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

Abstract

The invention relates to a superconducting synchrocyclotron (1) comprising: at least two ion sources (30, 33) for generating a beam referred to as a "therapy" beam and a beam referred to as an "imaging" beam, respectively, an axial injection line, a high-frequency modulation device (23) for generating, within the synchrocyclotron, a cyclic frequency function F(t) enabling the simultaneous acceleration of ions in the therapy and imaging beams, a rotary path modulator (110), two beam cut-off devices (34, 35) located upstream of the median acceleration plane for modulating the therapy and imaging beams synchronously with the rotation of the path modulator (110).

Description

[0001] Description

[0002] Title: Superconducting Synchrocyclotron with Simultaneous Acceleration of Multiple Ion Species and Hadron Therapy Facility

[0003] Technical field

[0004] The present invention relates to particle accelerators, and more particularly to synchrocyclotrons. These 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.

[0005] State of the art

[0006] The compactness of this type of accelerator allows for reduced physical dimensions and investment costs and makes installation in a hospital environment realistic.

[0007] Examples of superconducting synchrocyclotrons, enabling the acceleration of proton beams for high-energy proton therapy, are described in the following publications:

[0008] Gordon M., Wu

[0009] YJongen, P.Mandrillon, M.Abs, W.Kleeven, S.Quets, P. Verbruggen,” Development of the new IBA S2C2”, European Cyclotron Progress Meeting 2012 in PSI, Switzerland,

[0010] 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.

[0011] Hadrontherapy systems must meet efficiency and precision requirements, as it is important to know precisely where the dose is deposited, particularly when the target volume is close to organs at risk.

[0012] Existing installations can be improved in this respect. Description of the invention

[0013] There is therefore a need to further increase the performance of hadrontherapy facilities by overcoming the limitations of high-energy proton therapy.

[0014] There is also interest in improving the superconducting synchrocyclotrons used in such facilities.

[0015] Summary of the invention

[0016] The invention aims to meet all or part of these needs and achieves this by proposing a superconducting synchrocyclotron, comprising:

[0017] 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 buncher for grouping the ions delivered by the ion sources in bunches, before injecting them into a median acceleration plane of the synchrocyclotron, a high-frequency modulation device 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, 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 for modulating the path of the therapy ions in a target volume, two beam cutting devices ("chopper" in English) upstream of the median acceleration plane for modulating the therapy and imaging beams synchronously with the rotation of the path modulator, such that the ions of the therapy beam only pass through said at least one full region and those of the imaging beam only through said at least one empty region.,

[0018] Such a particle accelerator, whose frequency of the accelerating electric field is variable in 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 ex ions ( 4 Hey 2+ ), 12 C 6+ (Carbon 6+) or 7 Li 3+(Lithium 3+). The accelerator according to the invention can thus accelerate ions such as 7 Li 3+ although the load to mass ratio of the 7 Li 3+ (Z / A=0.43) is further away from the other ions which have a Z / A ratio close to 0.53.

[0019] The accelerator may have only one therapy ion source, for example an ex ion source ( 4 Hey 2+ ), 12 C 6+ (carbon 6+) or 7 Li 3+ (lithium 3+); alternatively, the accelerator comprises at least two sources of therapy ions, for example an ex ion source ( 4 Hey 2+ ) and an ion source 7 Li 3+ (lithium 3+). In this case, the synchrocyclotron is configured to allow the selection of one or other of the therapy ion sources, depending on the desired application.

[0020] When using only one ion therapy source a, the combiner operates at a given frequency Fg which is equal to the injection frequency of deuterons and a-ions. When two therapy ion sources are used and one or the other is selected, for example an ion source 7 Li 3+ and an ion source ex, the grouper preferably operates at a frequency F g median between the injection frequencies of therapy and imager ions.

[0021] In this case, the cyclic frequency law F(t) periodically passes through a first intermediate value Fi n ji greater than the frequency F g and suitable for injection and capture of deuterons, at a second intermediate value Fi n j2 less than the first and the frequency F g , suitable for injection and capture of the other type of ions, e.g. 7 Li 3+ the extraction of ions being carried out at a frequency F ex lower than Fi frequencies n ji and Fi n j2-

[0022] The grouper comprises a central electrode whose length is preferably equal to 3 |3X / 2 (|3=Vi / c, where Vi is the average of the speed of the different ions in the grouper, c the speed of light, and À the wavelength corresponding to the frequency of the grouper F g ).

