WO2017221360A1

WO2017221360A1 - Particle therapy apparatus

Info

Publication number: WO2017221360A1
Application number: PCT/JP2016/068592
Authority: WO
Inventors: 泰三本田; 功 ▲高▼橋; 和之花川; 昌広池田; 武一郎横井; 裕介坂本; 亮平神谷
Original assignee: 三菱電機株式会社
Priority date: 2016-06-23
Filing date: 2016-06-23
Publication date: 2017-12-28
Also published as: JP6091730B1; TWI628670B; JPWO2017221360A1; TW201801095A

Abstract

The present invention is capable of shortening the time for preparations in advance and achieving highly accurate beam irradiation by including: a scanning electromagnet that scans with a charged-particle beam; and an irradiation management device that calculates the value of a set magnetic field that corresponds to target irradiation position coordinates on a subject to be irradiated on which the scanning electromagnet scans with the charged-particle beam, and calculates a set current value of the scanning electromagnet on the basis of the value of the set magnetic field and the value of a predetermined amount of variation of the magnetic field from a return magnetic field in which the magnetic moment of the scanning electromagnet reverses into the opposite direction.

Description

Particle beam therapy system

The present invention relates to a particle beam therapy apparatus used for medical use and research, and more particularly to a scanning particle beam therapy apparatus such as spot scanning or raster scanning.

In a conventional particle beam irradiation apparatus that performs scanning irradiation, in order to scan a charged particle beam, a set current of a scanning electromagnet serving as a scanning unit is temporally changed. The set current value of the scanning electromagnet can be obtained by a theoretical formula from the specifications of the scanning electromagnet, the specifications of the scanning electromagnet power source, and the specifications of the irradiation beam (irradiation energy, incident beam position, etc.). However, the setting current value of the scanning magnet calculated by this theoretical formula is a theoretical value on the assumption that the specification of the scanning electromagnet, the specification of the scanning power supply, and the irradiation beam specification are not changed at all. Since it fluctuates due to various factors, there is a possibility that the irradiation position shifts and erroneous irradiation occurs.

For example, since a scanning electromagnet is generally a bipolar electromagnet, there is a possibility that the beam irradiation position may deviate from the assumed position due to the residual magnetic field due to the hysteresis of the electromagnet, despite the opening of the electromagnet. In addition, due to aging of some other equipment, the beam irradiation position may be shifted despite irradiation under the same conditions.

Therefore, in Patent Document 1, the set current value of the scanning electromagnet and the beam position data detected by the beam position monitor are stored, and a conversion table is used based on the stored set current value and the beam position data. A method for calculating a set current value of a scanning electromagnet is disclosed. Patent Document 2 discloses a method of calculating a command value to a scanning electromagnet using a polynomial model based on the passing position coordinates of a charged particle beam actually measured at the time of calibration.

Japanese Patent Laying-Open No. 2005-296162 (paragraph 0039, FIG. 2) International Patent Publication No. WO2010 / 143267 (paragraph 0043, FIG. 6)

However, in the methods of Patent Document 1 and Patent Document 2, it is necessary to store the irradiation position before adjustment of the charged particle beam in the patient QA (Quality Assurance) before treatment, and the patient QA takes time. there were. Further, in the conventional method using one function, there is a problem that an error becomes large when irradiating a more complicated target region.

The present invention has been made to solve the above-described problems, and has an object to provide a particle beam therapy system that can shorten the time required for preliminary preparation and can realize high-precision beam irradiation. Yes.

In the particle beam therapy system according to the present invention, a scanning electromagnet that scans a charged particle beam, a set magnetic field value corresponding to a target irradiation position coordinate scanned by the scanning electromagnet, and the set magnetic field value and the scanning electromagnet And an irradiation management device that calculates a set current value of the scanning electromagnet based on a value of a predetermined magnetic field change amount from a folded magnetic field in which the magnetic moment changes in the reverse direction.

According to the present invention, high-precision beam irradiation can be realized by calculating the set current value of the scanning electromagnet based on the value of the predetermined magnetic field change amount from the folded magnetic field.

