The present invention relates to the field of online beam monitoring. More particularly, the present invention concerns a device comprising several ionisation chambers allowing the measurement of the dose deposited by an ionising beam and the field of this beam.
Hadron-therapy is a branch of radiotherapy allowing the delivery with precision of a dose onto a target volume, a tumour, whilst preserving the surrounding healthy tissues. Hadron-therapy apparatus comprises an accelerator producing a beam of charged particles, means for transporting the beam and a radiation unit. The radiation unit delivers a dose distribution to the target volume and generally comprises means for monitoring the delivered dose. Two major modes for delivering beams of particles are used in hadron-therapy: one first delivery mode comprises so-called passive beam scattering techniques and a second more elaborate treatment mode comprises dynamic beam scanning techniques.
The passive scattering methods have recourse to an energy degrader adjusting the pathway of the particles as far as a maximum depth point of the region to be irradiated. The energy degrader is also used in combination with a range shifter wheel, a compensator and a patient-specific collimator allowing a dose distribution to be obtained which best coincides with the target volume. One major defect of this technique is that the neighbouring healthy tissues located upstream and outside the target volume may also be subjected to high beam doses. In addition, the need to use a compensator and a collimator specific to the patient's tumour and to the angle of irradiation makes this procedure complicated and costly.
One mode for delivering a dynamic beam comprises the so-called “PBS” methods (Pencil Beam Scanning) in which a narrow beam of particles oriented along axis z is scanned over a plane orthogonal to this axis z over the target volume by means of scanning magnets. By causing the energy of the beam of particles to vary, different layers in the target volume can be successively irradiated. In this manner the radiation dose can be delivered over the entirety of the target volume.
One first method of the so-called Pencil Beam Scanning technique is a method called spot scanning. With this method, the irradiation of layers of target volume is obtained by delivering a prescribed beam dose to discrete positions of this volume and interrupting the beam between each change of position.
Another Pencil Beam Scanning method is the so-called continuous scanning technique in which the beam is scanned continuously following a predefined pattern. During the scanning of a layer, the intensity of the beam may vary at every instant so as to deliver a precise dose at the right place in the target volume, such as specified in the treatment plan. In other more advanced beam delivery techniques, the scanning rate can be adjusted instant by instant, so as to have an additional degree of freedom to modulate the intensity of the beam.
With the PBS technique not only homogeneous distribution doses but also non-homogeneous doses can be delivered to a target volume. Typically, a combination of several treatments with beams from different directions is necessary to produce a “tailored” radiation dose which maximizes the dose in the target volume whilst protecting neighbouring healthy tissues. Although a three-dimensional dose distribution in the target volume resulting from radiation in a single direction may not be uniform, provision is made so that the contribution of each radiation in several directions produces a uniform dose in the target volume. A treatment which delivers beams depositing non-homogeneous doses in which integration of each beam contribution allows a homogeneous dose to be obtained in a target volume is called Intensity Modulated Particle Therapy (IMPT). The specification of the treatment is prepared by advanced treatment planning systems using optimisation algorithms to specify the number and the directions of beam treatments and the particle intensities to be delivered to each point in each layer to be irradiated.
Another example of a dynamic technique is a radiation technique which 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 in which the beam is continuously scanned assuming the form of a geometric pattern. The beam does not assume the shape of the contour of the target volume but is scanned over a predefined geometric surface area and lateral conformity is obtained by means of a collimator comprising several plates or by means of a patient-specific aperture.
Through the complexity of these different techniques, the verification of the dose sent to the patient is a crucial point. The calibration of hadron-therapy apparatus is standardized and is made using a water phantom which chiefly comprises a detector, generally an ionisation chamber or an array of pixels, which may or may not be able to be moved in a large container filled with water, the density and stopping power of water being similar to those of human tissues. This calibration is performed before treatment and the treatment plan is prepared on the basis of this calibration.
Ionisation chambers are standard dosimetry detectors generally used in radiotherapy. An ionisation chamber comprises a polarisation electrode separated from a collecting electrode by a gap comprising a fluid of any type.
There are several types of ionisation chambers such as so-called cylindrical ionisation chambers and ionisation chambers comprising parallel plates. Cylindrical ionisation chambers comprise a central or axial electrode generally in the form of a very thin cylinder insulated from a second electrode of hollow cylindrical shape or cap-shaped surrounding the said central or axial electrode. Ionisation chambers comprising parallel plates have a first plate supporting a polarisation electrode, this first plate being separated from a second plate comprising one or more collecting electrodes located opposite the polarisation electrode. The plates are separated by a gap comprising a fluid of any type. The perimeter of each collecting or polarisation electrode deposited on the plates is surrounded by an insulating resin itself surrounded by a guard electrode.
