JP2008175829A - Method and monitor for measuring particle radiation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a monitor for measuring particle radiation, a method for measuring particle radiation and a system for measuring particle radiation, capable of measuring radiation quantity with a high accuracy even if incident particle radiation beam has a time-dependent structure, furthermore, capable of constraining an influence by offset noise even if particle radiation beam intensity is small, and capable of performing a high accuracy position monitoring. <P>SOLUTION: The monitor for measuring particle radiation comprises: a container 1 on which particle radiation is incident; one or more high voltage electrodes 2i, 2ii, ... and one or more collection electrodes 3i, 3ii, ... installed in the container; an electric source circuit which applies a high voltage into the high voltage electrodes; and a measuring circuit 4 which is connected to the collection electrode and measures the particle radiation quantity to be monitored. Further, this monitor has a control mechanism for controlling the measuring circuit by external signal in a measuring status or non-measuring status. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a particle beam measurement method and a particle beam measurement monitor device applied to, for example, a particle beam therapy system.

  In recent years, particle beam therapy using protons and heavy particles has attracted attention as a method for treating cancer that accounts for about one third of the causes of death in Japan. In this method, by irradiating a cancer cell with a proton beam or a heavy particle beam emitted from an accelerator, only the cancer cell can be killed with almost no effect on the normal cell.

  In this particle beam therapy system, a dose monitor is used to control the dose irradiated to the affected area in the body. That is, as soon as the irradiation dose detected by the dose monitor reaches a predetermined dose determined in advance in the treatment plan, a beam stop command is sent to the beam control device to stop the treatment beam. Therefore, the accuracy of the dose control into the body depends on the dose measurement accuracy of the monitor device. As a dose monitoring device, an ionization chamber that collects charges generated by ionizing action of particle beams in a container with parallel electrodes, or an SEM that measures secondary electrons emitted from a secondary electron emission film disposed in the container. A device or the like is used.

  FIG. 15 shows a schematic configuration diagram of a conventionally used dose monitor apparatus.

  As shown in FIG. 15, one or more high voltage electrodes 2i, 2ii,... And one or more collection electrodes 3i, 3ii,. An ionization chamber is configured. Charges corresponding to the amount of the particle beam incident on the container 1 are collected at the collecting electrodes 3i, 3ii,. A measuring circuit 4 is connected to the collecting electrodes 3i, 3ii,..., And a pulse train corresponding to the signal amount from the collecting electrodes is output by the pulse output unit 5 in the measuring circuit 4. Further, the radiation dose is measured by counting the number of pulses sent from the pulse output unit 5 by the counter unit 6 in the measurement circuit 4.

  In the medical particle beam irradiation apparatus, when the number of pulses measured by the counter unit 6 in the measurement circuit 4 reaches a predetermined number of pulses determined in advance in the treatment plan, a beam stop command is sent to the beam control apparatus, and the particle Irradiation is stopped. A method of using a subtraction counter for the counter unit 5 and subtracting a predetermined number of pulses input in advance and sending a beam stop command when the count number becomes 0 is generally used.

  Further, as a dose monitor, even other methods, for example, an SEM apparatus that collects secondary electrons can be used with an equivalent circuit configuration.

  As a monitor device used in a particle beam therapy system, a beam shape monitor used for measuring a beam shape of a particle beam is known in addition to a dose monitor. As the beam shape monitor device, for example, a multi-strip type monitor in which the charge collection electrode of the ionization chamber is processed into a plurality of strips and a multi-wire type monitor in which the collection electrode is formed of a plurality of wires are known. Distribution according to the shape is output from each strip (each wire in the multi-wire type).

  FIG. 16 shows a schematic configuration diagram of a multi-strip monitor.

  As shown in FIG. 16, one or more high voltage electrodes 12i, 12ii,... And collecting electrodes 13i, 13ii,.

  Each of the collecting electrodes 13i, 13ii,... Has a configuration that is divided into a number of strips that are not electrically connected in one axial direction. A measuring circuit 14 is connected to these strips. Integration units 17a, 17b,... Are provided inside the measurement circuit, and the amount of electricity corresponding to the charge collected in each strip is stored. The voltages output from the integrating units 17a, 17b,... Are taken out as digital signals by A / D converters (hereinafter referred to as “ADC circuits”) 18a, 18b,. Since the charge collected in each strip corresponds to the beam shape, the distribution of the ADC circuits 18a, 18b,... Has a distribution corresponding to the beam shape.

  If the beam shape output from the beam shape monitor is abnormal, an interlock signal is sent to the control system and the treatment is interrupted.

  Conventionally, a particle beam therapy method is a method called a two-dimensional wobbler method, a double scatterer method, or the like, and is a method of performing treatment by one particle beam irradiation. As a more advanced treatment method of particle beam therapy, a method for aiming cancer cells with higher accuracy by irradiating the affected part in the body three-dimensionally has been proposed. A typical three-dimensional irradiation method is a treatment method in which irradiation is performed by virtually dividing a treatment site into three-dimensional lattice points, which is called a three-dimensional spot scanning method.

