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Purpose:To investigate the dosimetric characteristics of GMS BT-125-1 I-125 radioactive seed,including dose rate constant,radial dose functions and anisotropy functions.Methods:Dosimetric parameters of GMS BT-125-1 I-125 seed including dose rate constant,radial dose functions and anisotropy functions were calculated using the Monte Carlo code of MCNP5.Monte Carlo calculations were also performed for the PharmaSeed BT-125-1 I-125 seed,PharmaSeed BT-125-2 I-125 seed and model 6711 I-125 seed.The dosimetric parameters of GMS BT-125-1 I-125 seed were compared with those of PharmaSeed BT-125-1 I-125 seed,PharmaSeed BT-125-2 I-125 seed and model 6711 I-125 seed.The measurements of dosimetric parameters were performed using thermoluminescent dosimeters(TLDs)for GMS BT-125-1 I-125 seed.The results were compared with those of Monte Carlo simulation.Results:The MCNP5 calculated dose rate constant of GMS BT-125-1 I-125 seed was 1.011.The experimental measured dose rate constant of GMS BT-125-1 I-125 seed was 0.967.For radial dose function,the difference between GMS BT-125-1 I-125 seed and PharmaSeed BT-125-2 I-125 seed were typically less than 2.0%with a maximum of 3.3%.The largest differences were 8.1%and 6.2%compared with PharmaSeed BT-125-1 and model 6711 I-125 seed,respectively.For anisotropy functions,the difference between GMS BT-125-1 I-125 seed and PharmaSeed BT-125-2 I-125 seed was typically <10%with a maximum of about 9.6%when,and 22.9%when.Compared with Monte Carlo simulation,the largest differences of radial dose functions and anisotropy functions were 14.5%and 29.1%,respectively.Conclusions:The measured dose rate constant,radial dose functions and anisotropy functions for GMS BT-125-1 I-125 seed showed good agreement with Monte Carlo calculated values except for the r=0.5 cm and.The dosimetric parameters of GMS BT-125-1 I-125 seed are similar to those of PharmaSeed BT-125-2 I-125 seed,PharmaSeed BT-125-1 I-125 seed and model 6711 I-125 seed.There are differences of dosimetric characteristics among different radioactive seeds mainly due to the different material and length of markers in the seed.