1. 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

2. Our wish is that all children are safe and protected in radiology department!

3. 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.

4. 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.).

5. 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).

6. MATERIALS AND METHODS Irradiations:
137Cs gamma rays in air – for calibration
ISOVOLT 420 X Ray Unit ( 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

7. BABY PHANTOM

8. Voltage: 70 kV
Quantity of charge: 1.6 mAs
Time of irradiation: 5 ms
Size of the focus: 0.6 mm
Distance: 150 cm

9. BABY FIX

11. Dosimetry systems

12. RESULTS
Energy dependence in SSDL
Doses in diagnostic X-ray unit

13. 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

14. The energy dependence of TL and RPL dosimeters in SSDL
In air
On phantom
 : TLD  : RPLD
● : Calculated values of Hp(10)/Ka
 : TLD  : RPLD

15. Doll (unknown plastic)
Mean value and standard deviation (SD) of doses measured on “phantoms “ in diagnostic unit
Phantom
Doll (unknown plastic)
Bottle (water)
Dosimeter
RPL TL
Place of dosimeter
Back
Sternum
Entr.
Exit
Mean dose (mGy)
0.040
0.019
0.049
0.022
0.041
0.004
0.030
0.002
SD (mGy)
0.006
0.008
0.007
0.001 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

16. 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

17. CONCLUSION TLD (LiF:Mg, Cu, P ) (termoluminiscent dosimeter) RPL
(radiophotoluminiscent glass dosimeter)

18. TLD (LiF: Mg, Cu, P ) (termoluminiscent dosimeter)
High sensitivity
In spite of its anomalous energy dependence nearly tissue- equivalence
Agreement with earlier results

19. 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

20. 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.

21. ZAGREB

22. Thank you for your attention!
The authors are grateful to Chiyoda Technol Corporation, Japan for the support of this work.