The development of high-energy electron accelerators with very high-power electron beams has made X-ray processing a practical alternative to gamma-ray processing for applications, such as the sterilization of packaged medical devices and the preservation of foods, which require greater penetration than can be provided by energetic electron beams.
When an accelerated electron impinges upon any material it generates X-radiation or X-rays. Characteristic monoenergetic X-ray photons are produced by the electron interaction with orbital electrons; bremsstrahlung photons are produced by the interaction with the nucleus of an atom. High energy bremsstrahlung X-rays are a penetrating form of ionizing radiation.
X-rays are produced by interposing a metal target between the electron beam and the product to be treated. To enhance electron-to-photon conversion, these X-ray targets are made of high atomic number (high Z) metals. Water cooled tantalum is preferred for large area targets.
X-Ray treatment can be characterised by:
- Quality : X-ray sterilization Dose Uniformity Ratio (DUR) is much better than typical DUR of 1.45 for Gamma pallet processing.
- Efficiency: By designing a 2-level conveying system, most of the X-rays are captured by the products. Losses of X-rays are minimized compared with a 1-level conveying system where the products must be over-scanned in order to achieve good Dose Uniformity. Overscanning means “losing” X-rays above and below the products.
- Flexibilty: Ability to mix different products with different dose requirements in the same irradiation cycle is possible since the solution is based on an incremental dose concept. One increment consists of four passes of the pallet in front of the X-ray target (pallet irradiated from the top and bottom, front and rear side). The increment dose is the minimum dose the product can receive. Any multiple of the increment dose can be given to the product by adding increments (ie: if increments have a value of 2.5 kGy, 25 kGy can be given to the product with 10 increments).
- Capacity: Possibility to process very large volumes of medical devices on pallets with minimum labor required
X-Ray facility surface is about 4000 m2 feet and is designed to fullfill all norms requirements for treatment of food, medical and pharmaceutical products.
Product income and outcome area are separated, all relevant process steps are recorded by a software tracking system (Konntrack) to ensure traceability of product during all stage off treatment process.
| Construction |
2010 |
| Release for production
(Medical, pharmaceutical products) |
03/2011 |
| Manufacturer Electron
beam |
IBA S.A -
Belgium |
| Type of accelerator |
Rhodotron
TT 1000 |
| Power |
0-700 kW
output |
| Electron Beam current |
max. 100 mA |
| Energy |
7 MeV for
X-Ray conversion |
| Manufacturer Software
Tracking System : KonnTRACK |
Konnexis - Canada |
As for all electron accelerators, the Rhodotron operates on the basic principle that electrons gain energy when they cross a region where an axial electric field exists.
The originality of the Rhodotron lies in the fact, that this radial electric field is generated through a single accelerating cavity, which is crossed over several times by the electrons: the Rhodotron is a recirculating accelerator. This feature makes it possible to operate the machine in a continuous mode.
The electrons are generated in a vacuum environment by the source (or electron gun), located at the outer wall of the cavity. The electrons are then drawn away and accelerated by the radial electric field, which transmits energy to them. The electrons undergo a first acceleration toward the inner wall of the cavity. They then pass through openings in the centre conductor.
Since the electric field is reversed when they emerge in the second part of the cavity, they are accelerated a second time, completing a crossing of the diameter. The accelerated beam is then bent by an external magnet, which sends it back into the cavity for a second accelerating cycle. The electron beam therefore travels along a rose‑shaped path, which explains why the name Rhodotron was chosen ("Rhodos", in Greek, means rose).
At the exit of the accelerator, the cylindrical shaped beam of high‑energy electrons is transported or guided through beam lines from the accelerator to the radiation vault.
Conveyance mechanism is required to facilitate moving of pallets in front of X-Ray beam. Pallets are moved through a maze built from re-enforced concrete. The maze prevents X-Rays, which move in a straight line, from escaping the radiation room.
