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) for producing respectively a so-called "therapy" beam and a so-called "imaging" beam, an axial injection line, a high-frequency modulation device (23) for producing within the synchrocyclotron a cyclic frequency law F(t) allowing the simultaneous acceleration of the ions of the therapy and imaging beams, a rotary path modulator (110), two beam cut-off devices (34, 35) upstream of the median acceleration plane for modulating the therapy and imaging beams synchronously with the rotation of the path modulator (110). Figure for 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, called hadrontherapy, which use the Bragg peak characteristic of the increase in the 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 physical dimensions and investment costs and makes installation in a hospital environment realistic.

[0003] Examples of superconducting synchrocyclotrons, allowing 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] Hadrontherapy systems must meet efficiency and precision requirements, because it is important to know precisely where the dose is deposited, particularly when the target volume is close to organs at risk.

[0005] Existing installations can be improved in this regard. Statement of the invention

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

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

[0008] The invention aims to meet all or part of these needs and it 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 first type of ion and a so-called "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 packets, before injecting them into a median acceleration plane of the synchrocyclotron, - a high-frequency modulation device 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, placed on the path of the therapy and imaging beams after acceleration of the ions, comprising at least one full region and at least one empty region positioned alternately during the rotation of the modulator on the path of said beams, the path modulator making it possible to modulate the path of the therapy ions 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 through only said at least one full region and those of the imaging beam only said at least one empty region.

[0009] Such a particle accelerator, the frequency of the accelerating electric field of which is variable over time, is capable of accelerating, in addition to deuterons, on the same frequency program F(t), ions with an electric charge ratio Z to mass A close to that of deuterons, for example ions a (4He2+), 12C6+ (Carbon 6+) or 7Li3+ (Lithium 3+). The accelerator according to the invention can thus accelerate ions such as 7Li 3+ although the charge to mass ratio of 7Li3+ (Z / A=0.43) is further from the other ions which have a Z / A ratio close to 0.53.

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

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

[0012] In this case, the cyclic frequency law F(t) passes periodically 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 being carried out at a frequency Fex lower than the frequencies Finji and Finj2.

[0013] The grouper comprises a central electrode whose length is preferably equal to 3[3X / 2 ([3=Vi / c, where Vj is the average of the speed 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 acceleration electrode to the rotary capacitor.

[0015] The synchrocyclotron comprises 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, rotations of the beam of between 360° and 720° around the vertical axis.

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

[0017] The invention also relates to a hadrontherapy installation comprising a synchrocyclotron according to the invention, as defined above.

[0018] The installation may comprise 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 make it possible to deposit the therapeutic dose in the target volume and the ions of the “imaging” beam are used to produce, with the imager, a simultaneous image outside the target volume in order to obtain spatial information on the position of the target volume “live”.

[0020] This makes it possible to improve therapeutic performance: on the one hand, the ions in the therapy beam, which are heavier than the protons, improve the lateral and axial ballistic precision of the dose deposition in a tumor volume which requires deep paths. On the other hand, the use of therapy ions which are more ionizing than the protons increases the relative biological efficiency, thus allowing the destruction of so-called radio-resistant tumor cells. In addition, the installation offers the possibility of carrying out irradiation in a very short time, and the so-called "flash therapy" technique is feasible if this is desired.

[0021] The path modulator comprises, for example, a wheel driven in rotation, comprising blades each having an angular variation in their thickness, in particular in stages, the rotation of the path modulator being synchronized with the emission of the ions accelerated by the synchrocyclotron so 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 making it possible to obtain the positioning of the desired Bragg peak, and the ions of the imaging beam intended to reach the imager pass through the path modulator between the blades.

[0022] The installation according to the invention offers the possibility of irradiating mobile tumors, by making it possible to know precisely, thanks to the imager, where the dose is deposited at each instant. The invention allows the irradiation of "moving targets", for example due to the patient's breathing for lung tumors or swallowing for tumors of the ENT sphere, with highly ionizing ions, in a precise manner, thanks to the direct knowledge of the position of the dose deposit provided by the imager. Brief description of the drawings

[0023] The invention may be better understood by reading the detailed description which follows, of non-limiting examples of its implementation, and by examining the attached drawing, in which:

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

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

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

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

[0028] [Fig.5] is an exploded, schematic and partial view of part of the installation hadrontherapy located downstream of the synchrocyclotron, with scanning of therapy beams (for example made up of a or Li ions) and imager,

[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] An example of a synchrocyclotron 1 according to the invention is illustrated in [Fig. 1]. This synchrocyclotron 1 advantageously forms part of a hadrontherapy installation which aims to deliver a precise dose to a target tumor volume.

[0032] As illustrated, the synchrocyclotron 1 comprises an electromagnet which generally has a structure that is generally symmetrical with respect to a horizontal median acceleration plane PM and which passes through the section plane of the lower 10 and upper 11 yokes. 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 comprises an HF system which comprises 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 comprises a frequency modulator HF 23 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 comprises 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.l].

[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 ground cage 30 and a high voltage cage 31, - a source of imaging deuteron ions (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 very quickly, and whose operation is controlled by the position of a path modulator, as specified below.

