JP6266399B2 - Neutron capture therapy device - Google Patents

Description

  The present invention relates to a neutron capture therapy system that irradiates an irradiated object with a neutron beam.

  Patent Document 1 describes a neutron beam irradiation apparatus that can improve the irradiation accuracy. In this neutron beam irradiation apparatus, a neutron is generated by irradiating a target with an ion beam in a decelerator, and the generated neutron is decelerated and then irradiated to a patient. When irradiating neutrons, the patient is placed on a mounting table that is movable relative to the speed reducer.

JP 2009-189725 A

  In neutron capture therapy using a neutron irradiation apparatus as described in Patent Document 1, it is necessary to irradiate a predetermined amount of neutrons to the affected area of the patient, and the patient's posture is kept constant during the irradiation time. . However, if the irradiation time is long, it may be several tens of minutes. During this time, it has been a heavy burden on the patient to keep the patient's posture constant.

  Then, the objective of this invention is providing the neutron irradiation apparatus which can shorten the treatment time in neutron capture therapy.

  A neutron capture therapy apparatus according to an aspect of the present invention is extracted from a negative ion source that generates negative ions, an accelerating substance supply unit that supplies an accelerating substance that promotes the generation of negative ions to the negative ion source, and the negative ion source. A particle accelerating unit that accelerates the negative ions and emits a charged particle beam; and a neutron generator that irradiates the charged particle beam emitted from the particle accelerating unit to generate neutrons.

  In this neutron capture therapy apparatus, negative ions generated in a negative ion source are accelerated by a particle acceleration unit, and a charged particle beam is emitted from the particle acceleration unit. This charged particle beam is applied to the neutron generator to generate neutrons. Here, the negative ion source is supplied with an accelerating substance that promotes the production of negative ions from the accelerating substance supply unit, so the amount of negative ions generated in the negative ion source increases and is extracted from the negative ion source. The amount of beam current that is generated increases. As the amount of negative ion beam current supplied to the particle acceleration unit increases, the amount of beam current of the charged particle beam emitted from the particle acceleration unit also increases. And if the beam current amount of the charged particle beam irradiated to a neutron production part increases, the neutron flux produced | generated in a neutron production part will increase. According to this increase in neutron flux, the neutron flux generated per unit time increases, so the time required to irradiate a predetermined amount of neutrons is shortened. Therefore, the treatment time in neutron capture therapy can be shortened.

  The neutron generation unit may include a target that generates a neutron by being irradiated with a charged particle beam, and a diffusion unit that expands a neutron irradiation range in the neutron. According to this diffusion part, the neutron irradiation range is expanded. More specifically, the range of the irradiation range of the desired neutron amount is expanded. Therefore, since it becomes possible to irradiate a relatively large affected part with a single irradiation, the treatment time in neutron capture therapy can be further shortened.

  The neutron generation unit may further include a collimator that sets a neutron irradiation range in accordance with an irradiation target in the irradiated object, and the diffusion unit may be disposed adjacent to the collimator. According to this configuration, it is possible to set and expand the neutron irradiation range suitable for the irradiation target in the irradiated object.

  According to the neutron capture therapy apparatus of the present invention, the treatment time can be shortened.

FIG. 1 is a diagram schematically showing a neutron capture therapy apparatus. FIG. 2 is a diagram illustrating the negative ion source device according to the present embodiment. FIG. 3 is a graph showing the amount of negative ion beam current output from the negative ion source apparatus according to the present embodiment and the amount of negative ion beam current output from the negative ion source apparatus according to the comparative example. is there. FIG. 4 is a contour diagram showing the distribution of neutron flux in the neutron generation section having the diffusion plate and the distribution of neutron flux in the neutron generation section according to the comparative example having no diffusion plate. FIG. 5 is a graph showing the distribution of neutron flux in the neutron generation section having the diffusion plate and the distribution of neutron flux in the neutron generation section according to the comparative example having no diffusion plate.

  Embodiments of the present invention will be described with reference to the drawings. However, the following embodiments are exemplifications for explaining the present invention and are not intended to limit the present invention to the following contents. In the description, the same reference numerals are used for the same elements or elements having the same function, and redundant description is omitted.