  In this 3D spot scanning method, when the irradiation dose determined in advance in the treatment plan is reached, the particle beam irradiation is interrupted based on the beam stop command from the dose monitoring device, and the equipment setting is performed so that the next lattice point can be irradiated. Is changed. Then, after the device setting is completed, the next grid point is irradiated continuously. According to this method, unlike the conventional irradiation method in which treatment is performed with a single irradiation, irradiation is performed by dividing the treatment site into a number of regions, so that the irradiation time of each lattice point is shortened.

  On the other hand, a synchrotron accelerator is generally used as a medical particle beam accelerator. The particle beam emitted from the synchrotron accelerator has a temporally discontinuous beam emission pattern. That is, after a beam is emitted for a certain time (about 2 seconds), there is a time during which the beam is not emitted for a certain time (about 1 second), and the beam is emitted repeatedly according to this beam emission pattern.

  FIG. 17 shows the relationship between the irradiation pattern of the three-dimensional lattice points and the beam emission pattern in the three-dimensional spot scanning method. Here, the horizontal axis is a time axis.

  As shown in FIG. 17, the irradiation time of each lattice point is about 10 milliseconds to 1 second, which is shorter than one beam period. At this time, in addition to the case where the particle beam irradiation ends within one beam emission (spill) (A region in the figure), there is irradiation over two spills (B region in the figure).

  In an actual dose monitor, there are leakage currents and amplifier offsets, which cause signal noise. In the irradiation over two spills of the spot scanning method of FIG. 17, for example, the actual beam irradiation is about 10 milliseconds, whereas the dose is measured even during the time when the beam is not emitted for about 1 second. Will do. That is, there is a problem that the SN ratio (hereinafter referred to as “S / N”) is deteriorated by measuring the time when the beam is not emitted.

  Further, the three-dimensional spot scanning method is used with a smaller beam intensity than other treatment methods. This is because when irradiation is performed with a large beam intensity, the irradiation time at each irradiation point becomes too short, and beam control is not in time. For example, in the two-dimensional wobbler method currently used for treatment, the beam intensity is 10 8 particles per second, whereas in the three-dimensional spot scanning method, it is 10 7 per second. It is expected to be about one. That the beam intensity is small, that is, it is necessary to detect a smaller amount of ionization by the monitor device, which causes a deterioration in S / N.

  In an irradiation method such as three-dimensional spot scanning that irradiates a beam in the form of a three-dimensional lattice point, a system for monitoring the beam according to the position and shape of the particle beam is necessary. Here, since it aims at monitoring the beam position in particular, it will be referred to as a beam position monitoring device. However, the configuration itself of the device is the same as that of the beam shape monitoring device described above. However, the three-dimensional irradiation method requires accurate position calculation and beam shape calculation under the condition of short-time irradiation and a small amount of charge, as with the dose monitoring apparatus.

  In the beam position monitoring device, the charge generated by ionization by the particle beam is collected by being distributed to each strip (or each wire), so that it is more due to noise than the dose monitoring device that collects the entire surface of the collecting electrode. There is a problem that the error occurs more greatly.

  As described above, the conventional particle beam measurement monitor device and the measurement method using the same have had a problem that the irradiation dose of the particle beam cannot be measured accurately when the incident particle beam has a time structure.

  The present invention has been made in view of such circumstances, and an object thereof is a particle beam measurement method and a particle beam measurement method capable of accurately measuring a dose even when an incident particle beam has a time structure. It is to provide a monitor device.

  Another object of the present invention is to enable the influence of offset noise to be suppressed and to perform accurate position monitoring even when the particle beam intensity is small.

  In order to achieve the above object, the present invention is configured as follows.

  (1) The present invention includes a container, one or more high-voltage electrodes and one or more collection electrodes arranged in the container, a power supply circuit for applying a high voltage to the high-voltage electrodes, and a collection electrode And a mechanism for controlling a measurement or non-measurement state by an external signal.

  As a mechanism for controlling the measurement or non-measurement state, the pulse output unit of the measurement circuit has a mechanism for controlling the output or non-output state by an external signal. Further, the counter unit of the measurement circuit has a mechanism for controlling the counting or non-counting state by an external signal. Furthermore, it has a mechanism for controlling an input or non-input state with an external signal with respect to the integration part of the measurement circuit.

  In addition, as the shape of the collecting electrode according to the present invention, a multi-channel type formed by being divided into a plurality of parts can be used. As the multi-channel type, a multi-strip type formed by dividing into a plurality of strips and a multi-wire type formed by a plurality of wires are possible.

  (2) The present invention is a particle beam measurement apparatus having a monitor device, and has an offset value measurement unit of the monitor device.

  The offset value measuring unit includes a clock for measuring time and a counter unit for counting the number of clocks. Further, a dummy measurement unit is arranged as an offset value measurement unit.

