EP1393602A1 - Device and method for regulating intensity of a beam extracted from a particle accelerator - Google Patents

Device and method for regulating intensity of a beam extracted from a particle accelerator

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Publication number
EP1393602A1
EP1393602A1 EP02737673A EP02737673A EP1393602A1 EP 1393602 A1 EP1393602 A1 EP 1393602A1 EP 02737673 A EP02737673 A EP 02737673A EP 02737673 A EP02737673 A EP 02737673A EP 1393602 A1 EP1393602 A1 EP 1393602A1
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EP
European Patent Office
Prior art keywords
intensity
value
accelerator
ion source
measured
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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EP02737673A
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German (de)
French (fr)
Inventor
Bruno Marchand
Bertrand Bauvir
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Ion Beam Applications SA
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Ion Beam Applications SA
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Publication date
Application filed by Ion Beam Applications SA filed Critical Ion Beam Applications SA
Priority to EP02737673A priority Critical patent/EP1393602A1/en
Publication of EP1393602A1 publication Critical patent/EP1393602A1/en
Withdrawn legal-status Critical Current

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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H13/00—Magnetic resonance accelerators; Cyclotrons
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H7/00—Details of devices of the types covered by groups H05H9/00, H05H11/00, H05H13/00

Definitions

  • the present invention is in the technical field of regulating the intensity of a beam extracted from a particle accelerator.
  • the present "• invention relates to a device for the rapid and precise regulation of the intensity of a beam extracted from a particle accelerator, and more specifically from a cyclotron.
  • the present invention also relates to a method for regulating the intensity of the beam extracted from a particle accelerator.
  • the present invention finally relates to the use of this device or this method in proton therapy and in particular in the technique of "Pencil Beam Scanning".
  • Cyclotrons are circular particle accelerators which are used to accelerate positive or negative ions to energies of a few MeV or more. This type of device finds applications in different fields such as industry or medicine, more specifically in radiotherapy for the production of radioisotopes or in proton therapy, in order to treat cancerous tumors. Cyclotrons generally include five major components: the ion source which generates the ionized particles, the vacuum confinement device for the ionized particles, the electromagnet which produces the magnetic field guiding the ionized particles, the accelerator system.
  • the extraction device making it possible to divert the ionized particles from their acceleration trajectory then to evacuate them out of the cyclotron in the form of a beam with high kinetic energy. This beam is then directed to the target volume.
  • the ions are obtained by ionization, in a closed chamber, of a gaseous medium consisting of one or more gases, by means of electrons strongly accelerated by cyclotron electronic resonance under the action of a high frequency magnetic field injected into the enclosure.
  • Such cyclotrons can be used in proton therapy.
  • Proton therapy aims to deliver a high dose in a well defined target volume to be treated while sparing the healthy tissue surrounding the volume in question.
  • protons Compared to conventional radiotherapy (X-rays), protons have the advantage of depositing their dose at a precise depth depending on energy (Bragg peak).
  • X-rays X-rays
  • Bragg peak Several techniques for distributing the dose in the target volume are known.
  • Applicant describes an improved technique, called “pencil beam scanning", in which the beam must not be interrupted between the irradiation of each individual voxel.
  • the process described in this document consists in moving the beam continuously so as to "paint" the target volume layer by layer.
  • the intensity of the proton beam is regulated indirectly by an action on the supply current of the ion source.
  • a regulator is used which regulates the intensity of the proton beam.
  • this regulation is not optimal.
  • Double Diffusion Another technique used in proton therapy is the so-called "Double Diffusion" technique.
  • the modulation of the irradiation depth (that is to say of the energy) is carried out using a wheel known as a modulation wheel rotating at a speed of the order of 600 rev / min.
  • the absorbent parts of this modulator consist of a absorbent material, such as graphite or lexan.
  • the depth modulation obtained is fairly close to the predictions. Uniformity remains outside of the desired specifications. To achieve the uniformity specifications, rather than re-machining the modulation wheels, it is less expensive to use beam intensity regulation which is synchronized with the speed of rotation of the energy modulator.
  • the modulation function is therefore established for each energy modulator and is used as the path supplied as a setpoint to the beam intensity regulator.
  • a rapid and precise regulation of the intensity of the beam extracted from a particle accelerator is therefore also necessary in the double diffusion techniques using such a modulation wheel.
  • the present invention aims to provide a device and a method for regulating the intensity of a beam extracted from a particle accelerator, which does not have the drawbacks of the methods and devices of the state of the technical.
  • the present invention relates to a device for regulating the intensity of the beam extracted from a particle accelerator, such as a cyclotron, used for example for proton therapy, said particles being generated from a source. ion, characterized in that it comprises at least:
  • a comparator determining a difference between a digital signal representative of the intensity of the beam measured at the output of the accelerator and a setpoint value of the beam intensity
  • the device according to the invention may comprise an analog-digital converter converting the analog signal directly - representative of the intensity of the beam measured at the output of the accelerator, and providing a digital signal.
  • the device according to the invention will further comprise:
  • a low-pass filter filtering the analog signal directly representative of the intensity of the beam measured at the output of the accelerator, and providing a filtered analog signal; - a phase advance regulator sampling said filtered analog signal, compensating for the phase delay introduced by the low-pass filter, and supplying a digital signal to the comparator.
  • the device of the invention comprises means for updating the content of the reverse correspondence table.
  • the sampling frequency is preferably between 100 kHz and 200 kHz, and the cut-off frequency of the low-pass filter is preferably between 2 and 6 kHz.
  • the present invention also relates to a method of regulation, by means of a digital regulation device operating at a given sampling frequency, of the beam intensity extract of a particle accelerator, such as a cyclotron, used for example in proton therapy, said particles being generated from an ion source, characterized in that it comprises at least the following steps:
  • a corrected beam intensity value is determined, using a Smith predictor
  • a set value is determined for the supply of the arc current from the ion source.
  • the analog signal directly representative of the intensity of the beam measured by means of d is converted.
  • a digital analog converter to obtain a digital signal.
  • the analog signal is filtered directly representative of the intensity of the beam measured by means of a low-pass filter, giving a filtered analog signal;
  • the correspondence between a value for supplying the arc current of the ion source and a value of the intensity of the beam measured at the accelerator output is determined prior to regulation.
  • the values of the supply of the arc current corresponding to the beam intensity values above a limit are replaced by the supply value of the arc current corresponding to this limit.
  • the present invention also relates to the use of the device and the method of the invention in proton therapy and in particular in the techniques of "Pencil Beam Scanning" and “double diffusion".
  • Figure 1 shows a device for regulating the intensity of a beam extracted from a particle accelerator according to the prior art.
  • FIG. 3 shows an embodiment of a device for regulating the intensity of a beam extracted from a particle accelerator according to the invention.
  • FIG. 4 shows a second embodiment of a device for regulating the intensity of a beam extracted from a particle accelerator according to the invention.
  • a set value I c of the beam intensity is supplied to a conventional PID regulator 10, which determines a value I j ⁇ of the arc current of the ion source 20.
  • the intensity of the beam is measured by means of an ionization chamber 30, and the corresponding signal I is compared with the aid of a comparator "90 to the reference value le to provide an error signal.
  • a comparator "90 to the reference value le it is essential that the intensity of the beam varies simultaneously with the displacement, so as to obtain the conformity of the delivered dose.
