JP2013061295A - Neutron ray irradiation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a neutron ray irradiation device to be generally usable for various sizes of affected parts.SOLUTION: A neuron ray treatment device 1 includes: an accelerator; a target T for generating neuron rays with a charged particle ray P from the accelerator; a moderator 50 for decelerating the neutron rays and emitting a treatment neuron ray N; and a collimator 46 for irradiating a patient with the treatment neutron ray N from the moderator 50 through an opening 46a. When the treatment neutron ray N to be emitted through the opening 46a is made incident on a water phantom 60, any one of thermal neutron fluxes at predetermined reference positions Q2, Q3, Q4 is set to be equal to or more than 0.2 times of the thermal neutron flux at a reference position Q1 that is arranged on an irradiation center axial line C of the treatment neutron ray N and having a depth of 20 mm from an incident surface 60a.

Description

  The present invention relates to a neutron beam irradiation apparatus.

  As one of radiotherapy in cancer treatment or the like, there is boron neutron capture therapy (BNCT: BoronNCT) in which cancer treatment is performed by irradiation with a neutron beam. Conventionally, a neutron beam therapy apparatus (BNCT apparatus) for performing this boron neutron capture therapy has been developed. For example, in Patent Document 1, a proton beam (charged particle beam) is generated by an accelerator such as a cyclotron, and tantalum or A neutron beam is generated by irradiating a target such as tungsten with a proton beam, and the target is irradiated with the generated neutron beam.

JP 2007-240330 A

  In BNCT, it is necessary to apply neutron beam energy to the entire affected part even to a somewhat large affected part (tumor), and it is possible to irradiate the affected part of various sizes with neutron rays for general purposes. desired. However, in the technique of the above-mentioned Patent Document 1, no consideration is given to versatility that can deal with various sizes of affected areas.

  In view of such circumstances, an object of the present invention is to provide a neutron beam irradiation apparatus that can be used universally for an affected part of various sizes.

  The neutron beam irradiation apparatus of the present invention includes an accelerator that accelerates charged particles and emits a charged particle beam, a neutron beam generation unit that generates a neutron beam when a charged particle beam from the accelerator is incident, and a neutron from the neutron beam generation unit A collimator that has a decelerating unit that decelerates and emits a line, and an opening that defines an irradiation field of the neutron beam, and that irradiates the irradiated body with a therapeutic neutron beam from the decelerating unit through the opening. When the therapeutic neutron beam emitted from the incident surface of the water phantom is incident on the water phantom, the treatment neutron beam has a depth of 20 mm from the incident surface on the central axis of the irradiation field of the therapeutic neutron beam in the water phantom. The position is defined as a reference position Q1, the position 60 mm deep from the incident surface on the central axis in the water phantom is defined as the reference position Q2, and the edge of the collimator opening in the water phantom The position at a depth of 20 mm from the incident surface on the opening edge axis extending parallel to the central axis is the reference position Q3, and the position at a depth of 60 mm from the incident surface on the opening edge axis in the water phantom is the reference position. When Q4, the thermal neutron flux G2 at the reference position Q2 is 0.2 times or more the thermal neutron flux G1 at the reference position Q1, and the thermal neutron flux G3 at the reference position Q3 is 0 of the thermal neutron flux G1 at the reference position Q1. The accelerator, the neutron beam generation unit, and the deceleration unit are set so that the thermal neutron flux G4 at the reference position Q4 is 0.2 times or more the thermal neutron flux G1 at the reference position Q1. It is characterized by that.

  According to the neutron beam irradiation apparatus, neutron beam energy can be applied to a region between 20 and 60 mm in depth within the patient body at a position corresponding to the opening of the collimator at a somewhat high dose rate. Therefore, the treatment neutron beam having a dose necessary for treatment can be irradiated to the entire affected area even to a somewhat large affected area that exists over a depth of 20 to 60 mm.

  ADVANTAGE OF THE INVENTION According to this invention, the neutron beam irradiation apparatus which can be used universally with respect to the affected part of various magnitude | sizes can be provided.

