RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY

IAEAInternational Atomic Energy Agency

RADIATION PROTECTION INDIAGNOSTIC AND

INTERVENTIONAL RADIOLOGY

Part 16.1: Optimization of protection in fluoroscopy

Practical exercise

IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology

IAEA 16.1: Optimization of protection in fluoroscopy 2

Overview

• To become familiar with quality control tests in fluoroscopy.

• To measure the standard entrance dose rate to the patient

• To assess the patient thickness variation effect on scattered radiation

IAEAInternational Atomic Energy Agency

Part 16.1: Optimization of protection in fluoroscopy

Measurement of standard entrance dose rate

IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology


Fluoroscopy - Standard Dose Rate

Purpose :

• Measurement of dose rate at the entrance of patient for different thickness

• Effect on scattered radiation

Method :• Use different water equivalent absorber (acrylic, 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


Set-up for Set-up for measurement of measurement of standard dose standard dose rate.rate.


The ionization chamber should be protected The ionization chamber should be protected pressure and possible malfunctioning. It should pressure and possible malfunctioning. It should be in contact with the acrylic to include be in contact with the acrylic to include backscatter in the measurement. backscatter in the measurement.


UseUse 10 cm10 cm thickness of acrylic to simulate a thin thickness of acrylic to simulate a thin patient. The table to intensifier distance ispatient. The table to intensifier distance is 35 35 cmcm (this distance will be kept constant for the (this distance will be kept constant for the different patient thicknesses)different patient thicknesses)


The chamber is easily centred using the The chamber is easily centred using the fluoroscopic imagefluoroscopic image


The entrance The entrance dose rate isdose rate is

1.78 mGy/min.1.78 mGy/min.


The phantom The phantom thickness is thickness is nownow 20 cm20 cm..


The chamber now readsThe chamber now reads 8.85 mGy/min.8.85 mGy/min.


If the distance If the distance between the between the input screen of input screen of the intensifier the intensifier and the entrance and the entrance of the patient of the patient isis increased, i.e.,increased, i.e., extra 20 cm.extra 20 cm.The patient The patient entrance dose entrance dose rate will rate will increase.increase.


Note:Note: the chamber looks magnified (the the chamber looks magnified (the intensifier is further away from the patient).intensifier is further away from the patient).


Before (intensifier-table distance: 35 cm)

Now (intensifier-table distance: 55 cm)


The entrance dose The entrance dose rate with the rate with the intensifier at 55 cm intensifier at 55 cm from the table isfrom the table is 17.9 mGy/min17.9 mGy/min (to (to be compared with be compared with the previous value the previous value of 8.85 mGy/min).of 8.85 mGy/min).


Now the Now the phantom phantom thickness is thickness is increased up toincreased up to 30 cm30 cm of acrylic.of acrylic.


The patient The patient entrance dose entrance dose rate at the rate at the surface of the surface of the phantom phantom increases toincreases to 24.8 mGy/min24.8 mGy/min (the reading was (the reading was 8.85 with 20 cm 8.85 with 20 cm thickness).thickness).


The dose rate due to scatter radiation also The dose rate due to scatter radiation also increases with the patient thickness. Forincreases with the patient thickness. For 30 cm30 cm acrylic, acrylic, 3 mGy/h3 mGy/h is measured close to the is measured close to the phantom.phantom.


With theWith the high contrast modehigh contrast mode the dose rate for the dose rate for scatter radiation scatter radiation ((30 cm acrylic), increases to30 cm acrylic), increases to 7 mGy/h7 mGy/h.. The patient entrance dose rate is The patient entrance dose rate is now 59.6 mGy/min.now 59.6 mGy/min.


WithWith 10 cm10 cm acrylic the acrylic the dose rate due dose rate due to scattered to scattered radiation isradiation is 0.2 mGy/h. 0.2 mGy/h.


WithWith 20 cm20 cm acrylic the acrylic the dose rate due dose rate due to scattered to scattered radiation isradiation is 1 mGy/h. 1 mGy/h.


WithWith 30 cm30 cm acrylicacrylic the the dose rate due dose rate due to scattered to scattered radiation isradiation is 3 mGy/h. 3 mGy/h.


Note that with the extra thickness the image quality is extremely poor (the border of the chamber is hardly visible)


Fluoroscopy - Standard Dose Rate

Analysis :• should be < 25 mGy/min

Frequency :• acceptance, tube change

• generator repair

• intensifier repair

• 6 monthly

IAEA

Where to Get More Information

15.3: Optimization of protection in radiography 25

Quality Control in Diagnostic Imaging, Gray JE, Winkler NT, Stears J, Frank ED. Available at no cost. http://www.diquad.com/QC%20Book.html

RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY

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