  • a large pure dead time is due to the long travel time of a particle between its emission by the ion source 20 and its exit from the machine;
  • this characteristic can vary over time, as shown by the broken lines in Figure 2. This variation can occur quickly due to heating or cooling of the filament of the ion source during its setting service. It can also come from the aging of the filament. These two phenomena lead to variations in the characteristic with very different time constants; - the system is very noisy. The intensity of the beam generated by the ion source presents significant noise, in particular at the sampling frequency used for the measurement.
  • the evolution of the characteristic depends on two well-decoupled phenomena: the first, of short time constant, corresponds to the conditioning of the ion source, that is to say its temperature. Normal, continuous or intermittent high duty cycle operation heats the ion source quickly. This rapid establishment time in temperature could make it possible to work in an open loop, that is to say without taking account of the real characteristic of the system, using the conventional methods, during the conditioning time. However, this compromise greatly limits the use of a conventional method in intermittent operation with an average duty cycle, which often corresponds to the operating mode used.
  • the second phenomenon, of a longer time constant is due to the aging of the filament and of the ion source itself. This slower evolution of the characteristic could therefore give rise to the use of an average characteristic of the system. The use of an average characteristic however leads to a regulation which is either too slow or unstable.
  • the present invention therefore proposes to more specifically resolve this problem by using, according to a preferred embodiment, a regulating device 10 shown in FIG. 3 with the supply of the arc current from the ion source 20.
  • the ion source produces an ion beam, which is accelerated during its journey in the accelerator, is extracted therefrom, and passes through a measuring device 30 of the beam intensity at the exit of the accelerator.
  • This measuring device 30 can for example be an ionization chamber.
  • the regulator according to the invention has been applied for a cyclotron having the following exemplary and non-limiting characteristics:
  • This pure dead time corresponds to the travel time of the ions in the accelerator. It therefore corresponds directly to the time necessary to measure the influence of a modification of the setpoint of the arc of the ion source on the intensity of the beam of ions extracted from the machine.
  • the noise / signal ratio observed is around 150%.
  • the selected sampling frequencies generate a very low signal / noise ratio.
  • the following steps are carried out: - the set value of the intensity of the beam I c is supplied in the form of an analog signal 0- 10 V (10 V corresponding to a beam intensity of 300 nA); the beam intensity is measured by means of an ionization chamber 30 and the measurement I UberM is supplied to the regulating device 10 by means of an analog signal 0-15 ⁇ A (15 ⁇ A corresponding to an intensity of the 300 nA beam);
  • the correspondence table 40 numerically provides the non-linear relationship between the arc current of the source d IA ions, and the intensity of the IM beam, of ions extracted from the accelerator. It therefore makes it possible to identify the nonlinear characteristic of the system.
  • the output of the inverted correspondence table is converted into an analog signal of the 4-20 mA I type which is supplied by the regulating device 10 as a set value for supplying the arc current of the ion source. Simulations show that such a device allows good regulation. It is however sensitive to low frequency disturbances. To solve this problem, a preferred variant of the device according to the invention, shown in FIG. 4, has been developed.
  • a low-pass filter 60 and a phase advance regulator 70 are introduced into the feedback.
  • the filter 60 is for example a first order low pass filter.
  • the cutoff frequency is 4.5 kHz.
  • a phase advance regulator 70 filtered differentiator
  • Both the device of FIG. 3 and that of FIG. 4 include an inverted correspondence table 40.
  • the content of this table 40 is determined prior to each use of the device in the following manner:
  • the setpoint of the arc current of the ion source 20 is gradually increased from 0 to 20 mA in the form of a ramp of 100 ms;
  • the intensity of the beam is measured for each of the 4000 points sampled; - The table obtained is inverted, so as to provide a corresponding value of the arc current of the ion source I A, as a function of the intensity of the beam IM wait.
  • This inverted table is loaded into the regulating device 10. In practice, this operation is carried out a dozen times successively. This ensures that the parameters reach a plateau, corresponding to the filament operating temperature. In order to eliminate the noise, an average of the last 4 tables is calculated. These operations, performed automatically, last a maximum of 1.5 s. In a variant of the invention, the values of I corresponding to the values of I greater than a given limit are replaced by the value of I corresponding to this limit. The curves in Figure 2 are therefore clipped. This is a safety feature to guarantee that the intensity of the beam produced by the accelerator will never exceed this limit.
  • the device according to the invention is produced by means of an electronic card which uses digital technologies of the DSP (Digital Signal Processing) type.
  • the method of regulation according to the present invention has several advantages. First of all, it allows a controlled adaptation, that is to say it requires a very small computation time in comparison with modern methods of adaptive control and allows a very easy change of structure since the identification is made by construction of a correspondence table which it then suffices to invert numerically to linearize the characteristic of the system seen by the main regulator.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Radiation-Therapy Devices (AREA)
  • Particle Accelerators (AREA)

Abstract

The invention concerns a device (10) for regulating the intensity of a beam extracted from a particle accelerator, such as a cyclotron, used for example for protontherapy, said particles being generated from an ion source. The invention is characterised in that it comprises at least: a comparator (90) determining a difference epsilon between a digital signal IR representing the intensity of the beam measured at the output of the accelerator and a setpoint value IC of the beam intensity: a Smith predictor (80) which determines on the basis of the difference epsilon , a corrected value of the intensity of the beam IP; an inverted correspondence table (40) supplying, on the basis of the corrected value of the intensity of the beam IP a setpoint value IA for supplying arc current from the ion source (20).

Description

DISPOSITIF ET METHODE DE REGULATION DE L ' INTENSITE D'UN FAISCEAU EXTRAIT D'UN ACCELERATEUR DE PARTICULES DEVICE AND METHOD FOR CONTROLLING THE INTENSITY OF A BEAM EXTRACTED FROM A PARTICLE ACCELERATOR
Objet de l'inventionSubject of the invention
[0001] La présente invention se situe dans le domaine technique de la régulation de l'intensité d'un faisceau extrait d'un accélérateur de particules. [0002] La présente "• invention se rapporte à un dispositif destiné à la régulation rapide et précise de l'intensité d'un faisceau extrait d'un accélérateur de particules, et plus spécifiquement d'un cyclotron.The present invention is in the technical field of regulating the intensity of a beam extracted from a particle accelerator. The present "• invention relates to a device for the rapid and precise regulation of the intensity of a beam extracted from a particle accelerator, and more specifically from a cyclotron.
[0003] La présente invention se rapporte également à une méthode pour la régulation de l'intensité du faisceau extrait d'un accélérateur de particules.The present invention also relates to a method for regulating the intensity of the beam extracted from a particle accelerator.
[0004] La présente invention se rapporte enfin à l'utilisation de ce dispositif ou de cette méthode en protonthérapie et en particulier dans la technique de "Pencil Beam Scanning" .The present invention finally relates to the use of this device or this method in proton therapy and in particular in the technique of "Pencil Beam Scanning".
