JP2010117257A - Energy distribution formation device and particle beam irradiation system equipped with the device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an energy distribution formation device which can accurately form an extended Bragg curve with a broad SOBP (spread out Bragg peak) width, can be easily manufactured and makes it possible to curb manufacturing costs in a particle beam irradiation system. <P>SOLUTION: Rods 1 as first energy absorbers and columns 3 as second energy absorbers are laid out on a virtual plane 25a of a ridge filter 25. The rods 1 have stairways whose thickness varies stepwise in the X direction and are laid out in parallel with each other at prescribed intervals X0 in the X direction. The columns 3 are laid out discretely and periodically in the X and Y directions, respectively. The columns 3, which are provided in place of the stairways of the rods 1 where the area ratio in a prescribed area of the virtual plane 25a is lower than a prescribed ratio in its design, can form lower energy components than those of a particle beam formed by the stairways of the rods 1 which have the maximum thickness. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an energy distribution forming apparatus for forming a predetermined energy distribution in a particle beam and a particle beam irradiation system including the same.

  In a particle beam irradiation system that mainly treats cancer using particle beams, the particle beam irradiation means includes a ridge filter that is an energy distribution forming device for forming a predetermined energy distribution in the particle beam. . A conventional ridge filter generally refers to a structure in which a plurality of rod-shaped bodies as energy absorbers are periodically arranged on a plane (hereinafter referred to as a virtual plane) substantially perpendicular to the particle beam irradiation direction (see FIG. 11). In addition, an energy absorber absorbs part of particle beam energy to reduce energy, and absorbs part of particles to reduce particle beam intensity. That is, the ridge filter is composed of a plurality of rod-shaped bodies and a space where the rod-shaped bodies are not arranged.

  In the following, the direction that becomes the center of the particle beam irradiation direction is the Z direction, the length in the Z direction is “thickness”, and the two directions orthogonal to the Z direction and orthogonal to each other are the X direction and Y direction, respectively. The direction. A conventional ridge filter is composed of a plurality of rod-shaped bodies extending in the Y direction and having a length of several centimeters to several tens of centimeters arranged in parallel with each other at a predetermined interval in the X direction. In addition, each rod-like body is designed to have a staircase shape whose thickness changes stepwise in the X direction. Therefore, the particle beam after transmission is determined by the X coordinate of the position where the particle beam passes through the ridge filter. Kinetic energy will be different.

As a prior example, Patent Document 1 shows an example in which the thickness of each of a plurality of rod-shaped bodies constituting a ridge filter changes stepwise in the X direction, and each step continues in the Y direction. Has been. According to such a ridge filter, the energy distribution of the particle beam after passing through the ridge filter is adjusted by the arrangement of a plurality of rod-like bodies, the thickness of each step of the step-like rod-like body and the width in the X direction, and On the other hand, a predetermined dose distribution can be formed. Further, in Patent Document 2, each rod-like body is a step-like rod-like body having a constant thickness in the X direction and a stepwise change in the Y direction, and having a predetermined length in the Y direction. The ridge filter is configured by repeatedly arranging a plurality of stepped bar-like bodies in a line in the Y direction, and periodically arranging rows of the plurality of stepped bar-like bodies at a predetermined interval in the X direction. Yes.
Japanese Patent No. 3689610 JP 2000-202048 A

  Since the particle beam has an emittance with a predetermined width, the particle beam that did not pass through the rod-like body and the different thickness of the rod-like body after passing through the ridge filter, due to the angular distribution in the traveling direction of the particle beam. The particle beams that have permeated through the part are sufficiently mixed with each other and reach the irradiated part. Further, due to this mixing effect, a predetermined energy distribution is formed in the particle beam at the irradiated portion position. By irradiation with the particle beam having this energy distribution, a predetermined uniform dose distribution is formed over the three-dimensional region of the irradiated portion. The dose distribution in the Z direction in the irradiated part is called an enlarged Bragg curve (Spread / Out / Bragg / Peak: SOBP).