First, the outline | summary of the neutron capture therapy apparatus 1 provided with the negative ion source apparatus 100 is demonstrated, referring FIG. The neutron capture therapy device 1 is a device used to perform cancer treatment using boron neutron capture therapy (BNCT), and to a tumor of a patient 50 to which boron ( ¹⁰ B) is administered. Irradiate neutron beam N. The neutron capture therapy apparatus 1 includes a proton accelerator E1 having a negative ion source apparatus 100 and a cyclotron 2, a proton beam transport apparatus E2 having a beam duct 3, a quadrupole electromagnet 4 and a scanning electromagnet 5, and neutron irradiation as a neutron generator. Device 20.

  The neutron capture therapy apparatus 1 includes a cyclotron 2 as a particle acceleration unit. The cyclotron 2 is an accelerator that generates a charged particle beam R by accelerating negative ions (also referred to as negative ions) generated by the negative ion source device 100. The cyclotron 2 has a capability of generating a charged particle beam R having a beam radius of 40 mm and 60 kW (= 30 MeV × 2 mA), for example. The neutron capture therapy apparatus 1 is not limited to the cyclotron 2 as an accelerator, and a synchrotron, a synchrocyclotron, a linac, or the like may be used.

  The charged particle beam R emitted from the cyclotron 2 travels toward the target 6 through the beam duct 3. A plurality of quadrupole electromagnets 4 and scanning electromagnets 5 are provided along the beam duct 3. The scanning electromagnet 5 scans the charged particle beam R and controls the irradiation position of the charged particle beam R with respect to the target 6.

  The neutron capture therapy apparatus 1 includes a control unit S. The control unit S is an electronic control unit having a CPU, a ROM, a RAM, and the like, and comprehensively controls the neutron capture therapy apparatus 1.

  The control unit S is connected to a current monitor M that measures in real time the current value of the charged particle beam R irradiated to the target 6 (that is, charge and irradiation dose rate), and neutron capture therapy according to the measurement result. Control of each part of the apparatus 1 is performed. As the current monitor M, for example, a non-destructive DCCT (Direct Current Current Transformer) that can be measured without affecting the charged particle beam R can be used.

  The neutron irradiation apparatus 20 is irradiated with the charged particle beam R emitted from the cyclotron 2 and generates a neutron beam N irradiated by the patient 50. The neutron irradiation apparatus 20 includes a target 6, a shield 7, a moderator 8, a collimator 9, a neutron dose measurement apparatus 10, and a diffusion plate 11.

  The target 6 receives a charged particle beam R and generates a neutron beam N. The target 6 has a disk shape with a diameter of 160 mm, for example. The target 6 may be formed of, for example, beryllium (Be), lithium (Li), tantalum (Ta), or tungsten (W). The target 6 is not limited to a plate shape (solid) and may be liquid.

  The shield 7 shields the generated neutron beam N and gamma rays generated by the generation of the neutron beam N from being emitted to the outside of the neutron capture therapy apparatus 1. The moderator 8 has a function of decelerating the neutron beam N (attenuating the energy of the neutron beam N). The moderator 8 is configured by laminating a first moderator 8A and a second moderator 8B. The first moderator 8A mainly decelerates fast neutrons contained in the neutron beam N. The second moderator 8B mainly decelerates epithermal neutrons contained in the neutron beam N.

  The collimator 9 forms an irradiation field of the neutron beam N (irradiation range in a plane orthogonal to the traveling direction of the neutron beam N), and has an opening 9a through which the neutron beam N passes. The neutron beam N generated by the target 6 passes through the moderator 8 and then partially passes through the opening 9 a of the collimator 9, while the remaining part is shielded by the peripheral part that defines the opening 9 a of the collimator 9. As a result, the neutron beam N that has passed through the collimator 9 is formed into a shape corresponding to the shape of the opening 9a.

  The neutron dose measuring device 10 is a device that measures the dose and dose distribution of the neutron beam N irradiated to the patient 50 on the treatment table 51.

