1
Ð. Milkovic, M. Ranogajec-Komor, S. Miljanic,
Ž. Kneževic and K. Krpan Children Hospital
Srebrnjak Zagreb, CroatiaRuder Boškovic
Institute, Zagreb, Croatia
COMPARISON OF DIFFERENT DOSIMETRY SYSTEMS FOR
DOSE MEASUREMENTS IN DIAGNOSTIC RADIOLOGY
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 (40-300 kV, 1-20 mA) at
  the SSDL in air and on the water phantom (plastic
  bottle, F11 cm, V2.5 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
10
(No Transcript)
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
Mean value and standard deviation (SD) of doses
measured on phantoms in diagnostic unit
Phantom Doll (unknown plastic) Doll (unknown plastic) Doll (unknown plastic) Doll (unknown plastic) Bottle (water) Bottle (water) Bottle (water) Bottle (water)
Dosimeter RPL RPL TL TL RPL RPL TL 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 2.5 2.3 2.3 11.3 11.3 13.0 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 (LiFMg, 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
  LiFMg, 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 LiFMg, 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.