A subassembly for a particle detector, a particle detector and an imaging system comprising said subassembly and / or detector

Abstract

The present invention belongs to the field of particle position and energy detectors, preferably proton tracking detectors and residual range detectors in proton imaging systems. The object of the invention relates to a subassembly for a detector for detecting particles, preferably protons, and a detector comprising at least one subassembly. The invention further relates to an imaging system comprising said subassembly and / or detector. The subassembly consists of one layer of scintillating fibers, wherein each fiber within the layer is at least at one end provided with one photon detector, preferably a SiPM. Since each fiber of the subassembly is provided with its own photon detector, there is no need to form fiber bundles and combine them into separate channels for photon detection, which was a significant disadvantage of the currently known solutions.

Description

[0001] A SUBASSEMBLY FOR A PARTICLE DETECTOR, A PARTICLE DETECTOR AND AN IMAGING SYSTEM COMPRISING SAID SUBASSEMBLY AND / OR DETECTOR

[0002] Field of the invention

[0003] The present invention belongs to the field of particle position and energy detectors, preferably proton tracking detectors and residual range detectors in proton imaging systems. The object of the invention relates to a subassembly for a detector for detecting particles, preferably protons, and a detector comprising at least one subassembly. The invention further relates to an imaging system comprising said subassembly and / or detector.

[0004] Background of the invention and the technical problem

[0005] Proton therapy has been used for cancer treatment for more than seven decades. While first patients were treated as early as 1954, proton therapy did not become more widespread until approximately two decades ago after several technological advancements made it feasible to be used on a larger scale (Schreuder, A. N. Technological developments allowing for the widespread clinical adoption of proton radiotherapy; University College London, 2020). In proton therapy proton beams are used to target many different kinds of tumours, including brain tumours, spinal cord tumours, sarcomas, as well as benign tumours. More than 250,000 patients have already undergone proton therapy with many more eligible for it (PTCOG - Patient Statistics; available at: https: / / www.ptcog.site / index.php / patient-statistics-2). As the number of treated patients is growing every year, so is the number of proton beam facilities. Currently, there are more than hundred proton therapy centres worldwide, approximately one third of that in the USA (PTCOG - Facilities in Operation; available at https: / / www.ptcog.site / index.php / facilities-in-operation-public).

[0006] Unique properties of protons make them especially suitable to target localized cancerous tissues. The so-called Bragg peak phenomenon allows for applying most of the proton energy to the tumour with minimal harm to the surrounding healthy tissue, since highest energy loss of a travelling charged particle occurs effectively in the last few millimetres of its path with a sharp decline in its kinetic energy just before coming to a stop. This is in contrast to an x-ray beam, which dissipates energy along a much longer path with no sharp decline in dissipation rate. This difference in the stopping power curve renders proton therapy in principle a much more precise method than more conventional x-ray therapy, where healthy tissues typically suffer due to significant energy deposition.

[0007] In order to exploit the Bragg peak phenomena of the protons in clinical practice, a precise and reliable imaging method is crucial to determine the exact location, conversely stopping power of the target area in human body. Adequate proton energy is required for the Bragg peak to be positioned within the region of cancerous tissue, or else the healthy tissue might get affected with little to no radiation applied to the tumour.

[0008] X-ray imaging, i.e., x-ray computed tomography (CT) scanning is typically used to determine the stopping power of the tissue. This is, however, an indirect method of estimating the stopping power value, since CT-Hounsfield units, obtained by CT scan images have to be converted into stopping power. The calibration is performed based on direct measurements of stopping power and Hounsfield units in a tissue substitute, which may differ in radiological properties to the actual tissue that is to be targeted by proton therapy. Protons on the other hand enable direct measurement of the tissue stopping power in vivo on the patient before treatment, while depositing a lower dose of radiation than x-ray CT for the procedure. Although proton imaging has downsides, most notably degradation of image quality due to multiple scattering of protons, many efforts have been put into bringing proton imaging technology to life.

[0009] The aim of the invention is thus to provide a particle tracking detector and / or subassemblies thereof for detecting at least the position of particles, preferably protons, to build particle imaging systems, which could allow development or advancement in the field of proton therapy. Prior art

[0010] Several research groups have succeeded in building a working proton imaging system. A typical system consists of a proton beam source, one or more upstream tracking detectors, which are used to determine position and direction of the incoming proton, one or more downstream tracking detectors, used to determine position and direction of the outgoing proton, a space to place an object between the upstream and downstream detectors and a residual range detector, which is used to determine the residual range of a proton. A proton beam source and means for proton beam manipulation are usually provided by a certain research or medial institution, while the tracking detectors and residual range detector with accompanying electronics and hardware constitute the core technology of a particular imaging system prototype.

