Medical Device Sterilization
What are the Benefits of using X-ray for Terminal Sterilization of Medical Devices?
- Cost control – bringing a Rad Source unit in house provides protection against annual price increases, the rising cost of cobalt, and fluctuating transportation costs
- Because it is a form of ionizing radiation it’s effects on materials, packaging, and microorganisms is the same as gamma
- Just in Time (JIT) supply chain – Process product when you need it
- Reliable dose delivery – Min/Max ratio of 1.3
How is a Radiation Sterilization Validation performed?
A basic outline of the steps involved in the validation process are below, however it is highly recommended that you speak with a sterilization expert to fully understand the validation process.
The Three Primary Steps in the Sterilization Process are:
- Establish a Minimum Acceptable Dose
- Establish a Maximum Acceptable Dose
- Process Qualification (Dose Mapping)
To establish a minimum acceptable dose there are two primary methods, Method 1 and Method VDMax25. The first step for both methods is to establish the bioburden (type and quantity of microorganisms) of the product. This can be done by working with a reputable testing laboratory. Once the bioburden of the product has been established, tables found in the ISO 11137-2:2006 standard will provide the recommended verification dose.
The industry standard for a product to be considered sterile is a product that has a Sterility Assurance Level (SAL) that is 10-6 which means that it has a one in one million chance of not being sterile. The verification dose is a fraction of the sterilization dose predetermined to provide a SAL of 10-2 or one in one hundred chance that a product is not sterile. For a Method 1 validation, 100 product items are selected from a single batch. They are then irradiated at the verification dose and then tested for sterility. Assuming they pass the sterility test the minimum acceptable dose or sterility dose is selected from the corresponding table in ISO 11137-2:2006.
For a Method VDMax25, 10 product items are selected from three different production batches and irradiated at the verification dose and then tested for sterility. Again, assuming the product passes the sterility tests, the minimum accepted dose or sterilization dose is selected from the corresponding table in ISO 11137-2:2006.
The next step in performing a sterilization validation is establishing the maximum acceptable dose. Generally speaking, this is at least two times the minimum acceptable dose. Materials being exposed to the maximum acceptable dose must not be affected in form, fit, or function. Because X-rays and gamma rays affect materials in the same manner, all materials that are gamma compatible will also be X-ray compatible. Rad Source technologies can help with material selection and establishing the maximum acceptable dose by performing engineering runs. If you are interested in having a engineering run performed please click here.
The last step in performing a sterilization validation is process qualification. It is at this stage that dose mapping is performed to identify the irradiator dose distribution, reproducibility of the dose, and effects on the dose should a process interruption occur during dose delivery. This process involves irradiating at least three containers with product and strategically placed dosimeters. Using the results and mathematical modeling techniques, the following will be identified for routine processing:
- Optimal dosimeter placement
- The maximum and minimum dose levels within the container.
- The establishment of a container loading pattern
Once the validation is completed, periodic audits, generally every three months to address seasonal change on microorganisms, will be required. The audits are similar to the initial validations. The bioburden must be established and then verification doses performed followed by sterility tests. Method 1 requires 100 product items be irradiated using the verification dose and then tested for sterility while Method VDMax25 requires 10 product items be irradiated using the verification dose and then tested for sterility. Assuming the product passes the sterility tests no other work is required. Dose mapping should be redone if there is a change of product material, packaging method, and/or packaging configuration.
Who is the Ideal Candidate for a Rad Source X-ray Unit?
The ideal candidate is one who has low volume processing requirements and high value products.