Room: AAPM ePoster Library
Purpose: aim of this study is to compare two different methodologies to determine the absorbed dose to water of a 6 MV photon beam, using Fricke dosimetry.
Methods: In this study, two different methodologies were compared, in order to obtain the absorbed dose to water: one based on the National Research Council Canada (NRC) studies, using polyethylene bags filled with Fricke solution; and the other, based on the Radiology Science Laboratory of Rio de Janeiro State University (LCR/UERJ) studies, using PMMA gloves with the same external dimension of a Farmer chamber, filled with Fricke solution. Both methods consisted of irradiating a container filled with Fricke solution, and calculating the absorbed dose to water based on previous papers published about Fricke dosimetry. The irradiations were performed using a 6 MV photon and the Treatment Planning System (TPS) was used to estimate a dose of 20 Gy in the middle of the bags as well as of the ion chamber (IC) glove filled with Fricke solution and at the center of a Farmer IC placed inside of a similar PMMA glove. Non-irradiated control bags and gloves were prepared as a blank to calculate the dose at the Fricke solution.
Results: The mean absorbed dose to water at the bags was 20.55 ± 0.42 Gy, at the gloves was 20.85 ± 0.86 Gy, and at the IC was 19.97 ± 0.01 Gy. The result found for the glove with Fricke was 1,4% different from the bag's value, and they are 4,85% and 2,83%, respectively, different from the TPS. The standard deviations of the solution in the gloves are twice the deviation of the bags, which shows that the bags have better repeatability.
Conclusion: will continue this experiment by doing more measurements, and also MC simulation to consider the different geometry effects.