JP5904102B2 - Particle beam irradiation apparatus and control method thereof - Google Patents

Description

  The present invention relates to a particle beam irradiation apparatus and a control method thereof.

  As a more advanced irradiation method for particle beam therapy for cancer and the like, a scanning irradiation method is being developed in which the affected part of the body is cut into a three-dimensional lattice to perform irradiation. In this scanning irradiation method, the beam axis direction can be accurately adjusted to the affected part without using a shape collimator or a bolus, and the exposure to normal cells is suppressed as compared with the conventional two-dimensional irradiation method. be able to.

  At present, a spot scanning irradiation method that stops beam emission when the irradiation point is changed and a raster scanning method that does not stop beam emission when the irradiation point is changed are being studied.

  In order to ensure that the beam is irradiated at the correct position in the scanning irradiation method, a position monitor device is provided at the irradiation port.

  The position monitor device for scanning irradiation has, for example, a configuration in which collecting electrodes divided into a number of strips are housed in an ionization chamber. A measuring circuit is connected to each of these strips. An integration unit is provided inside the measurement circuit, and an amount of electricity corresponding to the charge collected in each strip is stored for each irradiation spot. The voltage output from the integrator is taken out as a digital signal by an A / D converter (hereinafter referred to as “ADC circuit”). Then, the spot position is calculated by performing operations such as centroid calculation on these digital signals.

  In the unlikely event that there is a difference in the current setting of the scanning electromagnet power source or the beam position deviation in the beam transport section from the upstream accelerator to the scanning device, there is a difference between the predetermined irradiation planned position and the position measured by the position monitor device. When it occurs, an interlock signal is output by a position monitoring mechanism (herein referred to as a position monitor controller) in the scanning control device, and treatment irradiation is temporarily suspended.

  On the other hand, there is a strong demand from doctors and radiologists to visually confirm during irradiation whether the dose profile for each slice, that is, the two-dimensional dose distribution at the time of scanning, is correct. Patent Document 1 discloses a technique for calculating a beam spot position (center of gravity position) from a signal from a position monitor device, and calculating and displaying a two-dimensional dose profile using the same signal from the position monitor device. .

JP 2011-161056 A

  However, in the above-described position monitoring device, when there is a sudden discharge between the collection electrodes, the calculated center of gravity position may be shifted from the actual beam irradiation position due to the influence of the discharge current. That is, there may be a case where a beam position having a value different from the actual beam position is output due to a malfunction of the position monitor device itself. As a result, even though the actual beam position is normal, it is determined that there is an abnormality, and beam emission may be stopped.

  If the irradiation is stopped (interrupted) due to an abnormality, it will be necessary to start over from the plan again after re-irradiation, requiring considerable effort and time, and stop the beam irradiation with erroneous information as much as possible. There is a request not to want.

The particle beam irradiation apparatus according to the present embodiment includes a beam generation unit that generates a particle beam, a beam scanning unit that two-dimensionally scans the generated particle beam according to a scan instruction value, and a scanning position of the particle beam The first linear electrodes of a plurality of channels are arranged in parallel in the first direction, and the second direction of the second linear electrodes of the plurality of channels is orthogonal to the first direction. This occurs when a sudden discharge occurs between the linear electrodes by obtaining the median from the sensor units arranged in parallel and the values of the plurality of signals output from the first and second linear electrodes. a median processing unit for removing noise, and the position of the center of gravity calculation unit for calculating a center of gravity of the particle beam from the median of the plurality of signals obtained, and the calculated the gravity center position and the preset reference scanning position When the error is larger than a predetermined value, characterized by comprising a control unit for stopping the emission of the particle beam.

