ARPANSA - Australian Radiation Protection and Nuclear Safety Agency

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This Page:

• What is the definition of a Diagnostic Reference Level?
• What is the objective of DRLs?
• What are the applications of DRLs?
• How are DRLs used?
• What are the regulatory requirements?
• What measurement quantities are commonly used?
• Estimating Effective Dose (mSv) from DRL assessment
• Australian National DRLs (NDRL)
• Examples of UK and European DRLs
• References

What is the definition of a Diagnostic Reference Level?

A Diagnostic Reference Level (DRL), is defined by the International Commission on Radiological Protection (ICRP)¹, as:

"a form of investigation level, applied to an easily measured quantity, usually the absorbed dose in air, or tissue-equivalent material at the surface of a simple phantom or a representative patient."

The ICRP recommends the establishment of diagnostic reference levels as a tool for optimising the radiation dose delivered to patients in the course of diagnostic and/or therapeutic procedures. The Council of the European Union²  defines DRLs as:

"dose levels in medical radiodiagnostic practices or, in the case of radio-pharmaceuticals, levels of activity, for typical examinations for groups of standard-sized patients or standard phantoms for broadly defined types of equipment. These levels are expected not to be exceeded for standard procedures when good and normal practice regarding diagnostic and technical performance is applied."

The ARPANSA national DRL is the 75th percentile (third quartile) of the spread of the median³ doses of common protocols from a national survey of imaging practices. A local practice reference level (PRL) is defined as the median value of the spread of doses for common protocols surveyed at the local radiology practice. The development of DRLs will be derived from a nationwide survey of local PRLs which, it is assumed, have produced images of acceptable diagnostic quality as defined by the reporting specialist.

What is the objective of DRLs?

The objective of a diagnostic reference level is to help avoid excessive radiation dose to the patient that does not contribute additional clinical information value to the medical imaging task⁴.

• Typically, diagnostic reference levels are used as investigation levels (i.e. as a quality assurance tool), they are advisory and NOT a dose limit, therefore should not be applied to individual patients.
• The application of a PRL is for the local imaging practice to establish a reference dose for their common imaging protocols that can be used for internal and external comparison.
• DRLs can also be used for international comparative dosimetry.

Top of Page What are the applications of DRLs?

DRLs, together with an optimisation process, help reduce unnecessary patient doses and the consequent radiation risks.
A diagnostic reference level can be used to:

• improve local, regional, or national distributions of observed doses for a general medical imaging task, by reducing the frequency of unjustified high or low dose values
• promote a narrower range of doses that represent good practice for a more specific medical imaging task
• promote an optimum range of doses for a specified medical imaging protocol
• provide a common dose metric for the comparison of PRLs between practices, protocols and modalities
• assess the dose impact of the introduction of new protocols
• provide compliance with the relevant state and territory regulatory requirements⁵.

Appropriate local review and action is required when the doses observed are consistently outside the selected diagnostic reference level, unless clinically justified. However this elevated dose with clinical justification should be an exception rather than the norm across multiple DRLs.

How are DRLs used?

PRLs can be used to:

• define local practice doses for common procedures
• compare PRLs with other similar protocols
• compare with other imaging practices’ PRLs
• compare with regional or national DRL
• provide a comparative dose metric for optimisation strategies
• comply with state and territory regulatory requirements.

DRLs are used to:

• compare against PRLs
• compare with international DRLs
• comply with state and territory regulatory requirements.

What are the regulatory requirements?

State and territory regulatory bodies require implementation of the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) Code of Practice (RPS 14)⁵ which requires the development and application of diagnostic reference levels.

The ARPANSA Code of Practice (RPS 14), Section 3.1.8 states that:

"the Responsible Person must establish a program to ensure that radiation doses administered to a patient for diagnostic purposes are:

1. Periodically compared with diagnostic reference levels (DRLs) for diagnostic procedures for which DRLs have been established in Australia; and
   
   
2. If DRLs are consistently exceeded, reviewed to determine whether radiation has been optimised."

In addition, the ARPANSA Safety Guide⁶, Section 7.8, suggests that:

"as part of the QA program, patient dose surveys are undertaken periodically to establish that the doses are acceptable when compared with published DRLs."

