Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J47/00—Tubes for determining the presence, intensity, density or energy of radiation or particles
  • H01J47/02—Ionisation chambers

Definitions

• the present invention relates to the field of online control of a beam. More particularly, the present invention relates to a device comprising a plurality of ionization chambers, for measuring the dose deposited by an ionizing beam and the field of this beam.
• the hadron therapy is a branch of radiotherapy, to accurately deliver a dose on a target volume, a tumor, while preserving the surrounding healthy tissue.
• a hadron therapy apparatus includes an accelerator producing a charged particle beam, a beam transport means, and an irradiation unit.
• the irradiation unit delivers a dose distribution to the target volume and generally comprises means for controlling the dose delivered.
• Two major modes of particle beam delivery are employed in hadron therapy: a first mode of delivery includes so-called passive beam scattering techniques and a second more elaborate mode of processing includes dynamic beam scanning techniques.
• Passive diffusion methods use an energy degrader that adjusts the path of the particles to the point of maximum depth of the region to be irradiated.
• the energy degrader is also used in combination with a modulation wheel and a patient-specific compensator and collimator to provide a dose distribution that best coincides with the target volume.
• a major flaw of this technique is that surrounding healthy tissues located upstream and outside the target volume may also be subjected to high doses of beams.
• the need to use a compensator and a collimator specific to the tumor of the patient and the angle of irradiation makes the procedure complicated and expensive.
• a dynamic beam delivery mode comprises the so-called "PBS" methods for Pencil Beam Scanning in which a thin beam of particles oriented along the z axis is scanned in a plane orthogonal to this z axis on the target volume by the medium of scanning magnets.
• PBS Pencil Beam Scanning
• By varying the energy of the particle beam different layers in the target volume can be irradiated successively. In this way, the radiation dose can be delivered over the entire target volume.
• a first method of the technique called “Pencil Beam Scanning” is a method called spot scanning.
• the irradiation of target volume layers is performed by the prescribed dose delivery of beam at discrete positions of that volume and interrupting the beam between each change of position.
• Another method of "Pencil Beam Scanning” is the so-called continuous scanning technique, where the beam is scanned continuously following a predefined figure.
• the intensity of the beam can vary at any time so as to deliver an accurate dose at the right place in the target volume, as specified in the treatment plan.
• the scanning speed can be adjusted instantaneously, so as to have an additional degree of freedom to modulate the intensity of the beam.
• Particle therapy or modulated intensity particle therapy.
• the specification of the treatment is carried out by advanced planning systems of processing using optimization algorithms to specify the number and directions of beam processing as well as the particle intensities to be delivered for each location in each layer to be irradiated.
• a dynamic technique is an irradiation technique that differs from PBS and is called a uniform scanning technique, in which a uniform dose is delivered to a target volume layer by layer, and where the beam is continuously scanned while taking the shape of a geometrical figure.
• the beam does not take the shape of the target volume contour, but it is scanned over a predefined geometric area and lateral compliance is achieved through a collimator with multiple blades or through a patient-specific aperture.
• the calibration of a hadron-therapy device is standardized and is carried out using a water phantom which mainly comprises a detector, generally an ionization chamber or a matrix of pixels, which can be moved or not. in a large container filled with water, water whose density and stopping power are similar to those of human tissues. This calibration is performed before the treatment and the treatment plan is performed based on this calibration.
• the ionization chambers are standard dosimetry detectors generally used in radiotherapy.
• An ionization chamber comprises a polarization electrode separated from an electrode collector by a gap or space comprising a fluid of any kind.
• the cylindrical ionization chambers comprise a central or axial electrode generally in the form of a very thin cylinder, isolated from a second hollow cylinder - shaped electrode or cap surrounding said central or axial electrode.
• the ionization chambers comprising parallel plates comprise a first plate supporting a polarization electrode, this first plate being separated from a second plate comprising one or more collector electrodes facing the polarization electrode.
• the plates are separated by a gap or space comprising a fluid of any kind.
• the perimeter of each collector or polarization electrode deposited on the plates is surrounded by an insulating resin, itself surrounded by a guard electrode.
• the fluid included in the gap or space between the collector and polarization electrodes of an ionization chamber used in dosimetry is most often a gas.
