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What is X-ray irradiation

Writer: Sterilization Time: 2020-09-18 Browse: 985 ℃

The mode of action of X-ray irradiation, the penetrating ability of X-ray irradiation, the technological parameters of X-ray irradiation, the advantages and disadvantages of X-ray irradiation and its cost are discussed.

Mode of action
Ionizing radiation in the form of x-rays generated by electrons hitting a target.
Medical device product requirements
Materials are compatible with radiation, penetrate full pallets with densities up to 0.50 g/cm3
Material compatibility
Wide range of polymer compatibility compared to gamma; some limitations due to oxidation effects.
Largest processing unit: Pallets or boxes

X-ray Processing

Product exposed to x-rays for a validated period of time to achieve a desired minimum dose.
Control system can quickly stop and start the source manually or automatically.
Tolerance for density variation:Very high.
Processing time for a typical 45-ft tractor trailer (~3,000 ft3): <24 hours typical but could process small batch quicker.

Processing parameters

There is a need to simultaneously monitor a number of parameters to ensure that the prescribed dose is delivered (e.g. beam current, cycle time, product size and density)

Product release parameters

In order to release product to market, the following are required:
  • Control of the product manufacturing processes to ensure supply of material and product packaging is consistent with the validated radiation process
  • A validated processing configuration in which an array of dosimeters have been measured to demonstrate the relationship between processing parameters and minimum and maximum dose to product and a routine dosimeter measurement (validation requirements and methods are well described in ISO 11137-1)
  • A measurement of routine dose for a given processing run, which indicates that a dose within specification has been delivered. This measurement can be made as soon as the irradiation process is complete, so there is no required waiting time before release.

Pros (specific to medical devices suitability) X-ray

  • Highest potential penetration depth in product.
  • Efficient and targeted delivery of dose.
  • Product holdup may be smaller than in acomparable gamma plant.
  • Ability to process in large volume quantities.
  • Ability to schedule multiple products to be processed at one time.
Cons (specific to medical devices suitability)
  • Technology has limited adoption, which means that backup facilities may not be available during maintenance or other shutdowns.
  • Few existing products are currently validated with the x-ray technology.
Switching existing products to x-ray will require revalidation.

X-ray Equipment

Penetrating capability
The spectrum of photons created from the x-ray target provides an overall penetration depth somewhat greater than gamma, assuming an input electron energy between 5 and 7 MeV.
System repair downtime (e.g.source/system for machine sources; system for Cobalt-60)
  • Can vary from hours to days.
  • Conveyor repair related items are generally quick.
  • Accelerator and x-ray converter-related issues can sometimes take days to repair.

Reliability and maintenance

Stable and reliable in a daily production environment. Actual operational experience has demonstrated ~90% uptime.

Pros (equipment-related)

  • X-ray offers the penetration advantage of gamma.
  • The source of radiation can be turned off, which allows for easy access and repair.
  • X-ray irradiators allow processing of totes and carriers up to full pallets of healthcare products.
  • Dependent on design conditions, x-ray can provide the opportunity to achieve a better DUR under like-for-like conditions with gamma.
The source energy is electricity and does not require the material to be transported.

Cons (equipment-related) X-ray

  • Potentially higher initial capital costs versus gamma as investment in “full capacity” may be necessary in initial investment.
  • Potential longer rate of return of investment .
  • Equal or greater complexity of equipment validation and maintenance to that of e-beam.
  • Need for ongoing replenishment of critical components over life of equipment.
  • Maintenance outsourcing or development of technical staff to manage and maintain equipment.
  • Reliable and very high electrical power consumption requirement.
  • Costly parts due to complexity.
  • Need for a nearby back-up facility in case of lengthy shutdown for repair.

Sterilization source

Cost of generator Includes accelerator, beamline, scan horn, equipment cooling system, removable or fixed x-ray target, installation, IQ and OQ. The cost of the
accelerator strongly depends on beam power. Production throughput is proportional to beam power. It is possible to increase the x-ray source capacity at a later stage by adding power modules to the accelerator or by adding a second accelerator (if planned in the initial facility design).

Process management

Typically tote or pallet conveyors.
Safety Systems
The Safety Access System prevents unauthorized access into the accelerator room and irradiation chamber. Should there be an authorized intrusion in the irradiation area, the safety system instantaneously stops the accelerator irradiation.

Specific Infrastructure

Shielding is usually made of concrete. A typical foot print for an x-ray or gamma irradiation system including shielding and conveyor is about 25m x 20m.
Irradiation Authorizations including compliance of design shielding and safety system according to standards.
Ancillary systems Includes water cooling, compressed air, ozone venting, fire prevention.

Common infrastructure

  • Land.
  • Building Warehouse.
  • Miscellaneous.
  • fences, racks, furniture, forklifts.
  • Local authorizations.
  • Building permits, fire department, environmental regulations such as noise.

Variable costs

Costs that are proportional to production

Operators typically work in shifts. Processing boxes requires more labor compared with pallet processing.

Consumption Typical accelerators have power efficiencies from 20 to 50%. Accelerator power consumption stops when products are not processed. Other power consumption is for office and other non- accelerator related components. X-ray systems require significantly more beam power compared with e-beam systems for similar throughput due to power losses in the x-ray converter.

Spare Parts
Spare parts stock may vary and can be expensive. The minimum spare parts to store are specialized consumables which require periodic replacements (e.g. cathode, tetrodes, klystrons, seals, filters, pipes). Other spare parts may be stored in order to reduce downtime in case of failure.
Spare parts required for the conveyor are similar compared with gamma.

Repairs / maintenance and ongoing Investment

Maintenance Engineer
Someone with specialized electronics and mechanics background needed for maintaining an accelerator.
Specialized expertise available from the manufacturer may be required due to equipment complexity.
The above is the X-ray irradiation instructions, if you have any other questions, please contact us.