Superconducting synchrocyclotron with simultaneous acceleration of multiple ion species and hadron therapy facility

Abstract

Superconducting synchrocyclotron (1) comprising: At least two ion sources (30, 33) to produce respectively a so-called "therapy" beam and an "imaging" beam, an axial injection line, a high-frequency modulation device (23) to produce within the synchrocyclotron a cyclic frequency law F(t) allowing the simultaneous acceleration of the ions of the therapy and imaging beams, a rotating path modulator (110), two beam-cutting devices (34, 35) upstream of the median acceleration plane to modulate the therapy and imaging beams synchronously with the rotation of the path modulator (110). Figure for the abstract: Fig. 5

Description

Title of the invention: Superconducting synchrocyclotron with simultaneous acceleration of multiple ion species and hadron therapy facility technical field

[0001] The present invention relates to particle accelerators, and more particularly to synchrocyclotrons. The latter constitute an interesting solution for accelerating protons and other light ions to high energies for medical applications in radiotherapy, known as hadron therapy, which uses the Bragg peak characteristic of the increase in dose delivered at the end of the path when these particles slow down in the tissues. State of the art

[0002] The compactness of this type of accelerator makes it possible to reduce the physical dimensions and investment costs and makes installation in a hospital setting realistic.

[0003] Examples of superconducting synchrocyclotrons, enabling the acceleration of proton beams for high-energy proton therapy, are described in the following publications: - Gordon M., Wu - Y.Jongen, P.Mandrillon, M.Abs, W.Kleeven, S.Quets, P.Verbruggen,” Development of the new IBA S2C2”, European Cyclotron Progress Meeting 2012 in PSI, Switzerland, - W. Kleeven et al., IBA, Louvain-la-Neuve (B), M.Conjat et al., AIMA Développement, Nice (F), “The IBA Superconducting Synchrocyclotron project S2C2”, Proc, of Cyclotron 2013, Vancouver, Canada.

[0004] Hadron therapy systems must meet efficiency and accuracy requirements, as it is important to know precisely where the dose is deposited, especially when the target volume is close to organs at risk.

[0005] Existing installations can be improved in this respect. Description of the invention

[0006] There is therefore a need to further increase the performance of hadron therapy facilities by overcoming the limitations of high-energy proton therapy.

[0007] There is also an interest in improving the superconducting synchrocyclotrons used in such installations. Summary of the invention

[0008] The invention aims to meet all or part of these needs and achieves this by proposing a superconducting synchrocyclotron, comprising: - At least two ion sources to produce respectively a so-called "therapy" beam with at least one type of ions and an "imaging" beam made up of deuterons, - an axial injection line comprising at least one high-frequency buncher to group the ions delivered by the ion sources into bunches, before injecting them into a mid-plane of acceleration of the synchrocyclotron, - a high-frequency modulation device to produce within the synchrocyclotron a cyclic frequency law F(t) allowing the simultaneous acceleration of ions from the therapy and imaging beams, - a rotating path modulator, placed on the path of the therapy and imaging beams after ion acceleration, comprising at least one solid region and at least one empty region which alternately position themselves during the rotation of the modulator on the path of said beams, the path modulator allowing the path of the therapy ions to be modulated in a target volume, - two beam-cutting devices (“chopper” in English) upstream of the median acceleration plane to modulate the therapy and imaging beams synchronously with the rotation of the path modulator, such that the ions of the therapy beam pass only through said at least one full region and those of the imaging beam only through said at least one empty region.

[0009] Such a particle accelerator, in which the frequency of the accelerating electric field is time-varying, is capable of accelerating, in addition to deuterons, ions with an electric charge-to-mass ratio Z to A close to that of deuterons, for example, alpha (4He2+), carbon (12C6+), or lithium (7Li3+) ions, using the same frequency program F(t). The accelerator according to the invention can thus accelerate ions such as 7Li3+, even though the charge-to-mass ratio of 7Li3+ (Z / A=0.43) is further from that of other ions which have a Z / A ratio close to 0.53.

