X-ray Sterilization: The Technology of the Future - IBA Industrial

X-ray Sterilization:The Technology of the FutureIBA Industrial - White PaperX-ray sterilization of medical products has been studied theoretically and experimentally, indetail, by the National Bureau of Standards, universities and accelerator manufacturers sinceit was first proposed over 40 years ago. Commercial use began approximately 15 yearsago but full commercial adoption has been slow because of the low output power of earlyaccelerators. The invention of the Rhodotron ® , IBA’s high-power, high-energy accelerator isquickly changing the landscape. Today there are sterilization facilities with X-ray capability inEurope, Japan and North America and a state-of-the-art pallet/X-ray facility is being built byLEONI Studer Hard AG at their facility in Switzerland, with a targeted commissioning date infirst half of 2010.Thanks to the fact that X-rays are directionally concentrated it is easy to capture a highfraction of the photon power emitted which means high penetration quality and highthroughput.X-rays:Ideal Physical Properties for SterilizationHigh-energy X-rays (bremsstrahlung) are high-frequency, shortwavelengthelectromagnetic photons. They are emitted whenhigh-energy electrons are stopped by a material which has ahigh atomic number. The efficiency for X-ray emission increaseswith the electron energy and the atomic number of the targetmaterial. Thin sheets of tantalum are used for the long targetsthat are needed for irradiating tall pallet loads of product. TheX-ray energy spectrum is very broad, with the maximum photonenergy being the same as the kinetic energy of the incidentelectrons. With X-ray energies of 5 MeV and 7 MeV (millionelectron volts), product penetration is greater than that providedby gamma rays from an un-collimated cobalt-60 source.High-energy X-rays are ideal for sterilizing large packages andpallet loads of medical devices. In contrast to gamma rays,which are emitted in all directions from a cobalt 60 source, highenergyX-rays are concentrated in the direction of the incidentelectron beam, and their angular dispersion decreases as theelectron energy increases. The high intensity in the forwarddirection enhances the efficiency of X-ray utilization and allows areduction in the size of the irradiation room. Only a few productcarriers are in the treatment room at one time and treatmenttime per carrier is reduced.Irradiation of small batches of products with different densitiesand doses becomes easy and economical.Figure 1 : X-ray penetrates deeper than other radiation techniquesallowing faster and better sterilizationDose Uniformity: Key to High QualityTreatmentThe directional concentration and high penetration capabilityof X-rays also allows you to treat pallet loads of low-densitymedical products with excellent dose uniformity. In order toobtain good dose uniformity and efficient X-ray utilization,product loads must be irradiated from both sides.The optimum thickness for two-sided treatment increases as thepackage density decreases.Figure 2 shows how Dose Uniformity Ratio is improved whenpresenting both sides alternatively to the X-ray source.1

IBA Industrial - White Paper“We are able to reach DURs between 1.3 and 1.5, dependingon density, when sterilizing medical devices on pallets”, saysJean-Louis Bol.Figure 4: IBA’s eXelis sterilization solution adding to pallets ofmedical devices incremental doses of 2.5 kGyProcessing Medical Devices on PalletsThe directional concentration property of X-rays makes themideal for sterilizing medical products on pallets. Sterilizing onpallets eliminates the costly process of de-palletization andre-palletization. Further reduced handling significantly reducesthe opportunity for product damage and stream-lines producttracking and quality assurance processes.Figure 2 : Increased DoseUniformity thanks to doubleside irradiation.For a typical European pallet of 1x1.2x1.8m, 15 cm woodframe, with 10 cm lateral gaps between products, tests andsimulations have shown that eXelis ® maintains DUR below 1.5for 0.3g/cm³ density medical devices (or 600 kg per pallet).When it comes to flexibility, eXelis ® also excels. Thanks to itsdirective X-rays and its single layer of products in front if theX-ray Source, you can mix pallets containing different productswith different densities and still achieve excellent DUR andthroughput results. Minimum and maximum doses in eachhorizontal layer of a 0.1 gm/cm³ pallet, when surrounded by 0.2gm/cm³ pallets, did not show any significant difference.The typical annual throughput of medical devices of aneXelis 1000 ranges from 120.000 to 160.000 m³ (4.2 to 5.6 millioncu.feet) depending on the dose required and the density of theproducts.“eXelis 1000 has a large throughput capability, excellent doseuniformity and high flexibility as products can be varied fromcarrier to carrier.” Says Jean-Louis Bol.Figure 3: X-ray properties ideally suited for pallet sterilizationeXelis ® : the X-ray Sterilization SolutioneXelis ® is IBA’s solution for X-ray processing; it is the idealalternative to gamma sterilization. The engine for an eXelis 1000sterilization center is a high-power 7 MeV, 560 kW Rhodotron ®accelerator. The center is also equipped with an incrementaldose product conveyance system, allowing a plannedirradiation dose to be delivered in variable increments. Forexample a typical sterilization dose of 25 kGy can be deliveredin 5 increments of 5 kGy or 10 increments of 2.5 kGy. Eachdose increment is delivered in four passes. The four passespresent the pallet to the source in four different positions, frontside up, back side up, front side down and back side down,resulting in excellent DUR. A transfer station which is located inthe irradiation room automates the process of inverting palletson the conveyor.Dose rateX-rays and gamma rays are both photons. They lose theirenergy in matter in the same manner and have a goodpenetration power. However, their different productionprocesses lead to different emission characteristics:••The X-ray emission is concentrated along onedimension meaning a large fraction of X-rays are emittedin the forward direction.Figure 5: eXelis ® self-standing up sidedown pallet inverter allowing achievingexcellent DURGamma ray emission is isotropic. 60Co pencils areusually laid out in a source rack with 2D extension.2

