Energy Response of an Imaging Plate to Low-energy Photons for Use in Dosimetry

Abstract

The precise energy-dependent response curve of the imaging plate to low-energy photons was obtained by reciprocally combining a calculation and an experiment. The calculation was carried out using the Monte Carlo particle transportation code EGS5. The experiment was carried out using monochromatic photons at the photon factory in KEK. Initially, there was a discrepancy between the calculation and the experiment because of light attenuation in the phosphor layer in the read-out m -1 and decreasing the imaging plate (IP) response exponentially with depth from the phosphor surface, it was indicated that the calculation result basically follows the experimental result. By using the response curve obtained in this paper, radiation dose can be evaluated accurately in the dose estimation using IP.KEY WORDS: imaging plate, image plate, phosphorescence detector, EGS5, BaFBr, KEK, photon factory, energy response, computed radiography, low-energy photon. Original Paper I INTRODUCTIONAn imaging plate (IP) is a two-dimensional radiation detector that was rst introduced by the current FUJIFILM Corporation in 1981.1) IPs are mainly used for X-ray diagnosis in hospitals, autoradiography in biological research elds, and to obtain electron microscope images in various research. Since their appearance, there has been an underlying demand for their use as dosimeters because of their useful features such as high sensitivity, repetitive use availability, wide dynamic range to radiation dose, and high-speed read-out. Several studies have already been carried out that apply an IP as a dosimeter. 2, 3)One of the techniques that has been proposed and focused on is a method that combines an IP with multiple lters. In this method, several lters are used to change the response of the IP to photons of different energies. In order to estimate gamma and X-ray doses by this method, it is necessary to investigate the energy-dependent response of the IP to photons with suf cient accuracy beforehand. The energy response of the IP has already been reported by several researchers. 2,4) However, these evaluations mainly rely on experiments and are thus empirical. It is necessary to give general versatility to the response by adding theoretical evaluations.This research aims to obtain the energy response of the IP accurately by reciprocally combining a calculation and an experiment to realize accurate dose evaluation, focusing on responses to low-energy photons around 30 keV, because responses in this region vary widely according to previous research.2, 4) The IP response was initially evaluated by the calculation, and then by the experiment. In the last, these two were compared to verify the evaluation method of the calculation.