Experimental determination of dosimetric characteristics of Best 125I brachytherapy source

125I brachytherapy sources are being used for interstitial implants in tumor sites such as the prostate. Recently, the Best 125I source became commercially available for interstitial brachytherapy treatment. Dosimetric characteristics (dose rate constant, radial dose function, and anisotropy function) of this source were experimentally determined, following the AAPM Task Group 43 recommendations, and were related to the NIST 1999 calibration assigned to this source. Measurements were performed in Solid Water phantom using LiF thermoluminescent dosimeters. The results indicated a dose rate constant, lambda, of 1.01 +/- 0.08 cGy h(-1) U(-1) for the new source. The radial dose function, g(r), of the new source was measured at distances ranging from 0.5 to 10.0 cm. The anisotropy function, F(r, theta), of the new source was measured at distances of 2, 5, and 7 cm from the source center. These data compare favorably with those from the Nycomed/Amersham Models 6711 and 6702 sources. The anisotropy constant, phi(an), of the Best 125I source was found to be 0.982. Complete dosimetric parameters of the new source are presented in this paper.