بررسی اثر ناهمگنی بافت استخوان بر توزیع دز چشمه‌ی براکی‌تراپی 103Pd مدل MED3633 به روش مونت‌کارلو

The determination of the dosimetry parameters of brachytherapy in the treatment of cancerous tumors as per the TG-43U1 protocol provided by the American Association of Physicists in Medicine should be done in the surrounding water source before clinical application. To achieve a good treatment result, various factors such as body tissues with different densities can have a decisive role so that proper results cannot be achieved for all body tissues only by applying water environment around the source with an approximate density of 1 gr / cm3. In this study, bone tissue with a density of 1.40 gr / cm3 was chosen as tissue subject to invasion by tumors using Monte Carlo code MCNP4C with a particles history of 2 × 109 particles, simulations were made in order to determine the dosimetry parameters at angels and diffrent distances and the relative difference between these two modes were compared with each other. the results of the radial dose function and anisotropy function in bone tissue heterogeneity Phantom and uniform phantom of water, it has been indicated that the relative differences of radial dose function at a distance of  0.75 cm is about 70% and at a distance of 0.5 cm it reaches  more than 190%. Also with increasing distance from the source (at distances greater than 1cm), the relative difference becomes about 90%. The relative difference of the anisotropy function in bone tissue phantom compared to the water phantom is visible at angles close to the source so that this difference is more than 40 percent in the zero-degree angle. The maximum relative difference in the use of bone tissue phantom instead of water phantom decreases by increasing the angle from 0 degrees to 90 degrees. Bone tissue phantom constant dose rate (0.840± 0.04) was derived to be larger than that of the water phantom (0.682± 0.02). Thuse we have shown that since the bone tissue has a density greater than water and contains compounds with atomic weight and atomic numbers different from those of water, it leads to the development of a considerable relative difference between the values of radial dose and the anisotropy function. Thus, when using the brachytherapy method in order to treat virulent tumors adjacent to bone tissue, the necessary corrections concerning dosimetry parameters of bone tissue must be applied in the design of the tables obtained in this study.