Is a worst case sterilization dose required prior to package performance testing for compliance to ISO11607-1(2006)? For example, if a normal dose is 25-40kGy, and we will not resterilize the packaging system or product, would a “worst-case dose” above 40kGy be required? The note following section 6.3.4 of ISO11607-1(2006) states, “Specified sterilization processes may include multiple exposures of the same or different sterilization processes.” and section 12.2.4.2 of AAMI TIR22:2007 states, “Packaging systems should be sterilized using a validated sterilization process, possibly performed multiple times to simulate worst-case conditions.” The use of the phrases “may include” and “possibly performed” lead me to believe that a worst case dose is not mandatory. @ Ask The Experts

Lisa Foster
Sterigenics
Vice President of SteriPro® Services
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Lisa Foster began her medical device career at Sterigenics International in 1989 in Quality Assurance. In 1997, Ms. Foster was named Vice President of Quality Assurance for Sterigenics, the global leader in sterilization services becoming V.P. of SteriPro® Services. Ms. Foster is an Executive Committee Member of the AAMI Sterilization Standards Board and Committee. She serves as Co-Chair and ISO delegate to AAMI/ISO/TC 198/WG2. She has served as co-chair for the AAMI Radiation Process Control Task Group, which developed TIR 29, Guide for Process Control in Radiation Sterilization.

Sterilization Q&A

Is a worst case sterilization dose required prior to package performance testing for compliance to ISO11607-1(2006)? For example, if a normal dose is 25-40kGy, and we will not resterilize the packaging system or product, would a “worst-case dose” above 40kGy be required? The note following section 6.3.4 of ISO11607-1(2006) states, “Specified sterilization processes may include multiple exposures of the same or different sterilization processes.” and section 12.2.4.2 of AAMI TIR22:2007 states, “Packaging systems should be sterilized using a validated sterilization process, possibly performed multiple times to simulate worst-case conditions.” The use of the phrases “may include” and “possibly performed” lead me to believe that a worst case dose is not mandatory.

Asked April 7th, 2009

The quick answer to your question regarding when the term “may” or “possibly” is used in a standard is: These terms are indeed “suggestive” and are not listing a requirement but instead are providing the reader with a point or obstacle to be considered.

Here is the long answer. It is strongly suggested by irradiation providers that 2X the minimum sterilization dose be examined for setting the maximum allowable sterilization dose. In other words, when a minimum SAL dose of 25 kGy is selected, a maximum dose of 50 kGy should be examined regarding the effects of radiation on the product and its packaging components. One would then set their dose range at 25 kGy to - 40 kGy for routine processing to ensure that if during routine irradiation the maximum dose is slightly exceeded then product can still be released. And as someone that has been the irradiation business for 20 years, I can assure you an overdose will occur sometime during the life of the product.

The idea here is that you can add radiation to underdosed product, but you cannot take radiation out of overdosed product. However, if one chooses to only perform packaging tests with product exposed to only maximum allowable dose (in this example 40 kGy), then one is still adhering to the standards ISO 11607, ISO 11137 and associated TIRs. Remember, a TIR is not a standard, and cannot be a normative reference in the world of ISO standards.

Another bit of information that may assist in packaging validation and dose selection is AAMI TIR 17:2008, Compatibility of materials subject to sterilization, which provides guidance on the radiation effects, as well as other sterilization methods, on different materials typically used in medical products. AAMI TIR 17:2008 can be purchased at www.aami.org.

Lisa Foster

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