The figure which shows the structural example of the particle beam irradiation apparatus which concerns on 1st Embodiment. The figure which shows the structural example of a strip type position monitor part. The figure which shows an example of the beam scanning path | route in a slice. The flowchart which shows the basic operation example of a particle beam irradiation apparatus. The timing chart which shows an example of the basic operation timing of a particle beam irradiation apparatus. The figure which shows typically the concept of gravity center position calculation. The block diagram which shows the detailed structural example of the beam shape calculation part containing the median process part which concerns on 1st Embodiment. The figure explaining the production | generation concept of a dose profile. The figure explaining the discharge phenomenon which generate | occur | produces in the electrode of a position monitor part, and the error signal from an electrode. The figure explaining the problem by the conventional time average process. The figure explaining the concept of the median process of a time direction. The block diagram which shows the detailed structural example of the beam shape calculation part containing the median process part which concerns on 2nd Embodiment. The figure explaining the concept of a spatial median process.

  Embodiments of the present invention will be described with reference to the accompanying drawings.

(1) Configuration FIG. 1 is a diagram illustrating a configuration example of a particle beam irradiation apparatus 1 according to the present embodiment. The particle beam irradiation apparatus 1 includes a beam generation unit 10, an emission control unit 20, a beam scanning unit 30 having an X electromagnet 30a and a Y electromagnet 30b, a dose monitoring unit 40, a position monitoring unit (sensor unit) 50, and a ridge filter. 60, a range shifter 70, a control unit 80, a beam shape calculation unit 90, a storage unit 97, a display unit 98, and the like. The control unit 80 includes a scanning control unit 81 and an abnormality determination unit 82 as its internal configuration. The beam shape calculation unit 90 includes a median processing unit 94 and a centroid position calculation unit 91 as its internal configuration.

The particle beam irradiation apparatus 1 is an apparatus for performing cancer treatment by irradiating a diseased beam 200 of a cancer patient 100 with a particle beam obtained by accelerating particles such as carbon and protons at high speed. In the particle beam irradiation apparatus 1, the affected part 200 can be discretized into three-dimensional lattice points, and a three-dimensional scanning irradiation method of sequentially scanning a particle beam with a small diameter at each lattice point can be performed. Specifically, the affected part 200 is divided into flat units called slices in the axial direction of the particle beam (Z-axis direction in the coordinate system shown in the upper right of FIG. 1), and the divided slices Z _i , slices Z _{i + 1} , slices are divided. Three-dimensional scanning is performed by sequentially scanning two-dimensional grid points (X-axis and Y-axis direction grid points in the coordinate system shown in the upper right of FIG. 1) of each slice such as Z _{i + 2} .

  The beam generation unit 10 generates particles such as carbon ions and protons, and generates a particle beam by accelerating these particles to energy that can reach deep into the affected area 200 by an accelerator (main accelerator) such as a synchrotron. ing.

  The emission control unit 20 performs on / off control of emission of the generated particle beam based on a control signal output from the control unit 80.

  The beam scanning unit 30 deflects the particle beam in a first direction (X direction) and a second direction (Y direction) orthogonal to the first direction, and scans the slice surface in two dimensions. The excitation currents of the X electromagnet 30a scanning in the X direction and the Y electromagnet 30b scanning in the Y direction are controlled.

  The dose monitor unit 40 is for monitoring the dose to be irradiated. In the casing, an ionization chamber that collects charges generated by the ionizing action of the particle beam with parallel electrodes, or a secondary arranged in the casing. The SEM (Secondary Electron Monitor) device for measuring secondary electrons emitted from the electron emission film is used.

  The ridge filter 60 is provided for diffusing a sharp peak of the dose in the body depth direction called a Bragg peak. Here, the diffusion width of the Bragg peak by the ridge filter 60 is set to be equal to the thickness of the slice, that is, the interval between the lattice points in the Z-axis direction.