It is a figure which shows the structure of the neutron beam therapy apparatus which concerns on one Embodiment of this invention. It is a schematic cross section which shows the vicinity of the neutron beam output part in the neutron beam therapy apparatus of FIG. It is a schematic sectional drawing which shows the state which installed the water phantom in the radiation | emission direction front of the neutron beam therapy apparatus of FIG. It is a figure which shows distribution of the neutron flux of a thermal neutron beam by an isoline when a neutron beam injects into the water phantom of FIG. It is a graph which shows distribution of the neutron flux (flux) of a thermal neutron beam on the irradiation center axis C in the water phantom of FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the same or equivalent elements will be denoted by the same reference numerals, and redundant description will be omitted. The terms “upstream” and “downstream” mean upstream (accelerator side) and downstream (patient side) of the emitted charged particle beam and neutron beam, respectively.

A neutron beam therapy apparatus (neutron beam irradiation apparatus) 1 shown in FIG. 1 is an apparatus for performing cancer treatment using boron neutron capture therapy (BNCT: BoronNCT), and a patient to whom boron 10 ( ¹⁰ B) has been administered ( Irradiation body 40) is irradiated with neutron beam N. The neutron beam treatment apparatus 1 includes an accelerator 10 (for example, a cyclotron), and the accelerator 10 accelerates charged particles (for example, protons) to generate and emit a charged particle beam P (for example, proton beam). The accelerator 10 here has, for example, the ability to generate a charged particle beam P having a beam radius of 40 mm and 60 kW (= 30 MeV × 2 mA).

  The charged particle beam P emitted from the accelerator 10 includes a horizontal steering 12, a four-direction slit 14, a horizontal vertical steering 16, a quadrupole electromagnet 18, 19, 20, a 90-degree deflection electromagnet 22, a quadrupole electromagnet 24, The light passes through the horizontal / vertical steering 26, the quadrupole electromagnet 28, the four-direction slit 30, the current monitor 32, and the charged particle beam scanning unit 34 sequentially, and is guided to the neutron beam output unit 36. The neutron beam output unit 36 emits (outputs) the neutron beam N generated by irradiating the target T with the charged particle beam P, and the patient 40 on the treatment table 38 is irradiated with the neutron beam N.

  The horizontal steering 12 and the horizontal / vertical steering 16, 26 perform beam axis adjustment of the charged particle beam P using, for example, an electromagnet. Similarly, the quadrupole electromagnets 18, 19, 20, 24, and 28 suppress the divergence of the beam of the charged particle beam P using, for example, an electromagnet. The four-direction slits 14 and 30 perform beam shaping of the charged particle beam P by cutting off the end beam.

  The 90-degree deflecting electromagnet 22 deflects the traveling direction of the charged particle beam P by 90 degrees. The 90-degree deflection electromagnet 22 is provided with a switching unit 42, and the switching unit 42 can remove the charged particle beam P from the normal trajectory and guide it to the beam dump 44. The beam dump 44 can check the output of the charged particle beam P before treatment or the like.

  The current monitor 32 measures the current value of the charged particle beam P irradiated to the target T of the neutron beam output unit 36 (that is, charge, irradiation dose rate) in real time. As the current monitor 32, a non-destructive DCCT (DC Current Transformer) capable of measuring current without affecting the charged particle beam P is used. A predetermined controller is connected to the current monitor 32. “Dose rate” means a dose per unit time (the same applies hereinafter).

  The charged particle beam scanning unit 34 scans the charged particle beam P and controls irradiation of the charged particle beam P to the target T. The charged particle beam scanning unit 34 here controls, for example, the irradiation position of the charged particle beam P with respect to the target T, the beam diameter of the charged particle beam P, and the like.

  As shown in FIG. 2, the neutron beam output unit 36 includes a target (neutron beam generation unit) T disposed at the downstream end of the beam duct 48 through which the charged particle beam P passes, and a neutron beam N generated at the target T. A moderator (deceleration unit) 50 that decelerates, a shield 52 provided so as to cover them, and a collimator 46 attached to the downstream end of the shield 52.

  The target T generates a neutron beam N when irradiated with the charged particle beam P. The target T here is made of beryllium (Be), for example, and has a disk shape with a diameter of 160 mm. The type of the target T is set according to the energy of the charged particle beam P of the accelerator 10. Specific examples of typical combination settings of the accelerator 10 and the target T will be given as setting examples 1 to 3 below.