• ionizing beam passes through the ionization chamber, ionization of the gas between the electrodes occurs and ion-electron pairs are created.
• An electric field is generated by applying a potential difference between the two electrodes of the ionization chamber. The presence of an electric field makes it possible to separate these ion-electron pairs and to make them drift on the electrodes respective, inducing a current at these electrodes which will be detected and measured.
• Phys. Reas. A 519 (2004) 674-686 discloses an ionization chamber comprising a cathode 25ym thick composed of a sheet of mylar on which was deposited aluminum, and an anode being composed of a sheet of Vetronite of 100mm thickness sandwiched between two 35mm copper sheets each.
• the said anode is segmented into 32 X 32 pixels on one side and each pixel is connected by a via passing through the Vetronite sheet to a track located on the other side of the anode. Each track connects a pixel to a signal measuring device.
• this pixel ionization chamber has certain disadvantages, a first of which is mechanical instability.
• the distance between the two electrodes is defined by an external armature. Mechanical deformation or microphonic effect can significantly affect the distance between the two electrodes, affecting the accuracy and precision of the measurement. Another problem with this device is its lack of
• this kind of detector always induces a diffusion of the beam in an angular and longitudinal way, from where the necessity to be able to realize a detector as "transparent” as possible, in other words of which the thickness equivalent-water (WET) is minimal so not to degrade the properties of the beam.
• WET thickness equivalent-water
• the equivalent-water thickness of a portion of material m of thickness l m traversed by a given particle beam and given energy is defined as the thickness of water producing the same loss. beam energy than the material portion m thickness l m .
• the water-equivalent thickness of a material m of portion I m crossed by an energy beam is given by the following equation:
• p m is the density of the material m, in g / cm ;
• p w is the density of the water, in g / cm 3
• a minimization of the equivalent-water thickness for an ionization chamber can be obtained by reducing the thickness of the plates supporting the electrodes and by using for these materials of relatively low average atomic mass.
• a first problem that must be taken into account is the increase of the capacitance at the electrodes on the support sheet. Indeed, too large load differences between the two faces of the same sheet may cause a breakdown of the sheet.
• A the area of the plate, the electrode
• d the thickness of the plate, the electrode.
• a second problem is the presence of microphonic noise affecting the distance between the electrodes and reducing the accuracy and accuracy of the measurement.
• US 6,011,265 discloses a detector comprising a single ionization chamber comprising a plurality of support sheets arranged in parallel and separated from each other by a gap.
• the ionization chamber described comprises:
• a first support sheet comprising a DE electrode
• a second support sheet comprising a collection electrode CE consisting of a plurality of elementary anodes
• said support sheets being made of an insulating material and metallized on their two faces so as to form a first metal plating 11 and a second metal plating;
• said metallized carrier sheets comprising a plurality of perforated holes, all forming an electron multiplier;
• a second polarization means B2 adapted to create a polarization voltage between said first metal plating 11 and said second plating metal plating 12 to form at each hole an electric field condensing zone in which a condensed electric field is generated, said condensed electric field operating to generate from said photoelectron, considered as a primary electron, an electronic avalanche ;
• a third polarization means B3 adapted to create a polarization voltage which is applied to said collecting electrode CE to enable detection of said electronic avalanche.
• the detector described in US 6,011,265 may also comprise a second set of elementary anodes disposed on the second face of the second support sheet so as to form a two-dimensional detector.
• the beam control devices used are ionization chambers operating in a saturated state, so that the charge collection efficiency is maximum. . It is therefore appropriate to minimize charge recombination phenomena following the ionization of the gas present inside an ionization chamber that can impair the saturation of the chamber and therefore the accuracy of the measurement. It is therefore not permissible for this type of beam to use an ionization chamber in which the charges produced following the ionization of the gas as described in document US Pat. No. 6,011,265 are amplified. GOALS OF THE INVENTION
• An object of the present invention is to provide a dosimetry device comprising a set of ionization chambers for controlling the dose of a beam sent to a patient, the device not having the disadvantages of the devices. of the prior art.
• the object of the present invention is to minimize the equivalent-water thickness of a dosimetry device in order to deliver a dose on the patient that is as accurate and accurate as possible.
• An additional object of the present invention is to obtain a good detection dynamic, in particular by removing or reducing the intrinsic capacity of the support plates of the ionization chambers while reducing the thickness of these plates. support.
