Enhancing the longevity of three-dimensional dose in a diffusion-controlled Fricke gel dosimeter.

Introduction: The principle of Fricke gel dosimeter is the oxidation of ferric ions on exposure to radiation. The major limitation in this dosimeter is the post-irradiation diffusion of ferric ions leading to degradation of spatial dose information.

Aims And Objectives: The primary objective of this study is to reduce diffusion of ferric ions post-irradiation and enhance the spatial stability of the dose for an acceptable period, within which it can be read out.

Materials And Methods: A novel method has been proposed to achieve this aim by incorporation of an anti-oxidant in the present Fricke gel dosimeter. The modified gel prepared in this study consisted of 50 mM sulfuric acid, 0.05 mM xylenol orange, 0.5 mM ferrous ammonium sulfate, and an optimal concentration of anti-oxidant. Different concentrations of the anti-oxidant (ascorbic acid and glycine) based gel dosimeters were prepared. The performance evaluations of the same were characterized dosimetrically with high energy photons (x- and gamma rays). Spectrophotometric measurements of gel dosimeters were performed at a wavelength of 585 nm and the post-irradiation diffusion was studied by observing the dose response over time. The spatial dose information from the large volume cylindrical gel phantoms was acquired using an in-house optical computed tomography scanner.

Results: Auto-oxidation and diffusion were controlled in the enhanced Fricke gel dosimeter by the incorporation of glycine as anti-oxidant. The post-irradiation dose in the gel dosimeter was stable up to 6 hours, thereby enhancing the longevity of three-dimensional (3D) dose.

Conclusion: The widely established limitations of Fricke gel dosimeter viz., auto-oxidation and diffusion were overcome using a novel method that incorporated optimal quantity of glycine as a suitable anti-oxidant. This modified Fricke gel dosimeter could be used as an effective 3D dosimeter for practical applications in radiotherapy.