans

Table 3: Australian Paediatric DRLs for Chest CT Scans

Table 4: Australian Paediatric DRLs for Abdomen-Pelvis CT Scans

Notes:

1. Dose indices for the Head region are based on the 16 cm reference phantom. Dose indices for all other scan regions are based on the 32 cm reference phantom.

New NDRLS paediatric data collection method

Paediatric data submission to the NDRLS will change. A new paediatric Excel workbook template will be made available on the ARPANSA website and will assist facilities to easily compare radiation doses used in paediatric CT scans against the new age- and weight-based DRLs. The workbook covers all the age or weight bands for each scan type in a single sample to simplify the collection and comparison process. Participating facilities are requested to email their completed workbooks to ndrld@arpansa.gov.au by 31 December each year, so that the data can contribute to the monitoring and future updating of the Australian paediatric DRLs.

Necessary image quality must not be compromised

Since the national DRLs have been reduced for adults (by around 10-20%) and modified for children, it is acknowledged that there will be an increase in the number of facilities exceeding these levels. It is important to emphasise that the DRLs are reference benchmarks and not dose limits. Being above the DRL is not necessarily bad practice, instead it is a prompt to check whether improvements can be made, i.e. to initiate an optimisation process. It is vital that the image quality required for the diagnostic task is maintained and this should not be sacrificed just to remain below the DRL. Facilities exceeding the DRL should seek assistance on possible optimisation by liaising with their medical physicist, CT applications specialist and radiologist/s and document their investigation.

Transitioning to the updated DRLs

The ARPANSA NDRLS MDCT portal will be adjusted on 1 July 2025 to enable surveys to be compared against the updated MDCT DRLs. Adult surveys started before 1 July 2025 but completed after the portal adjustment will be compared against the updated DRLs. Paediatric surveys started before 1 July 2025 but completed after the portal adjustment will be compared against the previous DRLs. Facilities conducting paediatric surveys are directed to use the new paediatric workbook template (see above).

Accreditors for the Diagnostic Imaging Accreditation Scheme (DIAS) have been advised to accept facility dose comparisons conducted against the existing DRLs until 31 December 2025. From 1 January 2026, as part of an application for accreditation (including re-accreditation), accreditors will require evidence that policies for undertaking a DRL comparison have been revised to include the updated MDCT DRLs, and that audits conducted after 1 January 2026 have been compared against the updated MDCT DRLs.

State and territory radiation regulatory authorities have also been briefed on the changes through discussions within ARPANSA’s Radiation Health Committee. ARPANSA has requested the radiation regulatory authorities to accept dose comparisons conducted against the existing DRLs until 31 December 2025 and require that audits conducted after 1 January 2026 be compared against the updated DRLs.