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National Diagnostic Reference Level Service Statistics
- Multi-Detector Computed Tomography Data (MDCT)
- MDCT Iterative Reconstruction
- Image Guided Interventional Procedures – Draft Survey Results
- NDRLS Data Overview
- Facility Registration
- Compliant Surveys
- FRL Data
- DRL Variation 2011 – 2013
- Impact of Iterative Reconstruction
- Draft Image Guided Interventional Procedures
The Medical Imaging Section (MIS) of the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) is conducting an ongoing national dosimetry service for common Multi Detector Computed Tomography (MDCT) protocols from which the first Australian diagnostic reference levels (DRLs) for MDCT have been calculated. The National Diagnostic Reference Level Service (NDRLS) began operation in August 2011 and data collected is collated on an annual calendar basis. The service is a collaborative project being conducted in partnership with the Commonwealth Department of Health (Health), the Royal Australian and New Zealand College of Radiologists (RANZCR), the Australasian College of Physical Scientists and Engineers in Medicine (ACPSEM), the Australian and New Zealand Society of Nuclear Medicine (ANZSNM) and the Australian Institute of Radiography (AIR).
Multi-Detector Computed Tomography Data (MDCT)
The current set of Australian Adult MDCT DRLs are calculated from data collected in 2011. The currents sets of Australian Paediatric (baby and child) MDCT DRLs were calculated from data collected by an independent RANZCR MDCT survey.
A technical report covering the first three years of the National Diagnostic Reference Level Service (2011-2013) is available at ARPANSA/TR171, February 2015.
Successful use of the service requires facility registration, appropriate staff contacts, logging of MDCT platforms and completion of individual surveys for specific protocols with sufficient patient dosimetry data to generate a facility reference level, FRL, formerly referred to as a practice reference level, PRL. The FRL is the median value of the CTDIvol and DLP dose metrics submitted per compliant survey.The following graphs and tables provide an overview of the NDRLS results to date:
- Facility Registrations
- Compliant Surveys
- FRL Data
- Data Variation
MDCT Iterative Reconstruction
Information from facilities concerning their use of iterative reconstruction (IR) has been collected since May 2013. Significant dose savings are apparent.
The following graphs provide an overview of the dose savings per protocol by applying IR technology:
Image Guided Interventional Procedures – Draft Survey Results
In October 2014 the NDRLS released the DRL survey for IGIP in an Excel spreadsheet format. Facilities need to register for participation and are sent a workbook with a choice of 5 procedures; normal coronary angiogram, 3 vessel or less cerebral angiogram, 4 or more vessel cerebral angiogram, abdominal angiogram and ERCP. NDRLS requests 30 patients to be logged per procedure type along with accompanying details of equipment.
The following tables and graphs provide an overview of the draft survey results:
- IGIP Facility Survey Data Input Table
- IGIP KAP Meter Calibration Survey
- IGIP Draft Survey Data Distributions 1
- IGIP Draft Survey Data Distributions 2
NDRLS Data Overview
To date, on a yearly and monthly current year basis, a brief overview of submitted data is as follows:
Table 1: NDRLS MDCT FRL Data Overview
|Adult Facility Reference Level Reports (FRL)||AbdomenPelvis||51||100||150||128||194||623|
Baby (0-4 yr)
Child (5-14 yr)
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A facility is a site of radiology and/or nuclear medicine and/or image guided interventional procedures defined by the allocation of a Medicare Location Specific Practice Number (LSPN). Previously there has been some confusion using the term practice to mean both (i) a site of practice and (ii) the performance of a radiological procedure. Recently the IAEA has suggested that (i) should be changed to the term facility. It is the intention of NDRLS to take up and apply this to our nomenclature and documentation.Top of Page Top of Page
NDRLS strongly suggests that 20 patients be logged per protocol for sufficient statistical validation. Facilities are unable to submit surveys with less than 10 patients acquired.
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The curves below show the cumulative distributions for the DLP and CTDIvol from adult DRL surveys submitted to ARPANSA between the end of April 2013 (when we started collecting information regarding iterative reconstruction) and the end of 2015. The plots display the percentage of surveys that achieved a facility reference level (FRL) below the dose specified on the x-axis.
The blue curve represents all of the submitted data, the green curve represents the surveys where iterative reconstruction (IR) was used and the red curve represents the surveys where IR was not used. The data portrayed is more recent than the data used to specify the current DRLs and, consequently, the DRLs do not match the 75th percentile of the plotted distributions – in general, the 75th percentile is considerably lower than the DRL.
The distributions for all protocols can be found at FRL Data.
DRL Variation 2011 – 2015
To investigate the change in DRL values over the survey periods, non-parametric statistical confidence intervals were calculated using the method of Conover.1
|*95% CI = 0.75N ± 1.96 √0.19N||where N = No. FRLs|
It is also important to note that since the data was not obtained from a random sample the DRLs are not statistically representative of the population. The 95% CI are purely based on sample size.
For the full set of graphs for 95% Confidence Intervals for DLP (mGy.cm) DRLs per protocol, see NDRLS Statistics - 95% Confidence Intervals for DLP DRLs per protocol.
For the full set of graphs for 95% Confidence Intervals for CTDIvol DRLs per protocol, see NDRLS Statistics - 95% Confidence Intervals for CTDIvol DRL per protocol.
Impact of Iterative Reconstruction
In April 2013 the MDCT survey form was modified to ask the participants to log their use of iterative reconstruction (IR) with a yes/no check box. Analysis of the subsequent data strongly indicates that the application of IR to all protocols substantially reduces the dose delivered to the patient.Top of Page Top of Page Top of Page
Draft Image Guided Interventional Procedures
In 2013 a number of Image Guided Interventional Procedures (IGIP) facilities were approached to participate in an IGIP survey trial. Some participants were also self-selected upon hearing of the trial.Submissions were received from 9 practices incorporating 14 interventional rooms. Most delivered the requested 30 patients undergoing a standard coronary angiogram with an unremarkable outcome.
Patient Inclusion Criteria
It was decided to survey a single cohort of patients who have undergone a coronary angiogram that resulted in a non-remarkable outcome. The participants were given the following data inclusion criteria:
“Patients with ‘Normal’ Coronaries. For purposes of definition, 'normal' coronaries are defined as those with no or physiologically insignificant diameter stenosis (<50% coronary diameter narrowing) by visual inspection in patients studied specifically to assess coronary anatomy.”
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A total of 305 patient cases were submitted, giving a reasonably well sized data set for analysis.
Kerma Air Product and Calibration Accuracy
It was recognised that a potential source of significant error was the accuracy of the kerma-air product (KAP, Gy.cm2) meters. Subsequent survey submissions reinforced this as a source of error.Top of Page Top of Page
1. Conover, W.J. (1980) Practical Nonparametric Statistics John Wiley and Sons, New York.
Further information on International Best Practice for Radiation Protection of Patients can be found on the International Atomic Energy Agency Radiation Protection of Patients website, which can be accessed via the following link:
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