  The range shifter 70 controls the irradiation position of the affected part 200 in the Z-axis direction. The range shifter 70 is composed of, for example, an acrylic plate having a plurality of thicknesses, and by combining these acrylic plates, the energy of the particle beam passing through the range shifter 70, that is, the range of the body is measured in the Z-axis direction of the affected slice 200 slices. It can be changed stepwise depending on the position. The size of the in-vivo range by the range shifter 70 is normally controlled to change at equal intervals, and this interval corresponds to the interval between lattice points in the Z-axis direction. As a method of switching the range of the body, in addition to a method of inserting an object for attenuation on the path of the particle beam as in the range shifter 70, the energy of the particle beam is changed by controlling the beam generator 10. The method may be used.

  The position monitor unit 50 is for identifying whether or not the particle beam beam scanned by the beam scanning unit 30 is in a correct position. It has parallel electrodes for collecting charges similar to the dose monitor 40. As for the charge collection electrode of the position monitor unit 50, linear electrodes (for example, a plurality of strip electrodes or electrodes made of a plurality of wires) are arranged in parallel in the X direction and the Y direction, respectively. An arrangement in which a plurality of strip electrodes are arranged is called a strip type, and an arrangement in which a plurality of wire electrodes are arranged is called a multi-wire type.

  FIG. 2 is a diagram illustrating a configuration example of the strip-type position monitor unit 50. As shown in FIG. 2, the position monitor unit 50 includes a plurality of strip electrodes (a plurality of first linear electrodes 50 a) arranged in parallel in the X-axis direction (first direction). A plurality of second linear electrodes 50b) are arranged in parallel in the Y-axis direction (second direction orthogonal to the first direction).

  The beam shape calculation unit 90 includes a median processing unit 94 and a gravity center position calculation unit 91. The median processing unit 94 obtains a median from the values of a plurality of signals output from the first and second linear electrodes 50a and 50b. The center-of-gravity position calculation unit 91 calculates the center-of-gravity position of the particle beam from the obtained median. More detailed operations of the median processing unit 94 and the gravity center position calculating unit 91 will be described later. Further, the beam shape calculation unit 90 calculates the shape of the particle beam as a scanning profile based on a signal output from the position monitor unit 50.

  The control unit 80 includes a scanning control unit 81 and an abnormality determination unit 82. The scanning control unit 81 instructs the beam scanning unit 30 on the beam scanning position based on the planned reference scanning position. Further, the abnormality determination unit 82 determines whether or not an error between the gravity center position calculated by the gravity center calculation unit 91 and a preset reference scanning position is larger than a predetermined value, and when the error is larger than the predetermined value. Outputs an interlock signal to the emission control unit 20 so as to stop the emission of the particle beam. In addition to controlling the entire beam irradiation apparatus 1, the control unit 80 performs irradiation dose measurement for each lattice point (for each spot), on / off control of beam emission for the emission control unit 20, and slice change for the range shifter 70. The range shifter thickness is controlled.

  Various functions of the control unit 80 and the beam shape calculation unit 90 can be realized by causing a processor (not shown) included in the apparatus 1 to execute a predetermined program. Or you may comprise by hardware, such as ASIC, and may implement | achieve combining hardware and software.

(2) Basic Operation FIG. 3 is a diagram illustrating an example of a scanning pattern on a slice. A trajectory pattern from the upper left starting lattice point to the lower right final lattice point is predetermined in the treatment plan, and the particle beam is sequentially scanned in one direction along this trajectory pattern.

  As described above, the scanning irradiation method includes a spot scanning irradiation method and a raster scanning irradiation method. In this embodiment, both irradiation methods can be implemented. In the spot scanning irradiation method, the beam emission is temporarily stopped when the spot position (the position of the irradiation grid point indicated by a circle in FIG. 3) is changed, and the beam irradiation is performed after the movement to the next spot position is completed. To resume. On the other hand, in the case of the raster scanning irradiation method, the beam emission is not temporarily stopped even when the spot position is changed, and the beam emission is continued even while the spot position is changed. Note that, in both the spot scanning irradiation method and the raster scanning irradiation method, the beam emission is stopped when the slice is changed.