  The shape of the collecting electrode according to the present invention can be a multi-channel type formed by being divided into a plurality of parts. As the multi-channel type, a multi-strip type formed by dividing into a plurality of strips and a multi-wire type formed by a plurality of wires are possible.

  That is, in the first aspect of the present invention, a multi-channel type in which one or more high-voltage electrodes and one or more collecting electrodes are arranged in a container into which particle beams are incident, and the collecting electrodes are divided into a plurality of parts. A particle beam measurement method for measuring the amount of charge by collecting the charge generated in the container with a collection electrode, wherein a discrete level is set for each channel output value, and an output exceeding the discrete level is output. There is provided a particle beam measurement method characterized in that at least one of a beam position, a beam shape, and a beam intensity is calculated only from an output value of a channel having the channel.

  The invention according to claim 2 is a multi-channel type in which one or more high-voltage electrodes and one or more collection electrodes are arranged in a container into which particle beams are incident, and the collection electrodes are divided into a plurality of parts. A particle beam measurement method for measuring the amount of charge by collecting charges generated in the container with a collection electrode, and a range of channels in which calculation is performed based on information on a predetermined beam position or beam size And a beam position or beam shape or beam intensity is calculated from only the output value of the limited channel.

  According to a third aspect of the present invention, a container into which the particle beam is incident, one or more high-voltage electrodes and one or more collection electrodes disposed in the container, and a high voltage is applied to the high-voltage electrode. And a measurement circuit for processing and calculating an output from the collection electrode, wherein the collection electrode is a multi-channel type in which the collection electrode is divided into a plurality of channels. It has a calculation mechanism that sets a discrete level as an output value and calculates at least one of the beam beam position, beam shape, and beam intensity from only the output value of a channel having an output exceeding the discrete level. A particle beam measurement monitor device is provided.

  In the invention according to claim 4, a high voltage is applied to the container into which the particle beam is incident, one or more high-voltage electrodes and one or more collecting electrodes disposed in the container, and the high-voltage electrode. And a measurement circuit for processing and calculating an output from the collection electrode, and a multi-channel type in which the collection electrode is divided into a plurality of pieces and designated in advance The range of channels to be calculated is limited based on at least one of the specified beam position and beam size information, and at least one of the beam position, beam shape, and beam intensity is calculated only from the output value of the limited channel Provided is a particle beam measurement monitor device characterized by including an arithmetic mechanism for performing the above operation.

  According to the present invention, the measurement can be interrupted when the particle beam is not incident on the container, whereby the output due to the noise signal when the particle beam is not incident can be suppressed. Therefore, it becomes possible to perform particle beam measurement with higher accuracy than in the past.

  In addition, according to the present invention, particle beam monitor measurement in which the influence of offset current output is suppressed is possible, and an accurate particle beam measurement monitor device, measurement method, and measurement system can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First Embodiment (FIGS. 1 and 2)]
FIG. 1 is a particle beam measurement monitor device according to a first embodiment of the invention. In the present embodiment, a case will be described in which the present invention is applied to a dose monitor apparatus of a medical particle beam irradiation apparatus, in particular, a case where an irradiation apparatus based on a three-dimensional spot scanning method is applied. In addition, about the site | part same as a prior art example, the symbol same as FIGS. 15-17 is also used.

  1, one or more high-voltage electrodes 2i, 2ii,... And one or more collection electrodes 3i, 3ii,... Are arranged inside the monitor container 1, thereby forming an ionization chamber.

  A measuring circuit 24 is connected to the collecting electrodes 3i, 3ii,. The measurement circuit 24 is provided with a pulse output unit 25 and a counter unit 26. The pulse output unit 25 is provided with an external signal input terminal 27.

  Next, a particle beam monitoring method using the particle beam measurement monitor device shown in FIG. 1 will be described.

  When the particle beam enters the monitor container 1, charges corresponding to the amount of the incident particle beam are collected on the collecting electrodes 3i, 3ii,. The signals collected by the collecting electrodes 3i, 3ii,... Are amplified as necessary by the measurement circuit 24, and correspond to the charge amount from the collecting electrodes 3i,. A pulse train is output. Further, the counter unit 26 in the measuring circuit 24 counts the number of pulses sent from the pulse output unit 25, thereby measuring the irradiation dose.

  FIG. 2 shows the relationship between the irradiation pattern of the three-dimensional lattice points, the beam emission pattern, and the pulse output time in the three-dimensional spot scanning method. In FIG. 2, it is assumed that a synchrotron accelerator is used as the beam emission pattern.

  As shown in FIG. 2, the particle beam emitted from the synchrotron accelerator has a temporally discontinuous beam emission pattern. That is, after a beam is emitted for a certain time (about 2 seconds), there is a time during which the beam is not emitted for a certain time (about 1 second), and the beam is emitted repeatedly according to this beam emission pattern.

