Transcript IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY Part 16.1: 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 16.1: Optimization of protection in
fluoroscopy
Practical exercise
IAEA
International Atomic Energy Agency
Overview
• To become familiar with quality control tests
in fluoroscopy.
• To measure the standard entrance dose rate
to the patient
• To assess the patient thickness variation
effect on scattered radiation
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IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
Part 16.1: Optimization of protection in
fluoroscopy
Measurement of standard entrance dose rate
IAEA
International Atomic Energy Agency
Fluoroscopy - Standard Dose Rate
Purpose :
• Measurement of dose rate at the entrance of
patient for different thickness
• Effect on scattered radiation
Method :
• Use different water equivalent absorber (acrylic, 20 cm
for a standard patient) or copper sheets (2 mm for a
standard patient
• Place dosimeter on input (x-ray tube side) of absorber
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Set-up for
measurement of
standard dose
rate.
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The ionization chamber should be protected
pressure and possible malfunctioning. It should
be in contact with the acrylic to include
backscatter in the measurement.
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Use 10 cm thickness of acrylic to simulate a thin
patient. The table to intensifier distance is 35
cm (this distance will be kept constant for the
different patient thicknesses)
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The chamber is easily centred using the
fluoroscopic image
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The entrance
dose rate is
1.78 mGy/min.
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The phantom
thickness is
now 20 cm.
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The chamber now reads 8.85 mGy/min.
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If the distance
between the
input screen of
the intensifier
and the entrance
of the patient is
increased, i.e.,
extra 20 cm.
The patient
entrance dose
rate will
increase.
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Note: the chamber looks magnified (the
intensifier is further away from the patient).
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Before (intensifier-table
distance: 35 cm)
Now (intensifier-table
distance: 55 cm)
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The entrance dose
rate with the
intensifier at 55 cm
from the table is
17.9 mGy/min (to
be compared with
the previous value
of 8.85 mGy/min).
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Now the
phantom
thickness is
increased up to
30 cm of acrylic.
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The patient
entrance dose
rate at the
surface of the
phantom
increases to
24.8 mGy/min
(the reading was
8.85 with 20 cm
thickness).
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The dose rate due to scatter radiation also
increases with the patient thickness. For 30 cm
acrylic, 3 mGy/h is measured close to the
phantom.
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With the high contrast mode the dose rate for
scatter radiation (30 cm acrylic), increases to
7 mGy/h. The patient entrance dose rate is
now 59.6 mGy/min.
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With 10 cm
acrylic the
dose rate due
to scattered
radiation is
0.2 mGy/h.
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With 20 cm
acrylic the
dose rate due
to scattered
radiation is
1 mGy/h.
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With 30 cm
acrylic the
dose rate due
to scattered
radiation is
3 mGy/h.
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Note that with the extra thickness the image
quality is extremely poor (the border of the
chamber is hardly visible)
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Fluoroscopy - Standard Dose Rate
Analysis :
• should be < 25 mGy/min
Frequency :
• acceptance, tube change
• generator repair
• intensifier repair
• 6 monthly
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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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