Dose Imaging in radiotherapy photon fields with Fricke and Normoxic-polymer Gels

Abstract

Gel dosimeters are integrating dosimeters, that enable dose verification in three dimensions. Optical analysis of gel dosimeters has demonstrated to be an available technique for imaging the absorbed in-phantom dose exposed to radiotherapy beams. The goal is to demonstrate the ability of gel dosimeters to achieve accurately and spatial resolution in dose mapping, also when high dose regions are produced by a complex three dimensional treatment planning. Two types of dosimeters are investigated, a Fricke gel (Fricke-Xylenol-orangeinfused gel) and a normoxic-polymer gel (polyacrylamide gel). Dosimeter gel samples of different shapes were exposed to photon fields, at various energies. Transmittance images were taken by means of a CCD camera and a spectrophotometer. In phantom 3-D images were realised with both dosimeter gels. An irradiation, using a linear accelerator, was realised in order to validate the method and techniques. Central axis depth dose profiles of the phantom were extracted and compared with ionization chamber measurements. Tissue-equivalence and other properties for both gels were studied using Monte Carlo techniques. Off-axis profiles and three dimensional dose distribution were obtained by simulations and compared with experimental dose distributions.