Jpn. J. Appl. Phys. 51 (2012) 046401 (8 pages)  |Previous Article| |Next Article|  |Table of Contents|
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Quenching Effect, Signal to Noise, Contrast to Noise Ratios on Scintillator Screens for Proton Beam Dosimetry System

Seonkyu Kim1, Se Byeong Lee1, Seung Hoon Yoo1, Sungkoo Cho1, Dong Wook Kim2, Dongho Shin1, Sung Yong Park3, Chan Hyeong Kim4, and Sang Hoon Lee1,4

1Proton Therapy Center, National Cancer Center, Goyang, Gyeonggi 410-769, Korea
2Department of Radiation Oncology, Kangdong Kyunghee University Hospital, Seoul 137-732, Korea
3Proton Therapy Center, McLaren Cancer Institute, Flint, MI 48532, U.S.A.
4Department of Nuclear Engineering, Hanyang University, Seoul 133-791, Korea

(Received June 13, 2011; revised January 3, 2012; accepted January 24, 2012; published online March 26, 2012)

There has been dosimetry using scintillator screen for proton quality assurance recently. To develop a proton beam dosimetry system using scintillator, we evaluated the dosimetric properties and imaging quality for three kinds of scintillator screens. Proton beam ranges of 6, 9, and 12 g/cm2 were determined in a water phantom using an ion chamber. Beam current was optimized about each scintillator screen at proton beam ranges of 6, 9, and 12 g/cm2. Dose rate was in beam condition of proton treatment. For comparison of the dosimetric properties, the quenching correction factors and standard deviations for the scintillator screens (C6H6, Gd2O2S:Tb, and Gd2O2S) were obtained using the relation between the light yield (scintillator-relative output) and the dose distribution (diode-relative output). The image qualities for the scintillator screens were compared, using the signal-to-noise ratio (SNR) and the contrast-to-noise ratio (CNR), in consideration of the physical properties of the scintillator materials. After correction of the quenching effect, the correction factor for scintillator screen Gd2O2S:Tb was the lowest, at 0.004 g/(cm2 MeV). The standard deviations of the difference between the yields measured by the scintillator screens and the diode detector averaged 1, 1.3, and 1.3, respectively, at all of the ranges from origin to the peak position. The dosimetric properties of scintillator screens were no large difference. The SNRs of the scintillator screens (C6H6, Gd2O2S:Tb, and Gd2O2S) averaged 28.67, 40.18, and 24.56, respectively, at all ranges. The CNRs of the scintillator screens (C6H6, Gd2O2S:Tb, and Gd2O2S) averaged 0.44, 0.33, and 0.42, respectively, at all ranges. The highest SNR and the lowest CNR of scintillator screen Gd2O2S:Tb were more excellent than those of the other scintillator screens. We evaluated the dosimetric properties in terms of the quenching-effect correction factors, standard deviations image qualities in terms of SNR and CNR about scintillator screens. The correction factor and standard deviation for scintillator screens made no large difference. Scintillator screen Gd2O2S:Tb had the highest value of SNR and the lowest value of CNR, and accordingly was considered to be best in proton beam imaging quality.

DOI: 10.1143/JJAP.51.046401

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