A Monte Carlo investigation of the dosimetric characteristics of the VariSource Ir-192 high dose rate brachytherapy source

An analytical Monte Carlo simulation code, incorporating in detail source c onstruction and dimensions, was used to investigate the dosimetric characte ristics of the VariSource Ir-192 high dose rate brachytherapy source. Dose- rate constant, radial dose functions, and anisotropy functions, utilized in the AAPM Task Group 43 dose estimation formalism, were calculated with the source centered in a spherical water phantom of 30 cm in diameter. The res ults, which are in agreement with the corresponding data available in the l iterature, are compared to those obtained in our previous study for the wid ely used microSelectron Ir-192 high dose-rate brachytherapy source. The dos e-rate constant was found to be equal to 1.043+/-0.005 cGy h(-1) U-1 for th e VariSource, compared to a value of 1.116+/-0.006 cGy h(-1) U-1 calculated for the microSelectron. Significant differences in the anisotropy of the t wo sources are observed only for polar angles close to their long axis and are due to their different dimensions. (C) 1999 American Association of Phy sicists in Medicine. [S0094-2405(99)03008-4].