Investigation of dose distribution of TheraSeed 200 103Pd brachytherapy seed on coaxial cylindrical phantom shells using Monte Carlo simulation

In this study, radial dosimetric characterization for specific internal geometry of seed source was determined. In this study, the separate contribution of radioactive components of the seed's unlikely single radioactive rod on dose distribution was investigated using model seed TheraSeed 200 source at parallel shells in a water phantom. TheraSeed 200 brachytherapy seed was modeled using EGSnrc-MP Monte Carlo simulation code. Dose contributions of radioactive components inside the seed were calculated on coaxial shells with different radii in a water phantom. Dose calculation points on shells were determined as only spatial. The study's spatial geometrical approach was considered. Dose distributions of two radiation emitters were compared on plotted data. In 0A degrees-90A degrees rotation area, left emitter's efficiency varied with distance. On shells with small radius, dose contribution (D1) of left emitter was weakly effective on total distribution; right emitter was the determinant factor on the total dose. By increasing shell radius, efficiency of two emitters comes close. It seems that geometrical specification of a seed is markedly effective on dose distribution. Differences between doses of two radioactive materials decrease rapidly beyond the seed borders. Consideration of this study can be applied for other seeds that have multiple radiation emitters to research the effects of their geometrical specification on dose distributions.