Monte Carlo dosimetry of the selectSeed I-125 interstitial brachytherapy seed

This work provides full dosimetric data for the new selectSeed I-125 prosta te seed source to be distributed by Nucletron B.V. The AAPM TG-43 dosimetri c formalism and the new 1999 NIST air kerma strength calibration standard h ave been followed. Ail kerma strength, dose rate constant, radial dose func tions, anisotropy functions, and anisotropy factors were calculated using M onte Carlo simulation. Corresponding calculations were also performed for t he commercially available 6711 seed source, which is of similar design, for reasons of comparison. The calculated dose rate constant of the selectSeed was 0.954 +/-0.005 cGyh h(-1) U-1 compared to 0.953 +/-0.005 cGy h(-1) U-1 for the 6711 source design. The latter value for the 6711 source suggests that the correction factor proposed by NIST for conversion of dose rate con stants to the new 1999 NIST calibration standard may be overestimated by 2- 3%. Radial dose functions of the two sources were found in good agreement f or radial distances up to 4 cm, the selectSeed being less penetrating at gr eater radial distances (similar to4% at 10 cm). The selectSeed source prese nts similar anisotropy characteristics with the 6711 source design. For bot h source designs, a distance and polar angle dependent discontinuity of ani sotropy function values was observed owing to the dose contribution of radi oactivity distributed on the ends of the cylindrical source cores. Variatio n of dosimetric parameters with possible variation in radioactive silver ha lide coating thickness of the silver source core of the new source was also investigated. (C) 2001 American Association of Physicists in Medicine.