  Here, the enlarged Bragg curve will be described with reference to FIG. In the figure, the horizontal axis represents the depth of the irradiated site, and the vertical axis represents the absorbed dose at the irradiated site due to the irradiation of the particle beam. In the figure, a curve indicated by 100 is an enlarged Bragg curve, and 101 is a Bragg curve by a particle beam before passing through the energy absorber or through a portion where the rod-shaped body of the ridge filter is not disposed, and absorption at the irradiated site. Depth dependence of dose is shown. Reference numerals 102 and 103 denote Bragg curves formed by particle beams that have passed through stepped portions having different thicknesses of the rod-shaped body constituting the energy absorber.

  FIG. 12 shows a large number of Bragg curves (A in the figure) by particle beams that pass through the stepped portions of different thicknesses of the rod-like body and are shifted to the low energy side. When the particle beam passes through a thicker portion of the rod-like body, the position of the Bragg curve peak (referred to as the Bragg peak) by the particle beam after transmission is shifted to a shallower side. That is, in FIG. 12, a Bragg curve 102 having a Bragg peak at the deepest position is a Bragg curve caused by a particle beam when passing through a stepped portion having the minimum thickness of the rod-shaped body, and a Bragg curve having a Bragg peak at the second deepest position. A curve 103 is a Bragg curve by a particle beam when passing through a step portion having the second smallest thickness of the rod-shaped body.

  Next, the height of each Bragg peak will be described. With respect to the peak height of the Bragg curve 101, the peak height of the Bragg curve due to the particle beam that has passed through the rod-shaped body is small. This is because the area ratio of the staircase portion corresponding to the predetermined permeation thickness of the rod-shaped body in the irradiation region of the particle beam is significantly larger than the area ratio of the portion where the transmission thickness is 0, that is, the portion where the rod-shaped body is not disposed. Due to the smallness.

  The enlarged Bragg curve 100 is realized by superimposing the particle beams transmitted through the stepped portions having different thicknesses of the rod-shaped body and the Bragg curves formed by the particle beams transmitted through the portion where the rod-shaped body is not disposed. The illustrated SOBP width is determined in accordance with the extent of the affected area in the Z direction. Due to the presence of this SOBP width, it becomes possible to uniformly irradiate the affected part with the particle beam regardless of the depth of the affected part.

  In order to realize a flat peak portion like the enlarged Bragg curve 100, the height of the Bragg peak having the peak at a shallow position is basically low, and the height of the Bragg peak having the peak at a deep position is It is better to stack it up. This is because the Bragg curve has a skirt portion having a certain height at a position shallower than the peak position, and this is superposed at the time of superposition. There are exceptions for fine-tuning. In FIG. 12, the peak height of the Bragg curve 102 is smaller than the peak height of the Bragg curve 103 having a peak at a shallower position, which corresponds to the above exception. In order to lower the height of the Bragg peak, the area ratio of the rod-shaped body portion having a thickness corresponding to the Bragg peak may be made smaller.

  As described above, the ridge filter is set such that the thickness of each step portion and the width in the X direction, the interval between the rod-like bodies, and the like are set so that the SOBP width is equal to the thickness of the affected part. The area ratio is determined. In general, the thickness of the affected part (tumor) is often 12 cm or less, but there are also more than that. Usually, when the thickness of the tumor increases, the deepest depth of the affected area increases and the required SOBP width increases, so that the maximum thickness of the ridge filter also increases. Further, as described above, in order to form a flat SOBP distribution, it is necessary to reduce the width in the X direction and reduce the area ratio as the thickness of each rod-shaped body increases.

