Activation Assessment (X-ray and electron beam)
Background
Radioactive material of natural origin is abundant and varies widely in both type and amount.
The energy from these materials, plus that of cosmic or cosmogenic origin, is called background radiation.
Artificial radioactivity is the result of human operation where it was not previously present.
Assessment of induced radioactivity in radiation-sterilized healthcare products is utilized to determine whether such activity is present at a level higher than background.
This assessment is considered from the perspective of employees within the medical device manufacturing supply chain and patient end-users:
- External exposure from sources outside a person’s body may be of concern for those who handle the product and/or packaging in the manufacturing supply chain (irradiation facility, distribution warehouse, or transportation of materials), and for healthcare workers (physicians and nurses) who handle the product.
- Internal exposure from sources inside a person’s body may be of concern for patients who have an irradiated product placed or implanted in their body.
When to conduct an activation assessment
ISO 11137-1 requires an evaluation of potential activation of materials irradiated under the following conditions:
- X-ray irradiation exceeding 7.5 MeV in energy
- Electron beam irradiation exceeding 11 MeV in energy
Where does STERIS conduct activation assessments?
As STERIS operates its X-ray irradiators at energy level below 7.5 MeV and electron beam irradiators at energy level below 11 MeV, activation testing is not required as part of compliance with ISO 11137.
Nevertheless, Customers can always request an activation test to be completed on their product.
In this case, activation testing is completed at the STERIS Applied Sterilization Technologies (AST) Radiation Technology Centers (RTC) in:
- Libertyville, Illinois, USA
- Däniken, Switzerland
Note: Aside from compliance with ISO 11137, there may be country or region-specific requirements for activation testing that requires assessment.
It is the responsibility of the device manufacturer to advise of any other requirements other than ISO 11137.
How is an activation assessment conducted?
Samples of the product being tested are irradiated to 10-20% above the product’s maximum established dose.
These samples will be tested in a detector that can measure extremely low levels of radiation to determine if any activation level can be found within the samples.
Interpretation of results
If the product shows an activity level greater than the detection limit of the system, it is considered “activated” and an assessment is completed.
The assessment identifies the isotope and determines whether the activity level is greater than the threshold for which the isotope is considered “radioactive”.
- If the assessment concludes that the activity level is less than the isotope’s radioactivity threshold, no additional action is required.
- If the assessment concludes that the activity level is greater than the isotope’s radioactivity threshold, the Customer and STERIS shall determine the appropriate path forward.
In most cases where activation is detected, the activity level is well below the exempt level to consider the product sample to be a radioactive hazard.
In addition, activation levels typically decay within minutes.
References:
- Hervé Michel, Thomas Kroc, Brian J. McEvoy, Deepak Patil, Pierre Reppert, and Mark A. Smith. Potential Induced Radioactivity in Materials Processed with X-ray Energy Above 5 MeV. Biomed Instrum Technol. 2021 Mar 1;55(s3):17-26. doi: 10.2345/0899-8205-55.s3.17. PMID: 34153999.
- ISO 11137-1:2025, Sterilization of health care products – Radiation – Part 1: Requirement for the development, validation and routine control of a sterilization process for medical devices.