  FIG. 4 is a flowchart showing an operation example of the particle beam irradiation apparatus 1 of the present embodiment. Each item necessary for the irradiation procedure is described in a data file called an irradiation pattern file, for example, and transferred to the control unit 80 before the start of treatment irradiation. In the irradiation pattern file, for each grid point, the thickness of the range shifter that gives the slice position, and the drive current values of the X electromagnet 30a and the Y electromagnet 30b that give the beam position (reference scanning position) corresponding to the grid point (X, Y) The irradiation dose for each lattice point is described in the order of irradiation.

  The control unit 80 reads the transferred irradiation pattern file and starts the processes after step ST1.

  First, the affected part is virtually divided into a plurality of slices with respect to the beam axis, and one of the divided slices is selected. First, for example, the slice Zi at the deepest position of the affected part is selected. Further, the combination of the incident energy of the particle beam and the acrylic plate in the range shifter 70 is selected and set according to the position of the selected slice (step ST1).

  Next, the number M of lattice points to be irradiated with the particle beam and the position (Xi, Yi) [i = 1 to M] of the lattice points, i.e., the spot to be irradiated, are selected according to the shape of the affected part in the deepest slice, and the beam The scanning unit 30 sets the direction of the particle beam at the lattice point position (Xi, Yi) on the slice (step ST2). Thereafter, emission of the particle beam is started (step ST3). The energy distribution of the particle beam output from the beam scanning unit 30 is expanded in the Z-axis direction by the ridge filter 60 so that the in-vivo range distribution width corresponds to the slice width.

  The irradiation dose for the lattice point (Xi, Yi) is monitored by the dose monitor unit 50. When the irradiation dose for the target lattice point reaches the planned dose, a dose expiration signal is output to the control unit 80, and the control unit 80 outputs this signal. Receive (step ST4).

  In step ST5, it is determined which method is the spot scanning method or the raster scanning method. In the case of the spot scanning method, the beam emission is temporarily stopped (step ST6), and the beam position is moved to the next spot. . This process is repeated up to the final spot of the target slice (step ST7).

  On the other hand, in the case of not the spot scanning method, that is, in the case of the raster scanning method, the beam emission is continued to the final spot without stopping the beam emission.

  When irradiation to one slice is completed (YES in step ST7), beam emission is once stopped in both the spot scanning method and the raster scanning method (step ST8), and the process returns to step ST1 to select the next slice. The setting of the range shifter 70 is changed. The above processing is repeated until the final slice is reached (step ST9).

  FIG. 5 is a timing chart showing the basic operation of the spot scanning method. The excitation currents of the two electromagnets shown in FIGS. 5A and 5B correspond to the position setting values in the biaxial directions (X, Y). When changing the spot position, a spot switching command (FIG. 5 (f)) is issued, and the excitation currents IX and IY change. When the spot position reaches the set value, a spot switching completion signal is output (FIG. 5 (g)). In the spot scanning method, the beam emission is stopped during the switching of the spot position, and the beam emission is started again after the completion of the switching of the spot position (FIG. 5C). When the dose measured by the dose monitor (dose monitor integrated dose, FIG. 5 (d)) reaches the set value after the start of beam extraction, a dose expiration signal (FIG. 5 (e)) is output to switch to the next spot position. A spot switching command (FIG. 5 (f)) is issued.

  As described above, in the particle beam irradiation apparatus 1 according to the present embodiment, the barycentric position of the particle beam is calculated using the signal output from the position monitor unit 50 as the particle beam passes. .

  FIG. 6 is a diagram schematically showing the concept of gravity center position calculation. As shown in FIG. 2, in the position monitor unit 50, a large number of strip-shaped electrodes are arranged in the X and Y directions, and a signal having a level corresponding to the dose of the passing particle beam is output from each strip. The Since the particle beam extends over a plurality of strips, signals are output from the plurality of strips. Each signal has an intensity corresponding to the shape of the particle beam at the position of each strip.