[0011] Different working principles of a tracking detector have been explored. After early attempts at using multi wire proportional chambers in the late seventies, scintillating fiber detectors and silicon strip detectors have become the most common technology for proton position and direction detection.

[0012] Detectors based on scintillating fibers consist of several layers of square or round fibers made of a scintillating material, which emits photons after interacting with a charged particle, i.e. , proton. Photons are then guided inside the fiber to the photon detector. To be able to track the position of a particle in two dimensions at least two parallel layers of scintillating fibers are required with fibers in one layer directed orthogonally with respect to the fibers in another layer. In order to increase the spatial resolution, two layers of parallel fibers, displaced by half the fiber thickness, are often used for one axis, resulting in four layers per detector. This way detected signal in two proximate fibers in different layers allows to determine the position of a proton with a precision below fiber thickness. In many cases two tracking upstream and downstream detectors are placed before and after the scanned object to allow measurement of incoming and outgoing proton direction. Construction of such and similar tracking detectors were reported by Pemler et al (A detector system for proton radiography on the gantry of the Paul-Scherrer-lnstitute. Nucl. Instrum. Methods Phys. Res. Sect. Accel. Spectrometers Detect. Assoc. Equip. 432, 483-495 (1999)), Coutrakon et al. (A New Proton CT Scanner. (2014)), Presti et al. (A real-time, large area, high space resolution particle radiography system. J. Instrum. 9, C06012 (2014)) and is presented also in patent US11116459B2.

[0013] Another common way of constructing a tracking detector is using silicon strip detectors, which essentially work as long rows of photodiodes, collecting electrons in the location, where charged particle passes through the detector. Similar to scintillating fiber detectors they are composed of two or more layers to enable measurement of proton position in x and y axis. Detection area in tracking detectors based on silicon strip detectors is typically quite small, ranging from about 5 x 5 cm2to approximately 10 x 10 cm2, which would not suffice for a full head scan. This limitation is due to the maximum size of the high-resistivity wafers. To overcome the size restriction, many sensors can be placed next to each other, however this inevitably introduces dead zones in the detection area, as each individual strip silicon detector is surrounded by approximately 1 mm thick dead edge. Attempts have also been made to overlap individual detectors to eliminate dead zones. This method on the other hand results in artefacts in the reconstructed images. Tracking detectors based on described technology have been reported by Scaringella et al. (A proton Computed Tomography based medical imaging system. J. Instrum. 9, C12009 (2014)), Esposito et al. (PRaVDA: The first solid-state system for proton computed tomography. Phys. Med. 55, 149-154 (2018)) and Sadrozinski et al. (Development of a Head Scanner for Proton CT. Nucl. Instrum. Methods Phys. Res. Sect. Accel. Spectrometers Detect. Assoc. Equip. 699, 205-210 (2013)).

[0014] Gas electron multipliers have also been used for tracking detector in a proton radiography system as reported byAmaldi et al. (Construction, test and operation of a proton range radiography system. Nucl. Instrum. Methods Phys. Res. Sect. Accel. Spectrometers Detect. Assoc. Equip. 629, 337-344 (2011 )). Gas electron multipliers have been developed at CERN for particle detection. They are essentially gas chambers with a thin perforated polymer foil inside placed between two electrodes and are capable of high-rate detection of charged particles. Unlike silicon strip detectors, they do not have considerable limitations on detection area, however they do require a gas circulation system.

[0015] Another key component of a proton imaging system is a residual range detector. By far the most common type of residual range detector consists of a stack of many thin plastic scintillating plates, each connected to a photon detector. As proton travels through the stack, it deposits energy in each scintillating plate. Since the energy loss per length travelled obeys the Bragg peak dependency, the most energy loss occurs right before the proton comes to a stop. The last scintillating plate, which provides a signal, therefore directly relays information of the proton’s residual range. Other possible variants of residual range detector include a matrix of thick scintillator blocks, each connected to a photomultiplier or a monolithic scintillating block as described in patent US11116459B2.

[0016] Another way of determining proton residual range in a proton imaging system has been proposed by Seiden (doi: 10.22323 / 1 .254.0025). In this approach ultra-fast silicon detectors could be used to determine time of flight (ToF) of a proton between two tracking detectors, from which proton energy and subsequently residual range could be extracted.