  In this case, an external signal synchronized with the particle beam emission from the synchrotron accelerator is input to the pulse output unit 27, and the pulse output is controlled only when the particle beam is incident on the monitor container 1.

  Therefore, in the present embodiment, by preventing the pulse output from being performed when the particle beam is not incident on the monitor container 1, it is possible to suppress the output due to noise during the time when the particle beam is not incident on the monitor container 1. Therefore, accurate particle beam monitor measurement can be realized.

[Second Embodiment (FIGS. 3 and 4)]
FIG. 3 is a system configuration diagram showing a particle beam measurement monitor device according to a second embodiment of the present invention.

  As shown in FIG. 3, one or more high voltage electrodes 2i, 2ii,... And one or more collection electrodes 3i, 3ii,. . A measuring circuit 34 is connected to the collecting electrodes 3i, 3ii,.

  In the measurement circuit 34, a pulse output unit 35 and a counter unit 36 are arranged. In this embodiment, the counter unit 36 is provided with an external signal input terminal 37.

  Next, a particle beam measurement method using the monitor device shown in FIG. 3 will be described.

  When the particle beam enters the monitor container 1, charges corresponding to the amount of the incident particle beam are collected on the collecting electrodes 3i, 3ii,. The signals collected by the collecting electrodes 3i, 3ii,... Are amplified by the measurement circuit 24 as necessary, and the pulse train corresponding to the charge amount from the collecting electrodes 3i, 3ii,. Is output. Further, the radiation dose is measured by counting the number of pulses sent from the pulse output unit 35 by the counter unit 36 in the measurement circuit 34.

  FIG. 4 shows the relationship between the irradiation pattern of the three-dimensional lattice point, the beam emission pattern, and the counter time in the three-dimensional spot scanning method. In FIG. 4, it is assumed that a synchrotron accelerator is used as the beam emission pattern.

  In the example of FIG. 3, an external signal synchronized with the particle beam emission from the synchrotron accelerator is input to the counter unit 36, and the pulse output is controlled only when the particle beam is incident on the monitor container 1.

  Thus, according to this embodiment, the output by the noise in the time when the particle beam does not enter the monitor container 1 can be suppressed. Therefore, accurate particle beam monitor measurement can be realized.

[Third Embodiment (FIGS. 5 and 6)]
FIG. 5 is a system configuration diagram showing a particle beam measurement monitor device according to a third embodiment of the present invention.

  As shown in FIG. 5, one or more high-voltage electrodes 2i, 2ii,... And one or more collecting electrodes 3i, 3ii,. ing. A measuring circuit 44 is connected to the collecting electrodes 3i, 3ii,.

  The measurement circuit 44 is provided with an integration unit 47, an ADC circuit 48, and a switch 49 that limits input to the integration unit.

  Next, a particle beam measurement method using the monitor device shown in FIG. 5 will be described.

  When the particle beam enters the monitor container 1, charges corresponding to the amount of the incident particle beam are collected on the collecting electrodes 3i, 3ii,. The signal collected by the collecting electrode is amplified by the measurement circuit as necessary, and an electric quantity corresponding to the electric charge collected by the integrating unit 47 is stored. The voltage output from the integration unit 47 is extracted as a digital signal by the ADC circuit 48.

  FIG. 6 shows the relationship between the irradiation pattern of the three-dimensional lattice point, the beam emission pattern, and the integration time in the three-dimensional spot scanning method. In FIG. 6, it is assumed that a synchrotron accelerator is used as the beam emission pattern.

  In the example of FIG. 5, an external signal synchronized with the particle beam emission from the synchrotron accelerator is input to the switch 49, and the integration is controlled only when the particle beam is incident on the monitor container 1. As described above, according to the present embodiment, the integration of the noise output during the time when the particle beam does not enter the monitor container 1 can be suppressed. Therefore, accurate particle beam monitor measurement can be realized.

  In the above first to third embodiments, an example of a dose monitoring device using an ionization chamber has been shown. However, if the monitor collects charges and performs measurement such as an SEM device, it is based on another method. Even a dose monitor device can be applied.

  Also, a beam position monitoring device and a beam shape monitoring device that are of a multi-channel type can be measured with high accuracy by using the same device configuration and measurement method. Further, as the multi-channel type, a multi-strip type monitor in which the collecting electrode is processed into a plurality of strips, a multi-wire type monitor in which the collecting electrode is formed with a plurality of wires, and other various shapes can be applied.

[Fourth Embodiment (FIGS. 7 and 8)]
FIG. 7 is a system configuration diagram showing a particle beam measurement monitor device according to a fourth embodiment of the present invention.

  As shown in FIG. 7, one or more high voltage electrodes 2i, 2ii,... And one or more collection electrodes 3i, 3ii,. . Charges corresponding to the amount of the particle beam incident on the monitor container 1 are collected at the collecting electrodes 3i, 3ii,. A measuring circuit 54 is connected to the collecting electrodes 3i, 3ii,.