Arrière-plan technologique et état de la technique [0005] Les cyclotrons sont des accélérateurs circulaires de particules qui sont utilisés pour accélérer des ions positifs ou négatifs jusqu'à des énergies de quelques MeV voire plus. Ce type d'appareils trouve des applications dans des domaines différents tels que l'industrie ou la médecine, plus précisément en radiothérapie pour la production de radio-isotopes ou en protonthérapie, en vue de traiter des tumeurs cancéreuses. [0006] Les cyclotrons comprennent généralement cinq composants majeurs : la source d'ions qui génère les particules ionisées, le dispositif de confinement sous vide des particules ionisées, l' électroaimant qui produit le champ magnétique assurant le guidage des particules ionisées, le système accélérateur haute fréquence destiné à accélérer les particules ionisées, et le dispositif d'extraction permettant de dévier les particules ionisées de leur trajectoire d'accélération puis de les évacuer hors du cyclotron sous forme d'un faisceau à haute énergie cinétique. Ce faisceau est ensuite dirigé vers le volume cible.Technological background and state of the art [0005] Cyclotrons are circular particle accelerators which are used to accelerate positive or negative ions to energies of a few MeV or more. This type of device finds applications in different fields such as industry or medicine, more specifically in radiotherapy for the production of radioisotopes or in proton therapy, in order to treat cancerous tumors. Cyclotrons generally include five major components: the ion source which generates the ionized particles, the vacuum confinement device for the ionized particles, the electromagnet which produces the magnetic field guiding the ionized particles, the accelerator system. high frequency intended to accelerate the ionized particles, and the extraction device making it possible to divert the ionized particles from their acceleration trajectory then to evacuate them out of the cyclotron in the form of a beam with high kinetic energy. This beam is then directed to the target volume.
[0007] Dans la source d'ions d'un cyclotron, les ions sont obtenus par ionisation, dans une enceinte fermée, d'un milieu gazeux constitué d'un ou plusieurs gaz, au moyen d'électrons fortement accélérés par résonance électronique cyclotronique sous l'action d'un champ magnétique haute fréquence injecté dans l'enceinte.In the ion source of a cyclotron, the ions are obtained by ionization, in a closed chamber, of a gaseous medium consisting of one or more gases, by means of electrons strongly accelerated by cyclotron electronic resonance under the action of a high frequency magnetic field injected into the enclosure.
[0008] De tels cyclotrons peuvent être utilisés en protonthérapie. La protonthérapie vise à délivrer une dose élevée dans un volume cible à traiter bien défini tout en épargnant les tissus sains entourant le volume considéré. En comparaison à la radiothérapie conventionnelle (rayons X), les protons présentent l'avantage de déposer leur dose à une profondeur précise dépendant de l'énergie (pic de Bragg) . Plusieurs techniques pour distribuer la dose dans le volume cible sont connues .[0008] Such cyclotrons can be used in proton therapy. Proton therapy aims to deliver a high dose in a well defined target volume to be treated while sparing the healthy tissue surrounding the volume in question. Compared to conventional radiotherapy (X-rays), protons have the advantage of depositing their dose at a precise depth depending on energy (Bragg peak). Several techniques for distributing the dose in the target volume are known.
[0009] La technique mise au point par Pedroni et décrite dans « The 200-Mev proton therapy project at the Paul Scherrer Insti tute : conceptual design and practical realization » MEDICAL PHYSICS, JAN. 1995, USA, vol .22, no . l , pages 37-53 , XP000505145 ISSN : 0094 -2405, consiste à découper le volume cible en volumes élémentaires appelés « voxels ». On dirige le faisceau vers un premier voxel, et lorsque la dose prescrite est atteinte, on interrompt l'irradiation en déviant brusquement le faisceau au moyen d'un aimant rapide (fast kicking magnet) . On règle alors un aimant de balayage de manière à diriger le faisceau vers un voxel suivant, et on réintroduit le faisceau de manière . à irradier ce voxel suivant. Ce processus est répété jusqu'à irradiation du volume cible en entier. Un des inconvénients de ce procédé est que, en raison des interruptions et rétablissements successifs du faisceau entre deux voxels, le temps de traitement est important, et peut atteindre plusieurs minutes dans des conditions typiques.The technique developed by Pedroni and described in "The 200-Mev proton therapy project at the Paul Scherrer Insti tute: conceptual design and practical realization" MEDICAL PHYSICS, JAN. 1995, USA, vol. 22, no. l, pages 37-53, XP000505145 ISSN: 0094 -2405, consists of cutting the target volume into elementary volumes called "voxels". We direct the beam towards a first voxel, and when the prescribed dose is reached, the irradiation is interrupted by abruptly deflecting the beam by means of a fast magnet (fast kicking magnet). A scanning magnet is then adjusted so as to direct the beam to a next voxel, and the beam is thus reintroduced . to irradiate this next voxel. This process is repeated until the entire target volume is irradiated. One of the drawbacks of this method is that, due to the successive interruptions and re-establishment of the beam between two voxels, the processing time is long, and can reach several minutes under typical conditions.
[0010] La demande de brevet O00/40064 de laPatent application O00 / 40064 of the
Demanderesse décrit une technique améliorée, dite « pencil beam scanning », dans laquelle le faisceau ne doit pas être interrompu entre l'irradiation de chaque voxel individuel.Applicant describes an improved technique, called "pencil beam scanning", in which the beam must not be interrupted between the irradiation of each individual voxel.
Le procédé décrit dans ce document consiste à déplacer le faisceau de manière continue de manière à "peindre" le volume cible couche après couche.The process described in this document consists in moving the beam continuously so as to "paint" the target volume layer by layer.
[0011] En opérant simultanément un déplacement du faisceau et une variation de l'intensité de ce faisceau, on parvient à conformer exactement la dose à délivrer au volume cible. La régulation de l'intensité du faisceau de protons est réalisée indirectement par une action sur le courant d'alimentation de la source d'ions. On utilise dans ce but un régulateur qui permet de réguler l'intensité du faisceau de protons. Toutefois, cette régulation n'est pas optimale.By simultaneously operating a displacement of the beam and a variation of the intensity of this beam, it is possible to exactly conform the dose to be delivered to the target volume. The intensity of the proton beam is regulated indirectly by an action on the supply current of the ion source. For this purpose, a regulator is used which regulates the intensity of the proton beam. However, this regulation is not optimal.
[0012] Une autre technique utilisée en protonthérapie est la technique dite de « Double Diffusion ». Dans cette technique, la modulation de la profondeur d'irradiation (c'est-à-dire de l'énergie), est réalisée à l'aide d'une roue dite roue de modulation tournant à une vitesse de l'ordre de 600 tr/min. Les parties absorbantes de ce modulateur sont constituées d'un matériau absorbant, tel que le graphite ou de lexan. Lors de la fabrication de ces roues de modulation, la modulation en profondeur obtenue est assez proche des prédictions . L'uniformité reste malgré tout en dehors des spécifications désirées. Pour atteindre les spécifications sur l'uniformité, plutôt que de ré-usiner les roues de modulation, il est moins onéreux d'utiliser une régulation de l'intensité du faisceau qui soit synchronisée sur la vitesse de rotation du modulateur d'énergie. La fonction de modulation est donc établie pour chaque modulateur d'énergie et est utilisée comme trajectoire fournie comme consigne au régulateur de l'intensité du faisceau. Une régulation rapide et précise de l'intensité du faisceau extrait d'un accélérateur de particules est donc nécessaire également dans les techniques de double diffusion utilisant une telle roue de modulation.Another technique used in proton therapy is the so-called "Double Diffusion" technique. In this technique, the modulation of the irradiation depth (that is to say of the energy) is carried out using a wheel known as a modulation wheel rotating at a speed of the order of 600 rev / min. The absorbent parts of this modulator consist of a absorbent material, such as graphite or lexan. During the manufacture of these modulation wheels, the depth modulation obtained is fairly close to the predictions. Uniformity remains outside of the desired specifications. To achieve the uniformity specifications, rather than re-machining the modulation wheels, it is less expensive to use beam intensity regulation which is synchronized with the speed of rotation of the energy modulator. The modulation function is therefore established for each energy modulator and is used as the path supplied as a setpoint to the beam intensity regulator. A rapid and precise regulation of the intensity of the beam extracted from a particle accelerator is therefore also necessary in the double diffusion techniques using such a modulation wheel.