The product conveyor system is synchronized with the accelerator, assuring that the beam is only operational when the conveyor system is moving at the defined speed. A production factor is used assuring that the conveyor speed is proportional to the beam power, so even for different power settings of the beam the amount of dose per cycle remains as defined.
All key parameters are continuously monitored for being within the predefined limits.
The design of conveyor system gives a great flexibility as the dose is a function of the increments. Pallets with different increments specification (or dose requirements) can be treated in the same time.
The conveyance mechanism meets the following pallet requirements:
- Pallet weight range: 50 - 1000 kg
- Pallet size: 80x120 (Euro) or 100x120 (Industrial)
- Process load height (Product + pallet): 195cm
- Pallets pass in front of the X-Ray beam on two levels
- Pallets can pass in front of the beam multiple times with
each pallet quadrant being exposed equally
- Conveyance mechanism moves pallets in front of the beam at a speed of 0.5 to 4.5 m/min. Speed regulation is independent of the number of pallets loaded on this section of the conveyor
- The beam area or treatment area conveyor is 3 m long (2 such sections – top and bottom)
- Conveyor mechanism provides a gap closing conveyor sequence so that minimal gap between pallet is constant
The product is treated from the 2 sides and the bottom pallet has to get the same double side treatment on the upper position. So it is a 4 passes system. The depth of the irradiation is made on the long side of the pallets (1.2 m).
In order to give dose flexibility, the treatment is given by ~2kGy increments, corresponding to one full sequence of 4 passes in front of the X-Ray target.
When multiple dose increments are required – let’s suppose 12 -, the corresponding container will travel 48 times (12 x 4) around the central wall in order to alternate the face which is presented to the X-Ray. After every 2 passes it is changing the level from bottom to upper or contrary.
- Conveyor/EBeam control The control system for the conveyance mechanism includes the following:
- Constant speed from 0.5 m/min to 4.5 m/min in beam conveyor
- Pallet catch-up control system that controls gaps between slave pallets from 10 to 200 mm
- Controlled acceleration and deceleration of pallets in horizontal plane and on the three elevators
- Pallet measurement ensures product stack fits into a pre-defined envelope in 3 dimensions
- Real time equipment status with diagnostics displayed on different SCADA stations
- Real time pallet movement display on any konnTRACK display
- Real time interaction with Electron Beam to control all
relevant process parameter (Beam current, Treatment
factor,...)
- Product Tracking
- Product processed by the irradiator is tracked from the time it is received until it has been shipped
- Each pallet is linked to a unique process run number. Detailed exposure records is recorded, stored and providing a detailed account of the irradiation process
- Capability of processing using X Ray as well as off-line Electron beam treatment
- Displays graphically pallets inside the loop area for any given cycle number and their accumulated exposure times
- Provides the irradiation lot summary report
- Predictive Schedule Module
- For each lot the system calculates the expected completion date and time according to the actual process specification and sends an alert if the desired completion data cannot be met
- Adjusts the schedule based on the real time sta
- Software for Control and Tracking system: KonnTRACK
tus of the irradiator
- Data Backup and Recovery
- Redundant hardware system for server and software virtualisation ensures high reliability of system.
- The database backup regime ensures that when the Database Server fails catastrophically no machine event is lost
- The data on the new PC is restored from the backup and the PLC Data Buffer
- PLC real time data backup assures minimal disruption if a PLC CPU has to be replaced
- Electronic signature
- Electronic signature and user login ensure full human traceability during all process steps.
- History
- All modification made are tracked and recorded in a log booked
- All alarm which appear during routine process have to be acknowledge before system could restart.
The irradiator design, Electron beam, conveyor, and software for control and tracking system are fully compliance with followings requirements:
- ISO 9001
- ISO 13485 - Medical devices -- Quality management systems
- ISO 11137 - Sterilisation of health care products: requirement for the development, validation and routine control of a radiation sterilization process for medical device
- 21 CFR Part 820 – Quality System Regulation (QSR)
- 21 CFR Part 11 – Electronic Records; Electronic Signatures
- GMP PIC'S