The Irradion unit integrates five robotic arms for X-ray imaging, ion beam tracking and for
positioning of the animal in respect to the beam. The system is portable, easy to be installed
and removed, since the plan is to offer it as a research platform for therapeutic ion beams.
The imaging subsystem of the Irradion is nearly identical to the industrial robotic scanner RadalyX. It integrates X-ray single photon counting imaging detector with 1 mm thick CdTe sensor. The detectors offer a very high detection efficiency combined with high resolution of 55 µm. This makes them ideal for small animal imaging as high-resolution images can be measured without excessively increasing the radiation dose. In addition, the fast frame rate3 of the detector allows dynamical imaging of the animal and adaptive adjustments of the irradiation based on animal movement in the future
Fig. 1 Irradion unit. It integrates 5 robotic arms. Two for X-ray imaging, two are for ion beam monitoring and proton CT and the fifth arm carries the animal.
In addition, the photon counting detectors allow X-ray photon energy discrimination which can be used to suppress scattered radiation, thus improving the image contrast. It can also serve to measure absorption spectra and recognize different types of materials (tissue). This is especially important for improvement of the irradiation planning where there is not always a simple connection between Hounsfield units of a common CT scan and irradiation properties of tissue.
Fig. 2 Spectral X-ray image of a PlastiMouse phantom (SmART Scientific Solutions BV). The colours are assigned to pixels based on similarities in the absorption X-ray spectra between different types of materials (tissue) found in the object. The sample was measured using the RadalyX robotic scanner.
The 3D CT imaging can be used for a variety of technical samples. The real-time X-ray
imaging can be applied for studies of dynamic processes including in in vivo specimens.
The flexibility of 6-axis robotic arms used in the scanner allows image acquisition by means of cone-beam Computed Tomography.
The spatial resolution of the CT reconstruction is currently about 100 µm. However, part of the project is improvement of the geometrical calibration that would improve the resolution to the native detector resolution of 55 µm.
The options of X-ray video recording and the real-time imaging will remain also in this imaging platform.
Fig. 3 3D visualisation of the plastimouse CT reconstruction and slices of the PlastiMouse CT volume. The data were measured using the RadalyX robotic scanner.
The animal positioning is implemented using smaller robotic arm. The animal is placed into heated bed with possibility to connect anesthetic gas. Advantage of this solution is in the possibility to freely position the animal with respect to the imaging robotic arms and/or with respect to the beam(s). One requirement is to allow exactly the same irradiation geometry with ion beams and photon beams. Positioning of the animal using the robotic arm allows integration of other irradiation beams (photons) at different locations near the system
Fig. 4 Positioning of a mouse bed for CT measurement.
The device will be equipped with a pair of particle tracking detectors based on Timepix3 pixel chips attached to two robotic arms. Timepix3 is the world’s first imaging detector operated in the list mode. The device does not measure only a sequence of images, but it produces a stream of data. Each word in the stream corresponds to a single particle hit and contains information on position, energy and time when the event occurred. The pixelated chips allow visualization of particles tracks through the device in 3D (using timing information from the charge collection across the sensor). One of these detectors will be ocated before the animal and the second behind. Tracks of protons or ions through the animal will be measured and this information will serve to reconstruct proton (ion) CT data and to improve irriadiation planning.The second robotic arm carrying the rear detector will carry also calorimeter to stop the particles and measure their residual energy. The calorimeter is based on very radiation hard YAG:Ce crystal with electronics operated in list mode and fully synchronized with the tracking detectors.
Fig. 5 Examples of tracks of various particles measured by the detector. On the left: alpha particles, MIPS, electrons, X-rays. On the right: proton tracks.
To ensure effective use of the Irradion system, an image-based treatment planning system is included. It enables beam planning and Monte Carlo dose calculation for photon and proton beams. It is based on the existing commercial products SmART-ATP and SmARTXPS (SmART Scientific Solutions BV), and provides an intuitive user interface for reading CT images of small animals, beam planning, dose calculation and dose analysis. Fig 8 provides a snapshot of one of the functions of the treatment planning system. In the Irradion project, the system is extended for proton dose calculation and the use of proton CT images for stopping power extraction.
Fig. 6 A snapshot of the user interface of SmART-ATP for visualization of the radiation dose from photon beams in a mouse specimen.