[0010] The accelerator may comprise only one therapy ion source, for example, an α (4He2+), 12C6+ (carbon 6+), or 7Li3+ (lithium 3+) ion source; alternatively, the accelerator comprises at least two therapy ion sources, for example, an α (4He2+) ion source and a 7Li3+ (lithium 3+) ion source. In this case, the synchrocyclotron is configured to allow selection of either therapy ion source, depending on the desired application.

[0011] When only one α therapy ion source is used, the grouper operates at a given frequency Fg which is equal to the injection frequency of the deuterons and the α ions. When two β therapy ion sources are used and one or the other is selected, for example a 7Li3+ ion source and an α ion source, the grouper preferably operates at a frequency Fg that is the median between the injection frequencies of the therapy and imager ions.

[0012] In this case, the cyclic frequency law F(t) periodically passes through a first intermediate value Finji higher than the frequency Fg and suitable for the injection and capture of deuterons, to a second intermediate value Finj2 lower than the first and the frequency Fg, suitable for the injection and capture of the other type of ions, for example 7Li3+ the extraction of the ions taking place at a frequency Fex lower than the frequencies Finji and Finj2.

[0013] The grouper includes a central electrode whose length is preferably equal to 3[3X / 2 ([3=Vi / c, where Vj is the average of the velocity of the different ions in the grouper, c the speed of light, and X the wavelength corresponding to the frequency of the grouper Fg).

[0014] The high-frequency modulation device preferably comprises a rotary capacitor and an HF line connecting an accelerating electrode to the rotary capacitor.

[0015] The synchrocyclotron includes an inflector, for example of the spiral type, to deflect the ions from the injection line towards the median plane. This inflector allows, for example, beam rotations of between 360° and 720° around the vertical axis.

[0016] The synchrocyclotron may include an extraction channel, in particular a septum electromagnetic channel, preferably allowing extraction yields greater than 60%.

[0017] The invention further relates to a hadron therapy installation comprising a synchrocyclotron according to the invention, as defined above.

[0018] The installation may include a collimator downstream of the synchrocyclotron and an imager downstream of the target volume to receive the deuteron beam. The collimator may be placed upstream of the path modulator.

[0019] The ions of the "therapy" beam allow the therapeutic dose to be deposited in the target volume and the ions of the "imager" beam are used to produce a simultaneous image outside the target volume with the imager in order to obtain spatial information on the position of the target volume "live".

[0020] This improves therapeutic performance: firstly, the ions in the therapy beam, being heavier than protons, improve the lateral and axial ballistic precision of dose deposition in a tumor volume that requires deep penetration. Secondly, the use of therapy ions that are more ionizing than protons It increases relative biological efficiency, thus enabling the destruction of so-called radioresistant tumor cells. Furthermore, the system offers the possibility of delivering irradiation in a very short time, and the "flash therapy" technique is feasible if desired.

[0021] The path modulator includes, for example, a rotating driven wheel, having blades each having an angular variation of their thickness, in particular in steps, the rotation of the path modulator being synchronized with the emission of ions accelerated by the synchrocyclotron such that the ions of the therapy beam intended to have their Bragg peak within the target volume pass through the blades with the thickness of material enabling the positioning of the desired Bragg peak to be obtained, and the ions of the imaging beam intended to reach the imager passing through the path modulator between the blades.

[0022] The installation according to the invention offers the possibility of irradiating moving tumors, by allowing the imager to precisely determine where the dose is deposited at any given moment. The invention enables the irradiation of "moving targets," for example, those moving due to the patient's breathing in the case of lung tumors or swallowing in the case of ENT tumors, with highly ionizing ions, in a precise manner, thanks to the real-time knowledge of the dose deposition position provided by the imager. Brief description of the drawings

[0023] The invention will be better understood upon reading the detailed description that follows, the non-limiting examples of its implementation, and upon examination of the accompanying drawing, on which:

[0024] [Fig. 1] schematically and partially represents, in perspective, an example of a synchrocyclotron according to the invention,

[0025] [Fig.2] represents an example of the frequency law F(t) of a synchrocyclotron according to the invention, accelerating α or 7Li3+ ions on the one hand, and D deuterons on the other hand,

[0026] [Fig.3] represents the phase space separators (q>,q>') for species a, D and Li and the corresponding capture zones,

[0027] [Fig.4] represents the path of different ions in water as a function of energy in MeV / nucleon,