[0023] The high frequency modulation device preferably comprises a rotating capacitor and an HF line connecting an accelerating electrode to the rotating capacitor.

[0024] The synchrocyclotron has an inflector, for example a 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.

[0025] The synchrocyclotron may include an extraction channel, in particular an electromagnetic septum channel, preferably allowing extraction efficiencies greater than 60%.

[0026] The invention also relates to a hadrontherapy installation comprising a synchrocyclotron according to the invention, as defined above. The installation may comprise a collimator downstream of the synchrocyclotron and an imager downstream of the target volume for receiving the deuteron beam. The collimator may be placed upstream of the path modulator.

[0027] The ions of the "therapy" beam allow the therapeutic dose to be deposited in the target volume and the ions of the "imaging" beam are used to create a simultaneous image outside the target volume with the imager in order to obtain spatial information on the position of the target volume "live".

[0028] This improves therapeutic performance: on the one hand, the ions in the therapy beam, which are heavier than protons, improve the lateral and axial ballistic precision of dose deposition in a tumor volume that requires deep paths. On the other hand, the use of therapy ions that are more ionizing than 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 can be used if desired.

[0029] 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 passing through the path modulator between the blades.

[0030] 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 moment. 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.

[0031] Brief description of the drawings

[0032] The invention may be better understood by reading the detailed description which follows, non-limiting examples of its implementation, and by examining the attached drawing, in which:

[0033] [Fig 1] schematically and partially represents, in perspective, an example of a synchrocyclotron according to the invention, [Fig 2] represents an example of frequency law F(t) of a synchrocyclotron according to the invention, accelerating ions a or 7 Li 3+ on the one hand, and deuterons D on the other hand,

[0034] [Fig 3] represents the separators of the phase spaces ( 0 , 0 ') for the species ex, D and Li and the corresponding capture zones,

[0035] [Fig 4] represents the path of different ions in water as a function of the energy in MeV / nucleon,

[0036] [Fig 5] is an exploded, schematic and partial view of part of the hadrontherapy installation located downstream of the synchrocyclotron, with scanning of the therapy beams (for example made up of a or Li ions) and imager,

[0037] [Fig 6] illustrates the effects of the grouper on the phase of the particles along the injection line, and

[0038] [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).

[0039] Detailed description

[0040] Figure 1 illustrates an example of a synchrocyclotron 1 according to the invention. This synchrocyclotron 1 is advantageously part of a hadrontherapy installation which aims to deliver a precise dose to a target tumor volume.

[0041] 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.

[0042] 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.

[0043] Synchrocyclotron 1 includes a frequency modulator HF 23 of the rotating 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 Figure 2. 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).

[0044] Synchrocyclotron 1 has an external injection line for the ions to be accelerated, extending along a vertical Z axis.

[0045] 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 Figure 1.

[0046] Each of these devices includes:

[0047] A therapy ion source 32, for example of the ECR (Electron Cyclotron Resonance) type for the therapy beams, for example alpha or lithium, inside a grounded 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 cut-off device (in English "chopper") 34 or 35, downstream of each of the sources, composed for example of an electrostatic capacitor, which makes it possible to cut the therapy or imaging beams very quickly, and the operation of which is controlled by the position of a path modulator, as specified below.

[0048] A deflection magnet 36 located on the vertical axis Z allows the beams from the sources to be deflected towards the axial injection line.

[0049] High quality vacuum is ensured by 37 pumps.

[0050] The HF 38 grouper operates in this example at a frequency F g.

[0051] The grouper 38 is for example of the double gap type with central electrode of length 3|3À / 2, the wavelength À corresponding to the frequency F g .

[0052] The grouper 38 operates in the example considered with its own generator at a median frequency F g 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. an arbitrary phase interval of 200° at the source output is reduced to 50° at the end of the injection line) as illustrated in Figure 6.