The Department of Health & Ageing (DoHA) Diagnostic Imaging Accreditation Scheme (DIAS), the Royal Australian & New Zealand College of Radiology (RANZCR) Quality and Accreditation Program and the Australian College on Healthcare Standards (ACHS) EQuIP 5 Accreditation Standards all require compliance with state and territory regulation which in turn requires compliance with the ARPANSA Code of Practice (RPS.14)⁵.

Top of Page What measurement quantities are commonly used?

From a practical perspective, the DRL should be expressed as an easily measured patient dose-related quantity for the specified imaging platform, for example, multi-detector computed tomography (MDCT):

• MDCT examinations – volume computed tomography dose index (CTDI_vol, mGy)^7,8 and the dose-length product (DLP, mGy.cm)^7,8. New CT scanners in accordance with Australian Standards, AS/NZS 32002.44⁹, should display the CTDI_vol and/or the DLP on the operator’s console after the selection of technique factors and prior to the initiation of x-rays. Average CTDI_vol and total DLP should be available at the end of the scan procedure⁸.
• Fluoroscopic examinations – dose area product (DAP, mGy.cm²), screening time (sec), number of acquired frames^7,8.
• General Radiographic examinations (film-screen CR & DR) – either entrance skin dose (ESD, mGy)⁷ or the dose area product (DAP, mGy.cm²)⁸.
• Mammography – the mean glandular dose (MGD, mGy)^7,8.
• Nuclear Medicine – adult reference activity (MBq)⁸.

Estimating Effective Dose (mSv) from DRL assessment

As seen above, different imaging modalities have different basic dose metrics. To compare these dose metrics and gain some information on the radiation dose delivered and the consequent population statistical risk it is useful to convert the individual DRL dose metrics into approximate effective dose (ED, mSv).

• MDCT – DLP to ED¹⁰
• Fluoroscopy & Radiography – DAP to ED¹¹
• Nuclear Medicine – Activity to ED¹²
• Mammography – MGD to ED¹³

It should be noted that these effective dose conversions are to be used with caution. They should not be applied to an individual but rather are statistical estimates of a dose and risk to a population who may receive that dose.

Australian National DRLs (NDRL)

ARPANSA, in collaboration with other stakeholders, is currently establishing a national survey program for the development of national DRLs. ARPANSA will accept all submitted patients with their recorded weight rather than define a reference sample population based on a specific weight range. International comparisons can be made retrospectively by simply extracting the appropriate weight range.

Due to its significantly higher population dose contribution, the first NDRL survey will be applied to MDCT. This will be followed by interventional fluoroscopic procedures, nuclear medicine, mammography and general radiography & fluoroscopy.

The ARPANSA NDRL project will initially give emphasis to the higher dose modalities. ARPANSA will provide an easy to use tool for all modalities but until these are developed and distributed each practice is encouraged to undertake paper based local surveys to establish their own PRLs as soon as possible.

Examples of UK and European DRLs

Table 1: UK & EU MDCT DRLs¹⁴

Table 6: Comparison of Head, Chest, and Abdominal CT Dose Values with DRLs Given in European Guidelines

Examination	Mean Value	3rd-Quartile Value	United Kingdom Study (3rd-Quartile Value)	European DRL
Head CT
CTDI w (mGy)	39	47	66	60
DLP (MGy - cm)	544	527	787	1050
Chest CT
CTDI w (mGy)	9.3	9.5	17	30
DLP (MGy - cm)	348	447	488	650
Abdominal CT
CTDI w (mGy)	10.4	10.9	19.0	35
DLP (MGy - cm)	549	696	472	780

Note: Data are mean and 3rd quartile values for the examinations performed in the entire patient sample.  CTDI_w – weighted CT dose index.

