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: 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 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

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 In air On phantom  : TLD  : RPLD ● : Calculated values of Hp(10)/Ka  : TLD  : RPLD

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

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.