[0017] This same concept of determining proton energy via ToF measurement has later been incorporated in a patent US10231679B2, where author’s main embodiment includes the use of large area picosecond photon detectors (LAPPD) for ToF-based method of determining proton energy. ToF-based residual range detector for proton imaging has thus far not been constructed in practice. The main limitation is the requirement for very fast proton detectors with low jitter and it is not yet clear which detector type can be used for ToF detector in practice, without a significant price increase compared to already established residual range detector technologies.

[0018] The technical problem

[0019] Despite the fact that several proton imaging system models have been developed so far, the transfer of the technology from the proof of principle prototypes to commercial clinical systems has not been achieved yet, as there are to the best of our knowledge no available clinical systems on the market. There are still a lot of technical issues to overcome in order for the technology to make a breakthrough and become a standard method of choice in cancer therapy centers.

[0020] Of the components of a fully functioning proton imaging system, proton beam source together with a scanning system is provided by the treatment facility, since the same proton beam is used for therapy after the imaging is performed. Tracking detectors and residual range detector are thus corner stones of an imaging system. It is, however, currently not clear what the optimal technology of choice for tracking detectors and residual range detectors is, due to every technology having several positive as well as negative aspects.

[0021] As evident from the Prior art chapter, two of the most researched and used concepts for tracking detectors are layers of scintillating fibers and silicon strip detectors. Most proton imaging systems rely on one of these two technologies for detector construction in some form or another. Silicon strip detectors stand out due to several unique characteristics, which make them extremely suitable for particle position detection. They have excellent efficiency, low noise, high acquisition rate in the MHz range, a high spatial resolution lower than 100 pm. Avery important characteristic from the point of view of producibility and serviceability of the proton imaging system is the ease of assembly. Strip silicon detectors can easily be mounted on a PCB as well as easily removed and replaced, which is a crucial requirement if a product is to be deliverable and serviceable in a reasonably short amount of time.

[0022] The main technical drawback of silicon strip detectors is a relatively small detection area. This is related to the wafer diameter, which typically does not exceed 16 cm. This suffices to construct maximum sized area of approximately 10 * 10 cm2, which is not a lot, considering that a full head scan requires detection area of approximately 30 * 30 cm2. Tiling the individual detectors to form a larger area results in relatively thick 1 mm dead strips in the image. Overlapping of silicon strip detectors is also not a good compromise, since reconstruction of images in such configuration leads to artefacts due to uncertainty in determining the cases when the proton passes overlapped regions and energy loss corrections. Lastly, silicon strip detectors are significantly costlier than detectors based on scintillating fibers.

[0023] Scintillating fiber-based tracking detectors are in principle not limited with detection area size, they typically have a worse spatial resolution than strip silicon-based detectors, however it can still go well below 1 mm, which is sufficient for all practical purposes in cancer therapy. Acquisition rates can achieve similar levels as with strip silicon detectors; however, proton detection efficiency is somewhat lower, in the range of 60%-70%. The main disadvantage of scintillating fiber-based tracking detectors is inconvenient and difficult assembly. Proton imaging system prototypes that use scintillating fiber technology in all cases reduce the number of signal reading channels by bundling different fibers together (e.g. every 10th fiber) and couple them to a single photon detector, e.g. silicon photomultiplier (SiPM). The resulted fiber bundles create a three-dimensional clutter, which requires manual handling and demands exceptional attention during assembly, which is at risk of an error during the bundling and coupling of the fibers to a detector. The complicated construction of a scintillating fiber-based detector also prohibits its simultaneous use as a ToF-based energy or residual range detector. This is due to clutter-forming scintillating fibers differing in total length between each other causing ToF measurement impossible, since variable fiber length introduces different time delays in each measurement, which can be much larger than actual ToF values.

[0024] The guiding of the fiber bundles within the tracking detector housing introduces additional downside of excess detector volume, which is an inconvenience from device’s usability point of view. Taking into account patient’s comfort and treatment experience the design considerations dictate slim appearance with as little bulky volume outside the detection area as possible.

[0025] The inherent characteristics of a bundled fiber detector design also imply poor serviceability of the system. Since every fiber is tangled up within a bundle, a procedure to replace any one fiber requires the service technician to dismantle practically the entire system in order to complete the task.

[0026] Since the proton imaging systems constructed so far were conceived as proof of principle prototypes, not a lot of effort has been put into making the tracking detectors easy to assemble, easy to service, compact with minimum volume outside detection area, being patient and user friendly with superb usability and low cost. These are the characteristics that a tracking detector should have in order to facilitate its implementation in clinical centers and integration into existing proton beam therapy apparatuses. The technical problem addressed by the present invention is thus design of an improved particle detector based on scintillating fibers.

