A comparison between two gel dosimeters for low dose measurements

摘要

Gel dosimeters have been developed for three dimensional (3D) radiation dose distributionmeasurements. The application of gel dosimetry method was limited to a relatively high dose range. Known geldosimetry systems have linear response that cover the dynamic range 2-10 Gy applied in the field of radiotherapy.This is mainly due to the fact that gel detectors are generally biased on the chemical effects of ionising radiationand hence possess similar dosimetric properties that the traditional chemical dosimeters have.Two different gel dosimeters were studied for the measurements of a relatively low radiation absorbed dose, whichis close to the level of doses used in other medical applications. First type was a radiochromic gel dosimeterconsisting of Ferrous-sulphate, Xylenol-orange ion indicator and Gelatin (FXG); while the other is a polymer geldosimeter known as (MAGIC), which consists of; Methacrylic acid, Ascorbic acid, Gelatin and Initiated byCopper. The response of both dosimeters was compared in the dose range 0.1-2 Gy. Minimum detectable dose,dosimeters stability with time and the tissue-equivalence of the detector materials were also investigated.Detectors were prepared, irradiated and stored following standard procedures. Quantitative evaluation wasperformed in the visible range of spectrum using double beam spectrophotometer.Both gel dosimeters showed linear response in the studied range, however the polymer gel was found to havebetter response. Gel dosimeters have good stability for pre and post irradiation but they require to be kept undersuitable conditions. Temperature and light are the prominent factors that affect the dosimeter stability. The effectsof temperature stability were investigated for the studied materials.Gel dosimeters properties in the studied range do not differ form the general characteristic reported in theradiotherapy range for both dosimeters, however the use of this detector type to measure doses in the radiationprotection range is still require detailed investigation and probably a modification of the measurement system tocover the low dose range.