Anisotropy function for 192Ir low-dose-rate brachytherapy sources:: an EGS4 Monte Carlo study

The anisotropy function of low-dose-rate Ir-192 interstitial brachytherapy sources was studied. Absolute dose rates around Ir-192 seeds with stainless steel or platinum cladding and a platinum covered wire have been estimated using the EGS4 Monte Carlo simulation system with a very well tested user code. Our results were compared with available experimental data. Excellent agreement between calculated and measured anisotropy function was found for stainless steel clad Ir-192 sources, except along the longitudinal axis of the sources. Dosimetry data for the platinum covered seed and 3 mm long wire with platinum cladding as well as for the stainless steel clad Ir-192 source are presented in TG43 format. The influence of phantom dimensions on the anisotropy function was found to be non-negligible over 7 cm, enhancing the anisotropy function by 1-2%. Our results have estimated statistical uncertainties below 1% at 1 sigma level up to 10 cm excluding the longitudinal axis where statistical uncertainties below 3% up to 10 cm are observed.