The fluid contained in the gap separating the collecting and polarisation electrodes of an ionisation chamber used in dosimetry is most often a gas. When an ionising beam passes through the ionisation chamber, the gas contained between the electrodes is ionised and ion-electron pairs are formed. An electric field is generated by applying a potential difference between the two electrodes of the ionisation chamber. The presence of an electric field allows these ion-electron pairs to be separated causing them to drift onto the respective electrodes, thereby inducing a current at these electrodes which will be detected and measured.
During treatment, it is also essential to monitor the dose delivered to the patient ensuring that it corresponds to the dose prescribed in the treatment plan, for example by means of an ionisation chamber. It must also be possible to detect any deviation of the beam. The document: “A pixel chamber to monitor the beam performances in hadron therapy”, R. Bonin et al., Nucl. Instr. & Methods in Phys. Reas. A 519 (2004) 674-686, describes an ionisation chamber comprising a cathode 25 μm thick composed of a mylar film on which aluminium has been deposited, and an anode composed of a Vetronite film of thickness 100 μm sandwiched between two films of copper each 35 μm thick. Using the PCB technique, the said anode is segmented into 32×32 pixels on one side and each pixel is connected by a via passing through the Vetronite film to a conductive trace located on the other side of the anode. Each trace connects a pixel to a signal measuring device. However, this pixel ionisation chamber has some shortcomings of which the first is mechanical instability. The distance between the two electrodes is defined by an external armature. Mechanical deformation or a microphonic effect may affect the distance between the two electrodes significantly, thereby affecting the accuracy and precision of measurement. Another problem with this device is its lack of <<transparency>> with respect to a beam. The non-negligible thickness of copper present on the anode induces beam scattering.
Document WO 2006126084 partly solves these problems by replacing the copper layers forming each pixel by graphite layers. Also an intermediate layer pierced with holes surrounding each pixel is provided between the anode and the cathode thereby forming a plurality of chambers. Attachment points fix the intermediate layer to the anode and cathode so as to allow air to pass and to stabilize the distance between the anode and the cathode.
Nonetheless, this type of detector always induces angular and longitudinal beam scattering, hence the need for the possible providing of a detector the most <<transparent>> possible, in other words whose water equivalent thickness (WET) is minimal so as not to degrade the properties of the beam.
In general, the water equivalent thickness of a portion of material m of thickness lm through which there passes a given beam of particles of given energy is defined as the water thickness producing the same loss of energy of the beam as the portion of material m of thickness lm. The water equivalent thickness of a material m of portion lm through which an energy beam is passed is given by the following equation:
Where:
pm is the density of the material m, in g/cm3;
pw is the density of water, in g/cm3;
lm is the thickness of the material, in cm;
is the stopping power of the material on the beam relative to the density of the material m, in MeV*cm2/g;
is the stopping power of water on the beam relative to the density of water, in MeV*cm2/g.
Minimisation of the water equivalent thickness for an ionisation chamber can be obtained by reducing the thickness of the plates supporting the electrodes and using materials for these plates of relatively low mean atomic weight. However, there is a limit thickness for these electrode-supporting plates below which several problems may arise.
One first problem to which consideration must be given is the increase in capacitance at the electrodes on the support film. Charge differences that are too high between the two sides of one same film may lead to breakdown of the film. For a planar capacitor, capacitance is given by
where:
εO: vacuum permittivity;
εr: relative permittivity of the material;
A: area of the plate of the electrode;
d: thickness of the plate of the electrode.
A second problem is the presence of microphonic noise affecting the distance between the electrodes and reducing the precision and exactitude of measurement.
Additionally, with a support plate of reduced thickness it becomes difficult for a via to be passed through the plate to connect one or more collecting or polarising surfaces with one or more conductive traces without affecting the mechanical stability of the plate.
