JP2011000378A - Charged particle beam irradiation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the irradiation time even when the number of spots increases and also apply a target dose of beams to each spot with good accuracy in a spot scanning method.SOLUTION: A central control device 46 decides a target beam current value in advance according to the target dose so that the irradiation time is substantially uniform at every spot. An accelerator control part 47 adjusts a current value of a charged particle beam emitted from a synchrotron 4 to obtain the target beam current value. The central control device 46 calculates a delay dose to the beam current value in advance, and on reaching a set dose obtained by subtracting the delay dose from the target dose, an irradiation device control part 48 and the accelerator control device 47 start the control to output an emission stop signal and stop beam emission.

Description

  The present invention relates to a charged particle beam irradiation system which treats a diseased part such as a tumor by irradiating a charged particle beam.

  A method for treating cancer by irradiating a patient with cancer (tumor) or the like with a charged particle beam (ion beam) such as a proton beam is known. This charged particle beam irradiation system used for irradiation of the charged particle beam includes a charged particle beam generator, a beam transport system, and a treatment room.

  The charged particle beam accelerated by the charged particle beam generating apparatus reaches the irradiation apparatus in the treatment room through the beam transport system, and the distribution is expanded by the irradiation apparatus to form an irradiation field suitable for the shape of the affected part in the body of the patient.

  As a method for expanding the distribution with an irradiation apparatus, there is a method called a spot scanning method in which the position (spot) of irradiation with a thin beam is sequentially changed (scanned). In the spot scanning method, a scanning electromagnet is provided in the irradiation device, the beam is irradiated to the irradiation position of the spot with the excitation amount of the scanning electromagnet kept constant, the beam emission is stopped, and then the irradiation amount is changed by changing the excitation amount. In this method, the beam is emitted again and irradiated. The dose to be given to each spot is determined in advance as a target dose, and when the dose measured by the dose monitor in the irradiation apparatus reaches the target dose, the beam emission is stopped (Patent Documents 1 and 2).

  The beam current value at the time of irradiating each spot with a beam is usually constant regardless of the target dose of each spot. On the other hand, in Patent Document 2, in order to accurately irradiate each spot with a beam having a target irradiation amount, there is a method in which a beam current value is changed during irradiation of each spot and irradiation is performed with a small beam current value when emission is stopped. Proposed.

Japanese Patent Laid-Open No. 2005-50824 JP 2007-31125 A

  In the spot scanning method, in the conventional method of irradiating a beam with a constant beam current value regardless of the target irradiation amount during irradiation of each spot, when the target irradiation amount of each spot increases, the irradiation of each spot accordingly The time also becomes longer. As a result, especially when the number of spots is large, the irradiation time as a whole becomes long and the treatment time becomes long.

  In the method of Patent Document 2, the beam current value is changed during irradiation, and irradiation is performed with a small beam current value when extraction is stopped. However, since it takes time to switch the beam current value during irradiation of each spot, there is a possibility that the irradiation time of each spot becomes longer. As a result, the total irradiation time becomes longer and the treatment time becomes longer.

  A first object of the present invention is to provide a charged particle beam irradiation system capable of reducing the irradiation time and the treatment time even when the number of spots is increased in the spot scanning method.

  The second object of the present invention is to provide a charged particle beam irradiation system capable of shortening the irradiation time and accurately irradiating each spot with a beam having a target irradiation amount even when the number of spots increases in the spot scanning method. Is to provide.

  In order to achieve the first object, the present invention provides a charged particle beam generator having a function of adjusting a current value of a charged particle beam to be emitted, and a charged particle beam emitted according to a target irradiation amount of each spot. Adjust the current value. For this purpose, the target beam current value is determined according to the target irradiation amount of each spot. At this time, preferably, the beam current value is determined so that the irradiation time is substantially constant for each spot with reference to the target irradiation amount.

  In order to achieve the second object, the present invention outputs an emission stop signal to the charged particle beam generator before the irradiation amount of the charged particle beam irradiated to the irradiation position of each spot reaches the target irradiation amount. Then, the emission of the charged particle beam is stopped.

  In some cases, the charged particle beam generator needs a time due to a slight response delay until the beam is stopped after receiving the extraction stop signal, and there is an irradiation amount called a delayed irradiation amount applied during that time. The present inventors have found that the delayed irradiation dose depends on the beam current value.

  Therefore, the present invention outputs an extraction stop signal to the charged particle beam generator before the charged particle beam irradiation amount reaches the target irradiation amount.

  Preferably, in consideration of the delayed dose, the accuracy of dose is improved by the following method.

  The relationship between the beam current value and the delayed dose is measured and calculated in advance. A delayed dose for the beam current value determined based on the calculated relationship is calculated, and a set dose obtained by subtracting the delayed dose from the target dose is provided. When the irradiation amount measured by the dose monitor reaches the set irradiation amount, an extraction stop signal is output to start control for stopping the beam extraction. As described above, the irradiation amount including the delayed irradiation amount becomes the target irradiation amount, and the beam having the target irradiation amount can be accurately irradiated in a short irradiation time.

