IRRADIATING SYSTEM INCLUDING A TARGET-HOLDER MOUNTING IN A RADIATION-PROTECTION ENCLOSURE AND A DEVICE FOR DEFLECTING AN IRRADIATION BEAM

Abstract

Disclosed is a system for irradiating a target, including a particle accelerator configured to at least emit an irradiation beam according to an axis, a target-holder mounting outside the accelerator, including at least one port configured to receive a target holder for a target to be irradiated, and a radiation-protection enclosure surrounding the target-holder mounting. The particle accelerator is positioned outside the enclosure. The target-holder mounting is stationary relative to the particle accelerator. The port is offset relative to the axis of the irradiation beam and the system includes a deflection device, positioned in the radiation-protection enclosure and configured to divert the irradiation beam towards the port of the target holder in which the target to be irradiated is inserted.

Claims

1. A target irradiation system (1), comprising at least: a particle accelerator (10) configured at least to emit an irradiation beam (11) along an axis, a target holder mounting (20), positioned outside the accelerator facing the irradiation beam (11), comprising at least one port (21) configured to receive a target holder (22) configured to receive a target to irradiate, and a radiation protection chamber (30) surrounding the target holder mounting (20), the particle accelerator (10) being positioned outside the chamber (30), wherein the target holder mounting (20) is fixed relative to the particle accelerator (10) and wherein the port (21) is axially offset relative to the axis of the irradiation beam (11), and wherein the system (1) comprises a deflection device (40), positioned in the radiation protection chamber (30) and configured to deviate the irradiation beam (11) towards the port (21) of the target holder (22) in which the target to irradiate is inserted.

2. A system according to claim 1, wherein the radiation protection chamber (30) comprises an alternating arrangement of at least one layer comprising a dense material (31) and at least one layer comprising a hydrogen-rich material (32) comprising a neutron poison.

3. A system according to claim 2, wherein a layer of radiation protection of the radiation protection chamber near an inside surface of the chamber is a layer of dense material (31).

4. A system according to claim 2, wherein the hydrogen-rich material (32) is polyethylene (PE) with a boron filler as neutron poison in an amount of approximately 5% to 7% (atomic).

5. A system according to claim 2, wherein the dense material is tungsten and/or lead.

6. A system according to claim 3, wherein the radiation protection chamber (30) further comprises an additional radiation protection part (33) which surrounds the target holders mounted on the target holder mounting, within a wall of the radiation protection chamber.

7. A system according to claim 6, wherein the radiation protection additional part (33) is of dense material.

8. A system according to claim 6, wherein the radiation protection chamber comprises a wall which comprises an additional thickness (34) of hydrogen-rich material positioned between the radiation protection additional part (33) of the target holders and the innermost layer of dense material (31).

9. A system according to claim 8, wherein the radiation protection additional part (33) is of tungsten (W) and is of thickness comprised between approximately 5 cm and approximately 15 cm and wherein the wall of the radiation protection chamber (30) next comprises: The additional thickness (34) of hydrogen-rich material of a thickness comprised between approximately 5 cm and approximately 15 cm, and is of PE having 5% boron filler; The innermost layer of dense material (31) of a thickness comprised between approximately 3 cm and approximately 8 cm, and is of tungsten (W); A next layer of hydrogen-rich material (32) of a thickness comprised between approximately 25 cm and approximately 40 cm, and is of PE having 5% boron filler; A following layer of dense material (31) of a thickness comprised between approximately 2 cm and approximately 8 cm, and is of lead (Pb); and An outermost layer (32) of hydrogen-rich material of a thickness comprised between approximately 15 cm and approximately 30 cm, and is of PE having 5% boron filler.

10. A system according to claim 1, wherein the deflection device 40) is configured to emit a magnetic field having a value between 1 and 2 Tesla (T), for example the magnetic field is of the order of 1.4 Tesla.

11. A system according to claim 1, wherein the deflection device (40) comprises at least one electromagnetic quadrupole positioned on a path of the irradiation beam.

12. A system according to claim 1, wherein the deflection device (40) is composed of a dense material, for example copper and/or iron in particular.

13. A system according to claim 1, wherein the ports (21) are disposed in a same plane.

14. A system according to claim 13, wherein the plane in which the ports (21) are disposed is a horizontal plane.

15. A system according to claim 1, wherein the ports (21) are disposed in a volume.

16. A system according to claim 1, wherein the system comprises a device for adjusting the position of the irradiation beam (51) and a device for adjusting the focus of the irradiation beam (52), and wherein the position adjusting device (51) and the focus adjusting device (52) are positioned upstream of the deflection device (40).