Document U.S. Pat. No. 6,011,265 describes a detector comprising a single ionisation chamber comprising a plurality of support films arranged in parallel and separated from each other by a gap. The described ionisation chamber comprises:
The detector described in U.S. Pat. No. 6,011,265 may also comprise a second assembly of elementary anodes arranged on the second side of the second support film so as to form a two-dimensional detector. However, in hadron therapy techniques which notably use beam currents of high intensity, the beam monitoring devices used are ionisation chambers operating at saturation for maximum efficacy of charge collection. Therefore, phenomena of charge recombination must be minimized subsequent to ionisation of the gas present inside an ionisation chamber, which may be detrimental to saturation of the chamber and hence to precision of measurement. As a result, it is not possible for this type of beam to use an ionisation chamber in which there is amplification of the charges produced subsequent to ionisation of the gas, such as described in document U.S. Pat. No. 6,011,265.
It is therefore necessary to be able to produce a detector that is sufficiently transparent to a radiotherapy beam so that the dose is delivered to the patient with accuracy and precision, minimising the phenomena of scattering and deterioration of the beam. The construction of a said detector must also take into account problems of capacity, microphonic effect and mechanical stability.
It is one of the objectives of the present invention to obtain a dosimetry device comprising an assembly of ionisation chambers which enables monitoring of the dose of a beam directed onto a patient, the device not having the disadvantages of the prior art devices.
More specifically, the objective of the present invention is to minimise the water equivalent thickness of a dosimetry device so as to deliver a dose to a patient which is the most accurate and precise as possible.
An additional objective of the present invention is to obtain good detection dynamics, in particular by eliminating or reducing the intrinsic capacitance of the support plates of the ionisation chambers whilst reducing the thickness of these support plates.
A further objective of the present invention is to provide a device whose collecting electrodes maintain uniform response over their entire surface by preventing the deformation of these support plates of narrow thickness subjected to a strong electric field.
A further objective of the present invention is to provide a device able to measure with precision both the dose deposited by a beam and the field of this same beam.
A further objective of the present invention is to provide a <<universal>> device allowing measurement of the properties of a beam obtained using both a passive delivery technique and a dynamic technique.
According to a first aspect, the present invention relates to a device for the online monitoring of an ionising beam generated by a radiation source and delivered to a target, the said device comprising a plurality of support films arranged in parallel and separated from each other by a gap; the said support films being positioned perpendicularly relative to the central axis of the ionising beam and forming a succession of ionising chambers of which at least one ionising chamber is formed using support films having a thickness of 100 μm or less; each of the support films having on its two surfaces one or more electrodes set at a potential such that the two sides of each of the support films has the same polarity; the support films being arranged so that the successive support films have alternate polarisation; the said device further having additional means capable of equilibrating the electrostatic forces present inside the said ionisation chamber formed using support films having a thickness equal to or less than 100 μm.
Preferably, in the device of the invention, the at least one ionisation chamber is made using support films having a thickness of less than 20 μm, preferably equal to or less than 15 μm, more preferably equal to or less than 10 μm, further preferably equal to or less than 5 μm, still further preferably equal to or less than 1 μm.
Preferably in the device of the invention, the additional means comprise a rigid plate, parallel to and positioned facing the support film comprising a collecting electrode on each of its sides, and taking part in the formation of the ionisation chamber made using support films having a thickness equal to or less than 100 μm; the rigid plate further comprising at least one electrode placed at a potential capable of equilibrating the electrostatic forces present inside the ionisation chamber.
Preferably, in the device of the invention, the additional means comprise a rigid or flexible plate, preferably flexible, parallel to and positioned opposite the support film comprising a polarising electrode on each of its sides, and taking part in the formation of the ionisation chamber prepared using support films having a thickness equal to or less than 100 μm; the rigid or flexible plate further comprising at least one electrode placed at a potential capable of equilibrating the electrostatic forces present inside the ionisation chamber.
Preferably, in the device of the invention, the gaps between each support film are constant.
Preferably, in the device of the invention, at least one of the support films having a thickness equal to or less than 100 μm comprises an electrode at least on one of its surfaces, preferably a collecting electrode, connected to measuring electronics via a conductive trace located on the same side of the support film as the side comprising the said electrode, so that the mechanical stability of the said support film is not detrimentally affected.
Preferably, the device of the invention comprises support films having collecting electrodes on their two surfaces alternating with support films having polarising electrodes on their two surfaces.
Preferably, in the device of the invention, each collecting electrode electrode is connected to measurement electronics by a conductive trace located on the same side of the support film as the side comprising the said collecting electrode.
Preferably, in the device of the invention, some collecting electrodes assume the shape of strips arranged in parallel.