IBA Industrial - White PaperTherefore, the X-ray and G-ray sources are rather different andthe dose rates in the product will also be different.The dose rate is the amount of radiation given per unit of time,such as kGy/min. Simulations based on X-ray and GammaMedical Device Sterilization facility modeling show a dose ratetwo times higher for X-rays compared with Gamma rays.The Future of Electricity versus CobaltThree major issues are driving industry to look for alternatives togamma sterilization: cobalt prices, the future availability of cobalt60 and the increasing regulations regarding the transportationof cobalt 60 which are also driving up the cost of gammasterilization.Cobalt producing reactors are becoming old and will requireexpensive upgrades in the coming years. This not only includesthe cobalt producing reactors in Russia but also includes themajor cobalt reducing reactors in Canada. Many industryparticipants are forecasting significant cobalt price increasesin the next decade. Availability is also likely to be an increasingissue as reactor shutdowns for re-tooling are lengthy and thereis very little new cobalt production capacity planned.Sterilization CostThe price of an eXelis 1000 is comparable to the price of a 3.5 MCicapacity gamma facility. In contrast, however, the capacity ofan eXelis 1000 is equivalent to the capacity of a 4.5 MCi capacitygamma facility.A financial model which considers both the direct and indirectcosts of operating a sterilization center demonstrates that thecost to process a pallet of medical products in an eXelis 1000 ismuch lower than the cost of processing a pallet in a gammafacility, when considering an annual throughput of 100.000 m³/year (3.5 million cu.feet/year). The higher the throughput, thehigher the savings. Savings of up to 20% can be achieved withproduction volumes higher than 125.000 m³ (4.4 million cu.feet)per year.For average electricity costs from 0,11 to 0,14$ per kWh and forCobalt costs from 2 to 2.5 $, yearly electricity operating costs ofan eXelis 1000 facility are equivalent to the cobalt 60 refill costs ina gamma center.The global regulatory environment regarding the transportationof cobalt 60 is currently difficult and regulations are increasingevery year. Air-freighting industrial quantities of cobalt 60 isno longer allowed and sea-freight is becoming increasinglydifficult. Very few carriers accept radio-active products and manyports globally refuse ships carrying cobalt. Cobalt sea freightshipments are commonly late and regularly delayed for periodsof up to 6 months because of the current regulatory environmentand it is anticipated that the future will only become morechallenging.Electricity is the answer to the issues which isotopes face,and also has the advantage that you can turn it off. You do nothave to run an eXelis ® 24 hours per day if you experience anunexpected product slowdown or if your current productionvolume is less than the capacity of your eXelis ® facility. “WitheXelis ® , you only pay for the power you use”, says Jean-LouisBol.An eXelis 1000 running at capacity will have a total electricalconsumption of 1200 kW. In stand-by mode, this consumptiongoes down to 30 kW making energy savings possible whenproduction stops (unlike Cobalt constant decay regardless ofproduction). This includes power for the Rhodotron ® ,conveyorsystem, cooling systems and auxiliary equipment. eXelis ® is alsoavailable with lower power Rhodotrons ® and lower capacitiesdepending on customer needs.Figure 6: Gamma facilities can’t adapt decay cost according toproduction needs like X-raySummaryWhen deciding on a sterilization technology one of the firstconsiderations is product compatibility. X-ray and gamma arevery similar in terms of their effects on medical plastics. You willnot have to plan a product re-design and/or material changeswhen switching from gamma to X-ray sterilization.“We are convinced that the eXelis 1000 is ideally suited toreplace gamma sterilization facilities; sterilization quality will beimproved, the process will be faster, the long-term economicalmodel is favourable, and there are no issues related to theavailability, transportation and disposal of radioactive sources.”Says Jean-Louis Bol.LEONI Studer Hard AG will be the first key industrial player toprovide large volume X-ray sterilization services. Their newfacility located in Daniken, Switzerland will be commissioned infirst half of 2010.www.iba-sterilization.com3