Experimental characterization of the dosimetric properties of a newly designed I-Seed model AgX100 ¹²⁵I interstitial brachytherapy source

Purpose: To measure the dosimetric properties of the Model AgX100 ¹²⁵I source for interstitial brachytherapy.

Methods and materials: The photon energy spectrum emitted by the AgX100 source was measured using a high-resolution germanium spectrometer customized for low-energy brachytherapy source spectrometry. The dose distribution around the source was measured using the 1×1×1 mm³ lithium fluoride thermoluminescent dosimeters in water-equivalent solid phantoms. The dosimetric parameters needed for dose calculation using the American Association of Physicists in Medicine Task Group No. 43 (TG-43) formalism were determined and compared with the results of a Monte Carlo simulation by an independent research group and with the TG-43 consensus values of the well-established model 6711 source.

Results: It was found that (1) the photon energy spectrum emitted by the AgX100 source was nearly identical to that emitted by the model 6711, (2) the dose-rate constant determined by the photon spectrometry technique (0.957±0.037 cGy·h⁻¹·U⁻¹) and by the thermoluminescent dosimeter technique (0.995±0.066 cGy·h⁻¹·U⁻¹) was within 1.5% of the corresponding values determined for the model 6711 source, and (3) the radial dose function and the anisotropy function of the AgX100 source were also found to be similar to the consensus data established for the model 6711 source in the TG-43 update report.

Conclusions: A comprehensive dosimetric characterization has been carried out for the model AgX100 ¹²⁵I source. The American Association of Physicists in Medicine TG-43 dosimetry parameters for this source has been determined from the experimental data.