Top of Page Table 2:   Recommended diagnostic reference doses for general radiography for individual radiographs on adult patients¹⁵

Radiograph	ESD per radiograph (mGy)	DAP per radiograph (Gy cm2)
Skull AP/PA	3	-
Skull LAT	1.5	-
Chest PA	0.2	0.12
Chest LAT	1	-
Thoracic spine AP	3.5	-
Thoracic spine LAT	10	-
Lumbar spine AP	6	1.6
Lumbar spine LAT	14	3
Lumbar spine LSJ	26	3
Abdomen AP	6	3
Pelvis AP	4	3

Table 3:   Recommended diagnostic reference doses for fluoroscopic/interventional examinations on adult patients.¹⁵

Examination	DAP per exam (Gy.cm2)	Fluoroscopy time per exam (mins)
Barium (or water soluble) swallow	11	2.3
Barium meal	13	2.3
Barium follow through	14	2.2
Barium (or water soluble) enema	31	2.7
Small bowel enema	50	10.7
Biliary drainage/intervention	54	17
Femoral angiogram	33	5
Hickman line	4	2.2
Hysterosalpingogram	4	1
IVU	16	-
MCU	17	2.7
Nephrostogram	13	4.6
Nephrostomy	19	8.8
Retrograde pyelogram	13	3
Sialogram	1.6	1.6
T-tube cholangiogram	10	2
Venogram (leg)	5	2.3
Coronary angiogram	36	5.6
Oesophageal dilation	16	5.5
Pacemaker implant	27	10.7

Table 4:   Recommended fluoroscopic/interventional diagnostic reference doses for complete examinations on paediatric patients¹⁵

Examination	Standard age (y)	DAP per exam (Gy.cm2)
MCU	0	0.4
	1	1.0
	5	1.0
	10	2.1
	15	4.7
Barium meal	0	0.7
	1	2.0
	5	2.0
	10	4.5
	15	7.2
Barium swallow	0	0.8
	1	1.5
	5	1.5
	10	2.7
	15	4.6

Table 5: Recommended diagnostic reference levels for CT examinations  (CTDI_vol and DLP )¹⁶

Patient group	Scan region	CTDI vol (mGy) single slice/ multi slice	DLP mGy.cm) Single slice/ multi slice
Adults	Brain Abdomen (liver metastases) Abdomen &pelvis (abscess) Chest, abdomen & pelvis (lymphoma staging or follow up) Chest (lung cancer) Chest Hi-res	55/65 13/14 13/14 22/26 10/13 3/7	760/930 460/470 510/560 760/940 430/580 80/170
Children   0-1 yr old   5 year old   10 year  old	Head Thorax Head Thorax Head Thorax	30 12 45 13 50 20	270 200 470 230 620 370

Dose values for adults relate to the 16cm diameter CT dosimetry phantom for examinations of the head and the 32cm diameter CT dosimetry phantom for examinations of the trunk.

All dose values for children relate to the 16 cm diameter CT dosimetry phantom.

Top of Page Table 6: Recommended diagnostic reference level for mammography for a typical adult patient

For film screen examinations using a grid, the mean glandular dose (MGD) is 2 mGy based on the 4.2 cm acrylic American College of Radiologists phantom17. Additionally for Digital Mammography, the MGD shall be ≤ 1 mGy for 2.0 cm PMMA (2.3 cm 50% adipose, 50% glandular breast) and ≤ 4.5 mGy for 6.0 PMMA (6.5 cm 50% adipose, 50% glandular breast )18

Table 7: Sample Australian nuclear medicine DRLs

Procedure Name	Nuclide	Chemical Form	Route of Administration	Most Common Activity 19 (Mode) (MBq)	Adult Reference Activity 19 (MBq)	Effective whole body dose 20(mSv)
Bone Scan	Tc-99m	MDP, HDP	iv	800	900	5.1
Myocardial perfusion - 2 day stress/rest (stress)	Tc-99m	MIBI	iv	600	900	7.1
Myocardial perfusion - 2 day stress/rest (rest)	Tc-99m	MIBI	iv	600	840	7.6
Thyroid	Tc-99m	pertechnetate	iv	200	200	2.6
Lung perfusion	Tc-99m	MAA	iv	200	200	2.2
Renal scan	Tc-99m	MAG3	iv	300	350	2.5

 

References

1. Radiological protection and safety in medicine. ICRP Publication 73. Ann ICRP 1996, 26 (2), 1 47.

2. Commission, E., The Health Protection of Individuals Against the Dangers of Ionizing Radiation in Relation to Medical Exposure. L180/22, O. f. O. P. o. E. C., Ed. European Commission: Luxemburg, 1997.