  According to the present invention, in the spot scanning method, even when the number of spots increases, the irradiation time can be shortened and the treatment time can be shortened.

  Further, it is possible to shorten the irradiation time and irradiate each spot with a beam having a target irradiation amount with high accuracy.

1 is a diagram showing an overall schematic configuration of a charged particle beam irradiation system according to an embodiment of the present invention. It is a cross-sectional drawing which shows the structure of the irradiation apparatus with which the charged particle beam irradiation system which is one embodiment of this invention is equipped. It is a figure which shows the dose distribution (relationship between the depth of an irradiation object, and the energy of an ion beam) obtained when an irradiation object is irradiated with an ion beam, and Fig.3 (a) is a single energy ion. FIG. 3B shows a case where a beam is irradiated, and a case where a Bragg peak is superposed by irradiating an ion beam of several energies at an appropriate intensity ratio. It is a figure which shows the dose distribution of the horizontal direction obtained when an irradiation object is irradiated with an ion beam. It is a conceptual diagram which shows the irradiation parameter memorize | stored in the database of the charged particle beam irradiation system which is one embodiment of this invention. It is a flowchart which shows the procedure in which a central controller calculates each value, such as a target beam current value. It is a conceptual diagram showing the change of the beam current value at the time of irradiating an irradiation object with an ion beam, FIG.7 (a) shows the time change of the beam current value when irradiating two spots, FIG.7 (b). Is one spot extracted from FIG. 7 (a). It is a figure which shows the example of the target irradiation amount which the central controller of the charged particle beam irradiation system which is one embodiment of this invention calculates, a target beam current value, and each irradiation amount. It is a flowchart which shows the irradiation procedure of the ion beam by the charged particle beam irradiation system which is one embodiment of this invention. It is a figure which shows the change of the beam current value at the time of irradiating an irradiation target with an ion beam, Fig.10 (a) shows the case where the conventional target beam current value is constant, FIG.10 (b) shows this invention. Therefore, the case where the beam current value is changed for each spot is shown.

  Hereinafter, a charged particle beam irradiation system according to a preferred embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing an overall schematic configuration of a charged particle beam irradiation system according to an embodiment of the present invention.

  The charged particle beam irradiation system 10 of this embodiment includes a charged particle beam generator 1, a beam transport system 2, a radiation treatment room 17, and a control system 7.

  The charged particle beam generator 1 includes an ion source (not shown), a linac 3 (previous charged particle beam accelerator), and a synchrotron 4 (accelerator). The synchrotron 4 includes a high-frequency application device 5 and an acceleration device 6. The high-frequency application device 5 includes a high-frequency application electrode (not shown) and a high-frequency application power source (not shown) disposed on the orbit of the synchrotron 4. The high frequency application electrode and the high frequency application power source are connected by a switch (not shown). The acceleration device 6 includes a high-frequency accelerating cavity (not shown) disposed in the orbit of the ion beam and a high-frequency power source (not shown) that applies high-frequency power to the high-frequency accelerating cavity. An exit deflector 11 connects the synchrotron 4 and the beam transport system 2.

  The beam transport system 2 includes a beam path 12, a quadrupole electromagnet (not shown), a deflection electromagnet 14, a deflection electromagnet 15, and a U-shaped deflection electromagnet 16. The beam path 12 is connected to an irradiation device 21 installed in the treatment room 17.

  A substantially cylindrical gantry 18 is installed in the treatment room 17. The gantry 18 is provided with a U-shaped deflecting electromagnet 16 that is a part of the beam transport system 2 and an irradiation device 21. A treatment bed called a couch 24 is installed inside the gantry 18.

  The gantry 18 has a structure that can be rotated by a motor. As the gantry 18 rotates, the U-shaped deflection electromagnet 16 and the irradiation device 21 rotate. By this rotation, the irradiation target 25 can be irradiated from any direction within a plane perpendicular to the rotation axis of the gantry 18.

  The structure of the irradiation apparatus 21 is demonstrated using FIG. The irradiation device 21 includes a scanning electromagnet 31, a scanning electromagnet 32, a beam position detector 33, and a dose monitor (irradiation amount detection device) 34. In the charged particle beam irradiation system 10 of the present embodiment, the irradiation device 21 includes two scanning electromagnets 31 and 32, and ion beams are respectively emitted in two directions (X direction and Y direction) in a plane perpendicular to the beam traveling direction. Deflection and change the irradiation position. The beam position detector 33 measures the position of the ion beam and the spread of the ion beam. The dose monitor 34 measures the amount of the irradiated ion beam. In the beam position detector 33, wires are stretched in parallel in the X direction and the Y direction at regular intervals. A high voltage is applied to the wire, and when the ion beam passes, the air in the detector is ionized, and the ionized charged particles are collected on the nearest wire. Measure the amount of charged particles collected. By stretching the wire at intervals sufficiently smaller than the spread of the ion beam, the beam distribution can be obtained, and the beam position (distribution center of gravity) and beam width (distribution standard deviation) can be calculated. In the dose monitor 34, two electrodes have a parallel plate structure, and a voltage is applied between the electrodes. When the ion beam passes through the dose monitor (irradiation amount detection device) 34, the air in the detector is ionized by the ion beam, and the ionized charged particles are accumulated on the electrode by the electric field in the detector and read out as a signal. It is. Here, since the amount of ion beam and the charge accumulated on the electrode are proportional, the amount of ion beam that has passed can be measured. There is an irradiation target 37 in the irradiation target 25, and a dose distribution that covers the irradiation target is formed in the irradiation target 25 by irradiating the ion beam. Here, in the case of treatment of cancer or the like, the irradiation target is a person and the irradiation target is a tumor (affected area).

