Radiation steriliser — dose mapping and quarterly audit
Cobalt 60 can be stored safely in a pool of water, while the chamber above the pool is surrounded by a thick concrete barrier
that prevents gamma rays from escaping when the gamma source is elevated into the irradiation chamber. Product intended for
sterilisation is packaged, palletised and transported into the irradiation chamber using a conveyor.
Once a minimum sterilising dose is established for the Master Product, a pallet load configuration and density is established.
Dose measuring devices called dosimeters are distributed throughout the packaged load to confirm that the minimum sterilising
dose is reached throughout the batch. Because the received dose can vary based on density, materials are typically qualified
to withstand up to 50 kGy. On a quarterly basis, the process is audited by, again, determining bioburden in 10 current product,
Master Product or SIP samples. Verification dose sterility tests are conducted on 10 additional samples.
Sterile product documentation
The sterilisation validation and irradiator batch data support both the supplier's claim for sterility for the singleuse system(s)
and the user's claim for cellculture process control and finished product sterility. Several documents serve to support both
system and finished product sterile claims. First, the supplier should provide a letter explaining the rationale for the sterile
claim of each specified system by part number, based on actual or Master Product validation. Suppliers can insert a Certificate
of Quality within the unit packaging stating that the product is sterile after irradiation. External irradiation indicators
that change colour upon exposure are not sufficiently quantitative to confirm sterility. A summary Sterilisation Validation
Report supporting the minimum sterilising dose, as well as the Dose Mapping Study Report and most current Quarterly Dose Audit
Report generated by the irradiator, should be provided by the system supplier. Original data and irradiator certificates,
however, may only be available during supplier audit. Lastly, the supplier should provide a Certificate of Irradiation for
the system lots in the batch, certifying the minimum dose recorded by the batch dosimeters.
This combination of sterilisation validation rationale, minimum dose sterilisation validation, batch load dose map, batch
irradiation dose certificate and quarterly dose audit serves to support the ongoing sterility of the single use system and
the sterile products produced with them. For more information on this subject, a good resource is available free of charge
in the form of the BPSA's Guide to Gamma Irradiation and Sterilization (3).
1. AAMI/ANSI/ISO 11137:2006, "Sterilization of health care products — Radiation — Part 1: Requirements for the development,
validation and routine control of a sterilization process for medical products; Part 2: Establishing the sterilization dose;
Part 3: Guidance on dosimetric aspects"(2006).
2. American Association of Medical Instrumentation, "Sterilization of health care products—Radiation—Substantiation of a sterilization
dose—Method VDmax", Technical Information Report TIR33:2005 (2005).
3. BPSA, "Guide to Irradiation and Sterilization of Single-use Systems" (2008).