• An additional object of the present invention is to have a device whose collecting electrodes keep a uniformity of response over their entire surface by preventing the deformation of these support plates of thin thickness and subjected to a high electric field.
• An additional object of the present invention is to provide a device that can measure both accurately the dose deposited by a beam and the field of the same beam.
• An additional object of the present invention is to provide a "universal" device for measuring both the properties of a beam obtained by a passive delivery technique as a dynamic technique.
• the present invention relates to an on-line control device for an ionizing beam generated by a radiative source and delivered to a target, said device comprising a plurality of support sheets arranged in parallel and separated. from each other by an interval; said support sheets being positioned perpendicularly with respect to the central axis of the ionizing beam and forming a succession of ionization chambers of which at least one ionization chamber is made using support sheets having a thickness less than or equal to at 100m; each of the support sheets having on both sides one or more electrodes set at a potential such that the two faces of each of the support sheets have the same polarity; the carrier sheets being arranged such that the successive carrier sheets have alternating polarization; said device further having complementary means capable of balancing the electrostatic forces present inside the said ionization chamber made using carrier sheets having a thickness less than or equal to 100 mm.
• the at least one ionization chamber is made using support sheets having a thickness of less than 20 ⁇ m, preferably less than or equal to 15 ⁇ m, and even more preferably less than or equal to 10 m, still more preferably less than or equal to 5 m, still more preferably less than or equal to 1 m.
• the complementary means comprise a rigid plate, parallel and located in front of the support sheet comprising on each of its faces a collecting electrode and participating in the formation of the chamber of ionization carried out using support sheets having a thickness less than or equal to 100 m; the rigid plate further comprising at least one electrode set to a potential capable of balancing the electrostatic forces present inside the ionization chamber.
• the complementary means comprise a rigid or flexible plate, preferably flexible, parallel and located in front of the support sheet comprising on each of its faces a polarization electrode and participating in the formation of the ionization chamber carried out using support sheets having a thickness less than or equal to 100 ⁇ m; the rigid or flexible plate further comprising at least one electrode set to a potential suitable for balance the electrostatic forces present inside the ionization chamber.
• the intervals between each support sheet are constant.
• At least one of the support sheets having a thickness less than or equal to 100 m comprises at least one of its faces an electrode, preferably a collector, connected to a measurement electronics by a track on the same side of the carrier sheet as that comprising said support foil electrode is prejudicially affected.
• the device according to the invention comprises support sheets having collector electrodes alternately on their faces with support sheets having polarization electrodes on both sides thereof.
• each collecting electrode is connected to a measurement electronics by a track located on the same face of the support sheet as that comprising said collector electrode.
• certain collecting electrodes take the form of strips arranged in parallel manner.
• the invention relates to a device for the measurement of ionizing beams, the device comprising a support sheet having two faces and having a thickness less than or equal to 100 m, preferably less than 100 .mu.m. 20 ⁇ m, still more preferably less than or equal to 15 ⁇ m, still more preferably less than or equal to 10 ⁇ m, still more preferably less than or equal to 5 ⁇ m, still more preferably less than or equal to 1 ⁇ m; the support sheet comprising on at least one of the faces an electrode, preferably a collector, connected to a measurement electronics by a track situated on the same face of the support sheet as that comprising the electrode.
• the electrode takes the form of a disc whose perimeter is separated by a gap or an insulating resin of a guard layer which extends over the rest of the support foil, and the disk-shaped electrode is connected to a measurement electronics by a track located on the same face of said support foil as the face comprising the disk-shaped electrode, the track being coated with an insulating resin, and the insulating resin is covered by a thin layer of conductive material which extends over the guard layer.
• the invention relates to a method for the on-line control of an ionizing beam generated by a radiative source and delivered to a target, the method comprising the steps of:
• the at least one ionization chamber is made using support sheets having a thickness of less than 20 ⁇ m, preferably less than or equal to 15 ⁇ m, and even more preferably less than or equal to 10 m, still more preferably less than or equal to 5 m, still more preferably less than or equal to 1 m.
• At least one of the support sheets having a thickness less than or equal to 100 ⁇ m comprises at least one of its faces an electrode, preferably a collector, connected to a measurement electronics by a track located on the same face of the support sheet as that comprising said electrode, so as to. the mechanical stability of the support sheet is prejudicially affected.