(Setting example 1)
As the accelerator 10, an electrostatic accelerator or a linear accelerator is used. The charged particle beam output from the accelerator 10 is a proton beam, and the proton energy of the proton beam is 1.9 to 10 MeV. For example, the accelerator 10 may output a 2.8 MeV proton beam at 20 mA or more. As the target T, a lithium target is used. In this case, metallic lithium (solid) may be used as the target T, or liquid lithium may be circulated and used as the target T.

(Setting example 2)
As the accelerator 10, a linear accelerator, a cyclotron, or FFAG (fixed magnetic field strong convergence accelerator) is used. The charged particle beam output from the accelerator 10 is a proton beam, and the proton energy is 8 to 40 MeV and 0.6 mA or more. As the target T, a helium target or a beryllium target is used.

(Setting example 3)
A cyclotron, synchrotron, or FFAG is used as the accelerator 10. The charged particle beam output from the accelerator 10 is a proton beam, and the proton energy is 30 MeV or more. As the target T, a target of heavy metal such as tantalum, tungsten, or mercury is used.

  The moderator 50 decelerates the neutron beam N emitted from the target T to obtain a therapeutic neutron beam N with reduced energy. The moderator 50 has, for example, a laminated structure made of a plurality of different materials. The material of the moderator 50 is appropriately selected according to various conditions such as the energy of the charged particle beam.

  The shield 52 shields the neutron beam N and gamma rays generated by the generation of the neutron beam N from being emitted to the outside, and is attached to the floor of the treatment room. The collimator 46 includes a circular opening 46a serving as an output port of the therapeutic neutron beam N, and defines an irradiation field of the therapeutic neutron beam N. Hereinafter, a virtual axis that passes through the center of the irradiation field defined by the collimator 46 (the center of the opening 46a) and extends in the upstream and downstream direction of the therapeutic neutron beam N is referred to as an “irradiation center axis”, and the symbol “C” is denoted by “C”. Attached is shown. The irradiation center axis C is orthogonal to the downstream end face of the opening 46a of the collimator 46.

  In the neutron beam output unit 36, the target (neutron beam generation unit) T is irradiated with the charged particle beam P scanned by the charged particle beam scanning unit 34, thereby generating a neutron beam. The generated neutron beam is decelerated by the moderator 50 to become a therapeutic neutron beam N. The therapeutic neutron beam N emitted from the moderator 50 passes through the opening 46 a of the collimator 46 and is irradiated to the patient 40 on the treatment table 38. The beam of therapeutic neutron beam N includes gamma rays, fast neutron rays, epithermal neutron rays, and thermal neutron rays. Of these, the thermal neutron beam mainly reacts with the boron 10 taken into the tumor in the patient 40 to exert an effective therapeutic effect. A part of the epithermal neutron beam included in the beam of the therapeutic neutron beam N also becomes a thermal neutron beam that is decelerated in the body of the patient 40 and exhibits the above therapeutic effect. A thermal neutron beam is a neutron beam having an energy of 0.5 eV or less.

  Next, setting of the intensity of the therapeutic neutron beam N output from the neutron beam therapy apparatus 1 will be described.

In setting the intensity of the therapeutic neutron beam N, it is necessary to appropriately adjust the equivalent dose rate of the treatment for the patient 40. Here, the items that affect the equivalent dose rate of treatment are mainly (a) the reaction between thermal neutron rays and boron 10, (b) the reaction between thermal neutron rays and nitrogen which is a biological constituent element, ( C) There is a reaction between fast neutron rays and hydrogen which is a biological constituent element, and (d) a reaction between gamma rays and a living body. That is, the equivalent dose rate of treatment with the therapeutic neutron beam N is expressed as the following formula (A).
(Equivalent dose rate of treatment) =
(Thermal neutron flux) ・ a1 + (thermal neutron flux) ・ a2 + (fast neutron flux) ・ b + (gamma ray flux) ・ 1.0… (A)
However, a1, a2, and b in the formula (A) are known coefficients.
The first term relating to the thermal neutron flux in the right side of the formula (A) occupies 90 to 95% of the equivalent dose rate of treatment. Therefore, in the neutron beam therapy apparatus 1, the equivalent dose rate of treatment with the therapeutic neutron beam N is adjusted by adjusting the thermal neutron flux. Hereinafter, adjustment of the thermal neutron flux in the therapeutic neutron beam N will be described.