  The barycentric position calculating unit 91 of the beam shape calculating unit 90 calculates the barycentric position, that is, the peak position of the particle beam using the signals output from each strip.

  FIG. 7 is a block diagram illustrating a detailed configuration of the beam shape calculation unit 90. The number (number of channels) of the X electrodes 50a and Y electrodes 50b of the position monitor unit 50 is not particularly limited. However, in the following description, the number of channels in both the X direction and the Y direction is 120 channels as an example. To do.

  The output current of the X electrode 50a is converted into a voltage by a current-voltage conversion (IV conversion) circuit 911a, amplified to an appropriate voltage by an amplifier 912a, and then converted into a digital signal by an AD converter (ADC) 92a. An offset correction process is performed on the digital signal by the data correction processing unit 93a in the next stage. Further, in the next median processing unit 94a, median processing described later is performed, and then input to the gravity center position calculation unit 91a.

  The IV conversion circuit 911a, the amplifier 912a, the ADC 92a, the data correction processing unit 93a, and the median processing unit 94a are provided for each of the X electrodes 50a. In this example, the number is 120 channels.

  Similarly, an IV conversion circuit 911b, an amplifier 912b, an ADC 92b, a data correction processing unit 93b, and a median processing unit 94b for 120 channels are provided for each of the Y electrodes 50b, and each output of the median processing unit 94b. Is input to the center-of-gravity position calculation unit 91b.

  The center-of-gravity position calculation units 91a and 91b determine the center-of-gravity position in the X-direction and the center-of-gravity position in the Y-direction of the particle beam from the amplitude values of the channel signals in the X-direction and Y-direction that have undergone offset correction processing and median processing. Each is calculated.

  The one-dimensional beam shape (X) extraction unit 95a obtains the one-dimensional beam shape in the X direction from the amplitude values of a plurality of X channel signals around the calculated X direction center of gravity position. For example, as shown in FIG. 6, the signal values of a total of 11 channels of the channel closest to the center of gravity position and the five channels before and after the channel are extracted to obtain the one-dimensional beam shape in the X direction. The one-dimensional beam shape (Y) extraction unit 95b similarly obtains the one-dimensional beam shape in the Y direction.

  The two-dimensional beam shape calculation unit 96 calculates the two-dimensional beam shape G (Xi, Yj) from the product of the one-dimensional beam shapes F (Xi) and F (Yj) in the X and Y directions obtained as described above. )

  The calculated two-dimensional beam shape G (Xi, Yj) is transferred to the storage unit 97. In the storage unit 97, as schematically shown in FIG. 8, the dose profile is generated by storing the two-dimensional beam shape G (Xi, Yj) in association with the position (Xi, Yj). The dose profile accumulated and stored in the storage unit 97 is sent to the display unit 98 in units of slices, for example, and the dose profile in units of slices is easily displayed on the screen W of the display unit 98 corresponding to the storage area of the storage unit 97. The

  The calculated center of gravity position is also output to the abnormality determination unit 82 of the control unit 80. The abnormality determination unit 82 determines whether or not an error between the calculated center of gravity position and a preset reference scanning position is larger than a predetermined value. When the error is larger than a predetermined value, an interlock signal is output to the emission control unit 20 to stop the emission of the particle beam. The calculation of the position of the center of gravity is performed at a constant cycle, for example, every 5 μs as shown in FIG.

(3) First embodiment (median processing in the time direction)
The position monitor unit 50 detects the size of the particle beam passing therethrough by applying a high voltage of several kV between the electrodes. For this reason, as shown in FIG. 9, a discharge may occur in a part of the electrode. Since a large current flows through the electrode where the discharge has occurred, as shown in FIG. 9, a very large signal (false signal) is output from the electrode even though the particle beam is not passing through. Become.

  As described above, the barycentric position of the particle beam is calculated using the magnitudes of signals output from the X electrode 50a and the Y electrode 50b of the position monitor unit 50. For this reason, when a discharge occurs, the calculated center of gravity position is shifted from the position of the particle beam actually irradiated.