• the complementary means comprise a rigid or flexible plate comprising at least one electrode set to a potential able to balance the electrostatic forces present inside said ionization chamber.
• the balancing step further comprises the application of a suitable voltage on the support sheets.
• the invention relates to the use of the device as described above for the online control of particle beams obtained by passive delivery techniques.
• the invention relates to the use of the device as described above for the online control of particle beams obtained by dynamic delivery techniques.
• FIG. 1 represents a first embodiment of the invention comprising one or two integral ionization chambers according to whether one of the support sheets situated at the end is flexible or rigid.
• FIG. 2 represents a face of a support sheet comprising a collector electrode connected to a measurement electronics.
• FIG. 3 shows a face of a support sheet comprising a disc-shaped collecting electrode connected to a measurement electronics.
• FIG. 4 shows a second embodiment of the invention in which all the carrier sheets are flexible.
• FIG. 5 shows a third embodiment of the invention comprising two integral ionization chambers and two band ionization chambers.
• FIG. 6 shows a fourth embodiment of the invention comprising two pairs of integral ion chambers and two pairs of band ionization chambers.
• FIG. 7 represents a fifth embodiment of the invention comprising integral ionization chambers, band ionization chambers, and two reference ionization chambers.
• FIG. 8 shows a sixth embodiment of the invention comprising integral ionization chambers, band ionization chambers, reference ionisation chambers and ionization chambers comprising disc-shaped collecting electrodes.
• FIG. 9 shows a seventh embodiment comprising two reference ionization chambers surrounded by two sets of ionization chambers, located on each side of these reference ionization chambers, a first set of ionization chambers comprising band ionization chambers and integral ionization chambers, a second assembly comprising band ionization chambers and ionization chambers comprising disk - shaped collecting electrodes.
• FIG. 1 represents the dosimetry device of the present invention comprising at least two ionization chambers comprising at least two flexible sheets supporting one or more electrodes and called “support sheets" 10, made of a material of low density, of atomic mass average less than 20, having good flexibility and good resistance to irradiation, such as biaxially oriented polyethylene terephthalate, better known as mylar, or poly (4,4'-oxydiphenylene-pyromellitimide) , more commonly known as kapton, these materials in no way constituting a limitation of the present invention
• the at least two support sheets have a thickness of between one micrometer and one millimeter, more preferably between one micrometer and one micrometer. the hundred micrometer, more preferably between one micrometer and twenty micrometers.
• At least two support sheets 10, 20 forming a first ionization chamber are covered on both sides with a layer of conductive material acting as an electrode.
• said conductive material is deposited on the support sheet by a deposition technique, so as to obtain a layer of conductive material between one nanometer and one micron, preferably between 100 nanometers and one micron, preferably between 100 and 500 nanometers.
• said conductive material is a metal or graphite, more preferably a metal.
• the support sheets of the present invention have the advantage of producing less diffusion and alteration of the properties of the beam. Nevertheless, the reduction of the thickness of the support sheets with respect to those commonly used in the state of the art results in the appearance of new problems, a first problem being the location of the track bringing the signal back to a device secondly, a second problem is a large capacitive effect on the sheets and a third problem is the vibration of the sheets when subjected to an electric potential.
• a collector electrode is connected to a track via a via passing an insulating layer disposed between the surface of the electrode and the support plate, said track returning the signal to a measuring device.
• Fig. 2 shows a carrier sheet of the present invention comprising a collector electrode 11 for a beam measurement delivered by a dynamic technique, this type of electrode being called an "electrode integral collector ", said collector electrode 11 being connected to a measurement electronics 9 by a track 13 located on the same face of the support sheet as the electrode 11.
• the said track is deposited on each support sheet using the same deposit technique as that used for electrode deposition.
• each collecting electrode and the track connecting it to the measuring apparatus is separated from a guard layer 12 by a vacuum 14 or an insulating resin 14 surrounding the perimeter of the collecting electrode.
• Fig. 3 shows a carrier sheet comprising a disk-shaped electrode for measuring a beam delivered by a passive technique.
