dosimetric characteristics of 137cs sources used in after loading selectron system by monte carlo method

background: for an effective treatment planning in brachytherapy, it is necessary to know the accurate source dosimetric information such as air kerma strength, exposure rate constant, dose rate constant and redial dose distribution. the usual method to determine these factors is thermo luminescent dosimeter (tld) dosimetry. nowadays, another more accurate method is known to be the monte carlo simulation, and it is widely used in determining of brachytherapy sources dosimetric factors. the aim of the present study has been determine to dose distribution of 137cs sources configuration used in interacavitary low dose rate (ldr) selectron brachytherapy by monte carlo simulation method. materials and methods: simulation has been performed for 137cs stainless-steel encapsulated source in 2.5 mm in diameter of selectron system. six different combinations of 137cs sources were simulated and each combination was put into different applicator. the monte carlo mcnp4c code was used for simulation. the number of history was taken 1 million for the calculation of air kerma strength and exposure rate constant and 0.1 million for calculating dose rate constant and redials dose distribution. results: maximum air kerma strength was obtained for the combination with fourteen active sources and found to be 919.3 |µ|gym2h-1 while its minimum value was 133.9 µ|gym2h-1 for the case with two active sources. maximum and minimum dose rate constant of 4.3 cgyh-1mci-1 and 2.1 cgyh-1mci-1 were obtained for the combination with eight and fourteen active sources, respectively. conclusion: the results indicated that the monte carlo simulation method may be useful to determine dosimetric characteristics of brachytherapy sources.