Re: Palladium Calibration

[Ccja@aol.com]

On a related question, someone asked or posted a comment some time ago, about
the correct multiplicative conversion factor to use when calculating the
actual activity of contained Pd103, in a Theragenics seed. I think that
someone stated that an individual at Theragenics had quoted a factor of 2.3,
telephonically, but without any citation of reference. An examination of the
basic data sheet for the seeds (which typically accompanies a shipment)
reveals the following statement (fourth sentence, under "Actions", top of
second column, first page).

"Total attenuation resulting from titanium encapsulation, x-ray marker, and
self absorption from the Pd-103 pellet is approximately 54% on average." I
read this to mean that the "apparent activity" represents 46% of the
contained activity, ergo, for the purposes of inventory, we should multiply
the apparent activity by the inverse of that number, i.e., 2.17 (or 2.2, if
you prefer), to obtain the "true" activity of the seeds. That is, the
quantity that the regulatory folks want to see. If anyone finds this
reasoning fallacious, please don't hesitate to let us know ASAP.

As an aside, I could have sworn that, six months or more ago, the figure
given for total attenuation was 72%, thus we've been using a conversion
factor of 3.6 (1/28%). The result being a 64% overestimate!! I've got to find
that document; I can't believe that I made that number up out of whole cloth.
Thanks again to Mary Ellen for waving a yellow flag over the calibration
issue.

chris alston
ccja@aol.com