[0028] [Fig.5] is an exploded, schematic and partial view of part of the installation hadron therapy located downstream of the synchrocyclotron, with beam scanning therapy (e.g., consisting of alpha or lithium ions) and imaging,

[0029] [Fig.6] illustrates the effects of the grouper on the phase of the particles along the line injection, and

[0030] [Fig.7] represents three views of an example of an inflector respectively in a vertical plane (left view), in horizontal projection made in the median plane of the synchrocyclotron (middle view), and in perspective (right view). Detailed description

[0031] Figure 1 illustrates an example of a synchrocyclotron 1 according to the invention. This synchrocyclotron 1 advantageously forms part of a hadron therapy installation designed to deliver a precise dose to a target tumor volume.

[0032] As illustrated, the synchrocyclotron 1 includes an electromagnet which generally has a symmetrical structure with respect to a horizontal acceleration median plane PM which passes through the cutting plane of lower yokes 10 and upper yokes 11. These yokes 10, 11 and the associated superconducting coils 12 (only the lower coil is shown, without the cryostat which contains the coils, their multilayer insulation and the electrical feedthroughs) are generally symmetrical with respect to the median plane PM.

[0033] The synchrocyclotron includes an HF system which includes a Dee 20 supported by two parallel stems 21 and 22. Such a bi-stem structure is described in application FR3055507A1 in the name of the applicant.

[0034] The synchrocyclotron 1 includes a HF 23 frequency modulator of the rotary capacitor type, which delivers a frequency law F(t) specific to the characteristics of the accelerated ions and which varies periodically with time, as illustrated in [Fig.2].

[0035] The acceleration of the particles takes place in accelerating spaces ("gaps" in English) defined between the Dee 20 and an anti-Dee 24 (the latter being only partially represented).

[0036] The synchrocyclotron 1 includes an external injection line for the ions to be accelerated, extending along a vertical axis Z.

[0037] This injection line is supplied by two devices arranged perpendicular to the vertical axis of the injection line, on either side of this axis, as illustrated in [Fig.1].

[0038] Each of these devices comprises: - A therapy ion source 32, for example of the ECR (Electron Cyclotron Resonance) type for therapy beams, for example alpha or lithium, inside a grounded cage 30 and a high-voltage cage 31, - an imaging deuteron ion source (for example of the Multi-cusp type inside a platform 33, - a beam-cutting device (in English, "chopper") 34 or 35, downstream of each of the sources, composed for example of a capacitor electrostatic, which allows the therapy or imaging beams to be cut off very quickly, and whose operation is controlled by the position of a path modulator, as explained later.

[0039] A deflection magnet 36 located on the vertical axis Z allows the beams from the sources to be deflected towards the axial injection line.

[0040] A high-quality vacuum is ensured by pumps 37.

[0041] The HF 38 grouper operates in this example at a frequency Fg.

[0042] The grouper 38 is, for example, of the double gap type with a central electrode of length 3[3X / 2, the wavelength / . corresponding to the frequency Fg.

[0043] The grouper 38 operates in the example considered with its own generator at a median frequency Fg between the injection frequencies Finjl and Finj2 of the particles to be accelerated, but nevertheless allows satisfactory grouping efficiencies to be achieved (for example up to 4 times, i.e. that an arbitrary phase interval of 200° at the source output is reduced to 50° at the end of the injection line) as illustrated in [Fig.6].

[0044] In the right-hand views of this figure, the final phases and the beam radius are shown respectively, with and without the effect of the grouper.

[0045] The grouper 38 does not operate continuously but in pulsed mode, that is to say during the times of capture of the ions to be accelerated, between the times “grouper on” and “grouper off” on the [Fig.2].

[0046] The packets grouped at the median frequency Fg are injected temporally during the capture times of the different ion species.

[0047] The grouper 38 is thus time-controlled and the operating time is controlled by the capture frequencies, as illustrated in [Fig.2].

[0048] A focusing device 39, for example of the Glaser lens type, makes it possible to ensure the focusing necessary at the entrance of an inflector 40 of the injection line, which is shown in isolation on the [Fig.7].