  The measurement circuit 54 includes an integration unit 57, an ADC circuit 58, and a processing unit 59 connected to the ADC circuit 58. The processing unit 59 is provided with an external input terminal 60 to receive an external signal.

  Next, a particle beam measurement method using the monitor device shown in FIG. 7 will be described with reference to FIG.

  FIG. 8 shows the relationship between the irradiation time of each three-dimensional lattice point, the beam emission pattern, and the integration time when the beam intensity is weak or a large dose is irradiated to the affected part in the three-dimensional spot scanning method. It is a thing. In FIG. 8, it is assumed that a synchrotron accelerator is used as the beam emission pattern, and one irradiation time is longer than the repetition time of the emission beam from the synchrotron accelerator.

  In the example shown in FIG. 7, an external signal synchronized with the particle beam emission stop signal from the synchrotron accelerator is input to the processing unit 59, and the processing unit 59 is supplied from the ADC circuit 58 in response to the input of this external signal. The data is transmitted to and sequentially held, and the charge of the integrating unit 57 is reset. When the processing unit 59 receives a measurement stop signal corresponding to the end of the irradiation time, data corresponding to the irradiation time is created based on the data held in the processing unit 59.

  In this way, no measurement can be performed during the time when the particle beam does not enter the monitor container, and an increase in error due to integration of noise output can be suppressed. Therefore, accurate particle beam monitor measurement can be realized.

  In the above embodiment, the measurement stop signal is input in response to the end of the irradiation time, but the same operation is performed by inputting another signal depending on the case, for example, when it is desired to know the measurement value during the irradiation time. It is also possible to make it.

  Although FIG. 8 shows the case of the three-dimensional spot scanning method, in other irradiation methods, for example, a three-dimensional wobbler method, a three-dimensional scatterer method, etc. are used to virtually irradiate the affected part in slices and perform irradiation. It can also be applied to cases. Even in this case, the relationship between the irradiation time and the beam emission pattern is the same as in FIG.

  Further, in the fourth embodiment, an example of a dose monitoring apparatus using an ionization chamber has been shown. However, if the monitor collects charges and performs measurement such as an SEM apparatus, it is a dose monitoring apparatus of another method. However, it can be applied effectively.

[Fifth Embodiment (FIG. 9)]
FIG. 9 is a system configuration diagram showing a particle beam measurement monitor device according to a fifth embodiment of the present invention.

  As shown in FIG. 9, one or more high voltage electrodes 12i, 12ii,... And collecting electrodes 13i, 13ii,. Each of the collecting electrodes 13i, 13ii,... Has a configuration that is divided into a number of strips that are not electrically connected in one axial direction. That is, this monitor device is a multi-strip type monitor device, and a measuring circuit 64 is connected to each of the strips of the collecting electrodes 13i, 13ii,. .., And ADC circuits 68 a, 68 b,... Are arranged inside the measurement circuit, and each measurement circuit element is connected to the processing unit 69. The processing unit 69 is provided with an external input terminal 70 to receive an external signal.

  Next, a particle beam measurement method using the monitor device shown in FIG. 9 will be described.

  When the particle beam enters the monitor container 1, charges corresponding to the beam shape are collected in each strip of the collection electrodes 13i, 13ii,. The signal collected in each strip is amplified as necessary by the measurement circuit, and the amount of electricity corresponding to the electric charge collected in each integrating section 67a, 67b,... Is stored. The voltages output from the integrating units 67a, 67b,... Are taken out as digital signals by the ADC circuit 68, respectively. Since the charge collected in each strip corresponds to the beam shape, the distribution of the ADC circuits 68a, 68b,... Shows the distribution corresponding to the beam shape.

  Here, it is assumed that there is a relationship between the irradiation pattern of the three-dimensional lattice points, the beam emission pattern, and the integration time in the three-dimensional spot scanning method shown in FIG.

  In the example shown in FIG. 9, an external signal synchronized with the particle beam emission stop signal from the synchrotron is input to the processing unit 69. In response to the input of the external signal, data is transmitted from the ADC circuit to the processing unit and sequentially held, and the charges of the integrating units 67a, 67b... Are reset. When the processing unit 69 receives a measurement stop signal corresponding to the end of the irradiation time, data corresponding to the irradiation time is created based on the data held in the processing unit 69. Further, the beam position or beam shape is calculated from the obtained data in each strip.

  Here, as a method for calculating the beam position and the beam shape, a method based on the center of gravity can be used. According to the calculation of the center of gravity, assuming that the output Pi of each strip is the position xi of each strip, the beam center position <X> = Σ (Pi · xi) / ΣPi, and the beam shape as the beam dispersion <σ> 2 = Σ (Pi -(<X> -xi) 2) / ΣPi can be used for evaluation.