17. A system according to claim 16, wherein the deflection device (40) differs from the position adjusting device (51).

18. A system according to claim 16, wherein the position adjusting device (51) and the focus adjusting device (52) are positioned outside the radiation protection chamber (30).

19. A system according to claim 16, wherein the position adjusting device (51) and the focus adjusting device (52) are positioned at least partly inside the radiation protection chamber, or even at least partly within the wall of the radiation protection chamber.

20. A system according to claim 16, wherein the position adjusting device (51) and the focus adjusting device (52) are for example conjointly formed by a pair of electromagnetic quadrupoles.

21. A system according to claim 16, wherein it comprises an automatic module (60) comprising a control module (61) and a command unit (62), the control unit (61) being configured to integrate information and measurements concerning the position and the focus of the irradiation beam (11) and to send instructions to the command unit (62), and the command unit (62) being configured to actuate the position adjusting device (51) and/or the focus adjusting device (52) and/or the deflection device (40) in order to optimize an interaction between the irradiation beam (11) and the target to irradiate.

22. A target holder assembly having a reference direction in which it is adapted to be subjected to an irradiation beam, comprising: a target holder mounting, adapted to be positioned facing opposite said direction, comprising at least one port configured to receive a target holder configured to receive a target to irradiate, and a radiation protection chamber surrounding the target holder mounting and being passed through by said direction, the assembly being wherein the target holder mounting is fixed relative to said direction and wherein the port is axially offset relative to that direction, and wherein the system comprises a deflection device, positioned in the radiation protection chamber and configured to deviate an irradiation beam received in said direction towards the port of the target holder in which the target to irradiate is inserted.

Description

[0104] The invention, according to an example embodiment, will be well understood and its advantages will be clearer on reading the following detailed description, given by way of illustrative example that is in no way limiting, with reference to the accompanying drawings in which.

[0105] FIG. 1 diagrammatically illustrates a system for irradiating a target according to an example embodiment of the present invention,

[0106] FIG. 2, composed of FIGS. 2a and 2b, diagrammatically illustrates examples of geometrical arrangements of the position of the ports.

[0107] FIG. 3 presents by way of indication a change in the mass M (in metric tons, T) of a radiation protection chamber according to its inside radius Ri (in millimeters, mm), and

[0108] FIG. 4 represents a synoptic diagram of driving a position adjusting device and a focus adjusting device by a control module.

[0109] Identical parts represented in the aforementioned figures are identified by identical numerical references.

[0110] FIG. 1 presents an irradiation system 1 comprising a particle accelerator 10, a target holder mounting 20 and a radiation protection chamber 30.

[0111] The particle accelerator 10 is for example a cyclotron. It is for example configured to emit an irradiation beam 11 comprising a beam of protons of several megaelectrons (MeV).

[0112] The radiation protection chamber 30 here surrounds the target holder mounting 20. The particle accelerator 10 is positioned outside the chamber 30.

[0113] The radiation protection chamber 30 for example takes the form of a hollow sphere, comprising a wall formed by stacking successive layers.

[0114] For example, the wall of the radiation protection chamber 30 comprises an alternating arrangement of a layer of a so-called dense material 31 and of a layer hydrogen-rich material 32.

[0115] In practice, it is preferable for the radiation protection chamber to comprise at least two layers, for example between two and ten layers, alternately forming a layer of dense material and a layer of hydrogen-rich material.

[0116] In order to limit the mass and bulk of the radiation protection, it is furthermore advantageous to position a layer of dense material 31 closest to target holders 22 mounted on the target holder mounting 20, as described later, to firstly attenuate the primary rays.

[0117] It is next preferable to alternate layers of hydrogen rich material 32, advantageously comprising neutron poison, with layers of dense material 31 which attenuate the last primary rays as well as the secondary rays arising from the neutron capture.

[0118] By way of illustration, in the present example embodiment of FIG. 1, starting from the outermost layer, the wall comprises four layers alternating hydrogen-rich material 32 and dense material 31 such that the innermost layer, that is to say situated closest to the target holders 22 is a layer of dense material 31.

[0119] Furthermore here, to reinforce the radiation protection, the target holders 22 mounted on the ports 21 of the target holder mounting 20 are surrounded by a radiation protection additional part 33 which is preferably of dense material. The radiation protection chamber wall then comprises an additional thickness 34 of hydrogen-rich material positioned between the radiation protection additional part 33 of the target holders and the innermost layer of dense material 31.

[0120] The hydrogen-rich material 32 is for example polyethylene (PE), optionally with a boron filler as neutron poison in an amount of approximately 5% to 7% (atomic). In the case of a cyclotron bombarding a target for producing .sup.18F at 20 A, digital simulations have shown an optimum attenuation if the PE has a filler of boron in an amount of approximately 7% (atomic).

