RADIAL DOSE DISTRIBUTION FROM IR-192 SEEDS AT DISTANCES FAR FROM THE SOURCE

Most current tissue attenuation and scattering factors for Ir-192 are valid only to distances of 15 cm or less. Monte Carlo calculations using the EGS4 computer code were used to calculate tissue attenuation and scattering factors for Ir-192 seed sources with both stainless steel encapsulation and with Pt encapsulation out to a distance of 32 cm from the sources. The data clearly show that polynomial tissue attenuation and scattering factors cannot be extrapolated beyond their range. Encapsulation specific factors are presented here that are valid at large distances from the source.