[0027] Description of the solution to the technical problem

[0028] The invention aims to provide a technical solution that addresses all shortcomings as well as complexity of the presently known solutions. The technical problem is solved as defined in the independent claims, wherein preferred embodiments of the invention are defined in the dependent claims.

[0029] The biggest issue to overcome when designing a viable scintillating fiber-based tracking detector is the fiber bundle clutter, which occurs due to reading channel number reduction, i.e. combining many separate fibers into a single channel. A resulting clutter is the main obstacle in achieving an easy to assemble, easy to service and a compact particle detector as well as an imaging system comprising at least one said detector.

[0030] The essence of the invention is that a subassembly for a detector for detecting particles, preferably protons, based on scintillating fibers is provided, wherein said subassembly may be designed in different manners to allow assembly of different detectors and thus various applications / constructions. The mentioned subassembly consists of one layer of scintillating fibers, wherein each fiber within the layer is at least at one end provided with one photon detector, for example a SiPM. There are several possible embodiments of the above-described subassembly for a particle detector.

[0031] In a first possible embodiment the subassembly consists of a layer of scintillating fibers, wherein every fiber within a layer is provided with one photon detector at one end of the fiber.

[0032] In a second possible embodiment the subassembly consists of a layer of scintillating fibers, wherein every fiber within a layer is provided with two photon detectors, one at each end of the fiber.

[0033] In further possible embodiments the subassembly consists of a layer of scintillating fibers, wherein some fibers within a layer are provided with one photon detector at one end, while other fibers within a layer are provided with two photon detectors, one at each end of the fiber. The number of fibers with two photon detectors and those with one photon detector is optional.

[0034] Since each fiber of the subassembly is provided with its own photon detector, there is no need to form fiber bundles and combine them into separate channels for photon detection. The length of each fiber within the layer can thus be equal or slightly larger than the width of the detection area. The fiber layer of a given subassembly defines the detection area of the subassembly, whereby each subassembly by definition enables measurement of at least one position coordinate of the incident particle, preferably proton, within the detection area plane. The optimal size of a detection area depends on the application. For full head scan of a patient a detection area of 30 cm x 30 cm would suffice, corresponding to the fiber length of 30 cm. However, the detection area may be significantly larger or smaller depending on the requirements of the imaging system and actual applications.

[0035] Since commercially available SiPM photon detectors come in sizes as small as 1 mm, they can be mounted to the end of each fiber in the immediate vicinity of the edge of the detection area. Fiber bundling as described in previously known solutions is thus avoided. Despite the fact that this slightly increases the electronic complexity of the system, it is more than offset by its general simplicity. Furthermore, there is significant price optimization due to notably shorter cumulative fiber length. Such configuration on one hand drastically reduces the requirement for space, while on the other hand enables easy fixation and replacement of any of the fibers, since they remain separate and virtually along a straight line.

[0036] In any of the above-described embodiments of tracking detector subassemblies and correspondingly tracking detectors described below, a small part of at least some fibers may lie in the area outside the detection area. There, part of the fibers may be slightly bent to provide necessary space for photon detector mounting, however this is not in any way detrimental to the design concept. The preferred maximum angle of bending is 45 degrees, wherein the range of preferred angles is from 0 to 45 degrees. Angles larger than 45 degrees are, however, possible.

[0037] The fibers used in tracking detectors and subassemblies thereof according to the invention may be made from any suitable scintillating material known to the skilled person, ranging from plastics to glass and even crystals. Additionally, a fiber can be made of a combination of materials, wherein different parts of the fiber can consist of different materials, said parts being connected to each other by optical bonding, adhesive bonding or any other method of joining different materials. For example, the part of the fiber lying within the detection area can be made of a scintillating crystal, while the small part of the fiber lying outside the detection area can be made of plastics, both said parts being connected to each other by some bonding method.

[0038] The subassembly according to the invention may be incorporated in a detector for detecting particles, wherein detection may relate to detection of particle presence, to tracking of particle, to measurement of particle energy and / or to analysis of particle propagation direction. At least one subassembly is used in the detector, preferably more. The scintillating fiber-based tracking detector can be constructed using one or more tracking detector subassemblies, defined above. One or more subassemblies can be stacked together, wherein intersection of detection areas of subassemblies, of which the tracking detector is comprised, form the detection area of the tracking detector. The subassemblies, which form the tracking detector, must be stacked in such a way that the tracking detector enables measurement of two orthogonal coordinates of the incident particle, preferably proton, within the detection area plane, thus effectively enabling to determine the particle position within said plane.