Buts de ' inventionAims of the invention
[0013] La présente invention vise à fournir un dispositif et une méthode destinés à la régulation de l'intensité d'un faisceau extrait d'un accélérateur de particules, qui ne présente pas les inconvénients des procédés et dispositifs de l'état de la technique.The present invention aims to provide a device and a method for regulating the intensity of a beam extracted from a particle accelerator, which does not have the drawbacks of the methods and devices of the state of the technical.
Résumé de 1 ' inventionSummary of the invention
[0014] La présente invention se rapporte à un dispositif de régulation de l'intensité du faisceau extrait d'un accélérateur de particules, tel qu'un cyclotron, utilisé par exemple pour la protonthérapie, lesdites particules étant générées à partir d'une source d'ions, caractérisé en ce qu' il comporte au moins :The present invention relates to a device for regulating the intensity of the beam extracted from a particle accelerator, such as a cyclotron, used for example for proton therapy, said particles being generated from a source. ion, characterized in that it comprises at least:
- un comparateur déterminant un écart entre un signal digital représentatif de l'intensité du faisceau mesurée à la sortie de l'accélérateur et une valeur de consigne de l'intensité du faisceau;- a comparator determining a difference between a digital signal representative of the intensity of the beam measured at the output of the accelerator and a setpoint value of the beam intensity;
- un prédicteur de Smith, qui détermine, à partir de cet écart, une valeur corrigée de l'intensité de faisceau; - une table de correspondance inversée, fournissant, .à partir de la valeur corrigée de l'intensité de faisceau, une valeur de consigne pour l'alimentation du courant d'arc de la source d'ions. [0015] En outre, le dispositif selon l'invention peut comprendre un convertisseur analogique-digital convertissant le signal analogique directement - représentatif de l'intensité du faisceau mesuré à la sortie de l'accélérateur, et fournissant un signal digital. [0016] De préférence, le dispositif selon l'invention comprendra en outre :- a Smith predictor, which determines, from this difference, a corrected value of the beam intensity; - an inverted correspondence table, providing, from the corrected value of the beam intensity, a set value for supplying the arc current of the ion source. In addition, the device according to the invention may comprise an analog-digital converter converting the analog signal directly - representative of the intensity of the beam measured at the output of the accelerator, and providing a digital signal. Preferably, the device according to the invention will further comprise:
- un filtre passe-bas filtrant le signal analogique directement représentatif de l'intensité du faisceau mesuré à la sortie de l'accélérateur, et fournissant un signal analogique filtré; - un régulateur à avance de phase échantillonnant ledit signal analogique filtré, compensant le retard de phase introduit par le filtre passe-bas, et fournissant un signal digital au comparateur.a low-pass filter filtering the analog signal directly representative of the intensity of the beam measured at the output of the accelerator, and providing a filtered analog signal; - a phase advance regulator sampling said filtered analog signal, compensating for the phase delay introduced by the low-pass filter, and supplying a digital signal to the comparator.
[0017] Avantageusement, le dispositif de l'invention comporte des moyens de mise à jour du contenu de la table de correspondance inversée .Advantageously, the device of the invention comprises means for updating the content of the reverse correspondence table.
[0018] La fréquence d'échantillonnage est de préférence comprise entre 100 kHz et 200- kHz, et la fréquence de coupure du filtre passe-bas est de préférence comprise entre 2 et 6 kHz.The sampling frequency is preferably between 100 kHz and 200 kHz, and the cut-off frequency of the low-pass filter is preferably between 2 and 6 kHz.
[0019] La présente invention concerne également une méthode de régulation, au moyen d'un dispositif de régulation digital fonctionnant à une fréquence d'échantillonnage donnée, de l'intensité du faisceau extrait d'un accélérateur de particules, tel qu'un cyclotron, utilisé par exemple en protonthérapie, lesdites particules étant générées à partir d'une source d'ions, caractérisée en ce qu'elle comprend au moins les étapes suivantes :The present invention also relates to a method of regulation, by means of a digital regulation device operating at a given sampling frequency, of the beam intensity extract of a particle accelerator, such as a cyclotron, used for example in proton therapy, said particles being generated from an ion source, characterized in that it comprises at least the following steps:
- on mesure l'intensité du faisceau à la sortie de l'accélérateur de particules;- the intensity of the beam at the exit of the particle accelerator is measured;
- on compare un signal digital représentatif de la mesure de l'intensité du faisceau avec la valeur de consigne de l'intensité du faisceau;- a digital signal representative of the measurement of the beam intensity is compared with the set value of the beam intensity;
- on détermine, au moyen d'un prédicteur de Smith, une valeur corrigée de l'intensité de faisceau;- a corrected beam intensity value is determined, using a Smith predictor;
- on détermine, à partir de cette valeur corrigée de l'intensité de faisceau, au moyen d'une table de correspondance inversée, une valeur de consigne pour l'alimentation du courant d'arc de la source d'ions.- From this corrected beam intensity value, by means of an inverted correspondence table, a set value is determined for the supply of the arc current from the ion source.
[0020] De préférence, dans la méthode selon l'invention, après la mesure de l'intensité du faisceau à la sortie de l'accélérateur de particules, on convertit le signal analogique directement représentatif de l'intensité du faisceau mesurée au moyen d'un convertisseur analogique digital pour obtenir un signal digital .Preferably, in the method according to the invention, after measuring the intensity of the beam at the output of the particle accelerator, the analog signal directly representative of the intensity of the beam measured by means of d is converted. '' a digital analog converter to obtain a digital signal.
[0021] Selon une forme d'exécution de la méthode selon l'invention, - on filtre le signal analogique directement représentatif de l'intensité du faisceau mesurée au moyen d'un filtre passe-bas, donnant un signal analogique filtré;According to one embodiment of the method according to the invention, - the analog signal is filtered directly representative of the intensity of the beam measured by means of a low-pass filter, giving a filtered analog signal;
- on échantillonne ledit signal filtré, et on compense le retard de phase introduit par le filtrage pour obtenir un signal digital.- Said filtered signal is sampled, and the phase delay introduced by the filtering is compensated for to obtain a digital signal.
[0022] Avantageusement, la correspondance entre une valeur pour l'alimentation du courant d'arc de la source d'ions et une valeur de l'intensité du faisceau mesurée à la sortie de l'accélérateur est déterminée préalablement à la régulation.Advantageously, the correspondence between a value for supplying the arc current of the ion source and a value of the intensity of the beam measured at the accelerator output is determined prior to regulation.