  As shown in FIG. 3, consider a case in which a water phantom 60 is installed on the downstream side of the collimator 46 and the therapeutic neutron beam N is incident from the incident surface 60 a of the water phantom 60. At this time, the incident surface 60 a of the water phantom 60 is brought into contact with the opening 46 a of the collimator 46. In the following, the radius of the opening 46a of the collimator 46 is assumed to be r.

  Here, when a neutron beam is incident on the water phantom 60 as described above, the neutron flux of the thermal neutron beam has a distribution as shown in FIG. FIG. 4 shows an isoline of the neutron flux of the thermal neutron beam in the plane including the irradiation center axis C, and is an example when the radius r of the opening 46a of the collimator 46 is 50 mm. In FIG. 4, a straight line with horizontal position = 0 mm corresponds to the irradiation center axis C, the vertical axis (horizontal position) represents the distance from the irradiation center axis C, and the horizontal axis (depth) from the incident surface 60a. Depth measured in the direction of the irradiation center axis C. Each value given to each isoline in FIG. 4 represents the ratio of the neutron flux value at each location to the peak neutron flux value (1.0). In the water phantom 60, the neutron flux (flux) of the thermal neutron beam on the irradiation center axis C shows a distribution as shown in FIG.

  As understood from FIGS. 4 and 5, the peak of the neutron flux of the thermal neutron beam is located at a depth of about 20 mm on the irradiation center axis C in the water phantom 60 irradiated with the therapeutic neutron beam N. is there. Then, the neutron flux gradually decreases from the peak position toward the periphery.

  In view of this knowledge, in the present embodiment, four reference positions Q1, Q2, Q3, and Q4 are defined in the water phantom 60 as shown in FIG. In addition, the neutron flux of the thermal neutron beam at each of the reference positions Q1, Q2, Q3, and Q4 is represented by G1, G2, G3, and G4, respectively.

  The reference position Q1 is a position at a depth of 20 mm from the incident surface 1a on the irradiation center axis C, and is a position where the neutron flux of the thermal neutron beam peaks. The reference position Q2 is a position having a depth of 60 mm from the incident surface 1a on the irradiation center axis C.

  Further, a virtual axis parallel to the irradiation center axis C through the edge 46c of the opening 46a of the collimator 46 is considered. Hereinafter, this virtual axis is referred to as an “opening edge axis”, and is denoted by a reference sign “D”. The opening edge axis D exists away from the irradiation center axis C by a distance equal to the radius r of the opening 46a (here, r = 50 mm). The reference position Q3 is a position having a depth of 20 mm from the incident surface 1a on the opening edge axis D. That is, the reference position Q3 is a position away from the irradiation center axis C by a distance r and 20 mm away from the incident surface 1a. Further, the reference position Q4 is a position having a depth of 60 mm from the incident surface 1a on the opening edge axis D. That is, the reference position Q4 is a position away from the irradiation center axis C by a distance r and 60 mm from the incident surface 1a.

  Since the distribution of the thermal neutron flux in the radial direction around the irradiation center axis C may be considered to be the same in each direction, the opening edge axis D is a cylinder having a radius r with the irradiation center axis C as the cylinder axis. Any position on the surface may be set. The reference position Q3 may be set at any position on the circumference of the radius r centered on the reference position Q1 in a plane orthogonal to the irradiation center axis C. Similarly, the reference position Q4 may be set at any position on the circumference of the radius r centered on the reference position Q2 in a plane orthogonal to the irradiation center axis C.

