RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY - PowerPoint by B1d9cb3O

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									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 / Objectives

• To become familiar with quality control test
  in fluoroscopy.
• To measure the standard entrance dose rate
  to the patient
• To assess the patient thickness variation
  effect on scattered radiation



    IAEA             16.1: Optimization of protection in f luoroscopy   2
  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 scatter radiation
Method :
  • use different water equivalent absorber (PMMA) on I.I.
    face (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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Use 10 cm thickness of polymethil methacrylate
to simulate a thin patient. The table to I.I.
distance is 35 cm (this distance will be kept
constant for the different patient thicknesses)




 IAEA               16.1: Optimization of protection in f luoroscopy   5
The chamber is easily centred due to the
small magnification (the I.I. is close to the
chamber).




 IAEA               16.1: Optimization of protection in f luoroscopy   6
                                   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 I.I. 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 I.I.
is further away from the patient).




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Before (I.I. - table couch
distance: 35 cm)




                                  Now (I.I. - table
                                  couch distance: 55
                                  cm)
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                            The entrance
                            dose rate with the
                            I.I. at 55 cm
                            distance from the
                            couch table is
                            17.91 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
                              polymethil
                              methacrylate.



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                                  The patient
                                  entrance dose
                                  rate at the
                                  surface of the
                                  phantom
                                  increases up to
                                  24.8 mGy/min
                                  (remember that
                                  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
PMMA, a value of 3 mGy/h can be measured
close to the phantom.




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With the high contrast mode the dose rate for
scatter radiation (30 cm PMMA), increases up to
7 mGy/h. The patient entrance dose rate is now
59.6 mGy/min.




 IAEA               16.1: Optimization of protection in f luoroscopy   17
                                 With 10 cm
                                 PMMA the
                                 dose rate due
                                 to scattered
                                 radiation is 0.2
                                 mGy/h.




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                                  With 20 cm
                                  PMMA the
                                  dose rate due
                                  to scattered
                                  radiation is 1
                                  mGy/h.




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                                  With 30 cm
                                  PMMA 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
  • I.I. repair
  • 6 monthly


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