[0039] There are many possible ways of constructing the scintillating fiber-based tracking detector using the subassemblies, which will be described below.

[0040] According to a first possible embodiment, the tracking detector comprises two tracking detector subassemblies, both having fibers provided with one photon detector, which is installed at one end of the fiber, wherein fibers in the layer of the first subassembly are directed orthogonally with respect to the fibers in the layer of the second subassembly. The tracking detector constructed in such a way enables measurement of position of the incident particle, i.e. determination of two orthogonal coordinates of a particle in tracking detector’s detection area plane.

[0041] A method for particle position detection using the above-described detector according to the first embodiment comprises the following steps:

[0042] - an incident proton traverses the detector passing through the n-th fiber of the layer of the first detector subassembly and the m-th fiber of the layer of the second detector subassembly,

[0043] - interaction of the proton and scintillating material results in emission of photons, which are then guided within the fibers in which the interaction took place,

[0044] - the photons reach the end of the n-th fiber of the layer of the first subassembly and the end of the m-th fiber of the layer of the second subassembly and are detected by the photon detector at the fiber’s end,

[0045] - photon detectors convey the information of proton position coordinates corresponding to n-th and m-th fiber in each layer to the processing unit.

[0046] A second possible embodiment of a tracking detectors comprises a subassembly having fibers with two photon detectors, i.e. one photon detector at each end of each fiber. The detector according to this embodiment enables measurement of a position of the incident particle, i.e. determination of two orthogonal coordinates of a particle in tracking detector’s detection area plane. A method for particle position detection using the above-described detector according to the second embodiment comprises the following steps:

[0047] - an incident proton traverses the detector passing through the n-th fiber of the detector subassembly at a certain point at a certain first distance from the first photon detector at one fiber end and at a certain second distance from the second photon detector at another fiber end,

[0048] - interaction of the proton and scintillating material results in emission of photons, which are then guided within the fiber, in which the interaction took place,

[0049] - photons reach photon detectors at each end of the n-th fiber at different instants, separated by a certain time interval.

[0050] - photon detectors convey the information of the incoming photons to the processing unit,

[0051] - processing unit calculates the position of the photon’s point of origin along the n-th fiber using time delay between both signals. Proton position coordinates correspond to the photon’s point of origin and the n-th fiber’s location within the detection area.

[0052] Regardless of the two described embodiments of a tracking detector, it is always possible to construct a working tracking detector using two subassemblies, wherein configuration of each of both subassemblies is completely optional, meaning that any fiber in any subassembly has either one photon detector at one end or two photon detectors, one at each end, wherein fibers in one subassembly are directed orthogonally to fibers in the other subassembly. A tracking detector constructed in such a way works either by using a method described for the first tracking detector embodiment, a method described for the second tracking detector embodiment or a combination thereof.

[0053] All of above-described tracking detector embodiments can be provided with an optional number of additional subassemblies, wherein said subassemblies are selected in the group of possible subassemblies described above, i.e. , with one photon detector per fiber, with two photon detectors per fiber, or with combination of fibers with one and two photon detectors per fiber. The scintillating fibers in additional subassemblies may be either in parallel, orthogonal or at any other angle to fibers in original subassemblies. Such addition of subassemblies can increase the spatial resolution of the tracking detector.

[0054] Any one of possible tracking detector embodiments can be provided with at least one holder for holding at least one subassembly of fibers. Preferably, one holder is used for two subassemblies, wherein one surface of the holder is configured to receive the layer of scintillating fibers of the first subassembly and the second surface of the holder is configured to receive the layer of scintillating fibers of the second subassembly.

[0055] The invention also allows combinations of two or more detectors. In a possible embodiment according to which two tracking detectors are placed one after another, separated by a certain finite distance, wherein the detection planes of both tracking detectors are parallel, the direction of the incident particle, preferably proton, can also be determined. Measurement of particle coordinates in detection area plane at both detectors conveys the information of particle movement perpendicular to the normal to detection area planes. Determination of absolute distance travelled in said direction together with the known distance between both detection area planes suffice to determine the particle direction.

[0056] The above-described scintillating fiber-based tracking detector according to the invention also allows for all fibers to have exactly the same length, which can be exploited for ToF measurement and therefore determination of particle’s residual range. When a particle, preferably proton, passes two such consecutive scintillating detectors, no uncontrolled random signal delay between both detectors occurs due to all fibers in both detectors being of equal length. This suggests that ToF can be measured to a great precision, especially when using advanced scintillating material with very short response time of approximately 100 ps. By adjusting the distance between both detectors, the precision of ToF measurement can be further increased.