[0121] The dense material 31, which mainly enables the primary and secondary high energy photons to be attenuated, is advantageously of tungsten for example. As tungsten is very dense, it enables a radiation protection chamber to be produced that is more compact and light. As tungsten is however difficult to machine, it may be replaced by other materials such as lead. As lead is less dense than tungsten, replacing the tungsten with lead however slightly increases the diameter of the radiation protection chamber and therefore its mass.

[0122] In a preferred example embodiment, the radiation protection additional part 33 is of tungsten (W) and has a thickness of approximately 6 cm. The wall of the radiation protection chamber 30 next comprises: [0123] The additional thickness 34 of hydrogen-rich material has an inside radius (Ri) of approximately 24 cm and an outside radius (Re) of approximately 30 cm, i.e. a thickness of approximately 6 cm, and is of PE having 5% boron filler; [0124] The innermost layer of dense material 31 has an inside radius (Ri) of approximately 30 cm and an outside radius (Re) of approximately 35.5 cm, i.e. a thickness of approximately 5.5 cm, and is of tungsten (W); [0125] The following layer of hydrogen-rich material 32 has an inside radius (Ri) of approximately 35.5 cm and an outside radius (Re) of approximately 64.5 cm, i.e. a thickness of approximately 29 cm, and is of PE having 5% boron filler; [0126] The following layer of dense material 31 has an inside radius (Ri) of approximately 64.5 cm and an outside radius (Re) of approximately 68.5 cm, i.e. a thickness of approximately 4 cm, and is of lead (Pb); and [0127] The outermost layer of hydrogen-rich material 32 has an inside radius (Ri) of approximately 68.5 cm and an outside radius (Re) of approximately 88.5 cm, i.e. a thickness of approximately 20 cm, and is of PE having 5% boron filler.

[0128] By way of example, if the cyclotron and the target holder mounting described here are used up to one hundred and sixty minutes per day and 23 days per month, it is possible to produce a radiation protection chamber of approximately 6.6 metric tons for an inside radius of 240 mm. Such a radiation protection chamber 30 thus makes it possible to reduce the dose rate outside the walls of 30 cm of ordinary concrete to less than 80 Sv/month, which is the limit set by the EURATOM directives for public areas.

[0129] The target holder mounting 20 is positioned facing the irradiation beam 11, in the radiation protection chamber 30.

[0130] It comprises several ports 21 each configured to receive a target holder 22, containing when the time comes a target to irradiate, which are axially offset relative to the irradiation beam 11.

[0131] Here, in order to simplify the representation, the target holder mounting 20 comprises two ports 21 each with one target holder 22, which are axially offset relative to the irradiation beam 11; as well as an additional port 21 positioned in alignment on the axis of the beam.

[0132] As FIG. 1 illustrates, according to the position of the port 21 considered, this makes it possible to reduce to a greater or lesser extent the direct leakage paths 12 that are produced when a target, inserted in the target holder mounted on the port 21 considered, is irradiated by the irradiation beam 11.

[0133] When targets of different types are inserted into the ports 21 or 21, it is preferable to position the targets generating the most intense neutron flux in the ports 21 forming the greatest angle with the irradiation beam 11. A target generating less radiation and/or which is less used, such as a charge target, may be inserted in the port 21 that is aligned on the axis of the beam when there is such a port.

[0134] For example, starting from the axis of the beam and moving away therefrom, a possible configuration would be to position a charge target in port 21 situated in alignment on the axis of the beam 11, then a target for producing .sup.11C then a target for producing .sup.18F. These targets are thus classified in increasing order of neutron flux generation at a constant current.

[0135] It is to be noted that if a port 21 or 21 is left vacant, that is to say that no target is inserted therein, it is preferable to place an obturator therein, forming a fluid-tight plug, in order to better ensure the sealing of the system.

[0136] The number of ports 21, or even the existence of a port 21, depends on the needs linked to the application considered.

[0137] In the context of applications of PET type, it is advantageous to be able to dispose of at least two target holders, in order to be able to use at least two different targets, for example between two and ten target holders to be able for example to use up to ten different targets. It is thus useful to have as many ports are there are target holders required.

[0138] According to the constraints of bulk that exist in the context of the application considered, the ports are for example arranged in a plane as illustrated in FIGS. 1 and 2a or in three dimensions, that is to say in a volume, as illustrated in FIG. 2b.

[0139] To address a target positioned in any one of the target holders of the ports 21 based on the same irradiation beam 11, the system 1 further comprises an irradiation beam deflection device 40, configured to orientate the irradiation beam 11 towards each of the ports 21, for example such that in operation, the protons bombard a target positioned in one of the target holders mounted on one of the ports 21 of the target holder mounting 20.