  A control system 7 provided in the particle beam irradiation system 10 of the present embodiment will be described with reference to FIG. The control system 7 includes a database (storage device) 42, a central control device 46, an accelerator control unit 47, and an irradiation device control unit 48. The database 42 is connected to an irradiation planning system 41 connected to the X-ray CT apparatus 40. Data necessary for irradiation created by the irradiation planning system 42 is recorded in the database 42. The central controller 46 is connected to an accelerator controller 47 and an irradiation device controller 48. The central controller 46 is connected to the database 42. The central controller 46 receives data from the database 42 and transmits necessary information to the accelerator controller 47 and the irradiation device controller 48 to control it. The accelerator controller 47 is connected to the charged particle beam generator 1, the beam transport system 2, and the gantry 18 and controls them. The irradiation device control unit 48 controls the amount of excitation current flowing in the scanning electromagnets 31 and 32 and processes each monitor signal in the irradiation device 21.

  The relationship between the target depth and the ion beam energy in the particle beam irradiation system 10 according to the present embodiment will be described with reference to FIG. FIG. 3 is a diagram illustrating the relationship between the depth of the irradiation target and the energy of the ion beam.

  FIG. 3 (a) shows the dose distribution that a single energy ion beam forms in the irradiation object as a function of depth. The peak in FIG. 3A is called a Bragg peak. Since the position of the Bragg peak depends on energy, the irradiation target can be irradiated at the position of the Bragg peak by adjusting the energy of the ion beam according to the depth of the irradiation target. Although the irradiation target has a thickness in the depth direction, the Bragg peak is a sharp peak, and therefore, as shown in FIG. By overlapping the peaks, a uniform high dose region (SOBP) having the same thickness as the irradiation target is formed in the depth direction.

  The relationship between the irradiation target spread in the direction perpendicular to the beam axis (the direction of the XY plane) and the ion beam will be described with reference to FIG. The direction perpendicular to the beam axis is called the transverse direction. The ion beam reaches the irradiation device 21 and then reaches a desired position in the lateral direction by two scanning electromagnets 31 and 32 installed vertically. The lateral spread of the ion beam can be approximated by a Gaussian distribution shape. By arranging Gaussian distributions at equal intervals and setting the distance between them to the standard deviation of the Gaussian distribution, the added distribution has a uniform region. The Gaussian distribution dose distribution arranged in this way is called a spot. Irradiating an ion beam to the irradiation position of one spot while keeping the excitation amount (excitation current amount) of the scanning electromagnets 31 and 32 constant, after stopping the emission of the ion beam, changing the excitation amount and irradiating the next spot The position is changed, and the ion beam is emitted again and irradiated (spot scanning method). In this way, a uniform dose distribution can be formed in the lateral direction by scanning the ion beam by the spot scanning method and arranging a plurality of spots at equal intervals.

  As described above, a uniform irradiation field can be formed by beam scanning in the horizontal direction by the scanning electromagnet and movement of the Bragg peak in the depth direction by changing the beam energy. A unit of an irradiation field that is irradiated with the same energy and spreads laterally by ion beam scanning with a scanning electromagnet is called a slice.

  Before irradiating the irradiation target 37 with the ion beam, the irradiation planning system 41 determines each parameter necessary for irradiation in advance. A method for determining parameters by the irradiation planning system 41 will be described.

  The irradiation object 25 is imaged in advance by the X-ray CT apparatus 40. The X-ray CT apparatus 40 creates image data of the irradiation target 25 based on the acquired imaging data, and transmits the image data to the irradiation planning system 41. The irradiation planning system 41 displays the received image data on the screen of a display device (not shown). When the operator designates an area to be irradiated on the image, the irradiation planning system 41 creates data necessary for irradiation and obtains a dose distribution when irradiation is performed using the data. The irradiation planning system 41 displays the obtained dose distribution on the display device. The area to be irradiated is specified so as to cover the irradiation target 37. The irradiation planning system 41 determines and determines the installation position, gantry angle, and irradiation parameters of the irradiation target that can form a dose distribution in the designated area.