[0057] The technical solution for scintillating fiber-based detector as described above allows for particle, preferably proton, position and direction measurement as well as ToF- based residual range measurement. This makes the need for a separate residual range detector obsolete, since only one additional scintillating fiber-based detector is required at a certain distance behind the downstream detector. Such dual function of a scintillating fiber-based detector represents a significant simplification of a particle imaging system with respect to systems developed thus far. Direction of particles can be measured by using at least two tracking upstream and downstream detectors, which are placed before and after the object to allow measurement of incoming and outgoing particle direction.

[0058] Preferred particles to use with scintillating fiber-based detector according to the invention and imaging systems using such detectors are protons. However, many other different particles, e.g. heavy charged particles, such as ions of elements like helium, lithium, boron, oxygen, carbon, etc. as well as any positive ions of any elements can be used, given that a suitable particle beam source is provided.

[0059] The detector according to the invention may be used in a particle imaging system, such as particle radiography system or particle tomography system, wherein at least one, preferably more such detectors are used. The imaging system comprises:

[0060] - a particle beam source arranged to emit a particle, preferably proton towards a patient, which may include proton beam scanning system,

[0061] - one or more upstream scintillating fiber-based tracking detectors according to the invention for detecting at least position, preferably also direction of incoming particles according to the invention,

[0062] - one or more downstream scintillating fiber-based tracking detectors according to the invention for detecting at least position, preferably also direction of incoming particles according to the invention,

[0063] - a space between said upstream and downstream detector or set of detectors to position at least a part of a patient’s body,

[0064] - a residual range detector or another scintillating fiber-based tracking detector according to the invention, which can function as a ToF-based residual range detector in combination with the downstream detector. A method for operation of imaging system according to the above description comprises the following steps:

[0065] - particle, preferably proton is emitted by the particle beam source,

[0066] - particle passes through the upstream or a set of upstream detectors, which measure particle’s position, preferably also direction before entering the patient,

[0067] - particle passes through the object, usually a part of a patient’s body,

[0068] - particle passes through the downstream or a set of downstream detectors, which measure particle’s position, preferably also direction after exiting the patient,

[0069] - particle hits the residual range detector, which measures particle’s energy. In case of scintillating fiber-based tracking detector replacing the separate residual range detector the residual range is determined by measuring time of flight of a proton between the downstream detector and the additional tracking detector, After the entire object is scanned, the processing unit reconstructs the image of the object.

[0070] The invention is useful for various applications, but mostly in particle imaging and particle-based treatments, preferably in proton imaging and proton-based treatments.

[0071] The invention will be described in further detail based on exemplary embodiments and figures, which show:

[0072] Figure 1 The subassembly according to the first embodiment comprising fibers provided with one photon detector per each fiber, wherein the photon detector is installed at one end of each fiber (figure 1 a) and the subassembly according to the second embodiment comprising fibers provided with two photon detectors, i.e. one per each end of each fiber (figure 1 b)

[0073] Figure 2 The scintillating fiber-based particle tracking detector according to the first embodiment, which comprises subassemblies with fibers provided with one photon detector per fiber

[0074] Figure 3 The scintillating fiber-based particle tracking detector according to the second embodiment, which comprises subassembly with fibers provided with two photon detectors, i.e. one photon detector at each end of the fiber

[0075] Figure 4 An imaging system comprising tracking detectors according to the invention

[0076] Figure 1 shows a scheme of the first 101 and the second embodiment 102 of a tracking detector subassembly. Both subassemblies are comprised of a layer of parallel scintillating fibers 103, 103’ and sets of photon detectors 104, 104’. In the case of the first embodiment every fiber 103 is at one end provided with a photon detector 104, while in the case of the second embodiment, every fiber 103’ is provided with two photon detectors 104’, one at each end. The layer of scintillating fibers in both cases corresponds to the detection area of the subassembly. In the case of the first embodiment, it is not necessary that all photon detectors lie on the same side of the layer. If there is tight space for photon detector placement, different fibers can have photon detectors on different sides of the layer, e.g. the position of photon detectors can alternate from one fiber to the next. The length and the number of scintillating fibers is optional and is chosen according to specific requirements of a specific imaging system.

