Dosimetric properties of interstitial brachytherapy sources

As part of the effort involved in a National Cancer Institute brachytherapy contract, the authors measured several dosimetric parameters of I-125 seed models 6702 and 6711. Measurements were made with TLD powder in capsules which had been calibrated by in-air ion chamber measurements. For reasons that are presented, the authors used a linear-source parameterization of the spatial dose rate variation. The authors' measured radial dose functions agreed well with values in the literature for both model seeds. However, the dose rate per activity at 1 cm was found to be 1.19 and 1.08 cGy (muscle)/(mCi hr) for the model 6702 and 6711 seeds, respectively, while 1.30 +- 0.05 is the range of values in the common use. (Does to water are 4.5% smaller.) Data analysis and uncertainties are discussed