[0140] The deflection device 40 is also positioned in the radiation protection chamber 30. It is to be noted that the deflection device 40 also participates in the radiation protection. For this, it is for example composed of a dense material, for example of copper and/or of iron in particular, which makes it effective for attenuating photons. In the context of a quadrupole, this is for example a core of iron surrounded by a copper wire.

[0141] The deflection device 40 comprises for example a deflector comprising for example a quadrupole formed from electromagnets, or preferably a dipole. Such a deflector is then positioned on a path of the irradiation beam 11 and is passed through by it, as FIG. 1 shows diagrammatically. Other deflection devices 40 may also be used according to the type and the energy of the accelerated particles, for example such as an electrostatic deflector for lighter particles (like electrons) and/or of lower energies.

[0142] In the case of a three-dimensional arrangement as in FIG. 2b, the beam 11 must then be deviated in two dimensions (whereas a deviation only in one dimension is necessary in the context of the arrangement of FIG. 2a), which may imply that the deflection device 40 will be more voluminous, inducing an increase in the internal volume of the radiation protection chamber 30, and therefore a greater inside radius Ri of the radiation protection chamber 30, which then increases the mass M of the radiation protection chamber 30, as FIG. 3 illustrates, which may create additional complexity.

[0143] The distance between a target holder of a port 21 and the ground at the location at which the system 1 is installed however limits the maximum possible dimension of the radiation protection chamber 30. Thus, it is advantageous to dispose the ports 21 in a horizontal rather than vertical plane.

[0144] This furthermore makes it possible to limit the dose rate at the floor and thus more easily install the system 1 above the ground floor of a building for example.

[0145] In the present example embodiment, in the interest of compactness, the distance separating the particle accelerator 10 from the target holder mounting 20 is for example very slightly greater than the distance established between a port 21 and the ground.

[0146] In order to ensure correct focusing and correct positioning of the irradiation beam 11 at the location of the deflection device 40 and of an entry window of each port 21, the system 1 here comprises an irradiation beam position adjusting device 51 and an irradiation beam focus adjusting device 52.

[0147] The deflection device 40 differs from the position adjusting device, in particular in that the deflection device 40 makes it possible to deviate the irradiation beam through angles of at least 5, whereas a position adjusting device only makes it possible to adjust a position of the point of impact or focal point of the beam, that is to say over scarcely a few tenths of degrees, typically less than 0.5.

[0148] In the present example embodiment, the position adjusting device and the focus adjusting device are mounted upstream of the deflection device 40, it being understood that upstream refers here to a direction of emission of the irradiation beam, from the accelerator towards the target holder mounting. They are furthermore both positioned here outside the radiation protection chamber 30; however, they could also be positioned at least partly inside the radiation protection chamber, or even at least partly within the wall.

[0149] The position adjusting device 51 and the focus adjusting device 52 are for example conjointly formed by a pair of electromagnetic quadrupoles. However, if the beam diverges sufficiently little, that is to say by typically of the order of less than 0.5, it is not necessary to use a focus and/or position adjusting device.

[0150] To facilitate and increase the reliability of use of such a device, the deflection device 40 is for example modifiable and drivable remotely in order to address a target selected from the multiple targets that can be inserted into each of the target holders 22. In parallel, the position adjusting device 51 and the focus adjusting device 52 of the irradiation beam may also be rendered automatic to optimize the irradiation of the target considered.

[0151] For this, the system 1 for example comprises, as is the case here, an automatic control module 60 comprising for example a control module 61 and a command unit 62.

[0152] It is then possible to control the position adjusting device 51 and the focus adjusting device 52 in order to perform the positioning in three dimensions of the focal point of the irradiation beam 11 relative to an entry window of the port 21 considered, or even of the port 21.

[0153] A geometric measuring module 63, for example of Beam Position Indicator (BPI) type, is for example possibly used here to send information to the control module 61 concerning the position and the dimensions of the beam 11 at the location of the entry window of the port 21, or even 21, containing the target to irradiate.

[0154] A module for measuring current 64 is for example also used to measure the current generated by the beam 11 on the target and communicate the current measurements to the control module 61.

[0155] This information and measurements enable the parameters to be adjusted of the devices for adjusting position 51 and focus 52 as well as of the deflection device 40 such that the interaction between the beam 11 and the target are optimal.

[0156] For this, the control module 61 integrates the information and measurements supplied by the module 63 and the measuring module 64 and sends instructions to the command unit 62 which actuates the position adjusting device 51 and/or the focus adjusting device 52 and/or the deflection device 40.