• the track of this collecting electrode must not be exposed to the beam, otherwise it will provide a measurement dependent on the field of this beam, this track is covered with a thin layer of insulating resin, itself covered with a thin layer conductive material extending over the guard layer.
• the capacitance of a capacitor is directly proportional to the area of the capacitor and inversely proportional to the distance separating the plates of the capacitor.
• a support sheet comprising a collector electrode on one side and a bias electrode on its other side can be likened to a capacitor.
• the risk of breakdown thereof is very high. .
• the breakdown of a sheet is a discharge occurring between the two isolated plates of capacitor when too many charges have accumulated on one side of this capacitor, the discharge damaging the insulating layer of the capacitor.
• Each support sheet 10, 20 comprises on both sides an electrode having the same polarization.
• a first support sheet 10 comprises on both sides a collector electrode 11, 15 preferably having a polarization close to that of the mass.
• the two faces of a second support sheet 20 each comprise a biasing electrode 21, 22 preferably connected by a track to a generator set to a positive or negative potential.
• Each track connecting a bias electrode to the generator is located on the same side of the carrier sheet as said bias electrode.
• Each support sheet 10, 20 is maintained in a support, for example, a support made of epoxy resin, said support ensuring good mechanical tension and good insulation of each support sheet.
• the two support sheets are fixed so that a gap is created between these two ci.
• the support comprises, for example, high electrical resistance spacers, the dimensions of which are calibrated with very small tolerances. High precision on the gaps separating the support sheets must be guaranteed because the field and therefore the electrostatic force depend on the applied voltage and the distance between each support sheet.
• the realization of a detector comprising flexible support sheets and of relatively thin thickness must also take into account the microphonic effect.
• the difference in potential created between two support sheets as fine as those of the present invention has the effect of curling and / or vibrating these support sheets which alters the detection of the charges created by the ionization of the gas between the two support sheets traversed by a beam since the gap between these two support sheets varies continuously.
• the external noise also produces the microphonic effect on such an ionization chamber, so the device must also minimize the contribution of the external noise.
• two plates or sheets 16, 18 are located on either side of the ionization chamber 1 formed by the two leaves 10, 20. These two plates or sheets 16, 18 comprise electrodes 17, 19 set at a potential chosen in such a way as to create an electrostatic force F E 2 which is balanced with the electrostatic force F E i created by the polarization support sheets 10, 20 of the ionization chamber 1.
• a first plate 16, preferably rigid, is located face and parallel to the collector electrode 15 located towards the outside of the ionization chamber 1.
• This plate 16 comprises an electrode 17 which is set to a potential chosen to balance the electrostatic force F E is' exerting on the support sheet 10 and resulting from the electric field created by the difference in polarity between the collector electrode 11 and the bias electrode 21 located towards the inside of the Ionization chamber 1.
• the gap separating the electrode 17 included on the first plate 16 of the electrode 15 included on the support sheet 10 is identical to the gap separating the collecting electrode 11 and the polarization electrode 21 included in FIG. Inside the ionization chamber 1. More preferably, the voltage applied to the electrode 17 of the plate 16 is equal to that applied to the polarization electrodes 21, 22 of the support sheet 20.
• a second plate 18, rigid or not, is located face and parallel to the support sheet 20 comprising the polarization electrodes
• This second plate 18 comprises an electrode 19 set to a potential chosen so as to balance the electric force FE1 created by the polarization of the electrodes 21, 22 of the support plate 20. It is not necessary that this second plate 18 is rigid if the electrode 19 included on this plate 18 is not a collecting electrode, this electrode 19 with the electrode 22 thus not forming an ionization chamber.
• the support sheet 10 comprising on both sides a collector electrode 11, 15, charges created by the ionization of the gas by the beam are collected on both sides of this sheet. Differences in the charges on each plate of the same sheet may result in a slight capacitive effect that may interfere with the measurement time at the measurement electronics.
• the electrical signal produced at the two collecting electrodes 11, 15 and resulting from the ionization of the gas is preferably physically summed before being sent to the measurement electronics.
• the support sheet 10 comprising the two collecting electrodes 11, 15 located on each side of this same sheet is therefore common to two ionization chambers, a first ionization chamber 1 being formed by the two support sheets 10, 20 and a second ionization chamber 2 being formed by the support sheet 10 comprising the collecting electrodes and the rigid plate 16. It is therefore preferable, in this case, that said ionization chambers 1, 2 have the same gap. This is why the plate 16, located facing the collecting electrode 15 of the support sheet 10 is a rigid plate, thus reducing the microphonic effects and ensuring a constant gap in the two ionization chambers 1, 2 necessary for a exact measurement and precise dose.
