The response of PAG density to dose: a model and experimental investigations

Abstract

X-ray computed tomography (CT) has emerged as a promising method of extracting three-dimensional (3D) dose information from polymer gel dosimeters. CT gel dosimetry has many practical advantages: ease of use, relatively low cost and accessibility to cancer hospitals and has been shown to have clinical potential. However, a primary disadvantage remains poor dose resolution due in part to the low sensitivity of CT contrast to dose. This CT contrast is the result of a small density change that occurs on polymerization and advanced understanding of this density change is required in order to optimize gel sensitivity to CT. This work proposes a simple model that describes the radiation induced density change in polyacrylamide gel (PAG) as a function of polymer yield and an intrinsic density change that occurs, independent of polymer yield, on polymerization. Using this model in combination with experimental CT and Raman spectroscopy work, several fundamental properties of the PAG density response to dose are discovered. The result is a valuable framework on which to focus future developments of more sensitive CT polymer gel dosimetry systems.