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Investigating the Impact of Polymer-Coating On the Dosimetric Characteristics of a 103Pd Brachytherapy Source Using Photon Spectroscopy

Z Chen

Z Chen*, J Kim, R Nath, Yale Univ School of Medicine, New Haven, CT

SU-E-T-25 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Synthetic polymers have been used to coat the surface of existing low-energy brachytherapy sources to improve their fixity in tissue in order to minimize seed migration in the patient. The purpose of this study was to evaluate the effects of the polymer-coating on the photon energy spectra emitted by Pd-103 seeds and to estimate its impact on the dosimetric characteristics of these seeds.

Methods: Two Pd-103 AnchorSeeds (Biocompatibles, Inc) and two Pd-103 TheraSeeds (Theragenics Corporation) were used in this study. The AnchorSeed is made from the TheraSeed by coating its surface with bio-absorbable polymeric anchoring rings and ribs. Photon energy spectra emitted by these seeds were measured using a high-resolution, high-purity Germanium (HPGe) photon spectrometer. The effects of polymer coating on the dose rate constant were quantified by comparisons of the coated seed with a non-coated seed.

Results: The relative photon energy spectrum emitted by the AnchorSeed was nearly identical to that emitted by the TheraSeed without polymer coating. The dose-rate constants determined from the emitted photon energy spectra for the two seed models were identical to the third digit after the decimal point (0.679 ± 0.037 cGyh-1U-1). Because the basic dosimetric property of a brachytherapy seed is fundamentally determined by the photon characteristics emitted by the seed, effects of the polymer-coating on the relative dosimetry data of TheraSeed is also expected to be minimal. Using a preexisting photon spectrometer, these measurements and calculations were completed in about 10 working hours.

Conclusion: The polymer coating used in the AnchorSeed has minimal impact on its dosimetric characteristics compared to the non-coated TheraSeed. We also demonstrate that photon spectroscopy provides a ready tool for the evaluation of impact of various coatings or other material changes in the seed manufacture process.

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