Transcript IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY Part 15.1: Optimization of protection in radiography Practical.

IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
RADIATION PROTECTION IN
DIAGNOSTIC AND
INTERVENTIONAL RADIOLOGY
Part 15.1: Optimization of protection in
radiography
Practical exercise
IAEA
International Atomic Energy Agency
Overview / Objectives
• Subject matter : quality control of
general radiography system
• Step by step procedure to be followed
to implement QC test:
• kVp Accuracy and Reproducibility
• Interpretation of results
IAEA
15.1: Optimization of protection in radiography
2
IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
Part 15.1 : Optimization of protection in
radiography
kVp measurement (Accuracy and Reproducibility)
IAEA
International Atomic Energy Agency
kVp measurement
Purpose :
• Image quality and patient dose are dependent
on any variation in the generator kilovoltage (kV)
of the x-ray set. Therefore an accurate kV
calibration is required.
• A non-invasive tube voltage check over the
range of kV used clinically should be performed
Equipment :
• An electronic device (like multi-function meter)
to measure : kVp, time, dose.
IAEA
15.1: Optimization of protection in radiography
4
Multi-Function Meters
IAEA
15.1: Optimization of protection in radiography
5
kVp Accuracy
• Before making measurements, one must
understand what “kVp” means
• There are 3 definitions of kVp, only one is
commonly used
• CAUTION : some mobile x-ray units use a
capacitor, and the kVp decreases during the
exposure
IAEA
15.1: Optimization of protection in radiography
6
kVp Definitions
IAEA
15.1: Optimization of protection in radiography
7
kVp Accuracy
Method :
• set meter at about 100 cm from focal spot or as
prescribed by the manufacturer
• set ~ 20 mAs
• measure kVp from about 60 - 120 kVp (e.g., 60,
70, 80, 100, and 120)
• calculate error between selected and measured
value
IAEA
15.1: Optimization of protection in radiography
8
kVp Accuracy
Analysis :
• The difference between selected and measure
kVp should be within  5%
Frequency :
• acceptance
• tube change, generator maintenance
• annual
IAEA
15.1: Optimization of protection in radiography
9
kVp Reproducibility
• This test checks that the kVp will stay the
same from exposure to exposure
Method :
• same setup, but at fixed 70 kVp
• make 5 exposures about 30 seconds apart (be
careful of tube load!)
IAEA
15.1: Optimization of protection in radiography
10
kVp Reproducibility
Analysis :
• calculate coefficient of variation (CV)
• CV = (standard deviation/mean) of the 5
readings
• CV must be less than 2%
Frequency :
• as for accuracy
IAEA
15.1: Optimization of protection in radiography
11
kVp Reproducibility
Further test :
• older x-ray units may have a mechanical
selector for kVp
• test this by moving the kVp dial up, down, then
back to 70 before each exposure
• a variation of  3 kVp is permitted
IAEA
15.1: Optimization of protection in radiography
12