[0039] A deflection magnet 36 located on the vertical axis Z makes it possible to deflect the beams coming from the sources towards the axial injection line.

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

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

[0042] The grouper 38 is for example of the double gap type with 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 makes it possible to achieve satisfactory grouping efficiencies (for example up to 4 times, i.e. 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 respectively represented, with and without the effect of the buncher.

[0045] The grouper 38 does not operate continuously but in pulsed mode, that is to say during the capture times of the ions to be accelerated, between the “grouper on” and “grouper off” times in [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 controlled in time and the operating duration 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 in [Fig.7].

[0049] The inflector 40 is for example of the spiral electrostatic inflector type, with two nested electrodes 130 and 140 which 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] presents a projection in the vertical plane X, Z, the X axis being by convention the axis of the accelerator "gap" of the Dee, the middle view in the horizontal plane, and the right view in perspective.

[0050] The synchrocyclotron comprises 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 make it possible to reduce the parasitic neutron fluxes resulting from beam losses on the extraction components. This reduction in neutron fluxes makes it possible to reduce the general activation of the internal components of the synchrocyclotron, which facilitates maintenance operations, and to reduce the thermal load on the superconducting coils due to the energy deposited by these particle fluxes. [Fig. 3] presents the classic phase space (<p,dq> / dt) with the separators and capture zones for different types of accelerated ions.

[0051] The a and D ions can be captured at the same time on the frequency law F(t). The 7Li3+ ions are captured later than the deuterons on the frequency law F(t), as illustrated in [Fig.2]. The hatched areas are the capture areas, i.e. any initial condition particle outside these areas is not accelerated by 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 ions and the 7Li3+ ions injected later on the frequency program F(t) are relatively similar, 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 in the tissues depending on their kinetic energy expressed in MeV / nucleon (the same kinetic energy in MeV / nucleon expresses that these ions have the same speed regardless of their mass). Indeed, ions with electric charge Z and mass A have a slowdown in matter which depends on the KTÛ ratio. 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] [Fig.4] shows the paths in water of different ions which can be accelerated by the synchrocyclotron according to the invention. • D: deuteron, i.e. 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 information purposes. • 7Li3+: Lithium nucleus stripped of its 3 electrons. Natural Lithium is formed 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, accelerable on the same frequency law than the a for irradiations at lower depths.

[0055] [Fig.4] shows by way of example that for an interval 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 comprises, 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 path modulator by conventional optical beam deflection elements depending on the specifics of the hadrontherapy installation. For example, an installation dedicated to head and neck tumors uses a horizontal fixed beam and does not require an isocentric rotating head.

[0058] The path modulator 110 makes it possible to change the energy of the extracted beams 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 around an axis parallel to the imaging and therapy beams, as illustrated in [Fig. 5]. Each blade comprises sectors of different respective thicknesses, making it possible to modulate the depth of the Bragg peak.

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

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

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

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

[0064] In the example of [Fig.5], the synchrocyclotron delivers simultaneous therapy beams a and imager D, the ion beam a 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] Note that the integration of the dose in the target volume (called SOBP, i.e. Spread Out Bragg Peak) due to the sum of the different Bragg peaks of variable energy, is affected by the deuteron beam. However, the contribution to the integrated dose is relatively low because it is upstream of the Bragg peak of the deuterons D, which will be in the imager. This minimal dose deposition is easily calculated by dosimetry programs as part of the preparatory planning of the treatment of the specific volume to be irradiated.

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

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

[0068] Other ion species can be accelerated.

[0069] Other types of inflectors may be used.

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

Claims

Claims

1. Superconducting synchrocyclotron (1) comprising: - At least two ion sources for producing respectively a so-called "therapy" beam with at least a first type of ion and a so-called "imaging" beam consisting of deuterons, - an axial injection line comprising at least one high-frequency grouper (38) for grouping the ions delivered by the ion sources in packets, before injecting them into a median acceleration plane, - a high-frequency modulation device (23) for producing within the synchrocyclotron a cyclic frequency law F(t) allowing the simultaneous acceleration of the ions of the therapy and imaging beams, - a rotary path modulator (110), placed on the path of the therapy and imaging beams after acceleration of the ions, comprising at least one full region (110a) and at least one empty region (110b) positioned alternately during the rotation of the modulator on the path of said beams,the path modulator for modulating the path of the therapy ions in a target volume, - two beam-cutting devices (34, 35) upstream of the median acceleration plane for modulating the therapy and imaging beams synchronously with the rotation of the path modulator (110) so that the ions of the therapy beam only pass through said at least one full 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 sources of therapy ions.

3. Synchrocyclotron according to claim 2, comprising a therapy ion source a and a therapy ion source 7Li3+, the synchrocyclotron being configured to allow one or the other of the therapy ion sources to be selected, depending on the desired application.

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

5. A superconducting synchrocyclotron according to any preceding claim, 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 the spiral type (130, 140) for deflecting the ions from the injection line towards a median plane (PM).

7. Hadrontherapy 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) for receiving the deuteron beam.

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