Tony Sollis*, Daniel Howell**, Hervé Michel***

* STERIS Applied Sterilization Technologies, Moray Road, Elgin Industrial Estate, Swindon, Wiltshire, SN2 8XS, UK

** STERIS Applied Sterilization Technologies, Roydsdale Way, Euroway Trading Estate, Bradford, W. Yorkshire, BD4 6SE, UK

*** STERIS Applied Sterilization Technologies, Hogenweidstrasse 6, CH-4658 Däniken, Switzerland

Target: Presentation

Subject: Sterilization dose qualification – how to define and achieve ISO 11137 and 13004 requirement with Electron Beam, Gamma and X-ray and impact of the sterilization dose selection.

ISO 11137-2 states as follows when delivering a verification dose.

The highest dose to product items shall not exceed the verification dose by more than 10 %.

The arithmetic mean of the highest and lowest doses to product items should not be less than 90 % of the verification dose.

The ability to achieve this tight dose range is primarily influenced by the product and the technology.

When during a dose audit exercise, the 90% rule can’t be achieved due to the technology and product configuration, the test of sterility has to be performed with a greater chance of failure.

For any given product it was determined the ability to achieve a dose greater than 90% of the arithmetic mean when delivering the verification dose for photon-based modalities are >95% whereas for electron beam this is much lower <66%. Therefore, when completing the sterilization dose audits utilising electron beam irradiation, there is a higher risk of not achieving 90% of the verification dose and obtaining a test of sterility failure due to underdose.

One solution to reduce this risk for consideration would be for Dose Audit verification doses to be performed in photon technologies, even when the routine sterilisation is performed in electron beam. This requires demonstration of microbicidal equivalence as per ISO11137-2 and experimentation to this affect will be referenced.

Another consideration when defining the sterilization dose, is the Vdmax value chosen according to the product bioburden level. By history, 25 kGy is chose by default without any other considerations. An extensive review of the microbial challenge presented by Customer products to radiation processing at STERIS AST & Laboratories proved that the vast majority of products are overprocessed. The study shows that approximately ~96% of products are suited to a sterilization dose less than 25kGy.

Reducing the risk in underdosing verification dose samples for electron beam and choosing the right sterilization dose will allow flexibility in radiation technology selection and may allow more product to be sterilized with one of those technology.

The purpose of this presentation is:

To present how the verification dose can be achieved for each technology and the challenges in achieving the verification dose for electron beam.
To consider a different approach on processing dose audits
To present a challenge to define how the sterilization dose is defined within the industry