I don't know of anyone that has had any luck using Biological Indicators
for radiation sterilization. They never seem to be able to get
reproducible results. I'm curious why you need to use a BI for Gamma. It
is world wide accepted practice to use the AAMI/ISO guidelines of
collecting bioburden data and using the appropriate sublethal dose to
verify the SAL. I have talked to many people in the industry (including
some friends at Nordion in Ontario - developer of the technology and really
the only supplier/constructor of cobalt irradiators, and folks I do
business with at Isomedix - probably the biggest contract sterilization
company in the US) about this in the past, and no one has found it to be
necessary to use BI's for gamma. No regulatory agency will nail you on
this (I've had my gamma sterilization validation crawled all over by the
FDA and ISO with no problems at all). If you can collect repeatable
bioburden data for your product you want to irradiate and with good dose
mapping within the load, you can really streamline your sterilization
process and cut your processing times down by quite a bit. If your product
is gamma stable, and you don't have time to do extensive bioburden and
sublethal dose studies, you can use the old AAMI practice of targeting
2.5MRad, and call it sterile; however, this is no longer acceptable for
producing medical devices or drugs.
Good luck
