Transcript IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY Part 16.2: Optimization of protection in fluoroscopy Practical.

IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
RADIATION PROTECTION IN
DIAGNOSTIC AND
INTERVENTIONAL RADIOLOGY
Part 16.2: Optimization of protection in
fluoroscopy
Practical exercise
IAEA
International Atomic Energy Agency
Overview / Objectives
• To become familiar with quality control tests
in fluoroscopy
• To measure the maximum dose rate to the
patient
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16.2: Optimization of protection in fluoroscopy
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IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
Part 16.2: Optimization of protection in
fluoroscopy
Maximum dose rate
IAEA
International Atomic Energy Agency
Fluoroscopy - Maximum Dose Rate
Purpose :
• to know the maximum dose rate to the patient
Method :
• place ~2mm lead over the image intensifier
• place a dosimeter ~ 30 cm from the intensifier
• operate unit at maximum kVp and mA
• measure dose rate
• X ray tube below the patient table
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Set-up for
measurement of
maximum dose
rate.
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The ionization chamber should be protected to
avoid pressure and possible malfunctioning. It
should be in contact with the acrylic to measure
also backscattering.
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The intensifier
should be as far as
possible from the
table with the x-ray
tube as close as
possible to the
patient position.
These are the worst
conditions in terms
of maximum
radiation dose to the
skin patient
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Note: the X-ray tube is placed very
close to the table.
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A radio-opaque marker (a key) can be used to
center the chamber in the image field
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The key shows the motion of the C-arm
or the table.
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The key should be removed after having
centred the chamber.
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A folded lead apron
is used to measure
the maximum dose
rate (use enough
layers to
approximate 2 mm
of lead). The lead
apron is placed over
the protected
chamber.
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Note: This geometry is the worst in terms of patient
radiation dose— the tube close to the table and the
intensifier far from the patient. It also increases the
scattered radiation dose to the physician and staff.
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The dose rate is
79.5 mGy/min
for this situation
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The image quality is poor. The chamber
edge is hardly visible.
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The generator selects the maximum
possible kV (110 kV for this equipment)
and 3.6 mA.
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In the high contrast mode with the same
geometry, the maximum of 110 kV and
7.34 mA is selected by the generator.
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The image quality is still poor although
slightly improved.
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In the high contrast mode the maximum
dose rate is 186.7 mGy/min.
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Fluoroscopy - Maximum Dose Rate
Analysis :
• FDA limits:
• normal-dose fluoroscopy: maximum air-kerma rate 88
mGy/min (30 cm from the image receptor)
• High-dose-rate fluoroscopy: maximum air-kerma rate
176 mGy/min (30 cm from image receptor)
Frequency :
• acceptance, 6-monthly
• tube change, generator repair
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Importance of quality assurance (QA)
• It is very important to have a QA
programmes established in your practice
and not to base dose controls on
specification provided by the manufacturer
or on the additional checks performed by the
manufacturer.
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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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