  In this way, the integration can be interrupted during the time when the particle beam does not enter the monitor container, and an increase in error due to the integration of the noise output can be suppressed. Therefore, it is possible to calculate the beam position or the beam shape with high accuracy, and to realize accurate particle beam monitor measurement.

  In the present embodiment, the multi-strip type monitoring device is shown, but the present invention can also be effectively applied to a multi-wire type, other multi-channel type monitoring devices, and the like.

[Sixth Embodiment (FIGS. 10 and 11)]
FIG. 10 is a system configuration diagram showing a particle beam measurement monitor device according to a sixth embodiment of the present invention.

  As shown in FIG. 10, one or more high voltage electrodes 2i, 2ii,... And collecting electrodes 3i, 3ii,. A measuring circuit 74 is connected to the collecting electrodes 3i, 3ii,. The measurement circuit 74 includes an integration unit 77, an ADC circuit 78, and a processing unit 79.

And a counter 82 that counts signals from the clock 81.

  Next, a particle beam measurement method using the monitor device shown in FIG. 10 will be described with reference to FIG.

  FIG. 11 shows the relationship between the integration time and the output obtained from the ADC circuit 78 when no particle beam is incident on the monitor container 1. In the monitor device, an output (offset current output) is output even when there is no input because the electrode in the monitor container 1 has a leakage current or the amplifier in the measurement circuit 74 has an offset. There is. This offset current output is generally a function of the integration time. In the example shown in FIG. 11, this offset current output is given by a linear expression (C · Δt + D) of the integration time Δt.

  In the monitoring apparatus shown in FIG. 10, the counter 82 starts counting the signal from the clock 81 in response to a signal synchronized with the start of particle beam incidence on the monitor container 1 and continues counting until the particle beam incidence on the monitor container 1 is completed. Is called. From the clock 81, a pulse signal having a certain frequency is output, whereby the integration time Δt can be obtained from the count value Nc until the particle beam is incident. From the obtained integration time Δt, the offset current output Q can be evaluated based on the coefficients a and b obtained in advance. When the output value that is not corrected is P, by using the value (PQ) in which the offset current output is corrected, the influence of the offset can be suppressed, and accurate particle beam monitor measurement is possible.

  In this embodiment, the integration start / end is given by a signal synchronized with the particle beam incidence, but the method of giving the integration time is arbitrary.

  In the present embodiment, an example of a dose monitoring apparatus using an ionization chamber has been described. However, a dose monitoring apparatus of another method may be used as long as it is a monitor that collects and measures charges such as an SEM apparatus. Can be applied effectively.

  Furthermore, in the present embodiment, a multi-channel type in which the collecting electrode is divided into a plurality of types, for example, a multi-strip type or a multi-wire type can also be used. In the multi-channel type, it is possible to evaluate the offset current outputs Qa = Ca · Δt + Da, Qb = Cb · Δt + Db... For each channel from the integration time Δt obtained by one time measuring unit.

[Seventh Embodiment (FIG. 12)]
FIG. 12 is a schematic configuration diagram showing a particle beam monitoring apparatus according to a seventh embodiment of the present invention.

  As shown in FIG. 12, one or more high-voltage electrodes 2i, 2ii,... And collecting electrodes 3i, 3ii,. A measuring circuit 84 is connected to the collecting electrodes 3i, 3ii,. The measurement circuit 84 includes an integration unit 87, an ADC circuit 88, and a processing unit 89.

  In the present embodiment, a dummy measurement unit 90 is connected to the processing unit 89.

  Similar to the measurement circuit 84, the dummy measurement unit 90 includes an integration unit 91 and an ADC circuit 92, and the integration unit 91 is connected to, for example, the outermost region of the dummy electrode 10. As long as the particle beam is not incident, the region to which the integrating unit 91 is connected may be another region.

  Next, a particle beam measurement method using the monitor device shown in FIG. 12 will be described.

  The offset current output Qd of the dummy measuring unit 90 for a certain integration time is a function of the integration time Δt. When the relationship between the offset current output of the measurement circuit 84 and the dummy measurement unit 90 and the integration time are both given by a linear expression as shown in FIG. 11, the offset current output Q at the collecting electrode is the offset current output of the dummy measurement unit. It can be evaluated by a primary expression Q = c · Qd + d of Qd. If the output value that is not corrected is P, by using the value (PQ) in which the offset current output is corrected, the influence of the offset can be suppressed, and accurate particle beam monitor measurement is possible.

  In this embodiment, the monitor device using the ionization chamber is applied. However, if the monitor collects charges and performs measurement such as an SEM device, it can be effectively applied to other dose monitor devices. it can.

  Furthermore, in the present embodiment, a multi-channel type in which the collecting electrode is divided into a plurality of types, for example, a multi-strip type or a multi-wire type can also be used. In the multi-channel type, it is possible to evaluate the offset current output Qa = Ca · Qd + Da, Qb = Cb · Qd + Db... For each channel from the offset current output Qd obtained by one dummy measurement unit.

