Application Issues

Early electron beam applications did not meet expectations and raised some serious issues regarding their overall suitability for medical device sterilization. As a result there are misconceptions that may still exist in peoples minds about the technology, including:

• Penetration
  Early application efforts utilized industrial accelerators with energy levels limited to 4 or 5 MeV. Processing capabilities were limited for case sterilization and most successful applications were accomplished on a single product basis. The present system designs have increased the energy to 10 MeV which has the ability to penetrate 35" (90 cm) of 0.10 g/cc bulk density using double sided irradiation, allowing a wide range of products for sterilization in their final shipping cases.

• Reliability
  The early applications were implemented with accelerators developed primarily for research purposes. These accelerator systems were based on designs and concepts that were developed to address research needs, providing as much energy as possible for the lowest cost. Early designs did not address a 24 hour per day, seven day per week duty cycle and "maintainability" requirements supporting medical product production requirements. Spares for critical components often took weeks or months to replace, whereas current requirements call for the system user to have critical items on-site. The present designs routinely achieve a 24 hour per day duty cycle. Today, systems routinely operate more than 7,000 hours per year, with maintenance performed in less than 8 hours per week. Unscheduled down time has been measured consistently at less than 5%.

• Process Interruptions
  Directly related to the issue of reliability was the issue of process interruption. If the system faulted during routine production processing, what was the impact on the dose integrity and the product? Initial systems were validated with the protocol that when the system shut down, the product in the beam would be identified and destroyed. Modern state-of-the-art control systems employing programmable logic controllers have made it possible to provide a process interruption procedure assuring a positive transition dose, thus maintaining dose integrity and saving impacted products