Analysis of the Fricke solution-PMMA interaction and potential effect on the accuracy of dose measurements

Abstract The Fricke dosimeter is a chemical solution whereby oxidation of ferrous ions to ferric ions occurs when submitted to ionizing radiation. It has been shown to be an effective standard method to improve the accuracy of dosimetry procedures and as an alternative to ionization chambers. The results are obtained by reading the optical density of the solution after it is irradiated, and the dose is obtained in the Fricke solution and, subsequently, converted to the absorbed dose to water by using a conversion factor. However, chemical oxidation in the solution can occur even in the absence of the ionizing radiation. The PMMA holder used in the current study contains approximately 1.8 cm3 of Fricke solution, which is sufficient for the dosimetry of brachytherapy sources. The aim of this paper was to study the interaction between the Fricke solution and the PMMA walls of a new holder for a period of time, prior to its use. This work demonstrates that the effect of this interaction is not negligible and can cause a systematic uncertainty of the final results if used in the first months after the holder is manufactured. After this, the reaction stabilizes making the PMMA material suitable for the Fricke dosimetry.