  In the conventional ridge filter in which the rod-shaped body is made of aluminum, for example, when the SOBP width is set to 15 cm, the maximum thickness of the ridge filter is about 7 cm, and the width in the X direction of the staircase portion having the thickness is several tens of μm to 0.00 mm. In order to realize this, extremely high machining accuracy is required. Similarly, when the conventional ridge filter described in Patent Document 1 is manufactured, processing with higher accuracy is required as the SOBP width increases. Here, when the processing accuracy is low, there arises a problem that the SOBP width of the enlarged Bragg curve does not match the design value, or the uniformity of the dose within the SOBP width deteriorates. On the other hand, when processing with high accuracy, there is a problem that the manufacturing cost is high in terms of processing equipment, processing steps, and the like. Further, in the energy distribution forming apparatus described in the cited document 2, since it is necessary to arrange a large number of complicated structures in a two-dimensional plane, the manufacturing cost of the ridge filter increases.

  The present invention has been made to solve the above-described problems, and in a particle beam irradiation system, an enlarged Bragg curve having a large SOBP width can be formed with high accuracy, and can be easily manufactured to reduce the manufacturing cost. An object is to provide a possible energy distribution forming device.

  Moreover, it aims at providing the highly accurate particle beam irradiation system provided with the said energy distribution formation apparatus.

  In the energy distribution forming apparatus according to the present invention, when the particle beam irradiation direction is perpendicular to the Z direction, the Z direction, and the two directions perpendicular to each other are the X direction and the Y direction, respectively, and the length in the Z direction is the thickness, A first energy absorber and a second energy absorber are disposed along a plane perpendicular to the Z direction, and the first energy absorber has a step portion whose thickness changes stepwise in the X direction. In addition, the flat portion, which is a constant thickness region of each staircase portion, is composed of a plurality of rod-shaped bodies extending in the Y direction while maintaining the thickness, and the plurality of rod-shaped bodies are mutually connected at a predetermined interval X0 in the X direction. The second energy absorber is arranged in parallel, and the second energy absorber has a plurality of thicknesses B having a predetermined thickness B that is larger than the energy absorption amount of the particle beam by the step portion having the maximum thickness A of the first energy absorber. From the structure Thus, the plurality of structures are arranged discretely and periodically in the X direction and the Y direction, respectively, and do not overlap the first energy absorber in the Z direction.

  The particle beam irradiation system according to the present invention includes a particle beam generating unit, a particle beam accelerating unit that accelerates a particle beam generated from the particle beam generating unit, and a particle beam accelerated by the particle beam accelerating unit. The apparatus includes a particle beam transport unit that leads to a position, and a particle beam irradiation unit that includes an energy distribution forming device installed at a predetermined position.

  According to the energy distribution forming apparatus of the present invention, an enlarged Bragg curve having a large SOBP width can be formed with high accuracy, and manufacturing is easy and manufacturing cost can be reduced.

Embodiment 1 FIG.
Embodiment 1 of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view on a plane including the central axis direction of particle beam irradiation for a portion showing particle beam irradiation means of the particle beam irradiation system according to Embodiment 1 of the present invention. FIG. 2 is a perspective view and a partially enlarged sectional view showing an energy distribution forming apparatus used in the particle beam irradiation system according to Embodiment 1 of the present invention. In the drawings, the same or corresponding parts are denoted by the same reference numerals.

  The particle beam irradiation system according to the first embodiment includes a particle beam generating means (not shown) such as an ion source, and a particle beam accelerating means such as a particle beam accelerator for accelerating the particle beam generated from the particle beam generating means ( A particle beam transporting means (not shown) for guiding the particle beam accelerated by the particle beam accelerating means to a predetermined position, and a ridge filter which is installed at the predetermined position and is an energy distribution forming device And a particle beam irradiation means.

  The particle beam irradiation means of the particle beam irradiation system in the first embodiment will be described with reference to FIG. In FIG. 1, reference numeral 20 denotes a particle beam irradiation unit, and reference numeral 21 denotes a particle beam beam guided by the particle beam transport unit and incident on the particle beam irradiation unit 20. Reference numeral 40 denotes a patient who receives treatment by the particle beam irradiation system, and is fixed to a treatment table (not shown) at the time of treatment. Reference numeral 41 denotes an affected part (tumor part) of a patient 40 which is an irradiated part to which the particle beam 21 adjusted by the particle beam irradiation means 20 is irradiated, and an arrow 42 indicates a part where the affected part 41 is most spread in the Z direction. It shows the thickness, that is, the maximum thickness of the affected area.

