DOSE-RATE DISTRIBUTIONS AROUND CO-60, CS-137, AU-198, IR-192, AM-241, I-125 (MODELS 6702 AND 6711) BRACHYTHERAPY SOURCES AND THE NUCLIDE TC-99(M)

Simple analytical functions derived from our point source Monte Carlo calculations on the combined attenuation and scatter factor, B exp(-mur), for Co-60, Cs-137 Au-198, Ir-192, Am-241, I-125 (models 6702 and 6711) brachytherapy sources and the nuclide Tc-99m, for water spherical geometries of radii R = 15 and 20 cm, are presented. Our results for the broadly used Co-60, Cs-137, Au-198 and Ir-192 brachytherapy sources can be compared directly and found in excellent agreement with the widely accepted data of Meisberger et al in the limited distance range for which the latter are valid. Our data, however, can be used with high accuracy outside this distance range. Many discrepancies observed among different data sets available in recent literature are. attributable to differences in geometries used. The results for the recently introduced Am-241 source are very dissimilar to those produced by any other currently used brachytherapy source. Dose rate distributions, based on the above simple functions, are proposed in accordance with the recommendations for calibration of the brachytherapy sources in terms of reference air kerma rate and were found to be in good agreement with data available in the literature. Our calculations for I-125 sources (models 6702 and 6711), provided that the characteristic x-rays from titanium encapsulation are taken into account, support recent experimental and theoretical dose rate distributions indicating that currently accepted values for I-125 may be overestimated.