Understanding Gamma Sterilization - This article outlines methods, validation standards, and documentation of sterilization of single-use products using gamma irradiation. - BioPharm International


Understanding Gamma Sterilization
This article outlines methods, validation standards, and documentation of sterilization of single-use products using gamma irradiation.

BioPharm International
Volume 25, Issue 2, pp. 18-22


Because of their size and complexity, single-use systems can present some technical difficulties when assessing bioburden and sterility after irradiation. Fortunately, the standard provides some practical strategies by allowing for the grouping of similar products into families so that validation only needs to be performed with a worst-case or representative unit. Product families are defined by common nature and source of raw materials, components, and product design and size, along with assembly process, equipment, and environment. A single master product can then be identified or constructed to be the representative or worstcase version of all the products in the family. Sterilization of comparable products in the family can then be rationalized as equivalent to the validated master product.

Although this reduces the number of different systems that need to be qualified, bioburden recovery and sterility testing of large complex systems can still present formidable technical challenges. Therefore, it is common to only validate the sterility of the internal product fluid-contact pathway (with closures at any ports or openings). The system exterior and inner packaged space, which receives the same radiation dose, can be considered microbially controlled, but not validated as sterile.

To further ease the technical challenge of aseptic handling for bioburden and sterility testing, the master product can also be broken into smaller subunits, termed sample item portions (SIPs). These can be tested separately and have their mean bioburden and sterility results combined to establish the validated sterilizing dose for the fully configured system.


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 sterilization is packaged, palletized, and transported into the irradiation chamber using a conveyor.

Once a minimum sterilizing 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 sterilizing 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 to ensure the minimum sterilizing does can be achieved throughout the batch. 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.


The sterilization 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 Sterilization Validation Report supporting the minimum sterilizing 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 sterilization validation rationale, minimum dose-sterilization 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.

Jerold Martin is senior vice-president of Global Scientific Affairs at Pall Life Sciences, Port Washington, NY, and chairman of the Board and Technology Committee at Bio-Process Systems Alliance, tel. 516.801.9086.


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).

For further information on this topic, see BioProcess Systems Alliance, "Guide to Irradiation and Sterilization of Single-use Systems," available at http://www.bpsalliance.org/guides/ as well as an educational webinar by J. Martin, and M. Senescu, "Sterilization of Single-use Systems by Gamma Irradiation," available at http://www.pall.com/biopharmwebinars/.

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