Monte Carlo and TLD dosimetry of an 192Ir high dose-rate brachytherapy source.

An analytical Monte Carlo simulation code has been used to perform dosimetry calculations around an 192Ir high dose-rate brachytherapy source utilized in the widely used microSelectron afterloaded system. Radial dose functions, dose rate constant and anisotropy functions, utilized in the AAPM Task Group 43 dose estimation formalism, have been calculated. In addition, measurements of anisotropy functions using LiF TLD-100 rods have been performed in a polystyrene phantom to support our Monte Carlo calculations. The energy dependence of LiF TLD response was investigated over the whole range of measurement distances and angles. TLD measurements and Monte Carlo calculations are in agreement to each other and agree with published data. The influence of phantom dimensions on calculations was also investigated. Radial dose functions were found to depend significantly on phantom dimensions at radial distances near phantom edges. Deviations of up to 25% are observed at these distances due to the lack of full scattering conditions, indicating that body dimensions should be taken into account in treatment planning when the absorbed dose is calculated near body edges. On the other hand, anisotropy functions do not demonstrate a strong dependence on phantom dimensions. However, these functions depend on radial distance at angles close to the longitudinal axis of the source, where deviations of up to 20% are observed.