[0049] The inflector 40 is, for example, of the spiral electrostatic inflector type, with Two interlocking electrodes 130 and 140 extend opposite each other, but have the particularity of injecting into a relatively high magnetic field (typically between 7 and 8 Tesla), which imposes a rotation greater than 360°, and generally between 360 and 720°, as illustrated in the middle view of [Fig. 7]. The left view of [Fig. 7] shows a projection onto the vertical X, Z plane, the X axis being by convention the axis of the Dee accelerator gap, the middle view is in the horizontal plane, and the right view is in perspective.

[0050] The synchrocyclotron includes a beam extraction channel 50, for example of the electromagnetic type, in particular with a copper septum. Such a channel allows to achieve relatively high extraction efficiencies (between 60 and 70%). These efficiencies reduce the stray neutron fluxes resulting from beam losses on the extraction components. This reduction in neutron fluxes decreases the overall activation of the synchrocyclotron's internal components, thus facilitating maintenance operations, and reduces the thermal load on the superconducting coils due to the energy deposited by these particle fluxes. Figure 3 shows the classic phase space (<p,dq> / dt) with separators and capture zones for different types of accelerated ions.

[0051] The α and D ions can be captured simultaneously according to the frequency law F(t). The 7Li3+ ions are captured later than the deuterons according to the frequency law F(t), as illustrated in [Fig. 2]. The shaded areas are the capture zones; i.e., any particle with an initial condition outside these zones is not accelerated by the synchrocyclotron 1. <ps représente la phase synchrone. Au-delà de la phase 90°, les particules sont décélérées (convention d'accélération en V.cos(q> ) ; the point - <ps représente le point fixe instable).

[0052] The capture times of the a, D and 7Li3+ ions injected later on the frequency program F(t) are relatively close, the capture times being for example typically between 10 and 15 qs depending on the frequency law, as illustrated in [Fig.2].

[0053] Furthermore, these ions with very similar Z / A ratios have distinct paths through tissues depending on their kinetic energy expressed in MeV / nucleon (the same kinetic energy in MeV / nucleon indicates that these ions have the same velocity regardless of their mass). Indeed, ions with electric charge Z and mass A decelerate in matter according to the ratio KTÛ. The path of ions with the same A / Z² ratio is therefore identical if they have the same kinetic energy, usually expressed in MeV per nucleon.

[0054] Figure 4 shows the paths in water of different ions that can be accelerated by the synchrocyclotron according to the invention. • D: deuteron, i.e. the nucleus of deuterium, the heavy stable isotope of Hydrogen. • a: helium nucleus (4He2+). a and protons (H1+) have the same A / Z2. The a and Protons of the same energy in MeV / nucleon have the same path. Although protons cannot be simultaneously accelerated with deuterons by the synchrocyclotron according to the invention, [Fig. 4] mentions them for illustrative purposes. • 7Li3+: Lithium nucleus stripped of its 3 electrons. Natural Lithium is made up of 2 stable isotopes: Lithium with mass A=6 (7.59% of natural Lithium) and Lithium with mass A=7 (92.41%). • 12C6+: Carbon nucleus stripped of its 6 electrons, can be accelerated on the same frequency law that applies to irradiations at shallower depths.

[0055] Fig. 4 shows by way of example that for a range typically between 180 and 200 MeV per nucleon, the deuterons accelerated by the synchrocyclotron according to the invention have a penetration depth greater than 45 cm, allowing their use for imaging.

[0056] The installation includes, on the path of the ions having left the accelerating cavity, upstream of the target volume, a collimator 100, which placed on the path of the beams defines their section, and a path modulator 110, as illustrated in [Fig.5], and downstream of the target volume an imager 120.

[0057] The installation may optionally be supplemented upstream of the beam path modulator by conventional optical beam deflection elements, depending on the specific requirements of the hadron therapy installation. For example, an installation dedicated to head and neck tumors uses a fixed horizontal beam and does not require an isocentric rotating head.

[0058] The path modulator 110 allows the energy of the extracted beams to be changed in order to best modulate the paths of the ions in the target volume.

[0059] The path modulator 110 comprises, for example, a wheel with blades 110a of an absorbing material, for example polycarbonate, rotating about an axis parallel to the imaging and therapy beams, as illustrated in [Fig. 5]. Each blade has sectors of different respective thicknesses, allowing the depth of the Bragg peak to be modulated.