  In the conventional particle beam irradiation apparatus disclosed in Patent Literature 1 and the like, offset correction is performed on the signals of the X electrode 50a and the Y electrode 50b that have been subjected to AD conversion, and thereafter, averaging processing is performed in the time axis direction. Then, the position of the center of gravity is calculated from the signal of each channel averaged in the time axis direction. However, in the conventional method of averaging in the time axis direction, an incorrect center of gravity position is calculated when a discharge occurs. FIG. 10 is a diagram schematically illustrating this phenomenon.

  In FIG. 10, for convenience of explanation, the number of electrodes (the number of channels) is 12, and the number of samplings averaged in the time axis direction is 10 from the first time to the tenth time. The horizontal direction of TB1 in FIG. 10 is the channel direction, that is, the spatial direction, and the vertical direction is the time direction. The numerical value in TB1 represents the magnitude of the signal output from each channel. In the example shown in FIG. 10, it is assumed that the particle beam passes through the vicinity of the channel “9” throughout the first to tenth sampling periods. On the other hand, a discharge usually occurs only for a very short time at one electrode (one channel). Therefore, in the example shown in TB1 of FIG. 10, it is set that the discharge has occurred in the seventh sampling of the channel “2”. Further, since the value of the error signal due to the discharge is usually larger than the value detected by the passage of the particle beam, the value of the error signal caused by the discharge is set to a large value of “100” in TB1 of FIG. ing.

  TB2 in FIG. 10 is a value obtained by averaging the signal values of the respective channels shown in TB1 in the time axis direction. The center of gravity calculated from the time average value of each channel of TB2 is the value “7.6” shown on the right side of TB2. This result means that the center of gravity has shifted to the channel 2 side under the influence of the large discharge signal of the channel 2.

  On the other hand, TB3 in FIG. 10 indicates a time average value when there is no discharge, that is, when the value of the seventh sampling signal of the channel “2” of TB1 is set to 0. The center of gravity calculated from the time average value of each channel of TB3 is the value “9.1” shown on the right side of TB3. That is, the original center-of-gravity measurement value when there was no discharge is “9.1”.

  As described above, in the conventional method using the averaging process, a large difference is generated in the calculation result of the center of gravity depending on the presence or absence of discharge, and it is difficult to eliminate erroneous detection due to discharge. Increasing the number of parameters of the averaging process can suppress false detection to some extent. However, increasing the parameter of the averaging process is not a preferable solution because the detection sensitivity when the beam position abnormality actually occurs becomes dull.

  Therefore, in the particle beam irradiation apparatus 1 of the present embodiment, the median is obtained from the values of a plurality of signals output from the X electrode 50a and the Y electrode 50b instead of the conventional method of obtaining the time average value, and from the obtained median. The center of gravity is calculated.

  As a first embodiment, the median processing in the time direction will be described with reference to FIG. The median process in the time direction is a process for obtaining a median in the time direction, that is, a median value, from the values of a plurality of signals output in time series from the X electrode 50a and the Y electrode 50b.

  More specifically, the values of a predetermined number (parameters) output from each of the X electrode 50a and the Y electrode 50b are arranged in ascending order, and the value located at the center when arranged in ascending order is the median in the time direction. Is selected.

  In the example shown in TB4 of FIG. 11, the median for three sampling data from the first time to the third time (that is, the parameter is 3) is obtained. The value shown in TB5 is the calculated median value. For example, in the channel “11”, when the first to third values are arranged in ascending order, “1”, “2”, and “3” are obtained, and the median value and the median value are “2”. In the channel “10”, when the first to third values are arranged in ascending order, “9”, “9”, and “10” are obtained, and the median value is “9”. Similarly, in the channel “2”, when the first to third values are arranged in ascending order, they become “0”, “0”, “100”, and the median value becomes “0”.