It is a block diagram which shows the main structures of the particle beam therapy apparatus in Embodiment 1 of this invention. It is a figure which shows the structure of the whole particle beam therapy apparatus in Embodiment 1 of this invention. It is a figure explaining the control method by the setting current of the scanning electromagnet in the particle beam therapy system in Embodiment 1 of this invention. It is a flowchart figure which shows the flow of the whole operation | movement of the scanning electromagnet in the particle beam therapy system in Embodiment 1 of this invention. It is a flowchart figure which shows the flow of calculation of the setting electric current value of the scanning electromagnet in the particle beam therapy system in Embodiment 1 of this invention. It is a flowchart figure which shows the flow of calculation of the setting electric current value of the scanning electromagnet in the particle beam therapy system in Embodiment 2 of this invention.

Embodiment 1 FIG.
FIG. 1 is a block diagram of the main configuration of a particle beam therapy system 100 according to Embodiment 1 of the present invention, and FIG. 2 is a bird's-eye view of the schematic configuration of the entire particle beam therapy system. As shown in FIGS. 1 and 2, the particle beam therapy system 100 according to the first embodiment includes a beam generation device 52, a beam transport system 59, two particle

beam irradiation devices

41a and 41b, and the like. The former stage accelerator 53, the accelerator 54, the beam transport system 59, the beam accelerated transport control apparatus 50, the particle beam irradiation apparatus 41, and the treatment plan apparatus 61 are provided. The front accelerator 53 accelerates the charged particles generated by the ion source to generate the charged particle beam 1. The accelerator 54 is connected to the pre-stage accelerator 53 and accelerates the generated charged particle beam 1 to a predetermined energy. The beam transport system 59 transports the charged particle beam 1 emitted after being accelerated to the energy set by the accelerator 54. The beam accelerated transport control device 50 controls each of the former stage accelerator 53, the accelerator 54, and the beam transport system 59. The particle beam irradiation apparatus 41 is installed downstream of the beam transport system 59 and irradiates the irradiation target 15 with the charged particle beam 1. The treatment planning device 61 determines the irradiation target 15 of the patient from image information obtained by X-ray CT or the like, and sets target irradiation position coordinates, target dose, target beam size, target accelerator setting, which are treatment plan data for the irradiation target 15, Generates a range shifter insertion amount and the like. The target accelerator setting includes set values of the beam energy and beam current of the accelerator 54.

The particle beam irradiation apparatus 41 includes a beam transport duct 2 that transports the incident charged particle beam 1a incident from the beam transport system 59, and incident charged particle beams in the X direction and the Y direction that are perpendicular to the incident charged particle beam 1a. Scanning electromagnets 3x and 3y that scan 1a, a position monitor 7, a position monitor unit 8, a dose monitor 11, a dose monitor unit 12, an irradiation management device 32, a scanning electromagnet power source 4, and a beam expanding device 16 , A beam expansion control device 17, a bellows 18, a vacuum duct 19, a ripple filter 20, a range shifter 21, and a range shifter unit 23. As shown in FIG. 1, the traveling direction of the incident charged particle beam 1a is the Z direction.

The scanning electromagnet 3x is an X-direction scanning electromagnet that scans the incident charged particle beam 1a in the X direction, and the scanning electromagnet 3y is a Y-direction scanning electromagnet that scans the incident charged particle beam 1a in the Y direction. The position monitor 7 detects a passing position (center of gravity position) and a beam size through which the outgoing charged particle beam 1b deflected by the scanning electromagnets 3x and 3y passes. Here, the beam size is an area passing through the XY plane perpendicular to the Z direction of the outgoing charged particle beam 1b. The position monitor unit 8 receives the passage position and beam size detected by the position monitor 7, converts the passage position and beam size into digital data, and generates measurement position coordinates and a measurement beam size.

The dose monitor 11 detects the dose of the outgoing charged particle beam 1b. The dose monitor unit 12 receives the dose detected by the dose monitor 11, converts the dose into digital data, and generates a measured dose.

The beam expanding device 16 expands the beam size of the outgoing charged particle beam 1b. The vacuum duct 19 secures a vacuum region through which the outgoing charged particle beam 1b passes. The bellows 18 connects the beam transport duct 2 and the vacuum duct 19 so as to extend and contract, and extends the vacuum region to the irradiation target 15. The ripple filter 20 is also called a ridge filter and has a convex shape. The ripple filter 20 causes the charged particle beam 1, which is a monochromatic beam having almost a single energy transmitted from the accelerator 54, to have a wide energy range.

