Gamma irradiation technology was established in the 1950’s and has developed to become the most commonly used irradiation sterilization technology. Today approximately 300 irradiation facilities globally are applying gamma irradiation for a wide range of beneficial applications. Gamma radiation sterilization keeps us safe and healthy and provides important socio-economic benefits that impact the daily lives of the world’s population. The largest application of gamma irradiation is the sterilization of single-use medical devices to ensure that surgery, wound care and other healthcare treatments can be performed with reduced risk of infection.
The technology and science of gamma irradiation is well understood by users and regulators. For this reason, it has been widely adopted by many industries to improve the safety and quality of their products. Regulators worldwide have approved a large number and wide range of healthcare products for treatment by gamma irradiation and today over 40% of single-use medical devices are sterilized with this technology. This makes it the highest volume irradiation sterilization technology by a considerable margin with volumes approximately equivalent to those treated with ethylene oxide (EO) gas. Gamma irradiation is therefore critical in ensuring that the healthcare industry can meet the global demand for sterile medical devices.
A well understood and established technology
Gamma irradiation is particularly suited for bulk sterilization as it offers good penetration of many types of materials, products, and packaging. This makes the technology particularly effective for the treatment of dense products and large packages including pallets. This is an advantage of gamma irradiation over electron beam (e-beam) technology whereas X-ray irradiation also has the capability to treat dense and large packages.
Gamma irradiation is a simple process when compared with other sterilization technologies. The process is controlled by a small number of parameters that can be easily determined and validated. Gamma irradiation uses durable industrial equipment, rather than high-tech machines, which results in high levels of reliability and uptime and a reduced need for skilled specialists to perform repair and maintenance work. An important feature of the gamma irradiation industry is the numerous processing facilities around the world that enable both local and global support of the medical device industry, often with the availability of additional or back-up facilities if needed.
Cobalt-60 at the core of gamma irradiation
Cobalt-60 is a radioactive isotope that produces the gamma radiation used to sterilize healthcare products. The amount of Cobalt-60 installed within an irradiator is one of the factors that determines the volume of product that can be processed. If an operator adds more Cobalt-60 then an increased volume of product can be sterilized. Cobalt-60 decays at a rate of ~12% per year making it necessary to replenish it in order to maintain a certain processing volume. If there is increased demand for sterile product then an operator will need to install Cobalt-60 to meet the increase in processing demand in addition to replacing that lost through decay.
The benefit of this is that a gamma irradiation facility is scalable, and the level of Cobalt-60 can be adjusted to meet demand without needing to make a full upfront investment to the maximum capacity of the irradiator. It is quite normal for a gamma irradiation business to start with a small investment in Cobalt-60 and then increase this as the business grows.
Cobalt-60 is therefore at the core of the process and its supply chain is critical in ensuring that the global demand for sterile medical devices can be met. Cobalt-60 is currently produced in 19 nuclear reactors and manufactured into radiation sources by a few very specialized suppliers.
In recent years there has been a tightness in Cobalt-60 supply that has been highlighted by irradiator operators and acknowledged by suppliers. This is a consequence of higher than historical demand for Cobalt-60 and the decision of one state run corporation to reduce output. Other suppliers are pursuing opportunities to increase production while also managing the impact of the temporary closure of some reactors for refurbishment. Reactors usually undergo refurbishment once during their working life and this allows them to continue operation and Cobalt-60 production for an additional 25-30 years. Reactor operators have reported that ongoing refurbishment activities are either on time or ahead of schedule. They also continue to announce when reactors have reopened post-refurbishment and when operating licences have been extended.
Cobalt-60 suppliers report that work continues to bring production on-line at several additional reactors that are of the same design as currently used. In parallel, new isotope production technology is being developed that will allow Cobalt-60 to be produced in other more common reactor types.
Industry is watching as the supply chain evolves and the various initiatives start having an impact in terms of Cobalt-60 availability. Meanwhile, demand for Cobalt-60 continues to grow driven by the increasing demand for sterile single-use medical devices.
Cobalt-60 safety and security
The gamma irradiation industry has an exemplary safety and security record and continues to innovate in order to improve and assure sustainability of the technology. The radioactive nature of Cobalt-60 does bring some particular requirements, however, the management of safety and security at a gamma irradiator is quite conventional and does not differ much from other industrial facilities. Those requirements specific to radioactive material are highly regulated and have been developed by the industry with decades of operational experience.
The industry aims to surpass regulatory requirements and is highly engaged in the evolution of safety and security arrangements. Recent examples of this engagement are the initiatives of the International Irradiation Association’s Gamma Working Group that has: developed a security best practice guide(1) and a security effectiveness assessment methodology(2) in partnership with World Institute of Nuclear Security; and is supporting Sandia National Laboratories through the U.S. Department of Energy/National Nuclear Security Administration’s (DOE/NNSA) Office of Radiological Security (ORS) to develop new types of physical protection measures.
