Radiation Source Use and Replacement Abbreviated Version (2008) / Chapter Skim
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6 PANORAMIC IRRADIATORS
6 PANORAMIC IRRADIATORS
Pages 101-116
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From page 101... ...
USES OF PANORAMIC IRRADIATORS Panoramic irradiators1 or gamma irradiation facilities are used to sterilize medical devices and products. They are also used to sterilize pharmaceuticals and consumer products (e.g., cosmetics)
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From page 102... ...
requires that the sterilization of invasive medical devices such as hypodermic needles and scalpels must achieve a sterility assurance level of 10−6.2 The sterility assurance level is the probability or frequency of contaminated products after processing, so a level of 10−6 corresponds to a one in a million chance that one live microbe is in the sterilized load. Three standard sterilization processes are employed worldwide by the majority of single-use medical device manufacturers: gamma irradiation, ebeam irradiation, and ethylene oxide (EO)
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From page 103... ...
. Some plastics discolor or become brittle upon irradiation, although there has been some progress in development of radiation-resistant polymers.3 But for the many products for which gamma irradiation is effective, manufacturers need only consider other business 3 Polyimide, liquid crystal polymer, polyether sulphone, polyetheretherketone, polyethylene terephthalate , and other similar plastics can all be made to be relatively radiation resistant, but many other common polymers such as polyoxymethylene, and polypropylene have poor radiation resistance.
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From page 104... ...
if economic, relatively simple, and appropriately sized irradiators can be developed. Large-Scale Gamma Irradiation Facilities that carry out large-scale irradiation using radionuclide radiation sources (gamma sources)
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From page 105... ...
The x-rays and gamma rays interact more weakly with fewer electrons. Figure 6-3 shows the relative dose versus depth in material for four different radiations: e-beam at 10 MeV, cobalt-60 with its 1.3-MeV gamma rays, and x-rays at 5 and 7 MeV.
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From page 106... ...
. 1.2 MeV FIGURE 6-3 Relative dose versus depth in material for four different radiations.
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From page 107... ...
X-ray irradiation so far has only been used for food irradiation in laboratory and demonstration-scale irradiators and in one moderate-size facility for irradiating packages, described below. Texas A&M University hosts the National Center for Electron Beam Food Research, which does research, training, and contract processing using linacs that deliver ebeam or x-ray irradiation.
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From page 108... ...
These devices would most likely be, in essence, self-contained irradiators, but they could replace some contract irradiation if the costs of purchase and operation turn out to be competitive. An effective system for irradiating a wider variety of products could be imagined as including a combination contract irradiation facility with a gamma irradiator for moderate- and high-density products and for low-dose-rate irradiation; an e-beam irradiator for low-density products and very-high-dose-rate irradiation; and an x-ray irradiator for high- and very-highdensity products and high-dose-rate irradiation.
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From page 109... ...
Accelerators increase throughput by increasing the beam power and conveyor speed, and so the configuration changes little. The factors that more clearly differentiate the cost of cobalt gamma irradiation from x-ray irradiation are listed in Table 6-2.
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From page 110... ...
Because there is no experience yet with a large-scale x-ray irradiator, the committee cannot state these assumptions with great confidence, and only offers them as the data it has available. Steam or Dry Heat Autoclaves and dry-heat ovens are routinely used in hospitals to sterilize reusable medical devices, but medical devices are increasingly being provided as single-use devices.
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From page 111... ...
, such as vacuum-pressure-sensitive products; nonvented, sealed products that do not allow for gas diffusion or penetration of EO gas; medical products that retain absorbed EO; products with extremely high densities or challenging physical configurations that would limit the permeation of EO; products with active pharmaceutical ingredients not validated for the effects of EO; and some orthopedic implants where radiation is needed to increase product strength characteristics, in addition to sterilization. EO sterilization typically comprises three stages: preconditioning, sterilization, and aeration.
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From page 112... ...
The EO concentration and cycle times vary greatly depending on the product, cycle conditions, and whether a conventional EO sterilization process is used or the three sterilization stages are performed together in the sterilization chamber. The EO concentrations are highest during the dwell stage and range from about 300 to 1,200 mg/l, with the average at about 650 mg/l (Hadley, personal communication, 2007)
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From page 113... ...
OSHA also requires: • monitoring employees to determine actual exposure to EO during work shift, • restricting access to EO areas to authorized personnel, and • implementing a system to provide emergency warning in the event of a release. In addition to the requirement to meet the sterility assurance level described above, FDA regulations specify permissible residual concentrations of EO on sterilized medical products.
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From page 114... ...
It is a technology that has been used for many years to sterilize medical products effectively. There have been no accidents or incidents involving mass casualties due to the use of EO.
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From page 115... ...
has one gamma irradiation facility dedicated to food irradiation research, Iowa State University operates the Linear Accelerator Facility for food irradiation, and Texas A&M University operates the National Center for Electron Beam Food Research, a semicommercial, semi-research facility for e-beam and x-ray food irradiation. A few other irradiation facilities can be contracted to irradiate foods, but do not do so routinely (aside from spices)
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From page 116... ...
The risks of EO should be judged relative to those associated with the use of radiation sources in panoramic irradiators. EO poses no area-denial radiological dispersal device risk, but the accidents and potential security risks, health risks associated with exposure, and pressures to encourage EO users to switch away from EO because of its toxicity indicate that encouraging a shift from irradiation to EO sterilization may not be desirable.
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