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IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology. RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY. Part 16.2: Optimization of protection in fluoroscopy Practical exercise. Overview / Objectives.

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radiation protection in diagnostic and interventional radiology

IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology

RADIATION PROTECTION INDIAGNOSTIC ANDINTERVENTIONAL RADIOLOGY

Part 16.2: Optimization of protection in fluoroscopy

Practical exercise

overview objectives
Overview / Objectives
  • To become familiar with quality control tests in fluoroscopy
  • To measure the maximum dose rate to the patient

16.2: Optimization of protection in fluoroscopy

fluoroscopy maximum dose rate
Fluoroscopy - Maximum Dose Rate

Purpose :

  • to know the maximum dose rate to the patient

Method :

  • place ~2mm lead over the image intensifier
  • place a dosimeter ~ 30 cm from the intensifier
  • operate unit at maximum kVp and mA
  • measure dose rate
  • X ray tube below the patient table

16.2: Optimization of protection in fluoroscopy

slide5

Set-up for measurement of maximum dose rate.

16.2: Optimization of protection in fluoroscopy

slide6

The ionization chamber should be protected to avoid pressure and possible malfunctioning. It should be in contact with the acrylic to measure also backscattering.

16.2: Optimization of protection in fluoroscopy

slide7

The intensifier should be as far as possible from the table with the x-ray tube as close as possible to the patient position.

These are the worst conditions in terms of maximum radiation dose tothe skin patient

16.2: Optimization of protection in fluoroscopy

slide8

Note:the X-ray tube is placed very close to the table.

16.2: Optimization of protection in fluoroscopy

slide9

A radio-opaque marker (a key) can be used to center the chamber in the image field

16.2: Optimization of protection in fluoroscopy

slide10

The key shows the motion of the C-arm or the table.

16.2: Optimization of protection in fluoroscopy

slide11

The key should be removed after having centred the chamber.

16.2: Optimization of protection in fluoroscopy

slide12

A folded lead apron is used to measure the maximum dose rate (use enough layers to approximate 2 mm of lead). The lead apron is placed over the protected chamber.

16.2: Optimization of protection in fluoroscopy

slide13

Note:This geometry is the worst in terms of patient radiation dose— the tube close to the table and the intensifier far from the patient. It also increases the scattered radiation dose to the physician and staff.

16.2: Optimization of protection in fluoroscopy

slide14

The dose rate is79.5 mGy/minfor this situation

16.2: Optimization of protection in fluoroscopy

slide15

The image quality is poor. The chamber edge is hardly visible.

16.2: Optimization of protection in fluoroscopy

slide16

The generator selects the maximum possible kV (110 kV for this equipment) and 3.6 mA.

16.2: Optimization of protection in fluoroscopy

slide17

In the high contrast mode with the same geometry, the maximum of 110 kV and 7.34 mA is selected by the generator.

16.2: Optimization of protection in fluoroscopy

slide18

The image quality is still poor although slightly improved.

16.2: Optimization of protection in fluoroscopy

slide19

In thehigh contrast modethe maximum dose rate is186.7 mGy/min.

16.2: Optimization of protection in fluoroscopy

fluoroscopy maximum dose rate20
Fluoroscopy - Maximum Dose Rate

Analysis :

  • FDA limits:
    • normal-dose fluoroscopy: maximum air-kerma rate 88 mGy/min (30 cm from the image receptor)
    • High-dose-rate fluoroscopy: maximum air-kerma rate 176 mGy/min (30 cm from image receptor)

Frequency :

  • acceptance, 6-monthly
  • tube change, generator repair

16.2: Optimization of protection in fluoroscopy

importance of quality assurance qa
Importance of quality assurance (QA)
  • It is very important to have a QA programmes established in your practice and not to base dose controls on specification provided by the manufacturer or on the additional checks performed by the manufacturer.

16.2: Optimization of protection in fluoroscopy

where to get more information
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

15.3: Optimization of protection in radiography