  The diffusing plate 11 serving as a diffusing unit spatially expands the irradiation range of the neutron beam N, and is disposed in the vicinity of the collimator 9. More specifically, the diffusing plate 11 is disposed between the second moderator 8B and the collimator 9. The diffuser plate 11 is a disk-shaped metal plate having an outer diameter comparable to that of the opening 9 a of the collimator 9. The diffusion plate 11 can be made of a material that can generate neutron scattering by atomic nuclei. For example, a stainless steel material (SUS material) or the like is used.

  Next, the configuration of the negative ion source device 100 will be described with reference to FIG. The negative ion source device 100 includes a negative ion source 102 and a vacuum box 104. The negative ion source 102 and the vacuum box 104 are connected by an insulating flange 106.

  The negative ion source 102 includes a chamber 108, a magnet 110, a plasma generation unit 112, a cesium introduction unit 114, and a plasma electrode 116.

  The chamber 108 includes a main body 108a having a cylindrical shape, and a lid 108b provided on one end side of the main body 108a. The main body 108 a forms the side wall of the chamber 108. At both ends of the main body portion 108a, flange portions 108c and 108d that protrude outward are provided. The lid portion 108b is detachably attached to a collar portion 108c located on one end side of the main body portion 108a, and opens or closes one end of the main body portion 108a. The chamber 108 communicates with a vacuum box 104 connected via an insulating flange 106. The vacuum box 104 is connected to a vacuum pump (not shown). Therefore, the inside of the chamber 108 and the vacuum box 104 is evacuated by the flow of the chamber 108 and the vacuum box 104 and the vacuum pump.

  The magnet 110 has a function of confining the plasma generated in the chamber 108 in the chamber 108. A plurality of magnets 110 are arranged on the outer peripheral surface side of the main body portion 108a. More specifically, the magnet 110 is positioned on the outer peripheral side of the chamber 108 in a state of being separated from the outer peripheral surface of the main body portion 108a. A cooling path (not shown) is provided between the magnet 110 and the outer peripheral surface of the main body 108a. In order to cool the magnet 110 or the wall portion of the main body 108a, a coolant such as water is circulated in the cooling path. The magnet 110 may be in close contact with the outer peripheral surface of the main body 108a without being separated from the outer peripheral surface of the main body 108a.

  The plasma generation unit 112 includes a main body 112a and a pair of filaments 112b extending outward from the end surface of the main body 112a (the other end side of the chamber 108 and the plasma electrode 116 side). The main body portion 112a is attached to the inner wall surface of the lid portion 108b. A DC power supply (not shown) is connected to the main body 112a. The DC power supply applies a voltage and a current to the filament 112b to generate heat, and causes a potential difference between the filament 112b and the chamber 108 (main body portion 108a).

  The cesium introduction part 114 is provided in the lid part 108b so as to penetrate the lid part 108b. The tip of the cesium introduction part 114 is located in the chamber 108. A cesium supply source 118 as a promoting substance supply unit is connected to the cesium introduction unit 114, and in this embodiment, cesium is supplied to the chamber 108 in a gas (vapor) state.

  The plasma electrode 116 is disposed between the insulating flange 120 provided on the flange portion 108d located on the other end side of the main body portion 108a and the insulating flange 106 on the vacuum box 104 side. The plasma electrode 116 is connected to a power source (not shown) having a variable voltage. By controlling the power supply to control the magnitude of the voltage applied to the plasma electrode 116, the plasma distribution in the chamber 108 is controlled, and the amount of negative ions extracted from the chamber 108 is controlled. The plasma electrode 116 has a through hole 116a through which negative ions generated in the chamber 108 can be drawn out of the chamber 108 (in this embodiment, the vacuum box 104 side). The plasma electrode 116 generates heat, for example, at about 250 ° C. due to heat input from the plasma.

  A pipe 116 b connected to the gas supply source 122 is provided in the vicinity of the plasma electrode 116. That is, the pipe 116 b is located on the other end side of the chamber 108. The gas supply source 122 includes a source gas source (hydrogen gas source) and an inert gas source (argon gas source). That is, the source gas and the inert gas from the gas supply source 122 are supplied into the chamber 108 from the other end side of the main body 108a through the pipe 116b.

