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Testing Services > Tests > Radiation Sterilization

Radiation Sterilization

Radiation Sterilization determines appropriate radiation sterilization doses for products which require a sterile label claim. It incorporates bioburden testing, a bioburden recovery efficiency test, a low radiation dose (verification dose), sterility testing and bacteriostasis/fungistasis testing. If a sterile label claim is required and if the sterilization method will be radiation, a validation is required to determine the appropriate sterilization dose. Nelson Labs has vast experience providing validations for complex or unique products or products which cannot handle large doses of radiation. Test complies with Radiation Sterilization standard AAMI/ISO 11137 and AAMI TIR 33.

The purpose of a radiation validation is to determine the appropriate sterilization dose for a product. Usually the sterilization dose must represent a sterility assurance level (SAL) of 10-6, which is a one in one million chance of a non-sterile product. The most common validation methods are (in order), VDmax (short for Verification Dose Maximum) and Method 1. Both of these methods are available in either a single batch validation format or a full, 3-batch validation. These radiation validations consist of three main phases:
  1. Bioburden test: This test determines the quantity of viable microorganisms on/in the product. This test is performed prior to any sterilization but after all other manufacturing steps, including packaging. Critical to this test is the performance of a recovery efficiency test to determine the effectiveness of the bioburden extraction method at removing microorganisms from the product.
  2. Application of verification dose: The bioburden results are taken to a table from the standard to determine the proper verification dose. The verification dose is then applied to a number of products. The dose is expected to sterilize all of the products except for one.
  3. Sterility test: The irradiated products undergo a test of sterility. The allowable number of non-sterile products from the test of sterility is 1 (for VDmax) or 2 (for Method 1). Critical to this test is the performance of a Bacteriostasis/Fungistasis test to demonstrate the lack of inhibition in the sterility test system.
If the number of non-sterile samples in the test of sterility meets the acceptance criteria, the radiation sterilization dose is validated. Additional testing should be performed on a quarterly basis (called a quarterly dose audit) to demonstrate that the sterilization dose continues to be appropriate for the product. The quarterly dose audits follow the same flow as described above but only involve samples from a single batch and include use of the verification dose determined in the validation rather than setting a new one.

Requirements of radiation validations and quarterly dose audits are provided in the AAMI/ISO standard 11137-2:2006 (currently under revision).
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Sue , Quality Assurance Manager , Medical Device Manufacturer


Radiation Sterilization Validations




“I strongly value the level of technical expertise provided by Nelson Labs study directors, the timeliness of testing, and the accessibility and open communication with Nelson Labs personnel.”
-       Sopheak, Validation & Sterilization Specialist, Medical Device Manufacturer & Packager
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