Monte Carlo Dose Calculation around the Isoseed® I25.S06 Brachytherapy Source in Water and in Different Media Using Gate 8.2

Abstract

Low dose rate (LDR) brachytherapy is widely used in treating tumors, including the brain, the eye tumors and the prostate cancer. Dosimetric characteristics of brachytherapy source before the clinical application are crucial as recommended by the American Association of Physicists in Medicine (AAPM). In the presented study, two dosimetric parameters of the iodine-125 ( ¹²⁵I ) model IsoSeed®I25.S06 source were calculated around a low dose rate ¹²⁵I source located in a spherical phantom with radius of 15.0 cm using  GEANT4 Application for Emission Tomography Monte Carlo code (version 8.2). As a result, we have obtained the radial dose function g_L(r) and the anisotropy function F(r, θ) in water. Moreover, to highlight the effect of media composition on the dose distribution, the radial dose function was obtained in different media, such as adipose tissue, lung, breast tissue and muscle. The obtained results were presented and compared with consensus data. These results are in good agreement with the reference data, except the values close to the end of the source for the anisotropy functions. The radial dose function is in a good deal with consensus data, especially for r>0.5 cm. In addition, the radial dose function was presented for the comparison between the dose distribution in water and different tissues. This study shows a small difference between the obtained results compared to the water. Especially in long distances from the source centre due to the atomic composition and densities, which may cause errors in the estimation of the dose around brachytherapy sources that are not taken into account by Task groupn.43 (AAPM). Thus, the ignorance of atomic composition and densities, by treatment planning systems incorporates a significant error in dose delivery to the patient with Low-energy photon sources