Monte Carlo calculations of AAPM Task Group Report No. 43 dosimetry parameters for the MED3631-A/(MI)-I-125 source

Brachytherapy dosimetry parameters for MED3631-A/(MI)-I-125 sources have be en determined in accordance with the AAPM Task Group No. 43 (TG-43) dosimet ry protocol. These data were calculated using the*F8 tally from the MCNP4B2 Monte Carlo radiation transport code with the DLC189 cross-section librari es. Due to motion of the I-125 resin beads and gold-copper markers within t he capsule, parameters such as the geometry function, radial dose function, dose rate constant, and anisotropy function were examined with the beads a nd markers having either "realistic" or ''ideal'' positions; the realistic position was a weighted combination of ''vertical'' and ''diagonal'' capsul e orientations. The dose rate constants for the realistic and ideal geometr ies, Lambda (realistic)(99st) and Lambda (ideal)(99std), were 1.066 and 1.0 67 cGyh(-1) U-1, respectively, which were within uncertainties of measured values by Wallace and Fan [Med. Phys. 26, 1925-1931 (1999)] and Li et al. [ Med. Phys. 27, 1275-1280 (2000)], 1.06 and 1.067 cGyh(-1) U-1, respectively . The calculated reference dose rate at r(0) = 1 and theta (0)=90 degrees f or the realistic source geometry was 0.7% less than for the ideal source ge ometry. The anisotropy constants, <(<phi>)over bar>(realistic)(an), for the realistic and ideal geometries were 0.948 and 0.965, respectively. <(<phi> )over bar>(realistic)(an) matched that (0.941) measured by Wallace and Fan, and <(<phi>)over bar>(ideal)(an) was significantly different from that (0. 948) calculated by Wierzbicki et al. [Med. Phys. 25, 2197-2199 (1998)] for an ideal MED3631-A/S I-125 source. (C) 2001 American Association of Physici sts in Medicine.