Investigation of the PAGAT polymer gel dosimeter using magnetic resonance imaging

Investigation of the normoxic PAGAT polymer gel dosimeter has been undertaken. The concentrations of the chemical components of the gel were varied and its response to ionizing radiation evaluated. Using MRI, the formulation to give the maximum change in the transverse relaxation rate R₂ was determined to be 4.5% N, N'–methylene-bis-acrylamide (bis), 4.5% acrylamide (AA), 5% gelatine, 5 mM tetrakis (hydroxymethyl) phosphonium chloride (THPC), 0.01 mM hydroquinone (HQ) and 86% H₂O. The optimal post-manufacture irradiation and post-irradiation imaging times were both determined to be 12 h. The R₂-dose response was linear up to 7 Gy with R₂-dose sensitivities of (0.183 ± 0.005) s⁻¹ Gy⁻¹, (0.182 ± 0.005) s⁻¹ Gy⁻¹ and (0.192 ± 0.005) s⁻¹ Gy⁻¹ when imaged at 12 h, 7 days and 24 days post-irradiation, respectively. The R₂-dose sensitivities were within the range of previously published values for the hypoxic PAG formulations. For the imaging parameters used in this study the optimum dose resolution was achieved for low doses. The normalized R2 edge response showed a high degree of spatial stability over a 24 day period. This study has shown that the normoxic PAGAT polymer gel has the properties of a dosimetric tool, which can be used in clinical radiotherapy. The PAGAT polymer gel has been shown to have similar qualities to the PAG polymer gel, while offering the significant advantage of simplification of the manufacturing procedure.