According to another aspect, the invention concerns a device intended to measure ionising beams, the device comprising a support film having two surfaces and having a thickness equal to or less than 100 μm, preferably less than 20 μm, more preferably equal to or less than 15 μm, further preferably equal to or less than 10 μm, still further preferably equal to or less than 5 μm, still further preferably equal to or less than 1 μm; the support film comprising an electrode on at least one of its surfaces, preferably a collecting electrode, connected to measurement electronics by a conductive trace located on the same side of the support film as the side comprising the electrode.
Preferably, in the device of the invention, the electrode assumes the shape of a disc whose perimeter is separated by a gap or insulating resin from a guard layer which extends over the remainder of the support film, and the disc-shaped electrode is connected to measurement electronics by a trace located on the same side of the said support film as the side comprising the disc-shaped electrode, the trace being coated with an insulating resin, and the insulating resin is coated with a thin layer of conductive material which extends over the guard layer.
According to another aspect, the invention concerns a method for the online monitoring of an ionising beam generated by a radiation source and delivered onto a target, the method comprising the steps of:
a) providing a plurality of support films arranged in parallel and separated from each other by a gap; the support films being positioned perpendicularly relative to the central axis of the ionising beam and forming a succession of ionisation chambers of which at least one ionisation chamber is formed using support films having a thickness equal to or less than 100 μm; each of the support films having one or more electrodes on its two surfaces;
b) placing each of the support films at a potential such that the two surfaces of each of the support films has the same polarity;
c) arranging the support films such that the successive support films have alternating polarisation;
d) determining the electrostatic forces present inside the ionisation chamber formed by support films having a thickness equal to or less than 100 μm;
e) equilibrating the electrostatic forces by means of additional means.
Preferably, in the method of the invention, the at least one ionisation chamber is made using support films having a thickness less than 20 μm, preferably equal to or less than 15 μm, more preferably equal to or less than 10 μm, further preferably equal to or less than 5 μm, still further preferably equal to or less than 1 μm.
Preferably, in the method of the invention, at least one of the support films having a thickness equal to or less than 100 μm comprises an electrode on at least one of its surfaces, preferably a collecting electrode, connected to measurement electronics by a trace located on the same side of the support film as the side comprising the said electrode, so that the mechanical stability of the said support film is not detrimentally affected.
Preferably, in the method of the invention, the additional means comprise a rigid or flexible plate comprising at least one electrode placed at a potential capable of equilibrating the electrostatic forces present inside the said ionisation chamber.
Preferably, in the method of the invention, the equilibration step further comprises the application of a suitable voltage to the support films.
According to another aspect, the invention concerns the use of the device as described above for online monitoring of beams of particles obtained using passive delivery techniques.
According to another aspect, the invention concerns the use of the device as described above for online monitoring of beams of particles obtained using dynamic delivery techniques.
The following drawings are given for illustration purposes and are not in any way to be construed as limiting the scope of the present invention. Also, the proportions of the different figures are not drawn to scale.
At least two support films 10, 20 forming a first ionisation chamber are coated on their two surfaces with a layer of conductive material acting as electrode. Preferably, the said conductive material is deposited on the support film by a depositing technique so as to obtain a layer of conductive material of between one nanometre and one micron, preferably between 100 nanometres and one micron, more preferably between 100 and 500 nanometres. Preferably the said conductive material is a metal or graphite, more preferably a metal.
Compared with known support plates in the state of the art and generally obtained using the PCB technique, the support films of the present invention have the advantage that they produce less scattering and deterioration of the properties of the beam. Nonetheless the reduction in the thickness of the support films compared with those commonly used in the state of the art results in the onset of new problems, one first problem being the locating of the trace returning the signal to a signal measuring device, a second problem being a major capacitive effect at the films, and a third problem being the vibration of the films when they are subjected to an electric potential.
Conventionally, a collecting electrode is connected to a trace by a via passing through an insulating layer arranged between the surface of the electrode and the support plate, the said trace returning the signal to measuring equipment. For a support film whose thickness it is desired to minimise, this arrangement is not desirable.
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 film comprising a collecting electrode on one surface and a polarisation electrode on its other surface can be likened to a capacitor. For a support film having a thickness as in the device of the present invention, with a potential difference between the two electrodes located on the two sides of the film, the risk of breakdown of the film is very high. The breakdown of a film is a discharge occurring between the two insulated plates of the capacitor when too many charges have accumulated on one side of the capacitor, the discharge damaging the insulating layer of the capacitor.