[0077] Figure 2 shows the first embodiment of a scintillating fiber-based tracking detector and its working principle. The detector is comprised of two tracking detector subassemblies according to the first subassembly embodiment 101 . Each subassembly consists of a layer of scintillating fibers 103 and a set of photon detectors 104, wherein fibers in the layer of the first subassembly lie orthogonally to fibers in the layer of the second subasembly. When a particle traverses the tracking detector, it firstly traverses n-th fiber of the first subassembly 201 and after that m-th fiber of the second subassembly 202. The path of the particle is depicted with 203. Interaction of the particle with the scintillating materials in each of the traversed fibers results in emission of photons, which are then guided inside scintillating fibers 201 and 202 in both directions. Photon paths are depicted with dotted lines 204. Eventually the emitted photons reach the n-th photon detector of the first subassembly 205 and the m-th photon of the second subassembly 206. Photons, which are travelling in the opposing direction of the photon detector do not contribute to the measured signal.

[0078] Figure 3 shows the second embodiment of a scintillating fiber-based tracking detector and its working principle. The detector is comprised of one tracking detector subassembly according to the second subassembly embodiment 102’. The subassembly consists of a layer of scintillating fibers 103’ and two sets of photon detectors 104’, wherein every fiber is provided with two photon detectors, one at each end. When a particle traverses the tracking detector, it traverses the n-th fiber 301 in the layer of the subassembly at a point 302, which is at a distance 303 from the photon detector 304 and at a distance 305 from the photon detector 306. The path of the particle is approximately perpendicular to the tracking detector detection plane defined by the layer of scintillating fibers. Interaction of the particle with the scintillating materials in the traversed fiber 301 results in emission of photons, which are then guided inside said fiber in both directions. Photon paths are depicted with dotted lines 307. Eventually photons reach photon detectors 304 and 306 with some time interval between both events. The measured time interval between photons reaching photon detectors 304 and 306 are used to calculate the position of point 302, where the interaction between particle and scintillating material took place.

[0079] A scheme of a particle imaging system using compact scintillating fiber-based tracking detectors is depicted in Figure 4. A particle beam source 401 emits a particle, which is directed towards the patient 402. The particle path is depicted by dashed line 403. In front of the patient there is an upstream or a set of upstream tracking detectors 404, while behind the patient a downstream or a set of downstream detectors 405 is positioned. Behind the downstream detector set either a separate residual range detector or another scintillating fiber-based detector 406 is placed, wherein the scintillating fiber-based tracking detector works as a ToF detector in combination with the downstream detector, since time-of-flight of protons between them can be determined, from which residual range is extracted.

Claims

Patent claims1. A subassembly (101 , 102’) for a detector for detecting particles, based on scintillating fibers, wherein the subassembly (101 , 102’) consists of one layer of scintillating fibers (103, 103’), wherein each fiber within the layer is at least at one end provided with one photon detector (104, 104’).

2. The subassembly (101 ) according to claim 1 , wherein every fiber (103) within the layer is provided with one photon detector (104) at one end of the fiber.

3. The subassembly (101 ) according to claim 2, wherein any two neighbouring fibers (103) within the layer are provided with the photon detector (104) placed on a different end of the layer.

4. The subassembly (102’) according to claim 1 , wherein every fiber (103’) within the layer is provided with two photon detectors (104’), one at each end of each fiber (103’).

5. The subassembly (101 , 102’) according to claim 1 , wherein some fibers (103) within the layer are provided with one photon detector (104) at one end, while other fibers (103’) within a layer are provided with two photon detectors (104’), one at each end of the fiber.

6. The subassembly (101 , 102’) according to any of the preceding claims, wherein the photon detector is a SiPM.

7. The subassembly (101 , 102’) according to any of the preceding claims, wherein at least a part of the fibers within the layer are slightly bent to provide necessary space for photon detector mounting.

8. The subassembly (101 , 102’) according to the preceding claim, wherein the angle of bending is from 0 to 45 degrees.

9. The subassembly (101 , 102’) according to any of the preceding claims, wherein fibers are:- made from any suitable scintillating material, preferably from plastics, glass or crystals,- made of a combination of materials, wherein different parts of the fiber can consist of different materials, said parts being connected to each other by optical bonding, adhesive bonding or any other method of joining different materials.

10. A particle detector for detecting particles, wherein the detector comprises two tracking detector subassemblies (101 ) according to any claim from 1 to 3, both subassemblies having fibers (103) provided with one photon detector (104), which is installed at one end of the fiber, wherein fibers in the layer of the first subassembly are directed orthogonally with respect to the fibers in the layer of the second subassembly.11 . The tracking detector according to the preceding claim, wherein the position of the particle is determined in the following manner:- an incident proton traverses the detector passing through the n-th fiber of the layer of the first detector subassembly and the m-th fiber of the layer of the second detector subassembly,- interaction of the proton and scintillating material results in emission of photons, which are then guided within the fibers in which the interaction took place,- the photons reach the end of the n-th fiber of the layer of the first subassembly and the end of the m-th fiber of the layer of the second subassembly and are detected by the photon detector at the fiber’s end,- photon detectors convey the information of proton position coordinates corresponding to n-th and m-th fiber in each layer to the processing unit.

