MONTE-CARLO DOSIMETRY OF THE VARISOURCE HIGH-DOSE-RATE IR-192 SOURCE

The purpose of the work is to calculate basic dosimetry data for a Var iSource high dose rate Ir-192 source in water. These basic dosimetry d ata, expressed in the dose calculation formalism endorsed by the Inter stitial Collaborative Working Group and AAPM Task group 43, include th e dose rate constant, the radial dose function, and the anisotropy fun ction. A modified version of the EGS4 Monte Carlo code was used to cal culate (1) the transverse-axis dose distribution at radial distances f rom 0.1 to 14 cm, (2) the two-dimensional dose distribution for axial and radial distances from 0.1 cm to 10 cm, and (3) the air-kerma stren gth, for the VariSource high dose rate Ir-192 source. From these Monte Carlo results the basic dosimetry data were derived. The calculated d ose rate constant for the high dose rate source is 1.044+/-0.2% cGy h( -1) per unit air-kerma strength. The anisotropy function exhibits 40%- 60% deviations from isotropy at positions on the long axis. The radial dose function for the source is nearly identical to that for a microS electron high dose rate Ir-192 source, except at radial distances smal ler than 0.5 cm where values for VariSource are 1.7%-2.8% smaller. The se basic dosimetry data were compared with corresponding results from other authors for high and low dose rate Ir-192 sources, as well as wi th Meisberger's fitting formula. (C) 1998 American Association of Phys icists in Medicine. [S0094-2405(98)01404-7].