Also, a major capacitive effect at the support film will result in delaying the transmission of charges towards the measuring electronics and increasing the detector response time. There is therefore a risk that detection of the dose deposited by the beam will be initiated at the time when the necessary dose has already been sent to the patient, and that an excess dose is sent damaging healthy tissues.
In the device shown in
Each support film 10, 20 is held in a support e.g. a support in epoxy resin, the said support guaranteeing good mechanical tensioning and good insulation of each support film. The two support films are secured so that a gap is created therebetween. The support comprises spacers for example having high electrical resistance, whose dimensions are calibrated with very small tolerances. The gaps separating the support films must have high guaranteed precision since the field, and hence the electrostatic force, depend on the applied electric voltage and on the distance between each support film.
Advantageously, the producing of a detector comprising flexible support films of relatively narrow thickness must also take into account the microphonic effect. The difference in potential created between two support films as thin as those of the present invention has the effect of buckling and/or vibrating these support films, which deteriorates the detection of the charges created by ionisation of the gas contained between the two support films through which a beam passes, since the gap between these two support films varies continuously. Similarly, external noise also produces a microphonic effect on said ionisation chamber; the device must therefore also minimise the contribution made by external noise.
To reduce this microphonic effect and more especially to obtain a uniform response of the collecting electrode over its entire surface, two plates or films 16, 18 are positioned either side of the ionisation chamber 1 formed by the two support films 10, 20. These two plates or films 16, 18 comprise electrodes 17, 19 placed at a potential chosen so as to set up an electrostatic force FE2 equilibrating with the electrostatic force FE1 created by polarisation of the support films 10, 20 of the ionisation chamber 1.
A first plate 16, preferably rigid, is positioned facing and parallel with the collecting electrode 15 located towards the outside of the ionisation chamber 1. This plate 16 comprises an electrode 17 which is placed at a potential chosen so as to equilibrate the electrostatic force FE1 applied to the support film 10 and resulting from the electric field set up by the difference in polarity between the collecting electrode 11 and the polarisation electrode 21 located towards the inside of the ionisation chamber 1. Preferably, the gap separating the electrode 17 contained on the first plate 16 from the electrode 15 contained on the support film 10, is identical to the gap separating the collecting 11 and polarisation 21 electrodes contained inside the ionisation chamber 1. More preferably, the voltage applied to the electrode 17 of plate 16 is equal to the voltage applied to the polarisation electrodes 21, 22 of the support film 20.
A second plate 18, which may or may not be rigid, is positioned facing and parallel with the support film 20 comprising the polarisation electrodes 21, 22. This second plate 18 comprises an electrode 19 placed at a potential chosen to equilibrate the electric force FE1 created by polarisation of the electrodes 21, 22 of the support plate 20. It is not necessary for this second plate 18 to be rigid if the electrode 19 contained on this plate 18 is not a collecting electrode, this electrode 19 together with electrode 22 therefore not forming an ionisation chamber.
Since the support film 10 comprises a collecting electrode 11, 15 on its two surfaces, charges created by ionisation of the gas by the beam are collected on the two sides of this film. Differences in the charges on each plate of one same film may lead to a slight capacitive effect, possibly interfering with measurement time at the measurement electronics. To avoid this inconvenience, the electric signal produced at the two collecting electrodes 11, 15 and resulting from ionisation of the gas is preferably physically summed before being sent to the measurement electronics. The support film 10 comprising the two collecting electrodes 11, 15 located on each side of this same film is therefore common to two ionisation chambers, a first ionisation chamber 1 being formed by the two support films 10, 20 and a second ionisation chamber 2 being formed by the support film 10 comprising the collecting electrodes and the rigid plate 16. It is therefore preferable in this case that these said ionisation chambers 1, 2 should have the same gap. This is why the plate 16 located facing the collecting electrode 15 of the support film 10 is a rigid plate, thereby reducing microphonic effects and guaranteeing a constant gap in the two ionisation chambers 1, 2 required for exact, precise dose measurement.
As in the preceding case, the signals collected on the collecting electrode of the ionisation chamber 1 and 2 are summed and sent towards measurement electronics e.g. a charge integrator.
