IntroductionSince the heart of the electronic brachytherapy system is a tube of a miniature x-ray and due to the increasing use of electronic brachytherapy, there is an urgent need for acquiring knowledge about the X-ray spectrum produced, and distribution of x-ray dose. This study aimed to assess the optimal target thickness (TT), the X-ray source spectrum, and the absorbed dose of two miniature sources of hemispherical and hemispherical-conical used in electronic brachytherapy systems, through a Monte Carlo simulation.MethodsConsidering the advantages of MCNPX Code (2.6.0), two input files corresponding to the characteristics of the investigated miniature sources were prepared for this code and then were used for simulation. The optimal thickness (OT) of gold and tungsten targets was determined for the energy levels of 40, 45, and 50 kilo-electron-volts.ResultsIn this study, the values of the size of the optimal thickness of 0.92, 1.01 and 1.06 μ for gold target and values of 0.99, 1.08 and 1.34 μ for tungsten target were obtained for energies 40, 45 and 50 keV that using these values, the optimum thickness of 0.92, X-ray spectrum within and outside targets, axial and radial doses for the used energy were calculated for two miniature sources.ConclusionIt was found that the energy of incident electron, target shape, cross-sectional area of the produced bremsstrahlung, atomic number of materials constituting of the target and output window are the factors with the greatest impacts on the produced X-ray spectrum and the absorbed dose.

Objective: The use of miniature X-ray source in electronic brachytherapy is on the rise so there is an urgent need to acquire more knowledge on X-ray spectrum production and distribution by a dose. The aim of this research was to investigate the influence of target thickness and geometry at the source of miniature X-ray tube on tube output. Method:Five sources were simulated based on problems each with a specific geometric structure and conditions using MCNPX code. Tallies proportional to the output were used to calculate the results for the influence of source geometry on output. Results:The results of this work include the size of the optimal thickness of 5 miniature sources, energy spectrum of the sources per 50 kev and also the axial and transverse dose of simulated sources were calculated based on these thicknesses. The miniature source geometric was affected on the output x-ray tube. Conclusion:The result of this study demonstrates that hemispherical-conical, hemispherical and truncated-conical miniature sources were determined as the most suitable tools.