  The irradiation parameters required by the irradiation planning system 41 include ion beam energy, position information (X coordinate, Y coordinate) of each spot in a plane perpendicular to the beam axis, and a target dose of the ion beam irradiated to each position. It is. That is, the irradiation planning system 41 divides the irradiation target (affected part) 37 into a plurality of slices in the depth direction based on the patient information input by the operator, and determines the required number of slices N and slice number i. Moreover, the irradiation planning system 41 calculates | requires the energy Ei of the ion beam suitable for irradiation according to the depth of each slice (slice number i). The irradiation planning system 41 further determines the number of irradiation spots Ni, the spot number j, the irradiation position (Xij, Yij) of each spot, and the target irradiation amount Dij of each spot according to the shape of each slice. decide. The spot irradiation position (Xij, Yij) is a target irradiation position on a plane perpendicular to the beam traveling direction (depth direction) of the irradiation target.

  The irradiation planning system 41 transmits the determined information to the database 42 based on an instruction from a doctor or the like. The transmission timing may be immediately after the determination of information, or may be at the start of irradiation preparation on the treatment day when the irradiation target 37 is irradiated with an ion beam. The database 42 records data output from the irradiation planning system 41. Of each data registered in the database 42, the data structure of irradiation parameters is shown in FIG. The irradiation parameter has the number of slices N and data of each slice. The data of each slice is composed of slice number i, energy Ei, number of spots Ni, and data of each spot. The spot data further includes a spot number j, an irradiation position (Xij, Yij), and a target irradiation amount Dij.

  An operation method of the charged particle beam irradiation system 10 of the present embodiment will be described. In order to start irradiation, the irradiation target is set on the couch, and the couch 24 and the irradiation target 25 are moved to a position designated by the irradiation planning system. Based on the information stored in the database 42, the charged particle beam irradiation system 10 prepares for irradiation as follows.

  The central controller 46 reads the data registered in the database 42, and outputs the beam current value when irradiating each spot from the irradiation parameter, the delayed irradiation amount irradiated after the output stop signal is output, and the output stop signal. The dose and the set integrated dose actually used in the extraction stop control are determined.

  FIG. 6 is a flowchart showing a processing procedure for the central controller 46 to determine the above values. The central controller 46 starts the processing procedure according to an instruction from a doctor or the like, for example. The central controller 46 may start the processing procedure in conjunction with the database 42 recording the data output from the irradiation planning system 41.

  In step 201 of FIG. 6, first, the central controller 46 obtains a target beam current value from the target dose. Next, in step 202, the delayed dose is obtained from the target beam current value. Next, in step 203, the set dose is calculated from the target dose and the delayed dose. Finally, in step 204, the set integrated dose is calculated from the set dose.

  Details of the method for determining each value will be described below.

[Step 201: Determine target beam current value from target dose]
It is preferable that the irradiation time of each spot is short in order to shorten the entire irradiation time. However, it takes time to reach the target value Iij (hereinafter referred to as the target beam current value) where the beam current value is set, and the target beam current value Iij is not reached when irradiation is performed in an extremely short time. With this in mind, the target beam current value Iij is set for each spot with reference to the target dose Dij. The simplest method is to set a target beam current value Iij proportional to the target dose Dij. That is, Dij = T0 × Iij (T0: target time constant)
And FIG. 7A shows temporal changes in the beam current value when two spots are irradiated. The vertical axis represents the beam current value I, and the horizontal axis represents the time t. In this example, the target irradiation amount of the first spot 51 is small and the target irradiation amount of the second spot 52 is large. By reducing the target beam current value 53 of the spot 51 and increasing the target beam current value 54 of the spot 52, the irradiation times of the two spots become substantially equal.

  Note that the target time constant need not be one. For example, when irradiating a spot with a large irradiation amount, it is desirable to increase the target beam current value. However, the maximum beam current value that can be emitted by the charged particle emission device is determined depending on the performance of the high-frequency application device. Therefore, when the irradiation amount is large, it is necessary to set a long target time constant and adjust the target beam current value within a range where the apparatus can emit light.

  In addition, the target beam current value may be set for each of the divided spots based on the irradiation amount. This can reduce the number of necessary target beam current values.

[Step 202: Determine delayed irradiation dose from target beam current value]
FIG. 7B shows one spot extracted from FIG. 7A. The vertical axis represents the beam current value I, and the horizontal axis represents the time t. The entire area 201 shown in the figure is equal to the dose irradiated to the spot. When the extraction starts, the beam current value increases to the target beam current value Iij after the time 202 required for rising, and when the extraction stop signal is received at time 204, the beam current value decreases and the extraction stops. At this time, the electric charge emitted after receiving the emission stop signal is referred to as a delayed dose QL. The area of the portion 205 filled with diagonal lines in FIG. 7B is equal to the delayed irradiation amount. Time 206 indicates the time when the irradiation amount reaches the target irradiation amount Dij when irradiation is performed up to that time. That is, the present invention controls to irradiate the spot with the same irradiation amount as when the beam is immediately stopped at time 206 by outputting an emission stop signal at time 204.

  The inventors have found that the delayed dose QL depends on the beam current value at the moment of outputting the emission stop signal. In the present embodiment, the beam current value at the moment of outputting the extraction stop signal can be regarded as the target beam current value. Therefore, the relationship between the target beam current value Iij and the delayed dose QL is obtained in advance. The delayed dose is measured for a plurality of different target beam current values, and the measured dose is approximated to represent the delayed dose as a function of the target beam current value. That is, QL = QL (Iij) is obtained in advance. The relationship between QL and Iij can be most easily expressed by assuming that the delayed dose and the target beam current value are proportional. Although the relationship between the delayed irradiation amount and the target beam current value is obtained here, it may be obtained and substituted as the relationship between the delayed irradiation amount and the beam current value when outputting the extraction stop signal.

