Transcript RADIATION PROTECTION IN DIAGNOSTIC RADIOLOGY

IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
RADIATION PROTECTION IN
DIAGNOSTIC AND
INTERVENTIONAL RADIOLOGY
Part 15.2: Optimization of protection in
radiography
Practical exercise
IAEA
International Atomic Energy Agency
Overview
• Subject matter : quality control of
general radiography system
• Step by step procedure to be followed
to implement the considered QC test:
• Radiation output linearity
• kVp and mA “compensation”
• Interpretation of results
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IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
Part 15.2: Optimization of protection in
radiography
The tube output measurement
IAEA
International Atomic Energy Agency
The tube output measurement
Purpose :
• To check that the radiation output [mGy/mAs]
remains constant as the mA is varied
Material:
• An electronic device (multi-function meter)
capable of measuring kV, time, and dose
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Radiation output linearity (I)
Method :
• Use an ion chamber or solid state detector at
~ 75 cm from the focal spot
• Place some lead vinyl under the detector to
standardize backscatter and protect the
phototimer
• Use manual mode, fixed 70 kVp and
exposure time (~ 100 ms)
• Measure dose at all mA settings used
clinically (also useful to measure kVp)
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Radiation output linearity (II)
Analysis :
• For each exposure, calculate the mAs, then
the radiation dose per mAs (this ideally
should be constant)
• Find the maximum and minimum values of
dose/mAs
• Calculate variation = (max - min)/(max + min)
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Radiation output linearity (III)
• The variation Should be < 0.1
• If > 0.1, then check the kVp - high values of
dose/mAs might be associated with high kVp
• If the tube has large and small focus
settings, measure linearity for each
separately
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Where to Get More Information
Quality Control in Diagnostic Imaging, Gray JE,
Winkler NT, Stears J, Frank ED. Available at no
cost. http://www.diquad.com/QC%20Book.html
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