Control of the position coordinate in the depth direction (Z direction) in the irradiation object 15 is performed by changing the acceleration energy of the accelerator 54 to change the energy of the incident charged particle beam 1a and the energy of the outgoing charged particle beam 1b by the range shifter 21. It is done by changing. The range shifter 21 adjusts the range of the charged particle beam 1 in small increments. A significant range change of the charged particle beam 1 is performed by changing the acceleration energy of the accelerator 54, and a range change of the small charged particle beam 1 is performed by changing the setting of the range shifter 21.

The irradiation management device 32 includes an irradiation control device 5 and an irradiation control computer 22. The irradiation control computer 22 reads out the treatment plan data from the server of the treatment planning device 61, and generates setting data rearranged in the irradiation order of a certain irradiation spot in the irradiation units divided to control the irradiation dose. That is, the setting data is sequenced treatment plan data. Based on the setting data, it is output to certain setting data by a command to each device.

The elements of the setting data are the target irradiation position coordinates, target dose, target beam size, target accelerator setting, range shifter insertion amount, and each element of the setting data is the target irradiation position coordinates, target dose, target This is data in which beam size, target accelerator setting, and range shifter insertion amount are sequenced. The setting data includes an accelerator setting command, a range shifter command, a command current, a command current, a beam size command, and a target dose.

The irradiation control computer 22 receives irradiation records such as measurement position coordinates, measurement dose, measurement beam size, etc. in pre-irradiation performed in the absence of a patient, and evaluates irradiation records. The irradiation control computer 22 generates a command current obtained by correcting the command current based on the measurement position coordinates, and transmits the command current or the command current to the scanning electromagnet power source 4. The irradiation control computer 22 receives irradiation records such as measurement position coordinates, measurement doses, and measurement beam sizes in the main irradiation actually irradiated to the patient, and stores the irradiation records in the main irradiation in the server of the treatment planning device 61. .

The irradiation control device 5 outputs a trigger signal, a force und start signal, a beam supply command, and a beam stop command, and controls the irradiation spot and irradiation dose in the irradiation target 15. The irradiation control device 5 changes the setting of each device for each irradiation spot by the trigger signal, starts measuring the irradiation dose of the irradiation spot by the count start signal, and controls the next irradiation spot when the measured dose reaches the target dose. When the irradiation for each of the irradiation sections (slices to be described later) divided into a plurality of irradiation objects is completed, a beam stop command is output to the beam accelerated transport control device 50 to stop the charged particle beam.

The scanning electromagnet power source 4 changes the set current of the scanning electromagnets 3x and 3y based on a command current that is a control input to the scanning electromagnet 3 output from the irradiation controller 5. The beam expansion control device 17 outputs a beam size command for setting the beam size in the position monitor 7 to the beam expansion device 16. The range shifter unit 23 outputs a range shifter command for changing the energy of the outgoing charged particle beam 1b to the range shifter 21.

FIG. 3 is a diagram for explaining a control method using the set current of the scanning electromagnet 3 in the particle beam therapy system 100 according to Embodiment 1 of the present invention. FIG. 3A shows a hysteresis curve showing the relationship between the set magnetic field and the set current in the particle beam therapy system 100, and FIG. 3B shows the spot position 60 irradiated to the irradiation target 15 corresponding to the set current. Show.

As shown in FIG. 3, the relationship between the set magnetic field and the set current of the scanning electromagnet 3 is that the magnetic field change amount with respect to the current change amount changes from the folded current (corresponding to 60-5 and 60-11 in FIG. 3) to a constant current. However, when a certain amount of current change is exceeded, it can be seen that the change in the magnetic field is proportional to the amount of current change.

From this relationship, if the magnetic field corresponding to the target irradiation position coordinates of the spot position 60 in the irradiation target 15 can be obtained as the setting magnetic field, the setting current can be obtained. The magnetic field BL, that is, the BL product, is a product of the magnetic field strength B and the effective length l of the magnetic pole of the operating electromagnet. The current value I is obtained from the target irradiation position coordinate Ps that is the irradiation planned position, the kinetic energy T and mass energy m ₀ c ^{2 of} the emitted charged particle beam, and the vertical distance L from the installation position of the scanning electromagnet to the irradiation position Ps. In consideration of the Lorentz force acting on the charged particle beam, the value of the BL product can be obtained from the position coordinates of the charged particle beam as shown in Equation (1).

