Transcript 19. Optimization of protection in mammography: Part 10

IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
RADIATION PROTECTION IN
DIAGNOSTIC AND
INTERVENTIONAL RADIOLOGY
Part 19.10: Optimization of protection in
mammography
Practical exercise
IAEA
International Atomic Energy Agency
Contents
• To be able to apply quality control
protocol to mammography equipment
• To measure the AEC performance
• Optical density control setting
• Short term reproducibility
• Long term reproducibility
• Object thickness compensation
• Tube voltage compensation
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IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
Part 19.10: Optimization of protection in
mammography
AEC
(Automatic Exposure Control)
IAEA
International Atomic Energy Agency
AEC system
• The performance of the Automatic Exposure
Control (AEC) system can be described by
the reproducibility and accuracy of the
automatic optical density control under
varying conditions, e.g., different object
thicknesses and tube voltages.
• An essential prerequisite for these
measurements is a stable operating filmprocessor and the use of the reference
cassette.
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Equipment needed
•
•
•
•
PMMA: plates 20 x 300 x 300 mm
Densitometer
Reference cassette
Dosimeter
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Optical density control setting:
central value and difference per step
• Produce exposures with a breast equivalent
phantom material with varying positions of
the optical density control selector
• A target value for the mean optical density
should be established according to local
preference.
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OD control setting: central value and
difference per step
Limiting value : The film density (base + fog
included) at the reference point
should remain within ± 0.20 in
density of the target value.
Target value is typically in the range:
1.30-1.80 (base + fog included)
The desirable control step difference
is 0.10;  0.20 per step is
acceptable
Frequency :
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Adjustable range > 1.00
Step size: every six months
Central density: daily
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(AEC) - Short term reproducibility
• Position the dosimeter in the x-ray beam but
without covering the AEC-detector.
• The short term reproducibility of the AEC system is
the deviation of the radiation dose for five
exposures with a breast equivalent phantom
Limiting value :
Frequency :
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The deviation must be < ± 5%;
desirable would be < ± 2%.
Every six months
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(AEC) - Long term reproducibility
• The long term reproducibility can be
assessed from the measurement of the film
optical density resulting from the exposure of
a breast equivalent phantom
Limiting value :< ± 0.20 optical density
acceptable;
< ± 0.15 desirable
Frequency : Daily
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Object thickness compensation (AEC)
• Compensation for object thickness is measured by
exposures of PMMA plates in the thickness range
20 to 40 mm, using the clinical setting for the AEC
Limiting value :
Desirable :
Frequency :
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All density variations must be within
± 0.20 of the target density.
± 0.15
Weekly
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Tube voltage compensation (AEC)
• Compensation for tube voltage is measured over
the clinical range of kV, filters, and target materials
Limiting value :
Frequency :
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All density variations must be
within ± 0.15 of the target density;
Desirable : ± 0.10
Every six months
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Where to Get More Information
European protocol for the quality control of the
physical and technical aspects of mammography
screening.
http://euref.org/index.php?option=com_phocado
wnload&view=category&id=1&Itemid=8
American College of Radiology Mammography
Quality Control Manual, Reston VA, 1999.
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