To: State Radiation Control Programs NRC Regional Office Programs

This correspondence serves as a follow-up to a previous letter dated March 10, 2000, which served to provide information about upcoming changes to Theragenics ' sealed source certification to indicate source activity and air kerma strength based on two different calibration methods. To summarize, the TheraSeed ® Model 200 brachytherapy implant seed contains Pd-103. Prior to 1999, since there had not been a NIST-traceable standard for Pd-103, Theragenics had been calibrating the seeds by using a NIST-traceable Cd-109 standard. The calibration provided results in terms of apparent activity, in units of mCi. The air kerma strength, in units of U, was then calculated. This information had been included on the seale