Transcript Naslo autor boplnica institut

COMPARISON OF DIFFERENT DOSIMETRY
SYSTEMS FOR DOSE MEASUREMENTS IN
DIAGNOSTIC RADIOLOGY
Đ. Milković, M. Ranogajec-Komor, S. Miljanić, Ž. Knežević and K. Krpan
Children Hospital Srebrnjak Zagreb, Croatia
Ruđer Bošković Institute, Zagreb, Croatia
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 METHODS
Irradiations:
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:
137Cs
water phantom (plastic bottle)
doll phantom
BABY PHANTOM
Voltage: 70 kV
Quantity of charge: 1.6 mAs
Time of irradiation: 5 ms
Size of the focus: 0.6 mm
Distance: 150 cm
BABY FIX
Dosimetry systems
Dosimeter system
Reader
Detector material
Annealing
Temperature (oC)
Time (min)
Preheat
Temperature (oC)
Time (min)
Readout
Temperature (oC)
Time (s)
RPL
FGD-200 Series
silver activated
phosphate glass
(Japan)
TL
Toledo 654
LiF:Mg,Cu,P
400
60
210
readout cycle
70
60
100
20
UV excitation
210
35
(China)
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
On phantom
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
2
Relative dose
Relative dose
In air
1.5
1
0.5
0
0
20
40
60
Mean photon energy (keV)
 : TLD
 : RPLD
80
0
20
40
60
80
Mean photon energy (keV)
 : TLD  : RPLD
● : Calculated values of Hp(10)/Ka
Mean value and standard deviation (SD) of
doses measured on “phantoms “ in
diagnostic unit
Phantom
Doll (unknown plastic)
RPL
Dosimeter
Bottle (water)
TL
RPL
TL
Place of
dosimeter
Back
Sternum
Back
Sternum
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
Dentrance/Dexit
Entr.: Entrance
2.5
2.3
Entr.
3.9
Exit
28.2
11.3
Entr.
19.5
Exit
154.9
13.0
Doses in diagnostic X-ray unit
On 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 sensitivity
Energy 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.