An optical method for three-dimensional dosimetry

Abstract

Accurate determination of the spatial distribution of the absorbed dose of ionising radiation plays an important role in radiotherapy, industrial radiation processing and many other applications. Computer calculations have frequently been used to estimate three-dimensional (3D) dose distributions in complex geometries and it becomes important to validate these by accurate 3D measurements. For this purpose we have been investigating the use of gelatin gels loaded with a modified Fricke solution which are pale orange in appearance and which, upon irradiation, become increasingly purple when viewed in normal light. This ferrous sulphate xylenol orange in gelatin gel (FXG) system displays very good properties, such as sensitivity, linearity and dynamic range, that make it suitable for 3D dosimetry applications. A high-speed optical tomography readout technique has been developed enabling two-dimensional projections of optical absorption data to be recorded rapidly. From these data the 3D absorbed dose distribution can quickly be derived with minimal degradation due to ion diffusion.