[Step 203: Calculate the set dose from the target dose and the delayed dose]
The set dose D0ij for outputting the emission stop signal of each spot is obtained by subtracting the delayed dose from the target dose.
D0ij = Dij−QL (Iij) = Dij−QL (Dij / T0)
Determined by

  As described above, the simplest case expressing the relationship between the delayed dose QL and the target beam current value Iij is a case where the delayed dose QL and the target beam current value Iij are assumed to be proportional. At this time, it can be expressed as QL = T1 × Iij using the proportionality constant T1. On the other hand, the target beam current value Iij can be obtained from Dij = T0 × Iij (T0: target time constant). Using these values, the expression D0ij = Dij−QL (Iij) for obtaining the set dose D0ij can be modified as follows.

D0ij = Dij−QL (Iij) = (T0 × Iij) − (T1 × Iij)
= (T0-T1) Iij
If we put T2 = T0-T1,
D0ij = T2 × Iij
Therefore, using the above formula (using the proportional constant T2), the set dose D0ij can be directly obtained from the target beam current value Iij.

[Step 204: Calculate the set integrated dose from the set dose]
A set integrated dose D1ij is set for each spot. The set integrated irradiation amount D1ij of a certain spot is a value obtained by adding the set irradiation amount D0ij of the spot to the total of the target irradiation amounts Dij of the spots irradiated before the spot.

  FIG. 8 is a diagram illustrating an example of the target irradiation amount and the target beam current value calculated by the central controller 46, the delayed irradiation amount, the set irradiation amount, and the set integrated irradiation amount.

  As described above, the simplest case is a case where the delayed dose QL and the target beam current value Iij are assumed to be proportional. In this case, QL = T1 × Iij can be expressed using a proportional constant T1. Further, the target beam current value Iij can be expressed as Dij = T0 × Iij (T0: target time constant).

  FIG. 8 shows the relationship between the target beam current value Iij and the target irradiation amount Dij and the relationship between the delayed irradiation amount QL and the target beam current value Iij in a proportional relationship, and T0 = 5 and T1 = 0.5. This is an example of the case (T2 = 4.5). The target dose Dij is a value output from the irradiation planning system, and the target beam current value Iij is obtained by dividing the target dose Dij by T0. The delayed irradiation dose QL is obtained by multiplying the target beam current value Iij by T1. The set dose D0ij is calculated by subtracting the delayed dose QL from the target beam dose Dij.

  The set integrated irradiation amount will be described by taking spot number 3 as an example. The set integrated dose for spot number 3 is 250 + 117 = 367 by adding the total target dose for spot number 1 and spot number 2 100 + 150 = 250 and the set dose 117 for spot number 3. The set integrated irradiation dose of other spots is obtained in the same manner. Although this table describes only the irradiation amount, the data of each spot has values such as a target beam current value, an irradiation position, and irradiation energy at the same time.

  When determining the target beam current value, the proportionality constant between the target irradiation amount and the target beam current value may be different for each irradiation energy. The relationship between the target beam current value and the delayed dose is preferably obtained by measuring data for all energy. However, when the number of energies is large, the relationship between the target beam current value of one energy and the delayed irradiation amount can be substituted. Alternatively, some of all energies may be selected, data representing the relationship between the target beam current value and the delayed irradiation amount may be acquired to obtain an approximate expression.

  The central control unit 46 calculates the current amount (excitation amount) for exciting the scanning electromagnets 31 and 32 from the irradiation position and its energy for each spot, in addition to the calculation of the target beam current value and the irradiation amount described above.

  With the above calculation, the central controller 46 transmits the irradiation parameter, the set irradiation amount, the set integrated irradiation amount, and the scanning electromagnet excitation current value to the irradiation device controller 48.

  The central controller 46 receives gantry angle information from the database 42 in addition to the irradiation parameters. The central controller 46 transmits the gantry angle information and the target beam current value to the accelerator controller 47.

  The accelerator controller 47 moves the gantry 18 to a desired gantry angle based on the received gantry angle information.

  Further, the central controller 46 determines the excitation current amount for exciting the synchrotron 4 and the electromagnet of the beam transport system 2 corresponding to the energy Ei of each slice, and the high frequency applied by the high frequency application device 5 based on the received irradiation parameters. The value and the value of the high frequency applied to the accelerator 6 are referred to from a memory (not shown) of the central controller 46 and transmitted to the accelerator controller 47.

  The high frequency application device 5 is configured to be able to change the intensity of the applied high frequency, and the current value of the ion beam emitted from the synchrotron 4 is adjusted by changing the intensity of the high frequency applied by the high frequency application device 5. When the value of the high frequency applied by the high frequency application device 5 is transmitted from the central controller 46 to the accelerator control unit 47, the accelerator control unit 47 applies the high frequency so that the intensity of the high frequency applied by the high frequency application device 5 becomes the value. The apparatus 5 is controlled to adjust the current value of the ion beam emitted from the synchrotron 4. That is, the charged particle beam generator 1 has a function of adjusting the current value of the ion beam (charged particle beam) emitted from the synchrotron 4.

