Modelling chemical and physical phenomena in polyacrylamide gel for radiation dosimetry.

摘要

Over the past decade there has been much interest in the development of three-dimensional gel dosimeters to aid the determination of the distribution and magnitude of absorbed radiation doses in clinical radiation therapy. A much studied dosimeter for verification of spatial dose distribution is the polyacrylamide system. Polyacrylamide gel (PAG) dosimetry is based on the radiation-induced copolymerization of acrylamide and bisacrylamide monomers in water and gelatin. Detection of the resulting spatial distribution of crosslinked-polymer within the dosimeter provides a promising means for calibration of three dimensional (3-D) radiation doses.;In this thesis, dynamic models were developed to describe the kinetic mechanisms and physical phenomena of the radiation-induced copolymerization of acrylamide and bisacrylamide monomers in PAG dosimeters. As a first step towards a valuable model for 3-D radiation dosimetry, a model was developed considering spatially uniform radiation dose distribution. The model is extended later to account for spatially non-uniform radiation dose distribution in one dimension.;The models can predict monomer and comonomer conversion, concentration of crosslinks, pendant double bonds and cyclized groups and temperature changes within the reaction medium, as a function of time and position. The predictions, computed under different experimental conditions and radiation doses, are consistent with the experimental findings in the literature.;The models will help in the understanding of chemical and physical phenomena and will provide a useful tool to optimize the polymer gel recipe to adapt the response of the dosimeter to different radiation therapy applications. More experimental data will be required to test model predictions and to estimate unknown model parameters.