In this action the experimental dosimetry measurements were performed for the new IsoSeed I25.S17plus brachytherapy seed in fulfillment of the AAPM recommendation for, at least one, experimental dosimetry characterization of new low energy seeds before their clinical implementation.

 

A batch of 100 LiF TLD-100 microcubes were used for the experimental determination of the dose-rate constant, radial dose and anisotropy functions, in irradiations performed using two SolidWaterTM phantoms. Monte Carlo (MC) simulations were used to determine appropriate correction factors that account for the use of SolidWater as a phantom material instead of liquid water and for the different energy response of the TLD dosimeters in the experimental 125I photon energies relative to the 6 MV x-ray photon beam used for the TLD calibration. Measurements were performed for four I25.S17plus seeds; one with direct traceability of air-kerma strength calibration to NIST, and three with secondary NIST traceability. 

 

A mean dose-rate constant, Λ, of (0.956 ± 0.043) cGy h-1 U-1 was experimentally determined for the I25.S17plus source, which agrees within uncertainties with the MC result of: (0.925 ± 0.013) cGy h-1 U-1 calculated independently for the same seed model in a previous study. A good agreement was also observed between the measured and the MC-calculated radial dose and anisotropy function values.

 

Experimental dosimetry results for the I25.S17plus 125I source verify corresponding independent MC results in the form of TG-43 dosimetry parameters. The latter are found in agreement

within uncertainties with sources of similar design incorporating a silver marker, such as the 6711.