After setting the reference positions Q1 to Q4 as described above, the neutron beam therapy apparatus 1 is set so as to satisfy the condition of the following expression (1).
G2 / G1 ≧ 0.2 and G3 / G1 ≧ 0.2 and G4 / G1 ≧ 0.2 (1)
The condition that satisfies the above formula (1) is hereinafter referred to as “reference irradiation condition”. The neutron beam therapy apparatus 1 that satisfies the above-mentioned reference irradiation conditions mainly selects the type of the target T appropriately and adjusts the current amount of ions (charged particle beam P) incident on the target T from the accelerator 10. Furthermore, it is realized by appropriately selecting 50 types of moderators.

  Thermal neutron fluxes G1 to G4 at reference positions Q1 to Q2 in the water phantom 60 are measured by the following method. A gold sample (for example, a gold wire) is placed in the water phantom 60. With the water phantom 60 installed as shown in FIG. Irradiate. Since gold has the property of absorbing and activating thermal neutrons, the gold sample in the water phantom 60 is activated by the therapeutic neutron beam N. After the irradiation is completed, the gold sample is collected, and a specific gamma ray emitted from the gold sample is measured to measure the activation amount of the gold sample. Furthermore, irradiation and measurement similar to the above are performed using a gold sample covered with cadmium, and the activation amount of the sample is measured.

  Since there is a known correlation between the activation amount of these samples and the thermal neutron flux, the above correlation is obtained by subtracting the activation amount of the gold sample covered with cadmium from the activation amount of the gold sample. The thermal neutron flux can be calculated based on the relationship. The thermal neutron fluxes G1 to G4 at the reference positions Q1 to Q4 are obtained by performing the above analysis on the parts located at the reference positions Q1 to Q4 among the gold sample and the gold sample covered with cadmium.

  The fast neutron flux of the therapeutic neutron beam N can also be calculated from the activation amount of the sample by using an indium sample or an aluminum sample instead of the gold sample. The gamma ray bundle of the therapeutic neutron beam N can also be measured using a TLD (thermoluminescence probe).

  Examples of specific settings for the combination of the accelerator 10, the target T, and the moderator 50 for satisfying the reference irradiation conditions will be given as setting examples A to D below.

(Setting example A)
The output from the accelerator 10 is a 30 MeV proton beam, and a beryllium target is used as the target T. The material of the moderator 50 is lead, iron, aluminum, or calcium fluoride.

(Setting example B)
The output from the accelerator 10 is an 11 MeV proton beam, and a beryllium target is used as the target T. The material of the moderator 50 is heavy water (D2O) or lead fluoride.

(Setting example C)
The output from the accelerator 10 is a 2.8 MeV proton beam, and a lithium target is used as the target T. The material of the moderator 50 is fluental (trade name; a mixture of aluminum, aluminum fluoride, and lithium fluoride).

(Setting example D)
The output from the accelerator 10 is a 50 MeV proton beam, and a tungsten target is used as the target T. The material of the moderator 50 is iron or full enthal.

  Then, the effect of the neutron beam therapy apparatus 1 set so that the reference | standard irradiation conditions may be satisfied as mentioned above is demonstrated.

Consider a case where boron neutron capture therapy (BNCT) is performed on a patient 40 using the neutron beam therapy apparatus 1. In calculating the equivalent dose of the therapeutic neutron beam N to the human body in BNCT, the following values are adopted as typical BNCT treatment examples.
Concentration of nitrogen as a human constituent element: 2%
Concentration in human body of boron 10 as input drug: 25 ppm
Normal skin CBE value: 2.5
Maximum dose for normal skin: 11 Gy-Eq
In general, in order to obtain a therapeutic effect of BNCT, it is necessary to irradiate the tumor with 20 Gy-Eq of thermal neutron beam. Note that the total equivalent dose in BNCT is equivalent to the equivalent dose due to nuclear reaction between thermal neutrons and boron (boron dose), equivalent dose due to nuclear reactions between thermal neutrons and nitrogen (nitrogen dose), and equivalent due to recoil hydrogen due to fast neutrons. It is expressed as the sum of the dose (hydrogen dose) and the equivalent dose from gamma rays.

  If it calculates based on said treatment example, when the patient is irradiated with the therapeutic neutron beam N of the neutron beam therapy apparatus 1 in BNCT, the position of the depth of 20 mm inside the body of the patient 40 on the irradiation center axis C The thermal neutron flux peaks at (corresponding to the reference position Q1). As the distance from the position corresponding to the reference position Q1 increases, the thermal neutron flux gradually decreases, and the thermal neutron flux at positions corresponding to the respective reference positions Q2, Q3, and Q4 has a value that is 0.2 times or more the above peak. .