  Since the median process is a process of extracting a value located at the center when data is arranged in ascending order, it is possible to remove sudden noise such as discharge. For this reason, the median process can reduce the error due to the discharge in the calculation of the position of the center of gravity than the average process, and the emission stop due to an erroneous interlock signal can be prevented.

  Moreover, in order to reduce the influence of a large signal due to discharge in the averaging process, it is necessary to increase the average parameter, but in the median process, it is possible to remove sudden false signals with a relatively small parameter. It is. Therefore, it is possible to increase the detection sensitivity when an actual beam position abnormality occurs.

  In addition, in the example shown in FIG. 11, although the parameter is set to 3, it is not limited to this number. For example, it is preferable that the parameter for the median processing can be changed according to the duration of sudden noise due to discharge or the like.

(4) Second embodiment (spatial median processing)
The median processing in the time direction performed in the first embodiment described above is processing for obtaining medians for a plurality of data output in time series from each channel. On the other hand, the spatial median processing performed in the second embodiment described below replaces the above-described median processing in the time direction with medians for a plurality of data output simultaneously from a plurality of channels at a certain sample time. This is the processing to be sought.

  FIG. 12 is a diagram illustrating a detailed configuration example of the beam shape calculation unit 90 according to the second embodiment. The difference from the first embodiment (FIG. 7) is that a median processing unit 99a, 99b extending over a plurality of channels is provided in place of the median processing units 94a, 94b provided individually for each channel. Is a point. The median processing units 94a and 94b in the first embodiment perform median processing in the time direction, whereas the median processing units 99a and 99b in the second embodiment perform spatial median processing. Also in the second embodiment, after the offset correction process is performed in the data correction processing units 93a and 93b, the spatial median process is performed immediately.

  FIG. 13 is a diagram illustrating the concept of spatial median processing performed by the median processing units 99a and 99b. In this spatial median processing, signals output from a plurality of channels arranged in parallel in a range of windows of a predetermined size centering on the channel of the electrode of interest among the plurality of X electrodes 50a and Y electrodes 50b. Find the median from the value. More specifically, it is processing that arranges values of signals output from a plurality of channels in the window in ascending order and sets a value located in the center when arranged in ascending order as a spatial median of the channel of interest. Therefore, the size of the window in the channel direction (that is, the spatial direction) becomes the size of the parameter to be subjected to median processing.

  TB6 in FIG. 13 illustrates the value of the output signal from each channel before performing the spatial median processing. The upper stage of TB6 is a signal value when there is no discharge, and the lower stage is a signal value when there is a discharge in channel “2”. As shown on the right side of TB6, the center of gravity calculated when there is no discharge is “9.0”, whereas the center of gravity when there is a discharge is “3.9”, which has a large error.

  TB7 and TB8 in FIG. 13 show the specific contents and results of the spatial median processing, respectively. In the example of FIG. 13, the size of the window is set to 3, and the above-described spatial median processing is performed. For example, if the channel of interest is “8”, the signal values of the three channels “7”, “8”, “9” in the window centered on the channel “8” are arranged in ascending order. “10” and “15” are obtained, and the median value and the median value are “10”. Therefore, the spatial median value for the channel of interest “8” is “10”. Further, if the channel of interest is “9”, the values of the three channels “8”, “9”, “10” in the window centered on the channel “9” are arranged in ascending order, “9”, “10” and “15” are obtained, and the median value and the median value are “10”. Therefore, the spatial median value for the channel of interest “9” is “10”.

  Similarly, if the channel of interest is “2”, the values of the three channels “1”, “2”, and “3” in the window centered on the channel “2” are arranged in ascending order. , “0”, “100”, and the median value and the median value are “0”. Therefore, the spatial median value for the channel of interest “2” is “0”. As described above, the abnormal signal value “100” of the channel “2” due to the discharge current before the spatial median processing is replaced with the normal signal value “0” by the spatial median processing.

