Verification of I-125 brachytherapy source strength for use in radioactive seed localization procedures

• The dose calibrator can be calibrated so that 125I seed assays are accurate to within 5% compared to theoretical source strength.
• The air kerma strength values were accurate for six seeds ranging from nominal 0.254 U to less than 8% of the nominal source strength.
• The air kerma strength values remained accurate when seeds were assayed on different days.
• Two different geometry configurations were sufficiently reproducible, each with its own unique cal number for a specific seed model and vendor.

A general-purpose nuclear medicine dose calibrator was assessed as a potential replacement for a dedicated air-communicating well-type ionization chamber (brachytherapy source strength verification instrument) for 125I seed source strength verification for radioactive seed localization, where less stringent accuracy tolerances may be acceptable. The accuracy, precision and reproducibility of the dose calibrator were measured and compared to regulatory requirements. The results of this work indicate that a dose calibrator can be used for 125I seed source strength verification for radioactive seed localization.