Transcript IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY Part 19.04: Optimization of protection in Mammography Practical.

IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
RADIATION PROTECTION IN
DIAGNOSTIC AND
INTERVENTIONAL RADIOLOGY
Part 19.04: Optimization of protection in
Mammography
Practical exercise
IAEA
International Atomic Energy Agency
Overview
• To be able to apply quality control protocol
to mammography equipment
• To measure the tube voltage accuracy and
reproducibility
• To measure the radiation output and linearity
IAEA
19.04 : Optimization of protection in Mammography
2
IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
Part 19.04: Optimization of protection in
Mammography
Topic 1: kV accuracy and reproducibility
IAEA
International Atomic Energy Agency
Accuracy of tube voltage
• Mammographic image quality and patient
dose are dependent on the kilovoltage (kV).
• A non-invasive tube voltage measurement
over the clinical kV-range at 1 kV intervals is
necessary
IAEA
19.04 : Optimization of protection in Mammography
4
Reproducibility of tube voltage
• The reproducibility is measured by repeated
exposures at one fixed clinical tube voltage,
e.g., 28 kV
• A digital kVp meter (designed for
mammography) is required
IAEA
19.04 : Optimization of protection in Mammography
5
Accuracy and reproducibility of tube
voltage
Limiting value : Accuracy for 25-31 kV: < ± 1 kV
Reproducibility < ± 0.5 kV
Frequency :
Annually
Equipment :
IAEA
Digital kVp meter
19.04 : Optimization of protection in Mammography
6
IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
Part 19.04: Optimization of protection in
Mammography
Topic 2: Measurement of radiation output linearity
IAEA
International Atomic Energy Agency
Measurements of Radiation Output (I)
• The tube output is determined by the ratio of
entrance surface dose (mGy) and mAs
• A high radiation output is desirable to ensure
that exposure times are sufficiently short to
minimize patient movement and discomfort
• The measurement can be performed either
in air or with a phantom
IAEA
19.04 : Optimization of protection in Mammography
8
Measurements of Radiation Output (II)
• The output is generally measured as a function kV
and mAs
• There are two experimental arrangements used for
the determination of the radiation output under
clinical conditions.
• An ionization chamber is positioned at a fixed distance
from the focal spot with the beam collimated to the
chamber
IAEA
19.04 : Optimization of protection in Mammography
9
Measurements of Radiation Output
(III)
X-Ray tube
Filter
FFD
Phantom
Ion chamber
Table top
IAEA
Lead sheet
19.04 : Optimization of protection in Mammography
10
Measurements of Radiation Output
(IV)
• In both geometries, a sheet of lead is placed
on the top of the table to obtain standard
backscatter conditions.
• The radiation output can be determined
under the following operating conditions:
Consistency checks for output are made by
repeating measurements at constant
exposure factors, e.g., 28 kV, 50 mAs
IAEA
19.04 : Optimization of protection in Mammography
11
Measurements of Radiation Output (V)
• The output is measured at various kVs , keeping
the mAs constant.
• The mAs required for the reference exposure
should be used
• Correct for the distance from the focal spot to the
detector. Calculate the output at 1 metre and the
output rate at a distance equal to the focus-to-film
distance (FFD).
IAEA
19.04 : Optimization of protection in Mammography
12
Measurements of Radiation Output linearity
• The linearity of the output with the tube
current can be determined by varying the
mAs, keeping the kilovoltage constant
IAEA
19.04 : Optimization of protection in Mammography
13
Tube output
Limiting value : acceptable: >30 mGy/mAs at 1 m
desirable: 40-75 mGy/mAs at 1 m
acceptable: > 7.5 mGy/s at a
distance equal to the FFD
desirable: 10-30 mGy/s at a
distance equal to the FFD
Frequency :
Equipment :
IAEA
Anually and when problems occur
Dosimeter, exposure timer
19.04 : Optimization of protection in Mammography
14
Digital systems
For systems with digital detectors additional
issues need to be considered in order to
optimize age quality.
Please see the training material on Digital
Radiology:
https://rpop.iaea.org/RPOP/RPoP/Content/Ad
ditionalResources/Training/1_TrainingMaterial/
DigitalRadiology.htm.
IAEA
19.4 : Optimization of protection in Mammography
15
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.
IAEA
19.04 : Optimization of protection in Mammography
16