[0060] In the illustrated example, the deuteron beam passes through the empty area 110b located between the blades of the modulator, then through the target volume to the imager 120.

[0061] The operation of the beam cutting device 35 disposed between the source and the grouper is controlled, for example by an optical signal, to the rotation of the path modulator, to allow the deuteron imaging beam to pass through the blades.

[0062] The beam-cutting device 34 operates such that the therapy beam ions always encounter the desired thickness sector of the blades and that the therapy ions are not present when no blade is located in the path of the therapy beam. The operation of the beam-cutting devices 34 and 35 takes into account the travel time of the ions between passing through the beam-cutting device 34 or 35 and the moment the ions reach the path modulator.

[0063] The imager 120 is for example constructed with multi-wire chambers (a device developed by Georges Charpak consisting of several successive grids allowing a 3-dimensional image of the trajectories of the particles to be produced).

[0064] In the example of [Fig.5], the synchrocyclotron delivers simultaneous α therapy and D imager beams, the α ion beam being stopped in the target volume and depositing its Bragg peak there and the deuteron beam passing through the patient and depositing its Bragg peak in the imager outside the patient.

[0065] It should be noted that the integration of the dose in the target volume (SOBP, i.e., Spread Out Bragg Peak), due to the sum of the different Bragg peaks of varying energy, is affected by the deuteron beam. However, the contribution to the integrated dose is relatively small because it is upstream of the deuteron Bragg peak D, which will be in the imager. This minimal dose deposition is easily calculated by dosimetry programs as part of the preparatory planning for the treatment of the specific volume to be irradiated.

[0066] Of course, the invention is not limited to the examples just given.

[0067] Thus, frequency laws F(t) other than that illustrated in [Fig. 2], in particular with other frequency values ​​and / or different paces, can be used.

[0068] Other ion species can be accelerated.

[0069] Other types of inflectors may be used.

[0070] The bi-stem linking the HF power supply to the Dee can be replaced by another linking system.< / ps>

Claims

Demands

1. A superconducting synchrocyclotron (1) comprising: - At least two ion sources to produce respectively a so-called "therapy" beam with at least one first type of ions and an "imaging" beam consisting of deuterons, - an axial injection line comprising at least one high-frequency grouper (38) to group the ions delivered by the ion sources into bunches, before injecting them into a median acceleration plane, - a high-frequency modulation device (23) to produce within the synchrocyclotron a cyclic frequency law F(t) allowing the simultaneous acceleration of the ions of the therapy and imaging beams, - a rotating path modulator (110), placed on the path of the therapy and imaging beams after acceleration of the ions, comprising at least one solid region (110a) and at least one empty region (110b) which alternately position themselves during the rotation of the modulator on the path of said beams,the path modulator allowing modulation of the path of therapy ions in a target volume, - two beam-cutting devices (34, 35) upstream of the median acceleration plane to modulate the therapy and imaging beams synchronously with the rotation of the path modulator (110) such that the ions of the therapy beam pass only through said at least one filled region (110a) and those of the imaging beam only through said at least one empty region (110b).

2. Superconducting synchrocyclotron (1) according to claim 1, comprising at least two therapy ion sources.

3. Synchrocyclotron according to claim 2, comprising a therapy ion source α and a therapy ion source 7Li3+, the synchrocyclotron being configured to allow selection of either of the therapy ion sources, depending on the desired application.

4. Synchrocyclotron according to any one of the preceding claims, the grouper (38) operating at a frequency Fg median between the injection frequencies of the therapy and imager ions.

5. Superconducting synchrocyclotron according to any one of the preceding claims, the high-frequency modulation device comprising a rotary capacitor (23) and an HF line (21,22) connecting an accelerating electrode (20) to the rotary capacitor (23).

6. Superconducting synchrocyclotron according to any one of the preceding claims, comprising an inflector, preferably of spiral type (130, 140) for deflecting ions from the injection line towards a median plane (PM).

7. Hadron therapy installation comprising a synchrocyclotron (1) according to any one of the preceding claims.

8. Installation according to the preceding claim, comprising downstream of the synchrocyclotron a collimator (100) and downstream of the target volume an imager (120) to receive the deuteron beam.

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