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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. COMPARISON OF DIFFERENT DOSIMETRY SYSTEMS FOR DOSE MEASUREMENTS IN DIAGNOSTIC RADIOLOGY.

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COMPARISON OF DIFFERENT DOSIMETRY SYSTEMS FOR DOSE MEASUREMENTS IN DIAGNOSTIC RADIOLOGY

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  1. Đ. Milković, M. Ranogajec-Komor, S. Miljanić, Ž. Knežević and K. KrpanChildrenHospital Srebrnjak Zagreb, CroatiaRuđer Bošković 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 lowdoses at low and variable energies have to be measured • there exists a considerable variation in radiation doses delivered to patients (different X-rayequipment, 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, 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

  10. Dosimetry systems

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

  12. 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

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

  14. Mean value and standard deviation (SD) of doses measured on “phantoms “ in diagnostic unit Entr.: Entrance

  15. 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

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

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

  18. 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

  19. 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.

  20. ZAGREB

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

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