  The vacuum box 104 is located on the downstream side of the chamber 108 from which the negative ion beam is extracted (the other end side of the chamber 108). The vacuum box 104 can hold the inside in a vacuum state, like the chamber 108. In the vacuum box 104, an electrode 124 such as an extraction electrode, a Faraday cup (not shown) for measuring the beam amount of the negative ion beam, a steering coil (not shown) for changing the trajectory of the negative ion beam, and the like are arranged. ing.

  In the negative ion source device 100 described above, when generating negative ions, the chamber 108 and the vacuum box 104 are first evacuated by a vacuum pump. Next, a source gas (hydrogen gas) is supplied into the chamber 108 from the gas supply source 122, and an accelerating substance (cesium gas) is supplied into the chamber 108 from the cesium supply source 118. The amount of cesium supplied by the cesium supply source 118 may be adjusted according to the amount of the negative ion beam to be extracted. Since the work function is reduced on the surface of the substance to which cesium has adhered, cesium has a function of promoting the generation of negative ions.

  Next, a current is passed through the plasma generation unit 112, and a voltage is applied between the plasma generation unit 112 and the chamber 108. When a voltage is applied between the filament 112b heated by the current flow and the chamber 108, thermoelectrons are emitted from the filament 112b to the chamber 108, and arc discharge occurs. The thermoelectrons collide with the hydrogen gas filled in the chamber 108 and eject electrons to make the hydrogen gas into plasma.

  Among electrons existing in the plasma, fast electrons and slow electrons are discriminated by a magnet. Negative ions are generated by the reaction of slow electrons or electrons on the surface of the plasma electrode 116 with hydrogen molecules, hydrogen atoms, or hydrogen ions in the plasma. The negative ions thus generated are drawn out of the chamber 108 through the opening of the plasma electrode 116 and introduced into the cyclotron 2 via the vacuum box 104.

By the way, in a boron neutron capture therapy (hereinafter referred to as BNCT) system using an accelerator neutron source in which the cyclotron 2 and the target 6 are combined, a negative hydrogen ion (hereinafter also referred to as “H ⁻ ”) beam extracted from the negative ion source device 100. Assuming that the amount is about 7 mA and the amount of proton beam current output from the cyclotron 2 is about 1 mA, the neutron irradiation time required for the treatment is about 1 hour at maximum. Thus, the neutron beam irradiation time is determined by the neutron dose obtained from the accelerator neutron source, and this neutron dose is determined by the amount of current of the charged particle beam R as a proton beam that can be output from the cyclotron 2. The amount of current of the charged particle beam R is determined by the amount of negative ion beam current supplied to the cyclotron 2.

In other words, the current amount of the charged particle beam R from the cyclotron 2 is determined by the beam current amount of negative hydrogen ions extracted from the negative ion source 102. Therefore, if the amount of H ⁻ beam current that can be output from the negative ion source device 100 can be increased, the neutron irradiation time for the patient 50 can be shortened, and the burden on the patient 50 can be reduced. In addition, if the neutron dose obtained from the accelerator neutron source can be increased, it is possible to enlarge the irradiation region (irradiation field) and to make the distribution of the neutron dose uniform by using the diffusion plate 11. Therefore, it is possible to treat a tumor that irradiates a uniform area with a uniform neutron beam.

  More specifically, if the irradiation area is simply enlarged, it can be achieved by adjusting the aperture of the collimator 9. However, only by adjusting the aperture of the collimator 9, the neutron dose outside the irradiation field becomes lower than the neutron dose near the center of the irradiation field (see FIG. 5), and it is difficult to perform efficient treatment. On the other hand, according to the neutron capture therapy apparatus 1, since the diffusion plate 11 is provided, it is possible to diffuse the neutron beam at the center of the irradiation field to the outside of the irradiation field and increase the dose outside the irradiation field. . Therefore, according to the neutron capture therapy apparatus 1, the neutron dose in the irradiation field can be made uniform while expanding the irradiation field of the neutron beam. The neutron capture therapy device 1 includes the negative ion source device 100 that can increase the amount of negative ions emitted, although the neutron dose at the center of the irradiation field is reduced by the arrangement of the diffusion plate 11. The neutron dose across the field can be raised to compensate for the decrease in dose at the center of the field.