[0023] Avantageusement, dans la correspondance entre une valeur de l'intensité du faisceau mesurée à la sortie de l'accélérateur et une valeur pour l'alimentation du courant d'arc de la source d'ions, les valeurs de l'alimentation du courant d'arc correspondant aux valeurs d'intensité de faisceau supérieures à une limite sont remplacées par la valeur d'alimentation du courant d'arc correspondant cette limite.Advantageously, in the correspondence between a value of the intensity of the beam measured at the output of the accelerator and a value for the supply of the arc current of the ion source, the values of the supply of the arc current corresponding to the beam intensity values above a limit are replaced by the supply value of the arc current corresponding to this limit.
[0024] Enfin, la présente invention se rapporte également à l'utilisation du dispositif et de la méthode de l'invention en protonthérapie et en particulier dans les technique de "Pencil Beam Scanning" et de « double diffusion ».Finally, the present invention also relates to the use of the device and the method of the invention in proton therapy and in particular in the techniques of "Pencil Beam Scanning" and "double diffusion".
Brève description des figuresBrief description of the figures
[0025] La figure 1 représente un dispositif de régulation de l'intensité d'un faisceau extrait d'un accélérateur de particules suivant l'art antérieur.Figure 1 shows a device for regulating the intensity of a beam extracted from a particle accelerator according to the prior art.
[0026] La figure 2 représente la caractéristique du système, c'est-à-dire la correspondance entre une valeur 1^ pour l'alimentation du courant d'arc de la source d'ions et une valeur I„ de l'intensité du faisceau mesurée à la sortie de l'accélérateur.2 shows the characteristic of the system, that is to say the correspondence between a value 1 ^ for the supply of the arc current of the ion source and a value I „of the intensity of the beam measured at the output of the accelerator.
[0027] La figure 3 représente un mode de réalisation d'un dispositif de régulation de l'intensité d'un faisceau extrait d'un accélérateur de particules selon l'invention. [0028] La figure 4 représente un second mode de réalisation d'un dispositif de régulation de l'intensité d'un faisceau extrait d'un accélérateur de particules suivant 1 ' invention. Problèmes à la base de la présente invention [0029] En utilisant une régulation classique, par exemple PID, pour la mise en œuvre de la technique diteFIG. 3 shows an embodiment of a device for regulating the intensity of a beam extracted from a particle accelerator according to the invention. FIG. 4 shows a second embodiment of a device for regulating the intensity of a beam extracted from a particle accelerator according to the invention. Problems underlying the present invention [0029] Using conventional regulation, for example PID, for the implementation of the so-called technique
"pencil beam scanning" telle que décrite dans la publication O00/40064 de la Demanderesse, on est confronté aux problèmes décrits ci-après."pencil beam scanning" as described in publication O00 / 40064 of the Applicant, we are confronted with the problems described below.
[0030] Ainsi que le montre la figure 1, une valeur de consigne Ic de l'intensité du faisceau est fournie à un régulateur PID classique 10, qui détermine une valeur Ij^ du courant d'arc de la source d'ions 20. L'intensité du faisceau est mesurée au moyen d'une chambre d'ionisation 30, et le signal correspondant I est comparé à l'aide d'un comparateur "90 à la valeur de consigne le pour fournir un signal d'erreur ε. Selon la technique de balayage continu du faisceau, il est indispensable que l'intensité du faisceau varie de manière simultanée avec le déplacement, de manière à obtenir la conformité de la dose délivrée .As shown in Figure 1, a set value I c of the beam intensity is supplied to a conventional PID regulator 10, which determines a value I j ^ of the arc current of the ion source 20. The intensity of the beam is measured by means of an ionization chamber 30, and the corresponding signal I is compared with the aid of a comparator "90 to the reference value le to provide an error signal. According to the continuous beam scanning technique, it is essential that the intensity of the beam varies simultaneously with the displacement, so as to obtain the conformity of the delivered dose.
[0031] Un tel système présente les difficultés suivantes :Such a system presents the following difficulties:
- un temps mort pur important est dû au temps de parcours important d'une particule entre son émission par la source d'ions 20 et sa sortie de la machine;a large pure dead time is due to the long travel time of a particle between its emission by the ion source 20 and its exit from the machine;
- la caractéristique du système, liant l'intensité du faisceau extrait de l'accélérateur de particules I à l'intensité du courant d'arc de la source d'ions I est fortement non linéaire, ainsi que le montre la figure 2;- the characteristic of the system, linking the intensity of the beam extracted from the particle accelerator I to the intensity of the arc current of the ion source I is strongly non-linear, as shown in FIG. 2;
- de plus, cette caractéristique peut varier au cours du temps, ainsi que le montrent les courbes en trait interrompu de la figure 2. Cette variation peut survenir rapidement en raison du chauffage ou du refroidissement du filament de la source d'ions lors de sa mise en service. Elle peut également provenir du vieillissement du filament. Ces deux phénomènes conduisent à des variations de la caractéristique avec des constantes de temps très différentes; - le système est fortement bruité. L'intensité du faisceau généré par la source d'ions présente un bruit important, en particulier à la fréquence d'échantillonnage utilisée pour la mesure.- In addition, this characteristic can vary over time, as shown by the broken lines in Figure 2. This variation can occur quickly due to heating or cooling of the filament of the ion source during its setting service. It can also come from the aging of the filament. These two phenomena lead to variations in the characteristic with very different time constants; - the system is very noisy. The intensity of the beam generated by the ion source presents significant noise, in particular at the sampling frequency used for the measurement.
[0032] La régulation d'un tel système en utilisant les méthodes classiques de régulation telles que les techniques de feedforward, de feedback par action proportionnelle, intégrale et dérivée (PID) et de boucles en cascade a été évaluée. En raison du temps mort pur important, toutes ces méthodes donnent des réponses soit trop lentes, soit instables. Les méthodes classiques ne permettent pas non plus d'adresser le problème d'une caractéristique du système fluctuant en fonction du temps en utilisant une valeur moyenne des caractéristiques sur une période donnée, car les variations de gain d'une réponse à l'autre sont dans un rapport très important.The regulation of such a system using conventional methods of regulation such as feedforward techniques, proportional, integral and derivative action feedback (PID) and cascade loops was evaluated. Due to the significant pure dead time, all these methods give responses that are either too slow or unstable. The conventional methods also do not make it possible to address the problem of a characteristic of the system fluctuating as a function of time by using an average value of the characteristics over a given period, since the variations in gain from one response to another are in a very important report.
[0033] L'évolution de la caractéristique dépend de deux phénomènes bien découplés : le premier, de constante de temps brève, correspond au conditionnement de la source d'ions, c'est-à-dire à sa température. Le fonctionnement normal, continu ou intermittent à rapport cyclique élevé, chauffe la source d'ions rapidement. Ce temps d'établissement rapide en température pourrait permettre de travailler en boucle ouverte, c'est-à-dire sans tenir compte de la caractéristique réelle du système, en utilisant les méthodes classiques, pendant le temps de conditionnement. Cependant, ce compromis limite fortement l'utilisation d'une méthode classique en fonctionnement intermittent à rapport cyclique moyen, qui correspond souvent au mode de fonctionnement utilisé. [0034] Le second phénomène, de constante de temps plus longue, est dû au vieillissement du filament et de la source d'ions elle-même. Cette évolution plus lente de la caractéristique pourrait donc donner lieu à l'utilisation d'une caractéristique moyenne du système. L'utilisation d'une caractéristique moyenne conduit cependant à une régulation soit trop lente, soit instable.The evolution of the characteristic depends on two well-decoupled phenomena: the first, of short time constant, corresponds to the conditioning of the ion source, that is to say its temperature. Normal, continuous or intermittent high duty cycle operation heats the ion source quickly. This rapid establishment time in temperature could make it possible to work in an open loop, that is to say without taking account of the real characteristic of the system, using the conventional methods, during the conditioning time. However, this compromise greatly limits the use of a conventional method in intermittent operation with an average duty cycle, which often corresponds to the operating mode used. The second phenomenon, of a longer time constant, is due to the aging of the filament and of the ion source itself. This slower evolution of the characteristic could therefore give rise to the use of an average characteristic of the system. The use of an average characteristic however leads to a regulation which is either too slow or unstable.