[Eighth Embodiment (FIGS. 13 and 14)]
FIG. 13 is a schematic configuration diagram showing a particle beam monitoring apparatus according to an eighth embodiment of the present invention.

  As shown in FIG. 13, one or more high-voltage electrodes 12i, 12ii,... And collecting electrodes 13i, 13ii,. Each of the collecting electrodes 13i, 13ii,... Has a configuration that is divided into a number of strips that are not electrically connected in one axial direction. That is, this monitor device is a multi-strip type monitor device. A measuring circuit 94 is connected to the collecting electrodes 13i, 13ii,. The measuring circuit has a plurality of integrating units 97a, 97b,..., ADC circuits 98a, 98b,... And a processing unit 99 connected to them.

  Next, a particle beam measurement method using the monitor device shown in FIG. 13 will be described with reference to FIG.

  FIG. 14 is an example of the output distribution of the ADC circuit for each strip for irradiation of a certain three-dimensional lattice point in the three-dimensional spot scanning method. In FIG. 14, the horizontal axis indicates the position coordinates of each strip.

  As shown in FIG. 14, the strip has a region having a Gaussian distribution-like distribution, and this region is a region where charges are generated by particle beam incidence and the charges are collected. However, there is an output region due to a slight offset current in addition to a region having a Gaussian distribution.

  Therefore, as a calculation method of the beam position / shape, for example, from the outputs Pa, Pb,... And the positions xa, xb,..., In each strip, the beam center position <X> = Σ (Pk · xk) / ΣPk, When σ> 2 = Σ (Pk · (<X> −xk) 2) / ΣPk is evaluated, an error becomes large due to the offset current in the strip region where no charge is collected, and accurate monitor measurement cannot be performed.

  However, according to the present embodiment, the discretion level is set in advance in the processing unit 99 shown in FIG. 13, and the strip output that does not reach the discreet level is not taken into the position calculation or is set to zero output. It is processed.

  As described above, according to the present embodiment, it is possible to suppress the influence of the offset current in the strip region where charges are not collected, and to perform accurate monitor measurement. The discretion level setting method is given as a constant value given in advance, as a function of integration time (for example, a linear expression), or as a function of the output of a strip having the maximum output (for example, several% of output) Can be.

[Ninth Embodiment (FIGS. 13 and 14)]
In the present embodiment, a monitor device having the same configuration as that of the eighth embodiment is used.

  According to this configuration, as shown in FIG. 14, the strip has an output region due to an offset current in addition to a region having a Gaussian distribution-like distribution corresponding to the collected charge amount.

  However, in the ninth embodiment, the processing unit 99 stores the beam position and beam width to be irradiated before the monitor container is irradiated with the particle beam. Based on the given beam position and beam width, the processing unit 99 limits the strip area used for calculating the beam center position or beam shape.

  As a method of this limitation, for example, given as a strip existing in X0 ± 2 · σ, where X0 is a beam position given in advance and σ is a beam width.

  As described above, according to the present embodiment, it is possible to suppress the influence of the offset current in the strip region where charges are not collected, and to perform accurate monitor measurement. Further, by limiting the strips used for position calculation, the amount of data to be calculated is reduced, the time required for position calculation is shortened, and high-speed control and short-time treatment are possible.

[Other Embodiments]
In each of the above embodiments, the control system of the three-dimensional spot scanning method has been mainly shown. However, as a treatment control apparatus that can use the present invention, other methods such as a three-dimensional raster scanning method and a three-dimensional wobbler method are used. The influence of a noise signal can be suppressed even for a three-dimensional irradiation method, and further to a conventional two-dimensional wobbler method and double scatterer method, and it is effective as an accurate monitor measurement apparatus and measurement system.

  In each of the above embodiments, an example of application in a monitoring apparatus for particle beam therapy has been described. However, the present invention can also be applied to a measurement apparatus for a simulated irradiation test using a phantom performed before particle beam therapy. In addition, as long as the purpose of suppressing the deterioration of S / N is not impaired, the present invention is also effective in a particle beam monitoring apparatus for particle beam irradiation for other purposes.

  Further, in each of the above embodiments, the case where the particle beam by the synchrotron accelerator is used has been described. However, if the particle beam has a spill structure in the time structure of the beam, various beams can be used effectively as well. it can.

  Furthermore, the configurations and methods shown in the sixth and subsequent embodiments can be effectively applied to the particle beam monitoring device in an accelerator outgoing beam that does not have a spill structure in the beam time structure, because the influence of offset noise can be suppressed. can do.