Where c is the speed of light and q is the amount of hexavalent charge. If the kinetic energy T of the emitted charged particle beam and the vertical distance L from the installation position of the scanning electromagnet to the irradiation position Ps are constant, the BL product is proportional to the target irradiation position coordinate (deflection amount) Ps. It can be expressed as equation (2).

Next, the set current I is obtained from the set magnetic field BL corresponding to the target irradiation position coordinates obtained by the above equation (2). In this calculation method, the value of the current flowing through the scanning electromagnet is calculated using the amount of change from the set magnetic field turning point. The magnetic field BL and the current value I vary between the state in which the magnetic moment has not changed completely and the state in which the magnetic moment has changed, with the amount of change in the magnetic field at which the magnetic moment of the iron core of the scanning magnet changes almost completely in the opposite direction. Because the relationship changes, different formulas are used.

For example, when increasing the magnetic field from the folded magnetic field BLr (corresponding to 60-5), if the increase in the set magnetic field BL is smaller than a predetermined magnetic field change amount ΔBLm corresponding to the change of the magnetic moment, the set current value I is Calculation is performed according to the equation (3) corresponding to the curve A of 3.

When the increase in the set magnetic field BL is equal to or greater than the predetermined magnetic field change amount ΔBLm, the set current value I is calculated by the equation (4) corresponding to the straight line B in FIG.

The magnetic field change amount from BLr (corresponding to 60-11) is set as the turning point when the magnetic field is turned back in the negative direction after raising the magnetic field, that is, when the absolute value of the magnetic field change amount is less than the predetermined magnetic field change amount ΔBLm, When | ΔBL | = | BL−BLr | <ΔBLm, the set current value I is calculated by the equation (5) corresponding to the curve C in FIG.

When the absolute value of the change amount of the set magnetic field BL from the folded magnetic field BLr (corresponding to 60-11) is equal to or greater than a predetermined magnetic field change amount ΔBLm, that is, | ΔBL | = | BL−BLr | ≧ ΔBLm, The set current value I is calculated by the equation (6) corresponding to the straight line D in FIG.

Here, a, d, and e are coefficients, and b is a constant, which are obtained by fitting from the magnetic field measurement results.

Thus, high-accuracy beam irradiation can be realized by obtaining the set current value using the corresponding BL-I conversion formula based on the change amount of the magnetic field whose proportional relationship changes.

Next, the operation of the particle beam therapy system 100 according to Embodiment 1 of the present invention will be described. 4 and 5 are flowcharts of control by the set current of the scanning electromagnet 3 in the particle beam therapy system 100. FIG. FIG. 4 shows the flow of the overall operation of the scanning electromagnet 3, and FIG. 5 shows the flow of calculation of the set current value of the scanning electromagnet 3.

First, the overall operation flow will be described with reference to FIG. First, the particle beam therapy system 100 sets the charged particle energy based on the treatment plan data of the treatment planning device 61 after the scanning electromagnet is demagnetized by the irradiation control device 5 of the irradiation management device 32 (step S401). (Step S402), the target position coordinates are set (Step S403).

Subsequently, the irradiation control computer 22 of the irradiation management device 32 calculates the set magnetic field BL corresponding to the target irradiation position coordinate by the above formula (2) (step S404), and based on the calculated set magnetic field BL, the corresponding BL The set current value I is calculated by using the conversion formulas (3) to (6) of −I (step S405). Steps S404 and S405 are features of the present invention, and a detailed flow of step S405 will be described later.

Next, the calculated set current value I is set as the current value of the scanning electromagnet by the irradiation control device 5 of the irradiation management device 32 (step S406), and particle beam irradiation is performed (step S407). Irradiation continues until the irradiation at the spot reaches the target dose value (step S408: No). When the irradiation at the spot reaches the target dose value (step S408: Yes), the next spot is irradiated (step S409: No). This is repeated (step S403 to step S409: No).

The irradiation spot is a layer divided in the Z direction, and is a layer corresponding to the kinetic energy of the charged particle beam 1, and is divided into a certain slice and the XY direction in each slice. When the irradiation becomes the final spot in one slice (step S409: Yes), the spot is irradiated in the next slice (step S410: No), and this is repeated (step S403 to step S410: No). Finally, the final spot of the final slice is irradiated (step S410: Yes), and the particle beam irradiation ends.