[0035] Il apparaît donc comme évident que les méthodes classiques de régulation ne peuvent pas résoudre de manière satisfaisante les problèmes du contrôle d'un tel système, c'est-à-dire un temps mort pur largement supérieur à la constante de temps principale du système (environ 4 fois) et une caractéristique non-linéaire évolutive et nécessitant une méthode de régulation adaptative. [0036] La régulation rapide et précise de l'intensité du faisceau extrait d'un accélérateur de particules se heurte donc à de nombreuses difficultés . Une telle régulation rapide et précise est cependant importante pour l'application de la technique du « pencil beam scanning ».It therefore seems obvious that conventional methods of regulation cannot satisfactorily solve the problems of controlling such a system, that is to say a pure dead time much greater than the main time constant. of the system (about 4 times) and an evolving non-linear characteristic requiring an adaptive regulation method. The rapid and precise regulation of the intensity of the beam extracted from a particle accelerator therefore encounters many difficulties. Such rapid and precise regulation is however important for the application of the “pencil beam scanning” technique.
Description d'une forme d'exécution préférée de l'invention [0037] La présente invention se propose par conséquent de résoudre plus spécifiquement ce problême en utilisant selon une forme d'exécution préférée un dispositif de régulation 10 représenté à la figure 3 avec l'alimentation du courant d'arc de la source d'ions 20. La source d'ions produit un faisceau d'ions, qui est accéléré au cours de son parcours dans l'accélérateur, en est extrait, et traverse un dispositif de mesure 30 de l'intensité du faisceau à la sortie de l'accélérateur. Ce dispositif de mesure 30 peut être par exemple une chambre d' ionisation. [0038] Le régulateur suivant l'invention à été appliqué pour un cyclotron présentant les caractéristiques exemplatives et non limitatives suivantes :Description of a preferred embodiment of the invention The present invention therefore proposes to more specifically resolve this problem by using, according to a preferred embodiment, a regulating device 10 shown in FIG. 3 with the supply of the arc current from the ion source 20. The ion source produces an ion beam, which is accelerated during its journey in the accelerator, is extracted therefrom, and passes through a measuring device 30 of the beam intensity at the exit of the accelerator. This measuring device 30 can for example be an ionization chamber. The regulator according to the invention has been applied for a cyclotron having the following exemplary and non-limiting characteristics:
- énergie fixe: 235 MeV - temps mort pur : 60 μsec. Ce temps mort pur correspond au temps de parcours des ions dans l'accélérateur. Il correspond donc directement au temps nécessaire pour mesurer l'influence d'une modification de la consigne du courant d'arc de la source d'ions sur l'intensité du faisceau d'ions extraits de la machine- fixed energy: 235 MeV - pure dead time: 60 μsec. This pure dead time corresponds to the travel time of the ions in the accelerator. It therefore corresponds directly to the time necessary to measure the influence of a modification of the setpoint of the arc of the ion source on the intensity of the beam of ions extracted from the machine.
- constante de temps principale : 15 μs . Elle donne une indication sur le temps nécessaire à l'établissement, en boucle ouverte, de la réponse du système à une modification de consigne. - caractéristique du système fortement non-linéaire, ce qui conduit à une caractéristique en boucle ouverte correspondant quasiment à celle d'un système à dynamique hybride (tout ou rien) .- main time constant: 15 μs. It gives an indication of the time required to establish, in an open loop, the system's response to a setpoint modification. - characteristic of the strongly non-linear system, which leads to an open-loop characteristic corresponding almost to that of a system with hybrid dynamics (all or nothing).
- évolution de la caractéristique au cours du temps. - signal mesuré très bruité. En effet, la source d'ions est instable, ce qui conduit un niveau de bruit très important pour l'intensité du faisceau après extraction.- evolution of the characteristic over time. - very noisy measured signal. Indeed, the ion source is unstable, which leads to a very high noise level for the intensity of the beam after extraction.
Le rapport bruit/signal observé est de l'ordre de 150%.The noise / signal ratio observed is around 150%.
En conséquence, lors d'une mise en œuvre digitale du régulateur, les fréquences d'échantillonnages retenues engendrent un rapport signal / bruit très faible.Consequently, during a digital implementation of the regulator, the selected sampling frequencies generate a very low signal / noise ratio.
[0039] Dans le dispositif de régulation de l'invention, représenté à la figure 3, les étapes suivantes sont réalisées : — la valeur de consigne de l'intensité du faisceau Ic est fournie sous la forme d'un signal analogique 0-10 V (10 V correspondant à une intensité du faisceau de 300 nA) ; - l'intensité de faisceau est mesurée au moyen d'une chambre d'ionisation 30 et la mesure I„ M est fournie au dispositif de régulation 10 au moyen d'un signal analogique 0-15 μA (15 μA correspondant à une intensité du faisceau de 300 nA) ;In the regulating device of the invention, shown in FIG. 3, the following steps are carried out: - the set value of the intensity of the beam I c is supplied in the form of an analog signal 0- 10 V (10 V corresponding to a beam intensity of 300 nA); the beam intensity is measured by means of an ionization chamber 30 and the measurement I „M is supplied to the regulating device 10 by means of an analog signal 0-15 μA (15 μA corresponding to an intensity of the 300 nA beam);
- ce signal analogique I est converti par un convertisseur- this analog signal I is converted by a converter
50 en un signal digital I ;50 in a digital signal I;
- ce signal I est comparé par le comparateur à la consigne- this signal I is compared by the comparator to the setpoint
Ic pour fournir un signal d'erreur ε; - ce signal d'erreur ε est fourni au régulateur de type « Prédicteur de Smith » 80;I c to provide an error signal ε; this error signal ε is supplied to the regulator of the “Smith predictor” type 80;
- la sortie IP du prédicteur de Smith 80 est alors fournie à l'entrée d'une table de correspondance inversée 40. La table de correspondance 40 fournit de manière numérique la relation non-linéaire entre le courant d'arc de la source d'ions I A, et l'intensité du faisceau I.M, d'ions extrait de l'accélérateur. Elle permet donc d'identifier la caractéristique non linéaire du système. La sortie de la table de correspondance inversée est convertie en un signal analogique de type 4-20 mA I qui est fourni par le dispositif de régulation 10 comme valeur de consigne pour l'alimentation du courant d'arc de la source d'ions. [0040] Des simulations montrent qu'un tel dispositif permet une bonne .régulation. Il est cependant sensible aux perturbations basse fréquence. Pour résoudre ce problème, on a développé une variante préférée du dispositif suivant l'invention, représenté à la figure 4. Dans ce dispositif 10, on introduit dans la contre-réaction un filtre passe-bas 60 et un régulateur à avance de phase 70. Le filtre 60 est par exemple un filtre passe-bas du premier ordre . La fréquence de coupure est de 4,5 kHz . Afin de compenser le retard de phase introduit par le filtre, on utilise un régulateur à avance de phase 70 (dérivateur filtré), qui compense ce déphasage.- the output I P of the Smith predictor 80 is then supplied to the input of an inverted correspondence table 40. The correspondence table 40 numerically provides the non-linear relationship between the arc current of the source d IA ions, and the intensity of the IM beam, of ions extracted from the accelerator. It therefore makes it possible to identify the nonlinear characteristic of the system. The output of the inverted correspondence table is converted into an analog signal of the 4-20 mA I type which is supplied by the regulating device 10 as a set value for supplying the arc current of the ion source. Simulations show that such a device allows good regulation. It is however sensitive to low frequency disturbances. To solve this problem, a preferred variant of the device according to the invention, shown in FIG. 4, has been developed. In this device 10, a low-pass filter 60 and a phase advance regulator 70 are introduced into the feedback. The filter 60 is for example a first order low pass filter. The cutoff frequency is 4.5 kHz. In order to compensate for the phase delay introduced by the filter, use a phase advance regulator 70 (filtered differentiator), which compensates for this phase shift.