• FIG. 4 shows an embodiment of the invention in which the rigid plate 16 has been replaced by a support sheet 30, a polarization electrode of which is present on its two faces, this support sheet being preferably identical to the support sheet 20 comprising a bias electrode on both sides thereof.
• a set of two ionization chambers 1, 2 comprising a collector electrode common to these two ionization chambers and collecting the same quantity of charges.
• Two sheets 18, 40 respectively comprise electrodes 19 and 41 preferably set to a potential identical to or close to that of the collecting electrodes.
• These sheets 18, 40 are located on either side of said set of ionization chambers, and their electrodes create a balancing electrostatic force F E2 opposite to the electrostatic forces F E 'exerting on the support sheets 10, 30 comprising bias electrodes set for example at a negative potential.
• the sheets 18, 40 located on either side of said set of ionization chambers 1, 2 need not be rigid since no charge is collected in the space formed by these sheets 18,
• the signals collected on the collecting electrode of the ionization chamber 1 and 2 are summed and sent to a measurement electronics, for example a charge integrator.
• FIG. 5 represents another mode of embodiment of the present invention dedicated to the technique called "Pencil beam scanning".
• the device comprises an ionization chamber assembly parallel to each other, each ionization chamber comprising a thin flexible support sheet on which is deposited by a method of evaporation a thin layer of conductive material serving as collector electrode or polarization.
• Two support sheets 40, 18 on which are deposited by a method of evaporation of the electrodes are preferably grounded and located parallel on either side of said set of ionization chambers.
• the ionization chamber assembly comprises two subsets of ionization chambers.
• a first subset of ionization chambers comprises two integral ionization chambers 203, 204 measuring the dose deposited by the beam. This first subset of ionization chambers comprises:
• a first support sheet 105 comprising on both its faces a polarization electrode
• a second carrier sheet 104 comprising on both sides a collector electrode, this carrier sheet being common to the two ionization chambers 203, 204 of the first subset of ionization chambers, the collector electrode covering at least 90% of the support sheet, being surrounded by a guard electrode and whose structure is that shown in Figure 2; a third support sheet 103 comprising on both its faces a polarization electrode, this support sheet being common with the ionisation chamber 203 of the first subassembly of ionization chambers and with one of the ionization chambers 202 of the second subset of ionization chambers.
• a second subset of two ionization chambers 201, 202 comprises:
• a second carrier sheet 102 on which band-shaped collecting electrodes surrounded by a guard layer separated from these electrodes by an insulating material is deposited, so as to measure the beam field, each band of one side of the carrier sheet being connected to a measurement electronics by a track located on the same face of said second carrier sheet.
• a third support sheet 101 comprising on both its faces a polarization electrode.
• the first subset of ionization chambers 203, 204 is adjacent to the second subset of ionization chambers 201, 202, an ionization chamber 203 of the first subassembly having a support sheet 103. common with an ionization chamber 202 of the second subset of ionization chambers.
• the first subset of ionization chambers comprises two integral ionization chambers 203, 204, formed by a support sheet
• a polarization electrode comprising on each face a polarization electrode, and a support sheet 104 common to the two ionization chambers 203, 204, the sheet of support 104 comprising a collector electrode on each side.
• the set of ionization chambers of the device of the present invention comprises a third and a fourth subset of ionization chambers, as shown in FIG. 6.
• the integral ionization chambers 203, 204, 205, 206 are located inwardly of the device while the ionization chambers 201, 202, 207, 208, including band-shaped electrodes are located towards the ends of the device. This arrangement makes it possible to have a stable and precise signal in the integral ionization chambers 203, 204, 205, 206 measuring the dose deposited by the beam.
• a carrier sheet comprising a collector or non-collector electrode and grounded on each side is alternated with a carrier sheet comprising a bias electrode on each face.