12. A particle detector for detecting particles, wherein the detector comprises at least one subassembly (102’) having fibers (103’) with two photon detectors (104’), i.e. one photon detector on each end of each fiber according to claim 4.

13. The tracking detector according to the preceding claim, wherein the position of the particle is determined in the following manner:- an incident proton traverses the detector passing through the n-th fiber of the detector subassembly at a certain point at a certain first distance from the first photon detector at one fiber end and at a certain second distance from the second photon detector at another fiber end,- interaction of the proton and scintillating material results in emission of photons, which are then guided within the fiber, in which the interaction took place,- photons reach photon detectors at each end of the n-th fiber at different instants, separated by a certain time interval.- photon detectors convey the information of the incoming photons to the processing unit,- processing unit calculates the position of the photon’s point of origin along the n-th fiber using time delay between both signals. Proton position coordinates correspond to the photon’s point of origin and the n-th fiber’s location within the detection area.

14. A particle detector for detecting particles, wherein the detector comprises two subassemblies according to claim 5, wherein configuration of subassemblies (101 , 102’) is either with one photon detector at one end or two photon detectors, one at each end, wherein fibers in one subassembly are directed orthogonally to fibers in the other subassembly.

15. The detector according to any claim from 10 to 14, wherein it further comprises an optional number of additional subassemblies, wherein said subassemblies are selected in the group of possible subassemblies described above, i.e., with one photon detector per fiber, with two photon detectors per fiber, or with combination of fibers with one and two photon detectors per fiber, wherein the scintillating fibers in additional subassemblies may be either in parallel, orthogonal or at any other angle to fibers in original subassemblies.

16. The particle detector according to claim from 10 to 15, wherein the length of each fiber within the layer is equal or slightly larger than the width of a detection area, wherein each subassembly by definition enables measurement of at least one position coordinate of the incident particle within the detection area plane.

17. The detector according to any claim from 10 to 16, wherein the detector is provided with at least one holder for holding at least one subassembly of fibers.

18. The detector according to the preceding claim, wherein one holder is used for two subassemblies, wherein one surface of the holder is configured to receive the layer of scintillating fibers of the first subassembly and the second surface of the holder is configured to receive the layer of scintillating fibers of the second subassembly.

19. The detector according to any claim from 10 to 18, wherein the detector comprises fibers having exactly the same length and is thus arranged to allow ToF measurement and therefore determination of particle’s residual range.

20. The detector according to any claim from 10 to 19, wherein the detector is arranged to detect particles selected in the group comprising protons, heavy charged particles, such as ions of elements like helium, lithium, boron, oxygen, carbon, as well as any positive ions of any elements.21 . An imaging system comprising at least one subassembly and / or detector according to any of the preceding claims.

22. The imaging system according to the preceding claim, wherein the imaging system comprises:- a particle beam source arranged to emit a particle, preferably proton towards a patient, which may include proton beam scanning system,- one or more upstream scintillating fiber-based tracking detectors according to the invention for detecting at least position, preferably also direction of incoming particles according to the invention,- one or more downstream scintillating fiber-based tracking detectors according to the invention for detecting at least position, preferably also direction of incoming particles according to the invention,- a space between said upstream and downstream detector or set of detectors to position at least a part of a patient’s body,- a residual range detector or another scintillating fiber-based tracking detector according to the invention, which can function as a ToF-based residual range detector in combination with the downstream detector.

23. A method for operation of the imaging system according to the preceding claim, wherein the method comprises the following steps:- a particle, preferably proton, is emitted by the particle beam source,- the particle passes through the upstream or a set of upstream detectors, which measure particle’s position, preferably also direction before entering the patient,- the particle passes through the object, usually a part of a patient’s body,- the particle passes through the downstream or a set of downstream detectors, which measure particle’s position, preferably also direction after exiting the patient,- the particle hits the residual range detector, which measures particle’s energy. In case of scintillating fiber-based tracking detector replacing the separate residual range detector the residual range is determined by measuring time of flight of a proton between the downstream detector and the additional tracking detector, and- reconstructing the image of the object with the processing unit after the entire object is scanned.

24. Use of the subassembly, the detector or the imaging system according to any of the preceding claims in particle imaging and particle-based treatments, preferably in proton imaging and proton-based treatments.

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