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Minimun Dose Validation
Medical Sterilization
Qualification of Electron Beam Processing
Validating Electron Beam Processing
The following protocol details the significant points which must be addressed during the validation of electron beam sterilization, as outlined in ANSI/AAMI/ISO 11137. The requirements of ISO 11137 fall into three major categories:
- Minimum Dose Determination
- Maximum Dose Determination
- Process Qualification (Dose Mapping)
Minimum Dose Determination
Definition - Minimum dose determination is the establishment of the minimum level of radiation which will effectively and consistently eradicate inherent bioburden levels within a specific product or product family.
Procedure - Minimum doses are established using Method 1 and/or Method 2 as defined in the ANSI/AAMI/ISO guideline for irradiation sterilization of medical devices. The most common approach for the establishment of a minimum dose is to use Method 1, otherwise known as a bioburden method. Bioburden analysis is performed by taking ten product samples from each of three separate production lots to a testing laboratory. The average bioburden for each lot and the grand average of all three lots are calculated. If a single lot is more than two times the grand average, that specific single lot average must be used. Based upon this bioburden analysis, the verification dose is determined by means of Table B.1 contained in the ISO guideline. If the specific average bioburden is not listed in the table, the next highest bioburden is utilized.
One-hundred samples of either a fourth production lot or one of the three original production lots are then subjected by the sterilizer to the verification dose necessary to achieve a 10-2 sterility assurance level. These 100 samples are then sent to the testing laboratory and incubated for a period of 14 days in TSB at 28 - 32°C. Acceptable results after this 14-day incubation are 0, 1, or 2 positives out of the 100 samples tested. If 0, 1, or 2 positives are obtained, the verification test has been successfully completed and a sterilization dose can be determined again based upon Table B.1 in the ISO document. A sterilization processing dose is normally based upon a 10-3 sterility assurance level for those devices that are non-invasive and do not contact blood or tissue, or 10-6 sterility assurance level for those devices which are invasive and/or have contact with blood or tissue.
If the results of the verification exceed two positives (i.e., 3 or more positives), and the positives cannot be attributed to sterility testing techniques, then Method 2 must be selected. Details on Method 2 can be found in the ISO guidelines.
Grouping of Products - The grouping of products can be used to minimize the amount of testing required to establish the minimum dose for each product and/or group of products. Factors to be considered for grouping of products for minimum dose establishment are typically based upon the manufacturing process itself, which includes handling of the product by employees, machine-made parts versus hand-assembled parts, materials of construction, and raw materials suppliers if a purchased sub-assembly is included in the manufacturing process.