Determination of the correction factors used in Fricke dosimetry for HDR 192Ir sources employing the Monte Carlo method

• Published in: Physica medica Vol. 84; pp. 50 - 55
• Main Authors: David, Mariano G., Salata, Camila, de Almeida, Carlos E.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.04.2021
• Subjects: Brachytherapy; Fricke dosimetry; Monte Carlo method; PENELOPE code; Fricke dosimetry; Monte Carlo method; Brachytherapy; PENELOPE code
• ISSN: 1120-1797; 1724-191X
• DOI: 10.1016/j.ejmp.2021.03.029

•Fricke dosimetry as primary standard for the determination of absorbed dose to water.•Monte Carlo method and the correction factors associated to Fricke dosimetry.•Reduced uncertainties associated to the determination of the absorbed dose to water;•Determination of absorbed dose to water for 192Ir HDR sources.•Absolute radiation dosimetry for HDR brachytherapy. Fricke dosimetry has shown great potential in the direct measurement of the absolute absorbed dose for 192Ir sources used in HDR brachytherapy. This work describes the determination of the correction factors necessary to convert the absorbed dose in the Fricke solution to the absorbed dose to water. Methods: The experimental setup for Fricke irradiation using a 192Ir source was simulated. The holder geometry used for the Fricke solution irradiation was modelled for MC simulation, using the PENELOPE. Results: The values of the factors determined for validation purposes demonstrated differences of less than 0.2% when compared to the published values. Four factors were calculated to correct: the differences in the density of the solution (1.0004 ± 0.0004); the perturbations caused by the holder (0.9989 ± 0.0004); the source anisotropy and the water attenuation effects (1.0327 ± 0.0012); and the distance from the center of the detection volume to the source (7.1932 ± 0.0065). Conclusion: Calculated corrections in this work show that the largest correction comes from the inverse squared reduction of the dose due to the point of measurement shift from the reference position of 1 cm. This situation also causes the correction due to volume averaging and attenuation in water to be significant. Future versions of the holder will aim to reduce these effects by having a position of measurement closer to the reference point thus requiring smaller corrections.