[0053] The right-hand views of this figure show the final phases and the beam radius, respectively, with and without the effect of the grouper. The grouper 38 does not operate continuously but in pulsed mode, i.e. during the capture times of the ions to be accelerated, between the "grouper on" and "grouper off" times in Figure 2.

[0054] Packets grouped at the median frequency F g are injected temporally during the capture times of the different ion species.

[0055] The grouper 38 is thus time-controlled and the operating time is controlled by the capture frequencies, as illustrated in Figure 2.

[0056] 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 Figure 7.

[0057] 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 has 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 Figure 7. The left view of Figure 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.

[0058] The synchrocyclotron has a beam extraction channel 50, for example of the electromagnetic type, notably with a copper septum. Such a channel makes it possible 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. Figure 3 shows the classic phase space (cp,dcp / dt) with the separators and capture zones for different types of accelerated ions.

[0059] The ex and D ions can be captured at the same time on the frequency law F(t). The ions 7 Li 3+are captured later than deuterons on the frequency law F(t), as illustrated in Figure 2. The hatched areas are the capture areas, i.e. any initial condition particle outside these areas is not accelerated by the synchrocyclotron 1. cp s represents the synchronous phase. Beyond the 90° phase, the particles are decelerated (acceleration convention in V.cos( ); the point -cp s represents the unstable fixed point). The capture times of ex, D and ions 7 Li 3+ injected later on the frequency program E(t) are relatively close, the capture times being for example typically between 10 and 15 ps depending on the frequency law, as illustrated in figure 2.

[0060] 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). In fact, ions with electric charge Z and mass A have a slowdown in matter which depends on the KTZ ratio. The path of ions with the same A / Z ratio 2 is therefore identical if they have the same kinetic energy usually expressed in MeV per nucleon.

[0061] Figure 4 shows the paths in water of different ions that can be accelerated by the synchrocyclotron according to the invention.

[0062] • D: deuteron, i.e. nucleus of deuterium, the heavy stable isotope of F Hydrogen.

[0063] • a: helium nucleus ( 4 Hey 2+). ex and W+ protons have the same KTZ. The a and protons of the same energy in MeV / nucleon have the same path. Although the protons cannot be simultaneously accelerated with the deuterons by the synchrocyclotron according to the invention, Figure 4 mentions them for information purposes.

[0064] • 7 Li 3+ : 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%).

[0065] • 12 C 6+ : Carbon nucleus stripped of its 6 electrons, accelerable on the same frequency law as the ex for irradiations at lower depth.

[0066] Figure 4 shows as an 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.

[0067] The installation comprises, on the path of the ions having left the accelerator 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 figure 5, and downstream of the target volume an imager 120.

[0068] The installation can 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. The path modulator 110 makes it possible to change the energy of the extracted beams to best modulate the ion paths in the target volume.

[0069] 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.

[0070] In the illustrated example, the deuteron beam passes through the empty area 110b located between the modulator blades, then through the target volume to the imager 120.

[0071] 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.

[0072] The beam cut-off 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 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 passage through the beam cut-off device 34 or 35 and the time when the ions reach the path modulator.

[0073] The 120 imager, for example, is built with multi-wire chambers (a device developed by Georges Charpak consisting of several successive grids allowing a 3-dimensional image of particle trajectories to be produced).

[0074] In the example of Figure 5, the synchrocyclotron delivers simultaneous therapy a and imager D beams, with the ion beam ex 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.

[0075] 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 D deuterons, 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.

[0076] Of course, the invention is not limited to the examples just given.

[0077] Thus, frequency laws F(t) other than that illustrated in Figure 2, in particular with other frequency values ​​and / or different speeds, can be used.

[0078] Other ion species can be accelerated. Other types of inflectors can be used.

[0079] The bi-stem connecting the HF power supply to the Dee can be replaced by another connection system.

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 making it possible to modulate the path of the 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) so that the ions of the therapy beam pass through only said at least one full region (110a) and those of the imaging beam only 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 source of therapy ions ex and a source of therapy ions 7 Li 3+ , the synchrocyclotron being configured to allow the selection of one or other 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 F gmedian between the injection frequencies of therapy and imager ions.

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