  Since the particle beam has a certain spread, a signal is detected in a continuous channel in the actual passage of the particle beam. On the other hand, discharge is usually generated in one channel. For this reason, by performing the spatial median processing described above, it is possible to remove an erroneous signal due to discharge. As a result, it is possible to prevent the emission stop due to an erroneous interlock signal based on erroneous information such as discharge, as compared with the conventional method in which time averaging processing is performed.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 Particle beam irradiation apparatus 10 Beam generation part 20 Ejection control part 30 Beam scanning part 50 Position monitor part 50a X electrode 50b of position monitor part Y electrode 80 of position monitor part Control part 81 Scan control part 82 Abnormality determination part 90 Beam shape Calculation unit 91 Center of gravity position calculation unit 94, 99 Median processing unit

Claims (10)

A beam generator for generating a particle beam;
A beam scanning unit that two-dimensionally scans the generated particle beam according to a scanning instruction value;
A sensor unit for detecting a scanning position of the particle beam, wherein a plurality of channels of first linear electrodes are arranged in parallel in a first direction, and a plurality of channels of second linear electrodes are arranged in the first direction. A sensor unit arranged in parallel in a second direction orthogonal to
A median processing unit for removing noise generated when a sudden discharge occurs between the linear electrodes by obtaining a median from a plurality of signal values output from the first and second linear electrodes;
A center-of-gravity position calculation unit that calculates the position of the center of gravity of the particle beam from the median of the plurality of signals obtained;
When an error between the calculated center of gravity position and a preset reference scanning position is larger than a predetermined value, a control unit that stops the emission of the particle beam;
A particle beam irradiation apparatus comprising: The median is
A median in a time direction obtained from values of the plurality of signals output in time series from each of the first and second linear electrodes;
The particle beam irradiation apparatus according to claim 1. The median processing unit
A value located in the center when the values of the plurality of signals output in the time series are arranged in ascending order is the median in the time direction,
The particle beam irradiation apparatus according to claim 2. The median is
Of the first and second linear electrodes of the plurality of channels, a spatial value obtained from values of signals output from a plurality of channels arranged in parallel in a window range of a predetermined size centered on the channel of interest. A median,
The particle beam irradiation apparatus according to claim 1. The median processing unit
A value located in the center when the values of signals output from the plurality of channels are arranged in ascending order is the spatial median of the channel of interest.
The particle beam irradiation apparatus according to claim 4. Generate a particle beam,
The generated particle beam is two-dimensionally scanned according to a scanning instruction value,
In order to detect the scanning position of the particle beam, a plurality of channels of first linear electrodes are arranged in parallel in a first direction, and a plurality of channels of second linear electrodes are perpendicular to the first direction. A signal is output from the first and second linear electrodes of the sensor arranged in parallel in the direction of
By Rukoto calculated a median from the value of the plurality of signals output from the first and second linear electrodes, it removes noise which occurs when a sudden discharge between the linear electrodes is generated,
Calculate the gravity center position of the particle beam from the median of the plurality of signals obtained,
When an error between the calculated center of gravity position and a preset reference scanning position is larger than a predetermined value, the emission of the particle beam is stopped.
A control method of a particle beam irradiation apparatus characterized by the above. The median is
A median in a time direction obtained from values of the plurality of signals output in time series from each of the first and second linear electrodes;
The method of controlling a particle beam irradiation apparatus according to claim 6. A value located in the center when the values of the plurality of signals output in the time series are arranged in ascending order is the median in the time direction,
The method for controlling a particle beam irradiation apparatus according to claim 7. The median is
Of the first and second linear electrodes of the plurality of channels, a spatial value obtained from values of signals output from a plurality of channels arranged in parallel in a window range of a predetermined size centered on the channel of interest. A median,
The method of controlling a particle beam irradiation apparatus according to claim 6. A value located in the center when the values of signals output from the plurality of channels are arranged in ascending order is the spatial median of the channel of interest.
The method for controlling a particle beam irradiation apparatus according to claim 9.

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