Australian national diagnostic reference levels for MDCT - ADULT

Introduction

Australian adult DRLs for MDCT were established from data obtained in 2011 via the NDRLS. The surveys have continued annually and are currently being reviewed to update the national DRLs. The service is ongoing with dose comparisons available in calendar year periods. See Statistics.

The following table presents the current adult DRLs for Multi Detector CT.

Table 1:   Australian adult (15+ years) MDCT DRLs
Australian ADULT (15+ years)
MDCT Diagnostic Reference Levels
Adult Protocol DLP (mGy.cm) CTDI vol (mGy)
Head 1000 60
Neck 600 30
Chest 450 15
AbdoPelvis 700 15
ChestAbdoPelvis 1200 30
Lumbar Spine 900 40

Note: CTDIvol values for the Head are based on the 16 cm PMMA reference phantom and Chest and Abdomen are based on the 32 cm PMMA reference phantom.

The service is ongoing with dose comparisons available in calendar year periods.

Results

A total of 80 radiology facilities registered for the service in 2011 with a total of 255 compliant individual surveys completed.

For each compliant individual survey completed, a report was generated that specified a Facility Reference Level (FRL), defined as the median of the spread of Dose Length Product (DLP, mGy.cm) values for that survey. These values were then rounded to the nearest factor of 100 or 50 (Chest only).

The Australian National DRL was defined as the 75th percentile of the spread of FRLs for each habitus/protocol. Only Australian Adult DRLs were calculated as no compliant surveys were completed for paediatric age groups.

Table 1 displays the Adult Australian National DRLs for the six habitus/protocols in terms of DLP (mGy.cm) and Computed Tomography Dose Index Volume (CTDIvol, mGy).

Figures 1 and 2 show the Australian Adult MDCT DRLs calculated for each habitus/protocol with 95% confidence intervals.

Figure 1: The Australian Adult MDCT DRL for Dose-Length Product (DLP, mGy.cm) with 95% confidence intervals

Graph showing Australian Adult MDCT DRLs - (95% CI) (six anatomical regions)

Figure 2: The Australian Adult MDCT DRL for the Volume Computed Tomography Dose Index (CTDIvol, mGy) with 95% confidence intervals.

Graph of Australian Adult MDCT DRLs - (95% CI) - six anatomical regions

Table 2 provides the specific number of FRLs used and the DRL value calculated for each protocol.

Table 2: Data used in the calculation of Australian national Adult MDCT DRLs.
Adult Protocol No. FRLs1 DRL2 DLP
(mGy.cm)
95% CI3
DLP
DRL2 CTDIvol
(mGy)
95% CI3
CTDIvol
Head 56 991.6 953.5 - 1055.4 60.8 55.9 - 66.3
Neck 30 597.3 527.3 - 750.4 31.6 23.0 - 38.5
Chest 44 458.3 407.1 - 572.3 14.3 12.9 - 20.5
AbdoPelvis 51 696.8 628.9 - 847.4 17.0 13.5 - 18.4
ChestAbdoPelvis 40 1147.8 1007.0 - 1279.2 31.7 24.3 - 33.6
Lumbar Spine 34 896.3 757.0 - 1086.7 43.3 31.4 - 50.4


Notes:

  1. Number of Facility Reference Levels (FRLs) used to obtain the National Diagnostic Reference Level (DRL) for a particular protocol. The FRL is the median Dose Length Product (DLP, mGy.cm) and Volume Computed Tomography Dose Index (CTDIvol, mGy) of a survey conducted by a facility with a minimum of 10 patients. A facility may have submitted results for more than one survey thus having multiple FRLs.
  2. The DRL is obtained by calculating the 3rd quartile (75th percentile) of the distribution of FRLs
  3. The 95% Confidence Interval (CI) of each protocol DRL was calculated using

*95% CI = 0.75N ± 1.96√0.19N    where N = No. FRLs

*Conover, W.J. (1980) Practical Nonparametric Statistics John Wiley and Sons, New York.

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 more information on DRLs or the Australian National DRL Service please see the Introduction and Fact sheet pages.


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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