  The ion beam irradiation procedure by the charged particle beam irradiation system 10 will be described with reference to FIG.

  The central controller 46 outputs the slice number i, the spot number j, and the energy information Ei to the accelerator controller 47 together with the irradiation start signal based on an instruction from a doctor or the like. When the first irradiation start is signaled, irradiation is started from slice number i = 1 and spot number j = 1. The accelerator controller 47 that has received the irradiation start signal activates the ion source. Ions (for example, protons (or carbon ions)) generated in the ion source are incident on the linac 3. The linac 3 accelerates and emits ions. The ion beam from the linac 3 is incident on the synchrotron 4. In step 101, the accelerator controller 47 controls the electromagnet of the synchrotron 4 and the acceleration device 6 to accelerate the ion beam incident from the linac 3 to the energy E 1 of slice number 1. That is, the accelerator control unit 47 controls the charged particle beam generator and accelerates the ion beam to a desired energy. This acceleration is performed by applying a high frequency from a high frequency power source to the high frequency acceleration cavity (giving energy to the ion beam that circulates the synchrotron 4 with high frequency power). Further, the accelerator controller 47 controls the excitation amount of the electromagnet of the beam transport system 2 so that the ion beam having the accelerated energy can be transported to the irradiation device 21.

  When the acceleration of the ion beam is completed in step 102 and the beam transport system 2 is ready, the accelerator controller 47 transmits an extraction preparation completion signal to the irradiation device controller 48.

  In step 103, the irradiation device controller 48 that has received the extraction preparation completion signal excites the scanning electromagnet 31 and the scanning electromagnet 32 with the amount of excitation current calculated by the central controller 46 corresponding to slice 1 and spot 1. In addition, the irradiation apparatus control unit 48 resets a dose counter that counts a signal from the dose monitor to 0, and sets the set integrated dose for slice 1 and spot 1.

  In step 104, the irradiation device control unit 48 confirms that the current flowing through the scanning electromagnets 31 and 32 has reached a desired value, and transmits an emission signal to the accelerator control unit 47.

  The accelerator controller 47 that has received the extraction signal in step 105 controls the high-frequency application device 5 to start extraction of the ion beam from the synchrotron 4. That is, a switch is connected and a high frequency is applied to the ion beam by the high frequency application device 5. The ion beam that orbits the synchrotron 4 within the stability limit moves outside the stability limit and is emitted from the synchrotron 4 through the extraction deflector 11. The current value of the emitted ion beam depends on the intensity of the applied high frequency. The emitted ion beam passes through the beam transport system 2 and enters the irradiation device 21 and is scanned by the scanning electromagnets 31 and 32. Then, the ion beam passes through the beam position detector 33 and the dose monitor 34 and reaches the irradiation target. To stop.

  During extraction in step 106, the irradiation apparatus control unit 48 counts the irradiation amount from the signal received from the dose monitor 34 with the dose counter, calculates the beam current value, and continues to transmit it to the accelerator control unit 47. In step 107, the accelerator controller 47 refers to the target beam current values of slice number 1 and spot number 1 being irradiated, and controls the high-frequency applying device 5 so that the beam current value being irradiated is equal to the target beam current value. Adjust the strength of the applied high frequency.

  When the irradiation amount counted by the dose counter reaches the set integrated irradiation amount, the irradiation device control unit 48 transmits an extraction stop signal to the accelerator control unit 47 in step 108.

  The accelerator controller 47 that has received the extraction stop signal in step 109 controls the high-frequency applying device 5 to stop the extraction. The ion beam emission from the synchrotron 4 is stopped by turning off the switch connecting the high-frequency application electrode and the high-frequency application power source to stop the application of the high frequency. Even after the irradiation device control unit 48 transmits the emission stop signal, the beam is irradiated for the delay of the response of the synchrotron 4. When the beam irradiation is completely stopped, the irradiation of slice number 1 and spot number 1 is completed.

  The irradiation device control unit 48 calculates the beam position based on the position detection signal, and confirms that the difference between the calculated beam position and the irradiation position of the spot data is equal to or less than a predetermined threshold value.

  In step 110, the irradiation apparatus control unit 48 compares the spot number N1 of the slice number 1 with the spot number j. If the spot number j does not reach the number of spots, the operation of step 103 is started to start irradiation of the next spot number j + 1. When the spot number j reaches the number of spots N1, the irradiation device control unit 48 outputs a deceleration signal to the accelerator control unit 47, and in step 111, the accelerator control unit 47 controls the electromagnet of the synchrotron 4 to The remaining ion beam is decelerated.

  In step 112, the slice number i is compared with the slice number N. If the slice number i does not reach the slice number N, the process proceeds to step 101, and preparation for irradiation of the next slice i + 1 is started. When the slice number i reaches the slice number N, the irradiation is completed.