Cobalt-60 is a non-soluble, non-dispersible and non-flammable metal. This makes it very different to Caesium-137 sources that contain water-soluble caesium chloride powder that can be easily dispersed and is difficult to decontaminate after dispersal. Caesium-137 has been subject to various projects internationally to remove and replace caesium irradiators whereas, in contrast, the US NRC has considered a number of scenarios and determined that it would be extremely difficult to use a Cobalt-60 source to contaminate a wide area (3). The properties of Cobalt-60 combined with the safety and security features of gamma irradiators, along with the scale of the radiation processing industry and the growing demand for sterile medical devices, makes such a remove and replacement project for Cobalt-60 both non-viable and inappropriate.
Challenging gamma irradiation
As with all industries and technologies, there are challenges along the way that need to be managed and addressed. Industry consolidation and the competitive environment are normal business challenges that are not unique to radiation processing and will continue to evolve over time. Operational and regulatory challenges are being met by industry through proactive collaboration and by forming good partnerships.
Regulations must support the growing need for medical devices and recognize and reflect any national strategy where healthcare has been identified for strategic growth. This includes regulation of the critical sterilization step such as that relating to the licensing and operation of irradiation facilities and the use and transport of Cobalt-60. Similar challenges can be found within the EO sterilization industry where the legislative and regulatory landscape surrounding EO emissions is causing companies to review their operations and reassess the viability of some businesses.
As with most technologies, alternatives are available and, to date, the choice for bulk medical device sterilization has been either gamma or EO. The most commonly available alternative irradiation technology has been e-beam that is already used for some medical device sterilization. Low penetration usually limits its application to low-density products, smaller packages, or surface treatment so, when compared with gamma irradiation, relatively small volumes of medical devices are processed with e-beam.
There is currently a growing interest in the use of X-ray irradiation for the sterilization of medical devices. X-ray is regarded as broadly equivalent to gamma irradiation in terms of performance due to its high penetration and some research suggests that it may offer some technical advantages over gamma. Many developments point to the fact that X-ray for radiation processing is coming of age and investment in the technology has started and is expected to accelerate over the short to medium term. This investment is being made now that the process is well understood and with improved machine reliability and a backdrop of constraints on existing gamma and EO sterilization capacity. It will take several years for the X-ray infrastructure to develop and the availability of the technology, both as a primary and a backup supply, is not yet a widespread alternative to gamma irradiation.
A great deal of complex, time consuming and costly qualification and validation is required before the number of materials and products approved for X-ray sterilization can be expanded. In many cases, the equivalent work will already have been done to enable treatment by gamma and it remains important to maintain this gamma qualification to ensure business continuity and flexibility in sterilization technology selection. The true efficiency, operating cost, and commercial competitiveness of X-rays will be better understood once large numbers of products have been approved and the use of the technology has been adopted for the sterilization of high volumes of medical devices.
The sustainability of gamma irradiation for healthcare applications
The healthcare industry has relied on gamma irradiation since the 1960s when demand for this sterilization technology started to grow. The technology is now applied globally and is backed up by a robust regulatory and operational infrastructure.
Meanwhile, advances in medical technology, greater access to healthcare and an ageing population with extended life expectancy, all create a sustainable demand for sterile medical products. The healthcare industry continues to grow as does its need for technology to meet their sterilization requirements.
Not all sterilization technologies are suitable for all medical devices and it is recognized that gamma, e-beam, X-ray and EO all have their place. However, due to the prevalence of gamma irradiation for medical device sterilization, there is no other technology or combination of other technologies available today that could meet global sterilization demand should there be a significant reduction in the use of gamma irradiation. One only has to look at the concerns raised by the closure of a small number of EO sterilization facilities and the FDA statement that ‘The impact resulting from closure of these and perhaps more facilities will be difficult to reverse, and ultimately could result in years of spot or nationwide shortages of critical medical devices, which could compromise patient care’ (4).
Alternative sterilization technologies continue to evolve, and some contract sterilization service providers have developed into technology neutral organizations offering a mix of sterilization technologies to the medical device industry. Meanwhile, gamma irradiation continues to be a cornerstone of medical device sterilization supported by an industry that is well placed to manage challenges and embrace new opportunities as they emerge.
- Joint iia/WINS Best Practice Guide 5.8 Security of Radioactive Sources Used in Industrial Radiation Processing
- Joint iia/WINS Methodology for assessing the effectiveness of security arrangements at gamma irradiation facilities
- U.S. NRC Backgrounder on Commercial Irradiators – February 2020 https://www.nrc.gov/reading-rm/doc-collections/fact-sheets/commercial-irradiators.html
- U.S. FDA Statement – Statement on concerns with medical device availability due to certain sterilization facility closures – October 2019 https://www.fda.gov/news-events/press-announcements/statement-concerns-medical-device-availability-due-certain-sterilization-facility-closures