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Đ. Milković, M. Ranogajec-Komor, S. Miljanić, Ž. Knežević and K. Krpan
Children Hospital Srebrnjak Zagreb, Croatia
Ruđer Bošković Institute, Zagreb, Croatia
COMPARISON OF DIFFERENT DOSIMETRY SYSTEMS FOR DOSE MEASUREMENTS IN
DIAGNOSTIC RADIOLOGY
Our wish is that all children are safe and protected in radiology department!
INTRODUCTION
Pulmonary X-rays are essential in the diagnostics of lung diseases of children and youth.
Chest radiography represents the majority of radiological examinations.
The starting basis for radiation protection is the exact determination of doses.
FEATURES:
very low doses at low and variable energies have to be measured
there exists a considerable variation in radiation doses delivered to patients (different X-ray equipment, different staff, etc.).
AIM
to test a new Shimadzu X-ray unit used for thorax examination of children
to compare a thermoluminescence (TL) dosimetry system based on LiF: Mg,Cu,P with the radiophotoluminescent (RPL) glass dosimetry system (FGD-200).
MATERIALS AND METHODSIrradiations:
137Cs gamma rays in air – for calibration
ISOVOLT 420 X Ray Unit (40-300 kV, 1-20 mA) at the SSDL in air and on the water phantom (plastic bottle, Φ=11 cm, V=2.5 l) – energy dependence
Energies: 33, 48, 65 keV
Dnom= 2 mGy (air kerma)
150 kV Shimadzu CH-200M unit in air
Phantoms:
water phantom (plastic bottle)
doll phantom
BABY PHANTOM
Voltage: 70 kVQuantity of charge: 1.6 mAsTime of irradiation: 5 msSize of the focus: 0.6 mmDistance: 150 cm
BABY FIX
Dosimetry systems
RESULTS
Energy dependence in SSDL
Doses in diagnostic X-ray unit
Energy dependence in SSDL
Relative dose in air: the mean values of doses measured (Dmeasured) “in air” relative to delivered doses specified as “air-kerma free-in-air” (Ka).On phantom: the mean values of the doses measured on the phantom relative to delivered doses specified as air kerma free-in-air
The energy dependence of TL and RPL dosimeters in SSDL
0.00.2
0.40.6
0.81.0
1.21.4
0 20 40 60 80
Mean photon energy (keV)
Re
lativ
e d
ose
0
0.5
1
1.5
2
0 20 40 60 80
Mean photon energy (keV)
Re
lativ
e d
ose
In air On phantom
: TLD : RPLD : TLD : RPLD
● : Calculated values of Hp(10)/Ka
Mean value and standard deviation (SD) of doses measured on “phantoms “ in
diagnostic unitPhantom Doll (unknown plastic) Bottle (water)
Dosimeter RPL TL RPL TL
Place of dosimeter
Back Sternum Back Sternum Entr. Exit Entr. Exit
Mean dose (mGy) 0.040 0.019 0.049 0.022 0.041 0.004 0.030 0.002
SD (mGy) 0.002 0.006 0.008 0.007 0.002 0.001 0.006 0.004
SD(%) 4.3 30.6 15.5 30.0 3.9 28.2 19.5 154.9
Dentrance/Dexit 2.5 2.3 11.3 13.0
Entr.: Entrance
Doses in diagnostic X-ray unitOn the doll: agreement of the dose values of RPL and TL dosimeters in entrance and exit beams On the water phantom: difference between the mean values measured in the ingoing beam with the two dosimeters
Reason: ▪ different materials of phantoms ▪ different energy absorption characteristics of the two dosimeters (below 50 keV) on water phantom
CONCLUSION
TLD (LiF:Mg, Cu, P )(termoluminiscent dosimeter)
RPL(radiophotoluminiscent glass dosimeter)
TLD (LiF: Mg, Cu, P ) (termoluminiscent dosimeter)
High sensitivity
In spite of its anomalous energy dependence nearly tissue- equivalence
Agreement with earlier results
RPL (radiophotoluminiscent glass dosimeter)
Higher sensitivityEnergy dependance “in air” is better than for LiF:Mg, Cu, P (33-65 keV mean energies)Energy dependance curve on the water phantom changes in opposite direction than the calculated Hp(10) values
The absolute difference from Hp(10) is not larger than for LiF:Mg, Cu, P
CONCLUSION
The measured dose values in X-ray diagnostic unit are in accordance with the characteristics found in SSDL for both dosimeters.
The RPL system seems to be suitable for dosimetric measurements in X- ray diagnostics.
ZAGREB
Thank you for your
attention!
The authors are grateful to Chiyoda Technol Corporation, Japan for the support of this work.
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