  In the above, the processing functions of step 106 of the irradiation device control unit 48 and step 107 of FIG. 9 of the accelerator control unit 47 are charged particles so as to adjust the current value of the charged particle beam emitted according to the target irradiation amount of each spot. The first control means for controlling the beam generator 1 is configured, and the processing functions of step 108 of the irradiation device control unit 48 and step 109 of FIG. 9 of the accelerator control unit 47 are the charged particles irradiated to the irradiation position of each spot. A second control means for controlling the charged particle beam generator 1 so as to stop the emission of the charged particle beam by outputting an extraction stop signal to the charged particle beam generator 1 before the beam dose reaches the target dose; Constitute.

  Further, the processing function of step 201 in FIG. 6 of the central controller 46 constitutes first calculation means for determining the target beam current value according to the target irradiation amount of each spot, and the processing of steps 202 to 204 in FIG. The function constitutes a second calculation means for determining the set dose according to the target beam current value.

  The irradiation monitor 34 constitutes an irradiation amount detection device that measures the irradiation amount of the charged particle beam irradiated to the irradiation position of each spot, and the second control means calculates the irradiation amount measured by the irradiation amount detection device. When the input dose reaches a set dose smaller than the target dose, an output stop signal is output to the charged particle beam generator 1 to stop the emission of the charged particle beam. Control. Whether or not the irradiation amount has reached a set irradiation amount smaller than the target irradiation amount is determined by comparing the irradiation amount with the set integrated irradiation amount.

  In step 108, instead of comparing the irradiation amount with the set integrated irradiation amount and outputting the beam extraction stop signal, the irradiation time is measured and the extraction stop signal is output when the irradiation time reaches a preset time. You can also. The irradiation time is measured from the time when the emission start signal is output, and is set to a preset time. The set time is the target time constant. After the set time has elapsed, an extraction stop signal is output, and after the beam extraction has stopped, the irradiation amount and the target irradiation amount are compared. Since the dose does not necessarily match the target dose, the difference is added to the target dose to be irradiated to the next spot. In order to change the target irradiation amount of the next spot, the irradiation time of the next spot is changed or the beam current value is changed. Specifically, when the irradiation amount is larger than the target irradiation amount, the next spot setting time is shortened from a preset time, or the target beam current value is decreased. When the irradiation amount is smaller than the target irradiation amount, the set time is lengthened or the target beam current value is increased. In order to bring the total irradiation amount close to a desired value, the difference between the irradiation amount and the target irradiation amount is adjusted by the irradiation amount of the next spot as described above.

  The effects obtained by using the system described above will be described.

  Since the target beam current value is determined according to the target irradiation amount of each spot, all the spots can be irradiated in the minimum necessary time. Therefore, irradiation time can be shortened and treatment time can be shortened.

  In addition, since the emission stop signal is output before the irradiation dose at each spot irradiation position reaches the target dose to stop the emission of the charged particle beam, the target beam current value is changed according to the target dose. In addition, it is possible to irradiate each spot with a beam having a target irradiation amount with high accuracy.

  FIG. 10 is a diagram for explaining the latter effect in comparison with the prior art.

  The delayed irradiation amount irradiated after outputting the emission stop signal depends on the beam current value. Therefore, when irradiation is performed with a different beam current value for each spot, the delayed irradiation amount varies greatly for each spot.

  A case where a conventional set dose is not provided will be described. FIG. 10A shows a case where the target beam current value is constant. The dose until the time when the first spot emission stop signal is output is A, the delayed dose is B, the dose until the time when the second spot emission stop signal is output is C, and the delayed dose is D. To do. By outputting the extraction stop signal based on the integrated dose of the measured dose output from the dose monitor, the delayed dose of consecutive spots is subtracted, so that the error of the spot dose is small. That is, taking the second spot in FIG. 10A as an example, the irradiation amount measured by the dose monitor is B + C, but the irradiation amount actually irradiated to the second spot is C + D. When the target beam current values are equal, the delayed irradiation doses B and D are approximately equal, so that irradiation can be performed with high accuracy.

  On the other hand, FIG. 10B shows a case where the beam current value is changed for each spot. Similarly to the case of FIG. 9A, the irradiation amount and delayed irradiation amount of the first spot are E and F, and the irradiation amount and delayed irradiation amount of the second spot are G and H. Since the delayed irradiation dose depends on the beam current value, F and H are expected to be different.

  In this embodiment, a delayed irradiation amount depending on the beam current value is obtained in advance, and the irradiation amount including the delayed irradiation amount is output by outputting an emission stop signal when the irradiation amount is subtracted by the amount of the delayed irradiation amount. Is made equal to the target irradiation amount of each spot. This makes it possible to irradiate each spot with a beam having a target irradiation amount with high accuracy.

  Further, the delayed irradiation amount depends particularly on the beam current value at the moment of outputting the extraction stop signal. According to the present embodiment, there is an advantage that the beam current value during irradiation should coincide with the target beam current value at the moment when the set irradiation amount is reached regardless of the beam current value immediately after the start of extraction.