The said collecting and polarisation electrodes extend over a region covering at least 90% of their support film so as to create and collect a maximum quantity of charges. A second sub-assembly of two ionisation chambers 201, 202 comprises:
The first sub-assembly of ionisation chambers 203, 204 lies adjacent the second sub-assembly of ionisation chambers 201, 202, one ionisation chamber 203 of the first sub-assembly having a support film 103 in common with an ionisation chamber 202 of the second sub-assembly of ionisation chambers. The first sub-assembly of ionisation chambers comprises two integral ionisation chambers 203, 204 formed by a support film 103, 105 comprising a polarisation electrode on surface side, and a support film 104 common with the two ionisation chambers 203, 204, the support film 104 comprising a collecting electrode on each surface.
Preferably, the assembly of ionisation chambers of the device of the present invention comprises a third and a fourth sub-assembly of ionisation chambers as illustrated in
One sub-assembly of two ionisation chambers 201, 202 having in common a support film 102 comprising collecting electrodes in strip form on each of its two surfaces. One ionisation chamber 202 of this sub-assembly is positioned adjacent an integral ionisation chamber 203 and has in common with this ionisation chamber 202 a support film 103 comprising a polarisation electrode on each of its two surfaces.
A second sub-assembly of two ionisation chambers 207, 208 has in common a support film 108 comprising collecting electrodes in strip form on each of its two surfaces. For reasons of clarity, only two measurement electronic devices connected to the electrodes are illustrated. One ionisation chamber 207 of this sub-assembly is positioned adjacent an integral ionisation chamber 206 and has in common with this ionisation chamber 206 a support film 107 comprising a polarisation electrode on each of its two surfaces. Finally, one support film 18, 40 comprising an electrode facing the polarisation electrodes positioned towards the outside of the ionisation chambers 201, 208 that are located at the ends of the assembly of ionisation chambers allows the equilibrating of electrical forces due to polarisation of the electrodes 101, 103, 105, 107, 109 and contributes towards stabilising the support films of each ionisation chamber of the assembly.
An additional sub-assembly of two ionisation chambers 301, 302 can be inserted in the said assembly of ionisation chambers as illustrated in
Preferably the first sub-assembly of ionisation chambers 201, 202, through which the beam passes and positioned at the input of the device, comprises collecting electrodes in strip form oriented along an axis x orthogonal to the axis of the beam. The last sub-assembly of ionisation chambers 207, 208, through which the beam passes, comprises collecting electrodes in strip form oriented along an axis y orthogonal to the axis of the beam and to the said axis x.
This device can be placed at the output of a radiation unit and scarcely perturbs beam properties on account of its low water equivalent thickness, minimising the effects of angular and longitudinal scattering. It is possible for example to calculate the water equivalent thickness of a detector of the present invention by considering the last example of
This example of embodiment of the invention comprises 13 mylar films, 26 layers of gold and 12 air gaps. The water equivalent thickness of said detector is therefore (13*2, 25E-04)+(26*1, 94E-04)+(12*5, 20E-04)=0.014 cm for a detector length of about 6.13 cm. The thicknesses of the different materials are given solely as examples, other thicknesses and other materials possibly being chosen to implement the present invention. Similarly, some support films may differ from each other in respect of thickness and the materials chosen.
A device allowing measurement of the field and dose of a beam obtained using a so-called passive delivery technique can be obtained by reproducing the same structure as one of the devices described in the preceding embodiments, and by replacing the integral ionisation chambers whose collecting electrodes cover almost all the surface of the support films, by ionisation chambers whose collecting electrodes contained on the support films are disc-shaped.
To reduce the number of ionisation chambers and support plates, whilst maintaining the redundancy characteristics of the device and the possibility of measuring beams obtained both with dynamic and passive delivery methods, each collecting electrode contained on a support film of an integral ionisation chamber and of an ionisation chamber with electrode of reduced size is connected to its own measurement electronics. One embodiment of the present invention is illustrated in
This embodiment therefore overall comprises thirteen support plates and have a water equivalent thickness of 0.014 cm for device measuring about 6 cm and able to be used for measuring the dose and field of different types of beam. Although a single high voltage generator is sufficient to polarise all the polarisation electrodes, this embodiment of the present invention comprises two high voltage generators HV2, HV3 connected to the polarisation electrodes in the manner described above, in order to have redundancy of the ionisation chambers and to ensure measurement of the dose in the event of a problem with one of the two generators or in the event of breakdown of one of the support films comprising a polarisation electrode.
Number | Date | Country | Kind |
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09172010.2 | Oct 2009 | EP | regional |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2010/064601 | 9/30/2010 | WO | 00 | 8/10/2012 |