Dose distribution along the transverse axis of a new 125I source for interstitial brachytherapy.

A new encapsulated source of 125I has been introduced for interstitial brachytherapy. This source, isoSTAR model 12501 (manufactured by Imagyn Corp.), consists of a welded titanium tube containing 125I as silver iodide uniformly coated on five silver beads. The dose rate constant and the radial dose function for this source were measured using lithium fluoride thermoluminescent dosimeters in a Solid Water phantom. The value of the dose rate constant is 0.95 cGy h(-1)U(-1) where the unit of air kerma strength is 1 U = 1 cGy h(-1)cm2. The air kerma strength was traceable to the year 2000 primary air kerma strength standard for the model 12501 source at the National Institute of Technology and Standards. The radial dose function for the source was very similar to that for the model 6711 source (manufactured by Nycomed Amersham) for radial distances up to 6 cm. However, the radial dose function is lower in value than that for the model 6702 source (manufactured by Nycomed Amersham) and the model MED3631-A/M Iogold source (manufactured by North American Scientific).