Radiological characterization and water equivalency of genipin gel for x-ray and electron beam dosimetry Tina Gorjiara, Robin Hill, Zdenka Kuncic et al. Abstract. For a polymer gel dosimeter to be of use in radiation dosimetry, it should display water-equivalent radiological properties. In this study, the radiological properties of the MAGIC (Methacrylic and Ascorbic acid in Gelatin Initiated by Copper) normoxic polymer gels were investigated. The mass density ( ) was determined based on Archimedes principle. The weight fraction of elemental composition and the effective atomic number (Z eff ) were calculated. The electron density was also measured with 90° scattering angle at room temperature. The linear attenuation coefficient (µ) of unirradiated gel, irradiated gel, and water were determined using Am-241 based on narrow beam geometry. Monte Carlo simulation was used to calculate the depth doses response of MAGIC gel and water for 6MV photon beam. The weight fractions of elements composition of MAGIC gel were close to that for water. The mass density was found to be 1027 ± 2 kg m 3 , which is also very close to mass density of muscle tissue (1030 kg m 3 ) and 2.7% higher than that of water. The electron density ( e ) and atomic number (Z eff ) were found to be 3.43 × 10 29 e m 3 and 7.105, respectively. The electron density measured was 2.6% greater than that for water. The atomic number was very close to that for water. The prepared MAGIC gel was found to be water equivalent based on the study of element composition, mass density, electron density and atomic number. The linear attenuation coefficient of unirradiated gel was very close to that of water. The µ of irradiated gel was found to be linear with dose 2-40 Gy. The depth dose response for MAGIC gel from a 6 MV photon beam had a percentage dose difference to water of less than 1%. Therefore it satisfies the criteria to be a good polymer gel dosimeter for radiotherapy.
Abstract
The aim of this project is to develop and to evaluate the CT based MAGAT (methacrylic acid, gelatine and tetrakis phosphonium chloride) polymer gel dosimetry for measuring 3D dose distributions in radiation treatment. The MAGAT gel was prepared based on the formulation proposed in the literature. The percentage depth dose (PDD) and beam profile of 8 x 8 cm2 field size photon beam from a 6 MV linear accelerator were measured. Monte Carlo simulation was carried out to calculate PDD and beam profiles in the simulated MAGAT gel phantom to verify the data measured using MAGAT gel dosimetry for the 8 x 8 cm2 field size. The PDD and beam profile calculated using simulated MAGAT gel phantom agreed very well with that measured using MAGAT gel dosimetry. However, there were some differences between the simulated PDD with that measured at the surface region due to the electron contamination at the surface of the simulated phantom. In conclusion, the results showed that the CT based MAGAT gel dosimetry system is promising method to measure three- dimensional dose distribution based on PDD and Beam profile measurement.
Keywords: MAGAT gel, CT, Monte Carlo simulation
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