By Mark Botting, Hans Hartmann, and Susie Perlman

Product sterilization using irradiation is an internationally accepted and widely utilized technology for processing medical devices, pharmaceuticals, tissue and biologics, and laboratory disposables. A proven method for sterilizing products since the 1950s, radiation sterilization has steadily gained market share because of its processing speed, parametric release capabilities, and cost competitiveness. Two such sterilization techniques used by medical device manufacturers, gamma and electron-beam irradiation, are now accepted by regulatory agencies worldwide.

While E-beam (beta) and gamma sterilization methods are employed widely in the medical device industry, x-ray sterilization is not as well known. However, despite its lack of exposure, it combines the best features of both, melding E-beam’s rapid turnaround times and processing flexibility with gamma’s pallet configuration processing and relatively low dose ratios.

Advantages of X-Ray Sterilization

Penetration and Dose Uniformity Ratio (DUR). X-ray sterilization offers better penetration characteristics than either gamma or E-beam techniques. While the E-beam environment is suitable for sterilizing low-density, lightweight, and consistently packaged products, it has difficulty sterilizing metals, liquids, and high-density or multicomponent products. And while gamma sterilization is somewhat better at penetrating dense products, it cannot always achieve the required DUR. In contrast, x-ray sterilization is well suited for processing products on pallets rather than in totes. In addition, it can also sterilize products with individual case configurations and those requiring tighter dose ranges, even in pallet configurations.

Enhanced Polymer Reaction. Because of x-ray sterilization’s very short exposure times, its radiation effects on materials—especially polymers—are often measurably less than those caused by gamma processing. In fact, the effects of x-ray processing are very similar to those associated with E-beam sterilization. The combination of shorter exposure times and improved DUR enables customers to use x-ray sterilization technology for medical device products that are currently treated using such processes as ethylene oxide (EtO).

Processing Speed and Flexibility. The shorter processing times associated with x-ray sterilization provide inventory advantages over traditional ethylene oxide and gamma cycles, reducing supply chain turnaround times by days. In addition, x-ray technology can process multiple products with different dose requirements within the same irradiation cycle, offering faster turnaround times than both gamma and E-beam methods. For example, the x-ray process can be based on incremental dosing cycles, whereby a single incremental dose can consist of four passes in front of the x-ray target. The product can therefore be subjected to any multiple of the incremental dose by adding increments. Thus, if the increments have a value of 2.5 kGy, 25 kGy can be applied to the product in 10 increments.

Environmental Advantages. While both gamma and EtO sterilization are recognized and accepted by regulatory bodies throughout the world as providing safe and sterile medical devices, these technologies have certain deleterious environmental consequences. Although sterilization service providers strive to ensure the safety of their processing technologies and employees, stricter regulation can result in increased manufacturing costs and device costs. In contrast, because x-ray technology is based on the use of electricity as the sterilization agent rather than cobalt-60 or ethylene oxide gas, it provides a much cleaner and more sustainable solution.

Regulatory Approvals and Validations. The layout and workings of an x-ray plant are designed to fulfill international standards, including ISO 13485 and ISO 11137 quality management system standards for medical devices; Sterilization of Healthcare Products—Radiation, Parts 1–3 (ISO 11137); CGMP; and FDA guidelines. In ISO 11137, x-ray technology is accepted as an alternative to gamma and E-beam methods. Furthermore, research concludes that the D-10 values of microorganisms are not significantly different when treated by either gamma rays or x-rays in both wet and dry conditions.

Conclusion

Because of its efficiency, flexibility, and technical advantages, x-ray processing will position itself as the preferred sterilization modality for many medical device products. And as the technology’s inherent processing strengths are better understood, it will expand globally and command manufacturers’ interest.
 

Mark Botting, is commercial director for the UK at Swindon, UK–based Synergy Health. Filling this position since 2008, he is responsible for sales and marketing for gamma, E-beam, and EtO technologies. In addition, he oversees three microbiological testing labs in the UK and Ireland. Reach him at [email protected].

Hans Hartmann is Synergy Health’s director of operations in Switzerland. With more than 30 years of experience in radiation-based technologies, he is the designer of E-beam, gamma, and x-ray equipment and also designed the company’s x-ray plant in Däniken, Switzerland. Reach him at [email protected].

Susie Perlman is U.S. director of customer relations and Marketing for Synergy Health’s Advanced Sterilization Technologies division. With nearly 20 years of experience at the company, she focuses on staff and client training and assistance for radiation-based technology. Reach her at [email protected].

Bob Michaels is senior technical editor at UBM Canon.

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