[0041] Tant le dispositif de la figure 3 que celui de la figure 4 comportent une table de correspondance inversée 40. Le contenu de cette table 40 est déterminé préalablement à chaque utilisation du dispositif de la manière suivante :Both the device of FIG. 3 and that of FIG. 4 include an inverted correspondence table 40. The content of this table 40 is determined prior to each use of the device in the following manner:
- le régulateur étant en boucle ouverte, la consigne du courant d'arc de la source d'ions 20 est portée progressivement de 0 à 20 mA sous la forme d'une rampe de 100 ms;- the regulator being in open loop, the setpoint of the arc current of the ion source 20 is gradually increased from 0 to 20 mA in the form of a ramp of 100 ms;
- l'intensité du faisceau est mesurée pour chacun des 4000 points échantillonnés; - la table obtenue est inversée, de manière à fournir une valeur correspondante du courant d'arc de la source d'ions I A, en fonction de l'intensité du faisceau IM„.- the intensity of the beam is measured for each of the 4000 points sampled; - The table obtained is inverted, so as to provide a corresponding value of the arc current of the ion source I A, as a function of the intensity of the beam IM „.
- Cette table inversée est chargée dans le dispositif de régulation 10. [0042] En pratique, cette opération est réalisée une douzaine de fois successivement. Ceci permet de s'assurer que les paramètres atteignent un palier, correspondant à la température de régime du filament. Afin d'éliminer le bruit, une moyenne des 4 dernières tables est calculée. Ces opérations, réalisées automatiquement, durent au maximum 1,5 s. Dans une variante de l'invention, les valeurs de I correspondant aux valeurs de I supérieures à une limite donnée sont remplacées par la valeur de I correspondant à cette limite. Les courbes de la figure 2 sont donc écrêtëes. Ceci est un élément de sécurité permettant de garantir que l'intensité du faisceau produit par l'accélérateur ne sera jamais supérieur à cette limite. [0043] Le dispositif suivant l'invention est réalisé au moyen d'une carte électronique qui fait appel aux technologies digitales de type DSP (Digital Signal Processing) . [0044] La synthèse du prédicteur de Smith à été réalisée dans le domaine de Laplace et la discrétisation est fournie par la transformée en Z par la méthode de correspondance pôles-zéros. Un sur-échantillonnage aurait été adéquat pour éviter tout problème lié à la discrétisation mais les technologies DSP du moment ne nous ont pas permis de monter au-delà de 100 kHz.This inverted table is loaded into the regulating device 10. In practice, this operation is carried out a dozen times successively. This ensures that the parameters reach a plateau, corresponding to the filament operating temperature. In order to eliminate the noise, an average of the last 4 tables is calculated. These operations, performed automatically, last a maximum of 1.5 s. In a variant of the invention, the values of I corresponding to the values of I greater than a given limit are replaced by the value of I corresponding to this limit. The curves in Figure 2 are therefore clipped. This is a safety feature to guarantee that the intensity of the beam produced by the accelerator will never exceed this limit. The device according to the invention is produced by means of an electronic card which uses digital technologies of the DSP (Digital Signal Processing) type. The synthesis of the Smith predictor was carried out in the Laplace domain and the discretization is provided by the Z transform by the pole-zero correspondence method. Oversampling would have been adequate to avoid any problem linked to discretization but the DSP technologies of the moment did not allow us to go beyond 100 kHz.
[0045] La méthode de régulation selon la présente invention présente plusieurs avantages. Tout d'abord, elle permet une adaptation commandée, c'est-à-dire qu'elle demande un temps de calcul très petit en comparaison des méthodes modernes du contrôle adaptatif et permet un changement de structure très facile puisque l'identification est faite par construction d'une table de correspondance qu'il suffit alors d'inverser numériquement pour linéariser la caractéristique du système vu par le régulateur principal .The method of regulation according to the present invention has several advantages. First of all, it allows a controlled adaptation, that is to say it requires a very small computation time in comparison with modern methods of adaptive control and allows a very easy change of structure since the identification is made by construction of a correspondence table which it then suffices to invert numerically to linearize the characteristic of the system seen by the main regulator.
[0046] En outre, elle offre une flexibilité importante puisqu'elle pourrait trouver sa place dans la régulation précise, reproductible, robuste et performante de toute source d'ions équipant un cyclotron et ce de par l'avantage d'une régulation de type adaptatif permettant la ré-identification de la caractéristique du système lorsque celle-ci évolue dans le temps. Elle permet donc l'identification et la régulation d'un autre accélérateur que le cyclotron C235 pour laquelle cette régulation à été développée à la base. In addition, it offers significant flexibility since it could find its place in precise, reproducible, robust and efficient regulation of any ion source equipping a cyclotron, and this by the advantage of type regulation. adaptive allowing the re-identification of the characteristic of the system when it evolves over time. It therefore allows the identification and regulation of another accelerator than the cyclotron C235 for which this regulation was originally developed.

Claims

REVENDICATIONS
1. Dispositif (10) de régulation de l'intensité du faisceau extrait d'un accélérateur de particules, tel qu'un cyclotron, utilisé par exemple pour la protonthérapie, lesdites particules étant générées à partir d'une source d'ions, caractérisé en ce qu'il comporte au moins :1. Device (10) for regulating the intensity of the beam extracted from a particle accelerator, such as a cyclotron, used for example for proton therapy, said particles being generated from an ion source, characterized in that it comprises at least:
- un comparateur (90) déterminant un écart ε entre un signal digital I représentatif de l'intensité du faisceau mesurée à la sortie de l'accélérateur et une valeur de consigne Ic de l'intensité du faisceau;- a comparator (90) determining a difference ε between a digital signal I representative of the intensity of the beam measured at the output of the accelerator and a reference value I c of the intensity of the beam;
- un prédicteur de Smith (80) , qui détermine, à partir de l'écart ε, une valeur corrigée de l'intensité de faisceau IP;- a Smith predictor (80), which determines, from the difference ε, a corrected value of the beam intensity I P ;
- une table de correspondance inversée (40) , fournissant, à partir de la valeur corrigée de l'intensité de faisceau IP, une valeur de consigne I pour l'alimentation du courant d'arc de la source d'ions (20) .- an inverted correspondence table (40), providing, from the corrected value of the beam intensity I P , a reference value I for supplying the arc current of the ion source (20) .
