RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY - PowerPoint PPT Presentation

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RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY

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To measure the tube voltage accuracy and reproducibility ... X-Ray tube. Filter. Ion. chamber. Lead slab. Table top. FFD. Phantom. IAEA ... – PowerPoint PPT presentation

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Title: RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY


1
RADIATION PROTECTION INDIAGNOSTIC
ANDINTERVENTIONAL RADIOLOGY
IAEA Training Material on Radiation Protection in
Diagnostic and Interventional Radiology
  • Part 19.4 Optimization of protection in
    Mammography
  • Practical exercise

2
Overview / objective
  • 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

3
Part 19.4 Optimization of protection in
Mammography
IAEA Training Material on Radiation Protection in
Diagnostic and Interventional Radiology
  • Topic 1 kV accuracy and reproducibility

4
Accuracy of tube voltage
  • Mammographic 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 whole
    used kV-range at 1 kV intervals should be
    performed

5
Reproducibility of tube voltage
  • The reproducibility is measured by repeated
    exposures at one fixed tube voltage that is
    normally used clinically (e.g. 28 kV)
  • A digital kVp-meter (specially designed for
    mammography) is presently the most suitable for
    this purpose

6
Accuracy and reproducibility of tube voltage
  • Limiting value Accuracy for 25-31 kV lt 1 kV
  • Reproducibility lt 0.5 kV
  • Frequency Every six months
  • Equipment Digital kVp-meter

7
Part 19.4 Optimization of protection in
Mammography
IAEA Training Material on Radiation Protection in
Diagnostic and Interventional Radiology
  • Topic 2 Measurement of radiation output -
    linearity

8
Measurements of Radiation Output (I)
  • The tube output is determined by the ratio of
    entrance surface dose (mGy) and focal spot charge
    (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
    under phantom conditions

9
Measurements of Radiation Output (II)
  • The output is generally measured as a function of
    tube and generator factors (e.g. kV, mA, s).
  • 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 focus of the X-ray tube in well
    collimated beam conditions.
  • The ionization chamber should be equipped with a
    suitable electrometer, preferably a direct
    readout device

10
Measurements of Radiation Output (III)
X-Ray tube
Filter
FFD
Phantom
Ion. chamber
Lead slab
Table top
11
Measurements of Radiation Output (IV)
  • In both geometry, 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 on the tube output are made by
    repeating measurements at constant exposure
    factors (e.g. 28 kV, 50 mAs)

12
Measurements of Radiation Output (V)
  • The output is measured at different kV by varying
    the kilovoltage in fixed steps while keeping the
    mAs product constant
  • Similar mAs product to that required for the
    reference exposure should be used for the
    measurement.
  • Correct for the distance from the focal spot to
    the detector and calculate the specific output at
    1 metre and the output rate at a distance equal
    to the focus-to-film distance (FFD).

13
Measurements of Radiation Output - linearity
  • The linearity of the output with the tube current
    can be examined by changing the mAs product while
    keeping the kilovoltage constant

14
Tube output
  • Limiting value acceptable gt30 mGy/mAs at 1 m
  • desirable 40-75 mGy/mAs at 1 m
  • acceptable gt 7.5 mGy/s at a distance equal
    to the FFD
  • desirable 10-30 mGy/s at a distance equal to
    the FFD
  • Frequency Every six months and when problems
    occur
  • Equipment Dosimeter, exposure timer
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