  Therefore, the neutron capture therapy apparatus 1 accelerates the negative ions generated in the negative ion source 102 with the cyclotron 2 and outputs a charged particle beam R from the cyclotron 2. This charged particle beam R is irradiated to the neutron irradiation device 20 to generate a neutron beam N. And since the cesium which accelerates | stimulates the production | generation of a negative ion from the cesium supply source 118 is supplied to the negative ion source 102, the quantity of the negative ion produced | generated in the negative ion source 102 increases, and the negative ion source apparatus 100 The amount of beam current drawn from increases. As the amount of negative ion beam current supplied to the cyclotron 2 increases, the amount of charged particle beam R emitted from the cyclotron 2 also increases. And if the electric current amount of the charged particle beam R irradiated to the neutron irradiation apparatus 20 increases, the neutron flux produced | generated in the neutron irradiation apparatus 20 will increase. According to this increase in neutron flux, the neutron flux generated per unit time increases, so the time required to irradiate a predetermined amount of neutrons is shortened. Therefore, the treatment time in neutron capture therapy can be shortened. As a result, the burden on the patient 50 can be reduced.

  The neutron irradiation apparatus 20 includes a target 6 and a diffusion plate 11. According to the diffusion plate 11, the dose distribution in the irradiation range is made uniform while the neutron irradiation range is expanded. More specifically, the range of the irradiation range of the neutron beam having a uniform desired dose distribution is expanded. That is, by increasing the amount of neutrons, the decrease in the amount of neutrons caused by the diffusion plate 11 is kept at an amount that does not cause any problems in treatment, the neutron beam is spatially expanded to increase the irradiation area, and the neutron dose in the irradiation field is made uniform. Can be planned. Therefore, since it becomes possible to irradiate a relatively large affected part with a neutron beam having a uniform dose distribution by one irradiation, the treatment time in neutron capture therapy can be further shortened.

  The neutron irradiation apparatus 20 further includes a collimator 9 that sets a neutron irradiation range according to the shape of the affected part in the patient 50, and the diffusion plate 11 is disposed adjacent to the collimator 9. According to this configuration, it is possible to set and expand the neutron irradiation range suitable for the shape of the affected area that is the irradiation target in the patient 50.

  In short, according to the neutron capture therapy apparatus 1, a high-current beam of hydrogen ions generated by the negative ion source apparatus 100 is incident on the cyclotron 2, accelerated to a predetermined energy, and then subjected to charge conversion to form a cyclotron as a proton beam. Ejected from 2. The proton beam is incident on the neutron irradiation device 20 to generate neutrons, and the generated neutrons are decelerated by the moderator 8 constituting the irradiation system, and the irradiation range is formed by the collimator 9, and irradiated to the affected part of the patient 50. The Here, when the diffusion plate 11 is installed upstream or downstream of the collimator 9, the amount of neutrons at the center of the irradiation field is reduced by the diffusion plate 11, but the amount of neutrons outside the irradiation field increases due to spatial expansion of the neutron beam. In addition, the difference between the neutron quantity at the center of the irradiation field and the neutron quantity outside the irradiation field is reduced. The decrease in the amount of neutrons at the center of the irradiation field can be compensated for by increasing the neutrons generated in the neutron irradiation device 20 by increasing the current of the hydrogen ion beam emitted from the negative ion source device 100. That is, since the neutron capture therapy apparatus 1 includes the negative ion source apparatus 100 capable of increasing the current, the burden on the patient 50 is reduced by shortening the irradiation time, and the neutron flux due to the installation of the diffusion plate 11 is reduced. The effect of expanding the neutron irradiation range while compensating for the decrease can be achieved.

  Next, Example 1 will be described. In Example 1, the beam current amount of negative ions output from the negative ion source device 100 according to the present embodiment and the beam current amount of negative ions output from the negative ion source device according to the comparative example were measured. . FIG. 3 is a graph showing the arc power on the horizontal axis and the beam current amount of negative ions on the vertical axis. The arc power is, for example, a product of a potential difference generated between the filament 112b and the chamber 108 in the negative ion source 102 and an arc discharge current.