For example, if irradiation is performed such that the thermal neutron flux G1 at the reference position Q1 is 5.0 × 10 ⁸ neutrons / cm ² / sec or more, 1.0 × 10 ⁸ neutrons / also at the peripheral reference positions Q2 to Q4. A thermal neutron flux of cm ² / sec (0.2 × 10 ⁸ neutrons / cm ² / sec) or more is irradiated. That is, a thermal neutron flux of 1.0 × 10 ⁸ neutrons / cm ² / sec or more is irradiated over a region within a radius r centered on the irradiation center axis C at a depth of 20 to 40 mm in the patient 40. Will be. Thus, according to the neutron beam therapy apparatus 1, sufficient irradiation of the therapeutic neutron beam N to obtain a therapeutic effect is performed on a relatively large tumor existing over a relatively large region as described above. Is possible. Therefore, the neutron beam therapy apparatus 1 can deal with relatively large tumors as described above, and can be used universally for tumors of various sizes.

  As mentioned above, although preferred embodiment of this invention was described, this invention is not restricted to the said embodiment, You may change in the range which does not change the summary described in each claim.

  For example, the configuration is not limited to the configuration in which the charged particle beam P is deflected 90 degrees using the 90-degree deflecting magnet 22, and the accelerator to the target may be arranged in a straight line without installing the 90-degree deflecting magnet. Further, the present invention may be applied not only to a type of treatment device that performs fixed irradiation, but also to a type of treatment device that performs rotation irradiation that rotates a target and a neutron beam output unit around a patient. Moreover, you may make it irradiate a charged particle beam to the fixed position on a target, without providing the charged particle beam scanning part 34. FIG. Moreover, you may provide the measurement means which can measure the dose of a neutron beam directly, without providing the current monitor 32. FIG.

  DESCRIPTION OF SYMBOLS 1 ... Neutron beam treatment apparatus (neutron beam irradiation apparatus), 10 ... Accelerator, 40 ... Patient (object to be irradiated), 46 ... Collimator, 46a ... Opening, 46c ... Edge of opening, 50 ... Moderator (deceleration part), 60 ... water phantom, 60a ... incident surface, C ... irradiation center axis (irradiation field center axis), D ... aperture edge axis, N ... therapeutic neutron beam, P ... charged particle beam, Q1 to Q4 ... reference position, T ... target (neutron beam generator).

Claims (1)

An accelerator that accelerates charged particles and emits charged particle beams;
A neutron beam generating unit for generating the neutron beam upon incidence of the charged particle beam from the accelerator;
A decelerating unit that decelerates and emits the neutron beam from the neutron beam generating unit;
A collimator that has an opening for defining an irradiation field of the neutron beam, and irradiates the irradiated body with the neutron beam from the moderator through the opening;
When the therapeutic neutron beam emitted from the opening of the collimator is incident on the water phantom from the incident surface of the water phantom,
In the water phantom, a position at a depth of 20 mm from the incident surface on the central axis of the irradiation field of the therapeutic neutron beam is set as a reference position Q1,
In the water phantom, a position at a depth of 60 mm from the incident surface on the central axis is defined as a reference position Q2.
In the water phantom, a position at a depth of 20 mm from the incident surface on the opening edge axis extending through the edge of the opening of the collimator and parallel to the central axis is defined as a reference position Q3.
When a position at a depth of 60 mm from the incident surface on the opening edge axis in the water phantom is set as a reference position Q4,
The thermal neutron flux G2 at the reference position Q2 is 0.2 times or more the thermal neutron flux G1 at the reference position Q1,
The thermal neutron flux G3 at the reference position Q3 is 0.2 times or more of the thermal neutron flux G1 at the reference position Q1,
The accelerator, the neutron beam generating unit, and the decelerating unit are set so that the thermal neutron flux G4 at the reference position Q4 is 0.2 times or more the thermal neutron flux G1 at the reference position Q1. Characteristic neutron irradiation equipment.

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