Simulation of Water Equivalency of Polymer Gel Dosimeters with GAMOS

Purpose: Polymer gel materials are used as dosimeters to provide three dimensional radiation dose distribution. An ideal gel dosimeter should offer radiological properties equivalent to water. This study aims to determine and compare the water equivalencies of various new polymer gel mixtures using Geant4-based Architecture for Medicine-Oriented Simulations (GAMOS) software program. Methods: To do this, percentage depth dose curves of the simulated polymer gel mixtures were compared with water curves. Different combinations of materials from 2 main classes were used in the mixtures: (1) Sodium Carboxymethyl Cellulose (SODIUM CMC), Polyvinyl Alcohol (PVA) and Polyethylene Glycol (PEG) as gel matrix, (2) 2-Hydroxyethyl Methacrylate (HEMA), 1-Vinyl-2-Pyrrolidinone (VP) and Diethylene Glycol Dimethacrylate (DEGDMA) as monomer. Each mixture also contained ultra-pure water and an antioxidant material called Tetrakis Hydroxymethyl Phosphonium Chloride ( THPC). Results: Percentage depth doses of gel mixtures and water was calculated for 6, 18 MV and 50, 70, 100, 150 kVp X rays. The mixture sample showing radiological behavior nearest to water over all energies was observed to be 31a (Water, PEG, HEMA, THPC), while the largest difference is observed in 11a (Water, SODIUM CMC, HEMA, THPC). Conclusion: As a result, simulated gel formulations were found to be radiologically water equivalent.