  Although the present embodiment has been described using a synchrotron as a charged particle beam extraction apparatus, even in the case of a cyclotron, a delayed irradiation amount is generated when the extraction of the ion beam stops, so the irradiation time can be shortened by the same control. It is.

DESCRIPTION OF SYMBOLS 1 Charged particle beam generator 2 Beam transport system 3 Linac 4 Synchrotron 5 High-frequency application device 6 Accelerator 7 Control system 11 Deflector for extraction 12 Beam path 14 and 15 Deflection magnet 16 U-shaped deflection electromagnet 17 Treatment room 18 Gantry 21 Irradiation Device 24 Couch 25 Irradiation target 31, 32 Scanning magnet 33 Beam position detector 34 Dose monitor 37 Irradiation target 40 X-ray CT device 41 Irradiation plan system 42 Database 43 Equipment control system 44 Positioning system 45 Irradiation field confirmation system 46 Central control device 47 Accelerator control unit 48 Irradiation device control unit

Claims (11)

A charged particle beam generator for emitting a charged particle beam;
An irradiation device that has a charged particle beam scanning device and irradiates an irradiation target to be irradiated with the charged particle beam emitted from the charged particle beam generation device;
The charged particle beam is emitted from the charged particle beam generation device by irradiating the irradiation position of one spot set on the irradiation target with a constant excitation amount of the scanning electromagnet of the charged particle beam scanning device. The charged particle beam generator so as to emit the irradiated particle beam again from the charged particle beam generator, and to irradiate the charged particle beam generator. A control device for controlling the irradiation device,
The charged particle beam generator has a function of adjusting the current value of the emitted charged particle beam,
The charged particle beam irradiation characterized by the said control apparatus having a 1st control means which controls the said charged particle beam generator so that the electric current value of the charged particle beam radiate | emitted according to the target irradiation amount of each spot may be adjusted. system. The control device further includes first calculation means for determining a target beam current value according to a target irradiation amount of each spot,
The said 1st control means adjusts the electric current value of the charged particle beam radiate | emitted from the said charged particle beam generator using the target beam current value determined by the said 1st calculating means, The said 1st calculating means is characterized by the above-mentioned. Charged particle beam irradiation system.   The controller outputs an emission stop signal to the charged particle beam generator before the charged particle beam irradiation amount irradiated to the irradiation position of each spot reaches the target irradiation amount, and the charged particle beam 2. The charged particle beam irradiation system according to claim 1, further comprising second control means for controlling the charged particle beam generation apparatus so as to stop the emission of the charged particle beam. The control device further includes an irradiation amount detection device that measures an irradiation amount of the charged particle beam irradiated to an irradiation position of each spot,
The second control means inputs an irradiation amount measured by the irradiation amount detection device, and outputs an emission stop signal to the charged particle beam generator when the irradiation amount reaches a set irradiation amount smaller than the target irradiation amount. The charged particle beam irradiation system according to claim 3, wherein the charged particle beam generator is controlled so as to stop the emission of the charged particle beam. The control device further includes first calculation means for determining a target beam current value according to the target irradiation amount of each spot, and second calculation means for determining the set irradiation amount according to the target beam current value. Have
The first control means adjusts the current value of the charged particle beam emitted from the charged particle beam generator using the target beam current value determined by the first calculation means,
The second control unit outputs an extraction stop signal to the charged particle beam generator when the irradiation amount measured by the irradiation amount detection device reaches a set irradiation amount determined by the second calculation unit. The charged particle beam irradiation system according to claim 4.   The first calculating means stores in advance a relational expression between a target irradiation quantity and a target beam current value at which a ratio of the target irradiation quantity and the target beam current value is constant, and the target expression is calculated using this relational expression. 6. The charged particle beam irradiation system according to claim 2, wherein the target beam current value is calculated from an irradiation amount.   The charged particle beam according to claim 2 or 5, wherein the first calculation means determines a target beam current value according to a target irradiation amount of each spot so that an irradiation time for each spot is constant. Irradiation system.   The second calculation means determines a delayed irradiation amount to be irradiated after the output of the extraction stop signal according to the target beam current value, and determines the set irradiation amount by subtracting the delayed irradiation amount from the target irradiation amount. The charged particle beam irradiation system according to claim 5. The control device further includes a storage device that stores a relationship between a current value of the charged particle beam and a delayed irradiation amount irradiated after the output of the extraction stop signal.
The charged particle beam irradiation system according to claim 8, wherein the second calculation unit determines the delayed irradiation amount with reference to the target beam current value in the relationship.   The second calculation means presets the relationship between the current value of the charged particle beam and the delayed dose irradiated after the output of the extraction stop signal as a function approximating measurement data, and uses this function. The charged particle beam irradiation system according to claim 8, wherein the delayed irradiation amount is determined from the target beam current value.   The second calculating means stores in advance a relational expression between the target beam current value and the set irradiation amount at which the ratio of the target beam current value and the set irradiation amount is constant, and the target beam current is calculated using the format during this period. The charged particle beam irradiation system according to claim 5, wherein the set irradiation amount is calculated from a value.

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