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Gel dosimeters are manufactured from radiation sensitive chemicals that, upon irradiation with ionising radiation, undergo a fundamental change in their properties as a function of the absorbed radiation dose. Over many years individuals have endeavoured to measure absorbed radiation dose distributions using gels. As long ago as 1950, the radiation-induced colour change in dyes was used to investigate radiation doses in gels.〔Day M J and Stein G 1950 Chemical effects of ionizing radiation in some gels ''Nature'' 166 146– 7〕 Further, in 1957 depth doses of photons and electrons in agar gels were investigated using spectrophotometry.〔Andrews H L, Murphy R E and LeBrun E J 1957 Gel dosimeter for depth dose measurements ''Rev Sci Instrum'' 28 329–32〕 Gel dosimetry today however, is founded mainly on the work of Gore ''et al'' who in 1984〔Gore J C, Kang Y S and Schulz R J 1984 Measurement of radiation dose distributions by nuclear magnetic resonance (NMR) imaging ''Phys Med Biol'' 29 1189–97〕 demonstrated that changes due to ionising radiation in Fricke dosimetry solutions,〔Fricke H and Morse S 1927 The chemical action of roentgen rays on dilute ferrous sulphate solutions as a measure of radiation dose ''Am J Roentgenol Radium Therapy Nucl Med'' 18 430–2〕 developed in the 1920s, could be measured using nuclear magnetic resonance (NMR). Gel dosimeters generally consist of two types; Fricke and polymer gel dosimeters and are usually evaluated or 'read-out' using magnetic resonance imaging (MRI), optical computer tomography (CT), x-ray CT or ultrasound. Since 1999 the DosGel and IC3DDose Conference Series on gel dosimetry has been held at various international venues. ==Fricke Gel Dosimeters== Gore ''et al'' investigated〔Gore J C, Kang Y S and Schulz R J 1984 Measurement of radiation dose distributions by nuclear magnetic resonance (NMR) imaging ''Phys Med Biol'' 29 1189–97〕 the nuclear magnetic resonance (NMR) relaxation properties of irradiated Fricke or ferrous sulphate dosimetry solutions〔Fricke H and Morse S 1927 The chemical action of roentgen rays on dilute ferrous sulphate solutions as a measure of radiation dose ''Am J Roentgenol Radium Therapy Nucl Med'' 18 430–2〕 showing that radiation-induced changes, in which ferrous (Fe2+) ions are converted to ferric (Fe3+) ions, could be quantified using NMR relaxation measurements. In 1986 Appleby ''et al''〔Appleby A, Christman E A and Leghrouz A 1986 Imaging of spatial radiation dose distribution in agarose gels using magnetic resonance ''Med Phys''. 14 382-4〕 reported that Fricke dosimetry solutions dispersed throughout a gel matrix could be used to obtain three-dimensional (3D) spatial dose information using magnetic resonance imaging (MRI). It was subsequently shown that irradiated Fricke-type gel dosimeters did not retain a spatially stable dose distribution due to ion diffusion within the irradiated dosimeters.〔Schulz R J, de Guzman A F, Nguyen D B and Gore J C 1990 Dose-response curves for Fricke- infused agarose gels as obtained by nuclear magnetic resonance ''Phys Med Biol'' 35 1611-22〕 Fricke solutions with various gelling agents such as gelatine, agarose, sephadex and polyvinyl alcohol (PVA) were investigated along with chelating agents such as xylenol orange (XO) to reduce diffusion. Numerous authors subsequently published results of their work to inhibit the ion diffusion with limited success and which was summarised by Baldock ''et al'' in 2001.〔Baldock C, Harris P J, Piercy A R, Healy B 2001 Experimental determination of the diffusion coefficient in two-dimensions in ferrous sulphate gels using the finite element method ''Australas Phys Eng Sci Med'' 24 19-30〕 By the early 1990s the diffusion problem was considered to be a significant one in the advancement of gel dosimetry. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「gel dosimetry」の詳細全文を読む スポンサード リンク
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