Next, the flow of calculation of the set current value of the scanning electromagnet 3 (step S405 in FIG. 4) will be described in detail with reference to FIG. First, in the case of spot irradiation of the first point after demagnetization (step S501: Yes), the folding magnetic field is set to zero (spot S502, BL _{(i = 0)} = O). In this case, since there is no influence of the folding magnetic field, the set current value I is calculated by the equation (7) (step S503).

In spot irradiation after the second point (step S501: No), first, it is determined whether or not the spot irradiation is immediately after the folding magnetic field (step S504). That is, BL _(i) > BL _(i-1) and BL _(i-1) ≤BL _(i-2) , or BL _(i) <BL _(i-1) and BL _(i-1) ≥BL _{( i-2)} . When the spot irradiation is immediately after the folding magnetic field (step S504: Yes), the folding magnetic field BLr is set to the magnetic field BL of the immediately preceding spot, and the folding current Ir is set to the current I of the immediately preceding spot (step S505, the folding magnetic field = BL _{( i = 0)} ).

Subsequently, it is determined whether the spot irradiation is in the direction of increasing the magnetic field (step S506). That is, it is determined whether BL _(i) > folding magnetic field BLr. When spot irradiation is in the direction of increasing the magnetic field (step S506: Yes) and the magnetic field is not separated from the folded magnetic field by a predetermined magnetic field change amount ΔBLh or more, that is, when BL _(i) <BLr + ΔBLh (step S507: No), the set current I Is calculated by equation (3) (step S508). When spot irradiation is in the direction of increasing the magnetic field (step S506: Yes) and the magnetic field is separated from the folded magnetic field by a predetermined magnetic field change amount ΔBLh or more, that is, when BL _(i) ≧ BLr + ΔBLh (step S507: Yes), the set current I Is calculated by equation (4) (step S509).

When the spot irradiation is in the direction of decreasing the magnetic field (step S506: No) and the magnetic field is not separated from the folded magnetic field by a predetermined magnetic field change amount ΔBLh or more, that is, BL _(i) <BLr + ΔBLh (step S510: No), the set current I Is calculated by equation (5) (step S508). When the spot irradiation is in the direction of decreasing the magnetic field (step S506: No) and the magnetic field is separated from the folded magnetic field by a predetermined magnetic field variation ΔBLh or more, that is, when BL _(i) ≧ BLr + ΔBLh (step S510: Yes), the set current I Is calculated by equation (6) (step S512).

As described above, the particle beam therapy system 100 according to Embodiment 1 of the present invention calculates the value of the set magnetic field corresponding to the target irradiation position coordinates by the irradiation management device, and calculates the magnetic field value and the iron core of the scanning electromagnet. Since the set current value is calculated based on the value of the predetermined magnetic field change from the turning point at which the magnetic moment changes in the opposite direction, the preparation time can be shortened and high-precision beam irradiation is possible. Can be realized.

Embodiment 2. FIG.
In the first embodiment, the folding magnetic field is used as it is at the folding point, but in the second embodiment, a case where a folding history is used will be described. The configuration of the particle beam therapy system according to the second embodiment is the same as that of the particle beam therapy system 100 according to the first embodiment, and a description thereof will be omitted.

The operation of the particle beam therapy system 100 according to Embodiment 2 of the present invention will be described. Basically, the flow is the same as that shown in FIGS. 4 and 5, but the flow shown in FIG. 6 is used instead of step S505 shown in FIG.

In the case of Yes in step S504 in FIG. 5, that is, in the case where the spot irradiation is immediately after the folded magnetic field and the predetermined condition for history erasure is met (step S601: Yes), the corresponding history is erased and the set magnetic field The folding magnetic field that is the base point of the calculation is reset to the folding history, that is, the information about the setting magnetic field and the setting current value in the past folding (step S602).