  Plots P1 to P5 in FIG. 3 show the beam current amount of negative ions output from the negative ion source device according to the comparative example. That is, in these plots P1 to P5, cesium is not supplied to the negative ion source device. Further, the plot P1 has a flow rate of hydrogen gas supplied to the negative ion source device of 3 sccm, the plot P2 has a flow rate of hydrogen gas supplied to the negative ion source device of 5 sccm, and the plot P3 shows the flow rate of hydrogen gas supplied to the negative ion source device. The flow rate of the supplied hydrogen gas is 8 sccm, the plot P4 is the flow rate of hydrogen gas supplied to the negative ion source device is 10 sccm, and the plot P5 is the flow rate of hydrogen gas supplied to the negative ion source device is 12 sccm. is there.

  When the plots P1 to P5 were confirmed, it was confirmed that the beam current amount of the negative ions output from the negative ion source device increased as the arc power supplied to the negative ion source device according to the comparative example increased. However, as the arc power increased, the negative ion beam current increment appeared to decrease with respect to the arc power increment. Therefore, even in the negative ion source device according to the comparative example that does not supply cesium, the beam current amount of negative ions can be increased by increasing the supplied arc power and the flow rate of hydrogen gas. It has been confirmed that there is a limit to the amount of beam current that can be increased.

  On the other hand, a plot P6 in FIG. 3 shows a beam current amount of negative ions output from the negative ion source device 100. That is, the plot P6 shows the beam current amount when cesium is supplied to the negative ion source 102. In this plot P6, the flow rate of hydrogen gas was set to 5 sccm to 7 sccm.

  When the plot P6 was confirmed, it was confirmed that the beam current amount of the negative ions output from the negative ion source 102 increased as the arc power supplied to the negative ion source 102 increased, as in the comparative example. It was also found that the amount of beam current per unit power clearly increased. For example, when the arc power is 1.5 kW, the beam current amount is about 5 mA when cesium is not supplied, whereas the beam current amount is about 8 mA when cesium is supplied. That is, by supplying cesium, it was confirmed that the beam current amount of negative ions per unit electric power supplied to the negative ion source 102 increased by about 1.5 times. Furthermore, in the range of 1.5 kW to 3.0 kW, there is no confirmation that the negative ion beam current increment gradually decreases with respect to the arc power increment as in the negative ion source device according to the comparative example. It was. It was also confirmed that a beam current amount of about 16 mA can be obtained when the arc power is about 3.0 kW.

  Thus, it was confirmed that the beam current amount of negative ions per unit power can be increased by supplying cesium to the negative ion source 102. In other words, the negative ion source 102 can reduce the amount of arc power to be supplied to the negative ion source 102 even when the same beam current amount is obtained. Accordingly, it can be confirmed that damage to the filament 102b and the like due to application of an excessive amount of electric power is reduced, time and labor required for maintenance of the negative ion source 102 are reduced, and the neutron capture therapy apparatus 1 can be operated efficiently. It was.

  Next, Example 2 will be described. In Example 2, the effect of the diffusion plate 11 was confirmed. In more detail, the spatial distribution of the neutron beam flux of the neutron production part which concerns on the neutron irradiation apparatus 20 which has the diffuser plate 11, and the comparative example which does not have the diffuser plate 11 was confirmed by calculation.

  The contour diagram shown in part (a) of FIG. 4 shows the distribution of neutron flux in the neutron irradiation apparatus 20 having the diffusion plate 11. The contour diagram shown in part (b) of FIG. 4 shows the distribution of neutron flux in the neutron generation part that does not have the diffusion plate 11. 4 (a) and 4 (b) show that the higher the color density, the higher the neutron flux. In FIG. 4A, a region A1 indicates a region where the diffusion plate 11 is disposed. The diffusion plate 11 was a disc made of a stainless steel material (SUS material). In FIGS. 4A and 4B, a region A2 indicates a phantom region that simulates a human body as an irradiated body. Further, the X direction in the figure is a direction along the central axis of the opening of the collimator 9, and the Y direction is a direction orthogonal to the X direction.