• FIG. 6 shows two subsets of two adjacent integral ionization chambers 203, 204, 205, 206, of which:
• a support sheet 104 is common to two ionization chambers 203, 204 and each of its two faces comprises a collector electrode;
• a support sheet 105 is common to two ionization chambers 204, 205 and each of its two faces comprises a polarization electrode
• a support sheet 106 is common to two ionization chambers 205, 206 and each of its two faces comprises a collector electrode;
• An ionization chamber 202 of this subassembly is located adjacent to an integral ionization chamber 203, and has in common with this ionization chamber 202 a support sheet 103 comprising a polarization electrode on each of its two surfaces.
• a second subset of two ionization chambers 207, 208 has in common a support sheet 108 comprising band-shaped collecting electrodes on each of its two surfaces. For the sake of clarity, only two measuring electronics devices connected to the electrodes are shown.
• An ionization chamber 207 of this subassembly is located adjacent to an integral ionization chamber 206, and has in common with this ionization chamber 206 a support sheet 107 comprising a polarization electrode on each of its two surfaces.
• a support sheet 18, 40 comprising an electrode facing the biasing electrodes located outwardly of the ionization chambers 201, 208 located at the ends of the ionization chamber assembly, allows the balancing of the forces electric due to the polarization of the electrodes 101, 103, 105, 107, 109 and contributes to the stabilization of the support sheets of each ionization chamber of the assembly.
• An additional subset of two ionization chambers 301, 302 can be inserted into said set of ionization chambers, as shown in FIG. 7.
• this subset of ionization chambers 301, 302 is disposed in the middle of the device, between the two subsets of integral ion chambers 203, 204, and 205, 206.
• This additional subset of chambers of Ionisation 301, 302 comprises a support sheet on which is deposited on both sides of its surface an electrode balancing the electrostatic fields inside the device and which can be used as collecting electrodes to provide a reference signal during a measurement in a water phantom, a non-swept beam which we would like to intercept the totality of the flow of particles during the measurement in the said phantom.
• a reference chamber In the case of a conventional measurement in a water phantom, it is difficult to position a reference chamber in a stream of particles without disturbing the measurement thereof. With one or more reference chambers in the device, such a measurement is no longer disturbed.
• the first subset of ionization chambers 201, 202 traversed by the beam and located at the entrance of the device comprises collecting electrodes in the form of strips oriented along an axis x orthogonal to the beam axis.
• the last subset of ionization chambers 207, 208 traversed by the beam comprises collector electrodes in the form of strips oriented along an axis y orthogonal to the axis of the beam as well as to said x-axis.
• This device can be placed at the output of an irradiation unit and slightly disturbs the properties of the beam by its low equivalent-water thickness, minimizing the effects of diffusion angularly and longitudinally.
• the equivalent-water thickness of a detector of the present invention can be calculated by considering the last example of FIG. 6 comprising 13 support sheets made of bi-oriented polyethylene terephthalate (mylar) of for example 2.5 ⁇ m thick and covered on both sides with a thin layer of gold or aluminum, for example 200 nm thick, each support sheet being separated from one another by an air gap of for example 5 mm.
• the various parameters of this example are shown in Table 1 for a beam of 200 MeV crossing this example device.
• This exemplary embodiment of the invention comprises 13 mylar sheets, 26 gold layers and 12 air gaps.
• the thicknesses of the different materials are given by way of example only, other thicknesses as well as other materials that can be selected for carrying out the present invention. Also, some carrier sheets may differ from one another with respect to the thickness and materials chosen.
• a device for measuring the field and the dose of a beam obtained by a so-called passive delivery technique can be achieved by taking up the same structure as one of the devices described in the previous embodiments, and by replacing the integral ionization chambers, the collecting electrodes of which cover almost the entire surface of the support sheets, by ionization chambers whose collecting electrodes included on the support sheets are disk-shaped.
• FIG. 8 shows another embodiment of the present invention allowing the dosimetry of particle beams obtained by dynamic techniques as well as the dosimetry of beams obtained by passive techniques.
• This embodiment shown in FIG. 8 comprises both integral ionization chambers 203, 204, 205, 206 and ionization chambers 401, 402, 403,
• two subsets of two integral ionization chambers and two subsets of two disk-shaped collecting electrode ionization chambers are disposed towards the middle of the device, for example symmetrically with respect to a set of two reference ion chambers 301, 302.
