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.

弗里克剂量计是一种化学溶液，当受到电离辐射时，铁离子会氧化为三价铁离子。它已被证明是提高剂量测定程序准确性的有效标准方法，并且是电离室的替代方法。通过读取溶液辐照后的光密度获得结果，并在弗里克溶液中获得剂量，然后使用转换因子将其转换为对水的吸收剂量。但是，即使没有电离辐射，溶液中也会发生化学氧化。本研究中使用的PMMA支架包含约1.8 cm ³Fricke溶液，足以进行近距离放射治疗源的剂量测定。本文的目的是研究Fricke解决方案与新支架的PMMA壁之间的相互作用一段时间，然后再使用。这项工作表明，这种相互作用的影响是不可忽略的，如果在支架制造后的头几个月使用，可能会导致最终结果的系统不确定性。此后，反应稳定，使PMMA材料适用于Fricke剂量测定法。