  Comparing the (a) part and (b) part of FIG. 4, in the range (x: −3 cm to +3 cm) in which the diffusion plate 11 is arranged in the X direction, the diffusion is compared with the case where the diffusion plate 11 is not arranged. When the plate 11 was disposed, it was confirmed that the neutron flux decreased.

  Next, in order to more specifically confirm the effect of expanding the neutron irradiation range by the diffusion plate 11, the distribution of the neutron flux along the line L in the portions (a) and (b) of FIG. 4 was confirmed. FIG. 5 shows the neutron flux distribution along the line L in the parts (a) and (b) of FIG. The horizontal axis of FIG. 5 shows the vertical axis (position along the X direction) of the parts (a) and (b) of FIG. 5, and the vertical axis of FIG. 5 shows the magnitude of the neutron flux. The graph G1 shows the distribution of neutron flux in the neutron irradiation apparatus 20 having the diffusion plate 11 (that is, the distribution of neutron flux in the case of part (a) in FIG. 4), and the graph G2 shows neutrons that do not make the diffusion plate 11 The distribution of the neutron flux in the generation part (that is, the distribution of the neutron flux in the case of part (b) in FIG. 4) is shown.

  When the graph G1 was confirmed, it was confirmed that the size of the neutron flux decreased in the range A3 where the diffusion plate 11 was disposed. In addition, the neutron flux increased at the base portions A4 and A5 of the graph G1. More specifically, in the range of +10 to +15 cm (base portion A5) and the range of -10 to -15cm (base portion A4) in the X direction, the size of the neutron flux is maximum as compared with the case where there is no diffusion plate. It was confirmed that it was about 10 times larger. In other words, in the distribution of neutron flux, the difference between the maximum value and the minimum value was reduced, and it was confirmed that the neutron flux distribution tends to be uniform. Accordingly, it was confirmed that the neutron irradiation range of neutrons can be expanded by arranging the diffusion plate 11. Furthermore, it has been confirmed that by optimizing the shape and installation position of the diffusion plate 11, the area where the neutron flux is uniform may be increased.

  The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.

  For example, the diffusion plate 11 may be disposed on the downstream side with respect to the collimator 9. Further, the shape and dimensions of the diffusion plate 11 may be appropriately designed according to the shape of the affected part of the patient 50.

DESCRIPTION OF SYMBOLS 1 ... Neutron capture therapy apparatus, 2 ... Cyclotron (particle acceleration part), 6 ... Target, 9 ... Collimator, 11 ... Diffusion plate (diffusion part), 20 ... Neutron irradiation apparatus (neutron production part), 100 ... Negative ion source apparatus , 102 ... Negative ion source, 108 ... Chamber, 108a ... Main body part, 108b ... Lid part, 110 ... Magnet, 112 ... Plasma generating part, 112b ... Filament, 116 ... Plasma electrode, 116a ... Through-hole, 118 ... Cesium supply source (Promoting substance supply unit), 122... Gas supply source.

Claims (2)

A negative ion source that generates negative ions;
An accelerating substance supply unit for supplying an accelerating substance that promotes the production of the negative ions to the negative ion source;
A particle acceleration unit that accelerates the negative ions extracted from the negative ion source and emits a charged particle beam;
A neutron generator that irradiates the charged particle beam emitted from the particle accelerator to generate neutrons, and
The neutron generation unit includes a target that is irradiated with the charged particle beam to generate the neutron, a moderator that decelerates the neutron generated by the target, and the neutron irradiation range while expanding the neutron irradiation range in the neutron And a collimator for setting the neutron irradiation range according to the irradiation target in the irradiated object,
The moderator is disposed on the upstream side of the collimator and larger than the collimator when viewed from a direction orthogonal to the irradiation axis of the neutron,
The diffusion unit is disposed between the moderator and the collimator, and is smaller than the collimator when viewed from a direction orthogonal to the irradiation axis, and an aperture through which the neutron included in the collimator passes. Larger than the neutron capture therapy device.   The neutron capture therapy apparatus according to claim 1, wherein the diffusion unit is disposed adjacent to the collimator.