Monte Carlo dosimetry of a new Ir-192 high dose rate brachytherapy source

This work provides full dosimetric data for a new high-strength Ir-192 sour ce currently launched by Varian Oncology Systems for use in their high dose rate remote afterloading systems. The active core length of the new source is reduced to 5 mm compared to a value of 10 mm for the existing VariSourc e source design, with all other geometric source and encapsulation details being similar. Dose-rate constant, radial dose functions, geometry factors, and anisotropy functions, utilized in the AAPM Task Group 43 dose calculat ion formalism, were calculated using Monte Carlo simulation. Results are co mpared with corresponding data published for the existing VariSource and mi croSelectron high dose rate sources. The dose-rate constant for the new Var ian source was found to be equal to 1.101+/-0.006 cGy h(-1) U-1 compared to values of 1.043+/-0.005 and 1.116+/-0.006 cGy h(-1) U-1 calculated for the existing VariSource and microSelectron sources, respectively. The radial d ose functions between the three sources are similar with the exception of t heir values at radial distances very close to the source (r approximate to2 mm) where differences of similar to3% are observed. The new Varian source demonstrates a smaller anisotropy relative to the existing VariSource sourc e design for polar angles close to the source longitudinal axis, due to its smaller active core length. (C) 2000 American Association of Physicists in Medicine. [S0094-2405(00)00511-3].