• Such a device may comprise a set of fourteen ionization chambers also counting ionization chambers 201, 202, 207, 208 including band-shaped electrodes.
• the device also comprises two support sheets 18, 40 located on either side of this set of ionization chambers and allowing equilibrium of the electrostatic forces and the stabilization of the distances between each support sheet.
• each electrode collector on a support sheet of an integral ionization chamber and a reduced-size electrode ionization chamber is connected to a measurement electronics of its own.
• An embodiment of the present invention is shown in Figure 9 and includes:
• first ionization chambers 201, 202 comprising strip-shaped collecting electrodes, these ionization chambers being formed by:
• a first support sheet 101 comprising on its two surfaces a polarization electrode, each electrode being connected to a voltage generator HV2; a second support sheet 102 facing the first support sheet 101 and having on its two surfaces band-shaped collecting electrodes arranged identically on both sides, each band of one face and each band of the the other side of the face of the support sheet being connected to the same measurement electronics;
• a third carrier sheet 103 facing the second carrier sheet 102 and having on both surfaces a bias electrode, each electrode being connected to a voltage generator HV2;
• a third ionization chamber 501 formed by:
• a fourth carrier sheet 119 facing the third carrier sheet 103 and having on the side facing the carrier sheet 103 an integral collecting electrode connected to a measurement electronics of its own;
• a fifth support sheet 120 facing the fourth support sheet 119 and comprising on its two surfaces a bias electrode connected to a voltage generator HV3
• the fourth support sheet 119 comprising on the side facing the fifth support sheet 120, an integral collecting electrode connected to a measurement electronics which is specific thereto;
• said fifth support sheet 120 a sixth support sheet 111 located opposite the fifth support sheet 120 and comprising on its two surfaces a collecting electrode;
• a seventh support sheet 121 facing the sixth support sheet 111 and comprising on its two surfaces a polarization electrode connected to a high voltage generator HV2;
• An eighth ionization chamber 504 formed by:
• a ninth support sheet 123 facing the eighth support sheet 122 and comprising on its two surfaces a polarization electrode
• said eighth support sheet 122 comprising a disk-shaped collecting electrode surrounded by a guard, the electrode being connected to a measuring electronics of its own by a track covered with an insulating resin, the electrode facing said ninth support sheet;
• a ninth and tenth ionization chamber 207, 8 comprising band-shaped electrodes, these ionization chambers being formed by:
• said ninth support sheet 123 comprising on both surfaces a bias electrode, each electrode being connected to a voltage generator HV3;
• a tenth support sheet 108 located opposite the ninth support sheet 123 and comprising on its two surfaces strip-shaped collecting electrodes arranged identically on both sides, each strip of a face of the support sheet and its opposite strip on the other side of the surface of the support sheet being connected to the same measurement electronics;
• an eleventh support sheet 109 located opposite the tenth support sheet 108 and comprising on its two surfaces a biasing electrode, each electrode being connected to a voltage generator HV3.
• the set of these ionization chambers is comprised between two support sheets 40, 18, each comprising an electrode preferably set to the same potential as the collecting electrodes and located facing the support sheets of the first and tenth ionization chambers. .
• This embodiment therefore comprises in all thirteen support plates and has a water-equivalent thickness of 0.014cm for a device measuring about 6cm and can be used for measuring the dose and the field of different types of beam.
• this embodiment of the present invention includes two high voltage generators. HV2, HV3 connected to the polarization electrodes as described above, in order to have a redundancy of the ionization chambers, and to ensure a measurement of the dose in case of a problem of one of the two generators or in case breakdown of one of the carrier sheets comprising a bias electrode.

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• Radiation-Therapy Devices (AREA)

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• 2010
  • 2010-09-30 EP EP10768204A patent/EP2483908A1/fr not_active Withdrawn
  • 2010-09-30 US US13/499,634 patent/US20120310030A1/en not_active Abandoned
  • 2010-09-30 KR KR1020127011206A patent/KR20120105440A/ko not_active Application Discontinuation
  • 2010-09-30 CN CN2010800544797A patent/CN102782799A/zh active Pending
  • 2010-09-30 WO PCT/EP2010/064601 patent/WO2011039330A1/fr active Application Filing
  • 2010-09-30 JP JP2012531435A patent/JP2013506823A/ja active Pending

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