When the absolute value of the magnetic field change amount ΔBL between a certain turn and the next turn is turned back in a state less than the predetermined magnetic field change amount ΔBLm, the magnetic moment is not completely reversed in the reverse direction. It will be folded. In such a case, in order to perform the conversion from the magnetic field to the current value more precisely, it is necessary to know the current magnetic moment conversion state. Information about the current value is required. Therefore, the set magnetic field BLr (n) and the set current value Ir (n) at the time of folding are recorded as a history. Although the direction of folding may be recorded, the direction of increase / decrease of the magnetic field is reversed in each folding, so that it is determined what number the history corresponds to the current setting magnetic field increase / decrease direction and the previous folding. For example, it is not always necessary to record the direction of folding at each folding.

The history deletion conditions are as follows. When the absolute value of the magnetic field change amount between the return setting magnetic fields becomes equal to or greater than the predetermined magnetic field change amount ΔBLm, the magnetic moment is completely reversed in the reverse direction. At this time, the history of the magnetic field BL in the past has no influence on the state of the magnetic moment, so that the history information so far can be deleted.

Further, the magnetic field BL changes in a direction opposite to the direction of change in the folding, and the absolute value of the difference between the magnetic field BL and the setting magnetic field in the folding is larger than a predetermined magnetic field change amount ΔBLm. The magnetic moment completely turns forward. Also in this case, the history information so far can be deleted.

If the current magnetic field BL _(i) is increasing in the positive direction and becomes larger than the maximum value of the past magnetic field BL, the maximum value of the past magnetic field BL smaller than the current magnetic field BL _(i) Since the influence on the state of the magnetic moment due to the maximum value of BL is erased by a larger maximum value or the current magnetic field, it can be deleted from the history. In this case, the local minimum value before the deleted local maximum value is set as a new folded magnetic field. Similarly, when the magnetic field BL changes in the negative direction, the influence of the past minimum value of the magnetic field BL is erased by a smaller minimum value or a current magnetic field. In this case, the maximum value before the deleted minimum value is set as a new folded magnetic field.

As described above, the particle beam therapy system 100 according to the second embodiment of the present invention uses the irradiation management apparatus when the spot irradiation is immediately after the turn-back magnetic field and the predetermined condition for history erasure is met. Since the history is deleted and the folding magnetic field is reset to the previous folding magnetic field and current value, the conversion from the magnetic field to the current value can be performed more precisely.

It should be noted that the present invention can be freely combined with each other within the scope of the invention, and each embodiment can be appropriately modified or omitted.

3, 3x, 3y scanning electromagnet, 32 irradiation management device, 100 particle beam therapy device.

Claims

A scanning electromagnet that scans the irradiation target with a charged particle beam;
A value of a set magnetic field corresponding to a target irradiation position coordinate on the irradiation target that scans the charged particle beam with the scanning electromagnet is calculated, and the setting magnetic field value and the magnetic moment of the scanning electromagnet change in opposite directions. A particle beam therapy system comprising: an irradiation management device that calculates a set current value of the scanning magnet based on a value of a predetermined magnetic field change amount from a magnetic field.
Assuming that the irradiation management device has the kinetic energy T of the charged particle beam, the mass energy m 0 c 2 , the vertical distance L from the installation position of the scanning electromagnet to the irradiation position Ps, the speed of light c, and the charge q, the following equation (1) The particle beam therapy system according to claim 1, wherein a value of the set magnetic field corresponding to the target irradiation position coordinates is calculated by (1).
When the irradiation management device increases the magnetic field from the folded magnetic field, if the increase in the set magnetic field BL is less than the predetermined magnetic field change amount ΔBL, the increase in the set magnetic field BL is determined by the formula (3) In the case where the change amount is greater than or equal to the magnetic field change amount ΔBL, a decrease in the set magnetic field BL from the set magnetic field of the folded magnetic field when the set magnetic field is turned back in a negative direction after raising the set magnetic field is predetermined according to Equation (4). When the decrease in the set magnetic field BL is less than a predetermined magnetic field change amount ΔBL, the set current value is calculated by the equation (6) when the change is less than the magnetic field change amount ΔBL. The particle beam therapy system according to claim 1 or 2.

a, d, e: coefficient b: constant Ir: current value in the folded magnetic field
2. The irradiation management device according to claim 1, wherein when the scanning by the scanning electromagnet is immediately after the folding magnetic field, the current history is erased and the folding magnetic field is reset to a past folding magnetic field and current value. The particle beam therapy system according to any one of claims 3 to 4.