  Furthermore, in the sixth and following embodiments, the multistrip type monitor device has been described, but the present invention can also be effectively applied to other multistrip type monitors such as a multiwire type monitor.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram which shows the monitor apparatus for particle beam measurement by 1st Embodiment of this invention. The figure which shows the relationship between the particle beam extraction pattern by the said 1st Embodiment, a beam irradiation pattern, and pulse output time. The schematic block diagram which shows the monitor apparatus for particle beam measurement by 2nd Embodiment of this invention. The figure which shows the relationship between the particle beam emission pattern by the said 2nd Embodiment, a beam irradiation pattern, and count output time. The schematic block diagram which shows the monitor apparatus for particle beam measurement by 3rd Embodiment of this invention. The figure which shows the relationship between the particle beam extraction pattern by the said 3rd Embodiment, a beam irradiation pattern, and integration time. The schematic block diagram which shows the monitor apparatus for particle beam measurement by 4th Embodiment of this invention. The figure which shows the relationship between the particle beam extraction pattern by the said 4th Embodiment, a beam irradiation pattern, and integration time. The schematic block diagram which shows the monitor apparatus for particle beam measurement by 5th Embodiment of this invention. The schematic block diagram which shows the monitor apparatus for particle beam measurement by 6th Embodiment of this invention. The figure which shows the relationship between the integration time in the said 6th Embodiment, and an offset current output. The schematic block diagram which shows the particle beam monitor apparatus by 7th Embodiment of this invention. The schematic block diagram which shows the particle beam monitoring apparatus by 8th Embodiment of this invention. The figure which shows the output distribution of each channel in a multistrip type | mold monitor apparatus. The schematic block diagram which shows the conventional particle beam monitor apparatus. The schematic block diagram which shows the multistrip type | mold monitoring apparatus of a prior art example. The figure which shows the relationship between the particle beam extraction pattern by a prior art example, a beam irradiation pattern, and pulse output and count time.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Monitor container 2i, 2ii, ... High voltage electrode 3i, 3ii, ... Collecting electrode 4 Measuring circuit 5 Pulse output part 6 Counter part 11 Monitor container 12i, 12ii, ... High voltage electrode 13i, 13ii, ... Collecting electrode 14 Measuring circuit 17a , 17b,... Integration units 18a, 18b,... A / D converter (ADC circuit)
24 measurement circuit 25 pulse output unit 26 counter unit 27 external signal input terminal 34 measurement circuit 35 pulse output unit 36 counter unit 37 external signal input terminal 44 measurement circuit 47 integration unit 48 ADC circuit 49 switch 54 measurement circuit 57 integration unit 58 ADC circuit 59 processing unit 60 external input terminal 64 measurement circuit 67a, b,... Integration unit 69 processing unit 70 external input terminal 74 measurement circuit 77 integration unit 78 ADC circuit 79 processing unit 80 time measurement unit 81 clock 82 counter 84 measurement circuit 87 integration unit 88 ADC circuit 89 processing unit 90 dummy measurement unit 91 integration unit 92 ADC circuit 94 measurement circuits 97a, 97b, ... integration units 98a, 98b, ... ADC circuit 99 processing unit

Claims (4)

One or more high-voltage electrodes and one or more collecting electrodes are arranged in a container to which particle beams are incident, and the collecting electrode is a multi-channel type divided into a plurality of parts, and charges generated in the container are It is a particle beam measurement method that collects charges by collecting electrodes and measures the amount of electric charge, and sets a discrete level for each channel output value, and determines the beam position from only the output value of the channel having an output exceeding the discrete level. A particle beam measuring method, wherein at least one of a beam shape and a beam intensity is calculated. One or more high-voltage electrodes and one or more collecting electrodes are arranged in a container to which particle beams are incident, and the collecting electrode is a multi-channel type divided into a plurality of parts, and charges generated in the container are A particle beam measurement method that collects charges with a collection electrode and measures the amount of electric charge, and limits the range of channels to be operated on the basis of information on the beam position or beam size specified in advance. A particle beam measuring method, wherein the beam position, beam shape, or beam intensity is calculated only from the output value of. A container into which a particle beam is incident, one or more high-voltage electrodes and one or more collection electrodes disposed in the container, a power supply circuit for applying a high voltage to the high-voltage electrodes, and the collection In a particle beam measurement monitor device having a measurement circuit for processing and calculating an output from an electrode, the collecting electrode is a multi-channel type in which a plurality of divided electrodes are formed, and a discrete level is set for each channel output value A particle beam measurement monitor apparatus comprising: an arithmetic mechanism that calculates at least one of a beam beam position, a beam shape, and a beam intensity from only an output value of a channel having an output exceeding the discrete level. A container into which a particle beam is incident, one or more high-voltage electrodes and one or more collection electrodes disposed in the container, a power supply circuit for applying a high voltage to the high-voltage electrodes, and the collection In a monitor for particle beam measurement having a measurement circuit for processing and calculating an output from an electrode, the collection electrode is a multichannel type in which a plurality of divided electrodes are formed, and the beam position and beam size specified in advance are It has a calculation mechanism that limits the range of channels to be calculated based on at least one of the information and calculates at least one of the beam position, beam shape, and beam intensity from only the output values of the limited channels. A monitoring device for particle beam measurement.

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