2. Dispositif selon la revendication 1, caractérisé en ce qu'il comprend en outre un convertisseur analogique-digital (50) convertissant le signal analogique I directement représentatif de l'intensité du faisceau mesuré à la sortie de l'accélérateur, et fournissant un signal digital I .2. Device according to claim 1, characterized in that it further comprises an analog-digital converter (50) converting the analog signal I directly representative of the intensity of the beam measured at the output of the accelerator, and providing a digital signal I.
3. Dispositif selon la revendication 1, caractérisé en ce qu'il comprend en outre :3. Device according to claim 1, characterized in that it further comprises:
- un filtre passe-bas (60) filtrant le signal analogique I directement représentatif de l'intensité du faisceau mesuré à la sortie de l'accélérateur, et fournissant un signal analogique filtré IF; - un régulateur à avance de phase (70) échantillonnant le signal analogique filtré IF, compensant le retard de phase introduit par le filtre passe-bas (60) , et fournissant un signal digital I„ au comparateur (90) . - a low-pass filter (60) filtering the analog signal I directly representative of the intensity of the beam measured at the output of the accelerator, and providing a filtered analog signal I F ; - a phase advance regulator (70) sampling the filtered analog signal I F , compensating for the phase delay introduced by the low-pass filter (60), and supplying a digital signal I „to the comparator (90).
4. Dispositif suivant l'une quelconque dès revendications précédentes, caractérisé en ce qu'il comporte des moyens de mise à jour du contenu de la table de correspondance inversée (40) .4. Device according to any one of the preceding claims, characterized in that it comprises means for updating the content of the inverted correspondence table (40).
5. Dispositif suivant l'une quelconque des revendications précédentes, caractérisé en ce que la fréquence d'échantillonnage est comprise entre 100 kHz et 200 kHz.5. Device according to any one of the preceding claims, characterized in that the sampling frequency is between 100 kHz and 200 kHz.
6. Dispositif suivant l'une quelconque des revendications 3 à 5, caractérisé en ce que la fréquence de coupure du filtre passe-bas (60) est comprise entre 2 et 6 kHz.6. Device according to any one of claims 3 to 5, characterized in that the cut-off frequency of the low-pass filter (60) is between 2 and 6 kHz.
7. Méthode de régulation, au moyen d'un dispositif de régulation digital (10) fonctionnant à une fréquence d'échantillonnage donnée, de l'intensité du faisceau extrait d'un accélérateur de particules, tel qu'un cyclotron, utilisé par exemple en protonthérapie, lesdites particules étant générées à partir d'une source d'ions7. Method of regulation, by means of a digital regulation device (10) operating at a given sampling frequency, of the intensity of the beam extracted from a particle accelerator, such as a cyclotron, used for example in proton therapy, said particles being generated from an ion source
(20), caractérisée en ce qu'elle comprend au moins les étapes suivantes : - on mesure l'intensité du faisceau (IM) à la sortie de l'accélérateur de particules;(20), characterized in that it comprises at least the following steps: - the intensity of the beam (I M ) is measured at the outlet of the particle accelerator;
- on compare au moyen d'un comparateur (90) un signal digital IR représentatif de la mesure de l'intensité du faisceau (IM) avec la valeur de consigne Ic de l'intensité du faisceau;- A digital signal I R representative of the measurement of the beam intensity (I M ) is compared by means of a comparator (90) with the set value I c of the beam intensity;
- on détermine, au moyen d'un prédicteur de Smith (80) , une valeur corrigée Ip de l'intensité de faisceau; - on détermine, à partir de la valeur corrigée IP de l'intensité de faisceau, au moyen d'une table de correspondance inversée (40) , une valeur de consigne I pour l'alimentation du courant d'arc de la source d'ions (20) .- a corrected value Ip of the beam intensity is determined, by means of a Smith predictor (80); - on the basis of the corrected value I P of the beam intensity, by means of an inverted correspondence table (40), a reference value I is determined for supplying the arc current from the source d 'ions (20).
8. Méthode de régulation selon la revendication 7, caractérisée en ce que, après la mesure de l'intensité du faisceau à la sortie de l'accélérateur de particules, on convertit le signal analogique I directement représentatif de l'intensité du faisceau mesurée au moyen d'un convertisseur analogique digital (50) pour obtenir un signal digital I R..8. A method of regulation according to claim 7, characterized in that, after measuring the intensity of the beam at the output of the particle accelerator, the analog signal I is converted directly representative of the intensity of the beam measured at by means of a digital analog converter (50) to obtain a digital signal I R ..
9. Méthode selon la revendication 7, caractérisée en ce que, après la mesure de l'intensité du faisceau à la sortie de l'accélérateur de particules :9. Method according to claim 7, characterized in that, after measuring the intensity of the beam at the outlet of the particle accelerator:
- on filtre le signal analogique I directement représentatif de l'intensité du faisceau mesurée au moyen d'un filtre passe-bas (60) , donnant un signal analogique filtré IF; - on échantillonne le signal filtré IF, et on compense le retard de phase à l'aide d'un régulateur à avance de phase (70) introduit par le filtrage pour obtenir un signal digital I R..the analog signal I is filtered directly representative of the intensity of the beam measured by means of a low-pass filter (60), giving a filtered analog signal I F ; - the filtered signal I F is sampled, and the phase delay is compensated for using a phase advance regulator (70) introduced by the filtering to obtain a digital signal I R ..
10. Méthode selon l'une quelconque des revendications 7 à 9, caractérisée en ce que la correspondance entre une valeur I pour 1 ' alimentation du courant d'arc de la source d'ions (20) et une valeur I de l'intensité du faisceau mesurée à la sortie de l'accélérateur est déterminée préalablement à la régulation.10. Method according to any one of claims 7 to 9, characterized in that the correspondence between an I value for the supply of the arc current from the ion source (20) and an I value of the intensity of the beam measured at the accelerator output is determined prior to regulation.
11. Méthode selon l'une quelconque des revendications 7 à 9, caractérisée en ce que, dans la correspondance entre une valeur I de l'intensité du faisceau mesurée à la sortie de l'accélérateur et une valeur I pour l'alimentation du courant d'arc de la source d'ions, les valeurs de I correspondant aux valeurs de I supérieures à une limite sont remplacées par la valeur de I correspondant cette limite.11. Method according to any one of claims 7 to 9, characterized in that, in the correspondence between a value I of the beam intensity measured at the output of the accelerator and a value I for the supply of the arc current of the ion source, the values of I corresponding to the values of I greater than a limit are replaced by the value of I corresponding to this limit.
12. Utilisation du dispositif selon l'une quelconque des revendications 1 à 6 en protonthérapie et en particulier dans les technique de "Pencil Beam Scanning" et de « double diffusion ».12. Use of the device according to any one of claims 1 to 6 in proton therapy and in particular in the techniques of "Pencil Beam Scanning" and "double diffusion".
13. Utilisation de la méthode de selon l'une quelconque des revendications 7 à 11 en protonthérapie et en particulier dans les techniques de "Pencil Beam Scanning" et de « double diffusion ». 13. Use of the method according to any one of claims 7 to 11 in proton therapy and in particular in the techniques of "Pencil Beam Scanning" and "double diffusion".
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US6873123B2 (en) 2005-03-29
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