Measurement of scatter radiation spectrum from radiographic units Poster No.:

C-0309

Congress:

ECR 2013

Type:

Scientific Exhibit

Authors:

N. Kalyvas , I. Vlachos , X. Tsantilas , I. Kandarakis , G.

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Panayiotakis ; Athens/GR, Patras/GR Keywords:

Radiation physics, Radioprotection / Radiation dose, Pediatric, Plain radiographic studies, Instrumentation, Physics, Quality assurance, Dosimetric comparison

DOI:

10.1594/ecr2013/C-0309

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Purpose Radiation protection of people found themselves besides X-ray tubes is important. These could be either radiation workers (interventional radiologists, radiographers, nurses, technicians) or people assisting the examination like parents holding their children in order to perform a radiograph. Protection measures include lead aprons or any other type of radiation shielding. In addition radiation workers have personal dosimeters to measure the radiation dose. One aspect that affects the type of the shielding and thickness of the material used for shielding, as well as the calibration of the personal dosimeters, is the scatter X-rays energy distribution. The purpose of this study is the measurement of the scatter X-ray energy spectrum.

Methods and Materials 3

A 20x24x29 cm water phantom was irradiated by a commercial X-ray tube, mounted on a Philips Optimus X-ray generator. The X-ray tube demonstrated an HVL equals to 2.5mmAl at 75KVp. The upper plane of the phantom was positioned at 70cm from the X-ray tube focal spot, to simulate typical examination geometries. The field size was 2

chosen 40x40 cm in order to enhance the maximum scatter radiation from the phantom. The irradiation conditions comprised tube voltages of 60kVp, 70KVp, 81KVp, 90KVp, 100KVp and 120kVp at a fixed mAs value of approximately 45 and an exposure time equals to 200ms. The quality of the X-ray beam was altered by additionally inserting 2mmAl, 0.1mmCu+1mmAl and 0.2mmCu+1mmAl in the X-ray beam, in order to simulate exposures conditions from interventional radiology and computed tomography X-ray tubes. An Amptek XR-100 CdTe spectrometer was positioned at right angles to the phantom at a distance of 50cm. The spectrometer was equipped with a collimator having a diameter of 0.2mm. The response of the spectrometer for various energies in terms of energy per bin and detector quantum efficiency per energy value was known. In addition the primary X-ray spectrum at 81kVp was obtained. The accuracy of the X-ray voltage measurement with the primary radiation was checked via a PTW Freiburg Diavolt Universal T43014 KVp/time meter. Furthermore the primary X-ray ESD was measured with a PTW Freiburg Diavolt E T11035 dosimeter.

Results The correction of the spectrometer with respect to the energy per X-ray bin was equal to (1/5.89) KeV and the quantum efficiency response (QE) was described by the formula: QE=-1.09959+E*f(E)

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where E is the X-ray energy and f(E) is the measured number of photons. The primary X-ray beam spectrum is shown in Figure 1. It corresponds to 62 keV mean energy and an ESAK equals to 2.03mGy. The peak energy of the spectrum is close to 85 KeV (measured 82.4 KVp). The increased values demonstrated with the spectrometer can be attributed to pile up effects at the CdTe detector. The ESAK value calculated was different than the ESD directly measured (2.87mGy). The first reason is the inability of the spectrometer to measure backscatter. In addition the spectrometer may not was directly aligned with the anode, thus photon counting losses in the primary beam measurement may have occurred. The scatter spectral distributions measured without additional filtration are shown in Figure 2 The mean scatter energies were calculated as 36.5KeV, 43.3KeV, 51.6KeV, 62KeV, 68.56KeV and 80KeV, for X-ray tube voltages of 60KVp, 70KVp, 60KVp, 81KVp, 90KVp, 100KVp and 120KVp respectively. In Figure 3 the scatter spectral distribution with an additional 2mmAl filtration is demonstrated. In Figure 4 the scatter spectral distribution with an additional 0.1mmCu+1mmAl filtration is demonstrated. In Figure 5 the scatter spectral distribution with an additional 0.2mmCu +1mmAl filtration is demonstrated. By observing Figures 3 through 5 it can be deduced that the additional filtration at 100KVp and 120KVp did not alter the shape and mean energy of the scatter radiation. A point worth commenting is that with the insertion of the copper filter combinations, the signal obtained by the spectrometer at 60KVp to 90KVp at 45mAs was very low. Images for this section:

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Fig. 1: The primary X-rays energy spectrum at 81KVp tube voltage

Fig. 2: The scatter X-rays energy spectrum at various tube voltages without any additional filtration.

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Fig. 3: The scatter X-rays energy spectrum with an additional filtration of 2.0 mmAl at the primary beam.

Fig. 4: The scatter X-rays energy spectrum with an additional filtration of 0.1mCu +1.0mmAl at the primary beam.

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Fig. 5: The scatter X-rays energy spectrum with an additional filtration of 0.2mmCu +1mmAl at the primary beam.

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Conclusion An X-ray spectrometer was used to measure the scatter X-ray energy distribution for various exposure conditions. The scatter X-ray mean energy ranged from 36.5KeV to 80KeV. The added filtration at 100kVp and 120KVp did not practically affect the measured This knowledge is of value in calibrating personal dosimeters, or designing radiation protective materials.

Acknowledgement The authors are obliged to the "Sismanoglio" General Hospital of Athens for all the assistance provided.

References L. Abbene, A. L. Manna, F. Fauci, G. Gerardi, S. Stumbo, and G. Raso, "X-ray spectroscopy and dosimetry with a portable CdTe device," Nucl. Instrum. Methods Phys. Res. A, vol. A571 pp. 373-377, 2007.

Personal Information N. Kalyvas and I. Kandarakis are with the Department of Medical Instruments Technology, Technological Educational Institute of Athens, 12210 Ag. Spyridonos Str., Egaleo, Athens, Greece I. Vlachos and G. Panayiotakis are with the Department of Medical Physics, School of Medicine , University of Patras, 26500 Patras, Greece. X. Tsantilas is with the Department of Medical Physics, Sismanoglio General Hospital of Athens, Sismanogliou 1, 151 26 Marousi, Greece.

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