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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. Contents. - PowerPoint PPT Presentation
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IAEAInternational Atomic Energy Agency
RADIATION PROTECTION INDIAGNOSTIC AND
INTERVENTIONAL RADIOLOGY
Part 19.10: Optimization of protection in mammography
Practical exercise
IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
IAEA 19.10: Optimization of protection in mammography 2
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
IAEAInternational Atomic Energy Agency
Part 19.10: Optimization of protection in mammography
AEC
(Automatic Exposure Control)
IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
IAEA 19.10: Optimization of protection in mammography 4
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 film-processor and the use of the reference cassette.
IAEA 19.10: Optimization of protection in mammography 5
Equipment needed
• PMMA: plates 20 x 300 x 300 mm
• Densitometer
• Reference cassette
• Dosimeter
IAEA 19.10: Optimization of protection in mammography 6
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.
IAEA 19.10: Optimization of protection in mammography 7
OD control setting: central value and difference per step
Limiting valueLimiting 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
Adjustable range > 1.00
Frequency Frequency :: Step size: every six monthsCentral density: daily
IAEA 19.10: Optimization of protection in mammography 8
(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 : The deviation must be < ± 5%; desirable would be < ± 2%.
Frequency : Every six months
IAEA 19.10: Optimization of protection in mammography 9
(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
IAEA 19.10: Optimization of protection in mammography 10
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 : All density variations must be
within ± 0.20 of the target density.Desirable : ± 0.15 Frequency : Weekly
IAEA 19.10: Optimization of protection in mammography 11
Tube voltage compensation (AEC)
• Compensation for tube voltage is measured over the clinical range of kV, filters, and target materials
Limiting value : All density variations must be within ± 0.15 of the target
density; Desirable : ± 0.10
Frequency : Every six months
IAEA
Where to Get More Information
15.3: Optimization of protection in radiography 12
European protocol for the quality control of the physical and technical aspects of mammography screening. http://euref.org/index.php?option=com_phocadownload&view=category&id=1&Itemid=8
American College of Radiology Mammography Quality Control Manual, Reston VA, 1999.