3. Mould, R., Introductory Medical Statistics. 3rd ed.; IoP: Bristol, 1995.

4. IAEA Radiological Protection for Medical Exposure to Ionizing Radiation; IAEA: Vienna, 2002.

5. Code of Practice for Radiation Protection in the Medical Applications of Ionizing Radiation (2008); RPS 14 Australian Radiation Protection & Nuclear Safety Agency.

6. Safety Guide for Radiation Protection in Diagnostic and Interventional Radiology (2008); RPS 14.1 Australian Radiation Protection & Nuclear Safety Agency.

7. Heggie, J.; Liddell, N.; Maher, K., Applied Imaging Technology. 4th ed.; St Vincent's Hospital: Melbourne, 2001.

8. ICRP, Diagnostic reference levels in medical imaging: review and additional advice. Ann ICRP 2001, 31 (4), 33-52.

9. SAA, Medical Electrical Equipment - Particular Requirements for Safety - X-Ray Equipment for Computed Tomography. In AS/NZS 3200.2.44 Ed 2.1, AS/NZS: Melbourne, 2005.

10. McCullough, C. AAPM Report No. 96: The Measurement, Reporting and Management of Radiation Dose in CT; AAPM: 2008.

11. Commission, E. Guidance on Estimating Population Doses from Medical X-Ray Procedures; European Commission: Chilton, UK, 2008.

12. ICRP, Radiation dose to patients from radiopharmaceuticals. Addendum 3 to ICRP Publication 53. ICRP Publication 106. Approved by the Commission in October 2007. Ann ICRP 2008, 38 (1 2), 1-197.

13. 6. Patient Dosimetry in Mammography. JOURNAL OF THE ICRU 2009, 9 (2), 53-63.

14. Tsapaki, V.; Aldrich, J. E.; Sharma, R.; Staniszewska, M. A.; Krisanachinda, A.; Rehani, M.; Hufton, A.; Triantopoulou, C.; Maniatis, P. N.; Papailiou, J.; Prokop, M., Dose Reduction in CT while Maintaining Diagnostic Confidence: Diagnostic Reference Levels at Routine Head, Chest, and Abdominal CT--IAEA-coordinated Research Project 10.1148/radiol.2403050993. Radiology 2006, 240 (3), 828-834.

15. Hart, D.; M.C., H.; Wall, B. F. Doses to patients from medical x-ray examinations in the UK - 2000 review; NRPB: Chilton, 2002.

16. Shrimpton, P. C.; Hillier, M. C.; Lewis, M. A.; Dunn, M., National survey of doses from CT in the UK: 2003. Br J Radiol 2006, 79 (948), 968-980.

17. Craig, A.; Heggie, J.; McLean, I.; Coakley, A.; Nicoll, J., Recommendations for a mammography quality assurance program [ACPSEM Position Paper]. Australas Phys Eng Sci Med 2001, 24 (3), 107-131.

18. Australia, B. National Accreditation Standards; BreastScreen Australia: Sydney, 2008.

19. Botros, G.; Smart, R. C.; Towson, J. E., Diagnostic reference activities for nuclear medicine procedures in Austrlaia and New Zealand derived from the 2008 survey. ANZ Nuclear Medicine 2009, 40 (4), 2-11.

20. ICRP, Radiation dose to patients from radiopharmaceuticals, Publication 80. In Annals of the ICRP, ICRP: Oxford, UK, 1998; Vol. 80.

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