  Hereinafter, the components of the particle beam irradiation means 20 will be described in the order in which the particle beam 21 passes. Reference numeral 22 denotes a wobbler electromagnet which is normally composed of two deflection electromagnets and is arranged so that the respective deflection directions are orthogonal to each other. The wobbler electromagnet 22 controls the deflection angle of the particle beam 21 incident by these two deflecting electromagnets, and scans the particle beam 21 in a predetermined orbit. Reference numeral 23 denotes a scatterer that is disposed on the downstream side of the wobbler electromagnet 22 and that scatters the particle beam 21 on a plane with a predetermined distance further downstream. The irradiation field forming means including these wobbler electromagnet 22 and scatterer 23 expands the irradiation field of the particle beam 21 in the XY direction. A dose monitor 24 is disposed downstream of the scatterer 23 and measures the dose of the particle beam 21 to perform dose management. However, the installation location of the dose monitor 24 is not particularly limited to this position.

  Reference numeral 25 denotes a ridge filter that is disposed on the downstream side of the wobbler electromagnet 22 and the scatterer 23 and includes an energy absorber that partially absorbs the energy of the particle beam 21 and reduces the energy. The ridge filter 25 increases the energy width in the Z direction of the particle beam 21 whose irradiation field is expanded in the XY directions by the wobbler electromagnet 22 and the scatterer 23, and the Bragg by the particle beam 21 after passing through the ridge filter 25. The curve is an enlarged Bragg curve having a predetermined SOBP width at the peak portion. In the ridge filter 25 shown in FIG. 1, 1 is a rod-shaped body that is a first energy absorber, 3 is a structure that is a second energy absorber, and 5 is a base plate to which the rod-shaped body 1 and the structure 3 are fixed. . In FIG. 1, in order to make the configuration of the ridge filter 25 easy to understand, the size of the rod-like body 1 and the structure 3 is drawn larger than the actual size with respect to the beam width of the particle beam 21.

  A range shifter 26 includes an energy absorber that is arranged on the downstream side of the ridge filter 25 and includes two plates having a substantially triangular cross-sectional shape. The two plates of the range shifter 26 are arranged such that the total thickness in the Z direction is constant regardless of the position. In addition, the total thickness of the two can be varied by translating relatively in opposite directions relative to each other in a plane orthogonal to the Z direction. The range shifter 26 adjusts the maximum beam energy of the particle beam 21.

  Reference numeral 27 denotes a collimator that is arranged on the downstream side of the range shifter 26 and narrows the irradiation field of the particle beam 21 into a predetermined shape. The collimator 27 is usually configured by combining a plurality of metal plates called collimator leaves, and has a leaf opening through which the particle beam 21 passes at the center. Reference numeral 28 denotes an energy compensator that is arranged on the downstream side of the collimator 27 and is composed of an energy absorber similar to the ridge filter 25. The energy compensator 28 adjusts the stop position of the particle beam 21 by changing its thickness two-dimensionally corresponding to the irradiation direction.

  Next, the operation of the particle beam irradiation unit 20 according to the first embodiment will be described. The particle beam 21 incident on the particle beam irradiation means 20 is scanned by a wobbler electromagnet 22 so as to draw a predetermined trajectory, for example, a circular trajectory, and forms, for example, a donut-shaped irradiation field in the affected area 41 of the patient 40. Furthermore, the beam size is expanded by passing through the scatterer 23, and the irradiation field in the affected area 41 is, for example, from a donut shape to a circular shape having a flat particle beam intensity within that range. The radius, thickness, and the like of the wobbler electromagnet 22 and the scatterer 23 are appropriately selected according to the affected part 41.

  Since the particle beam 21 has a small energy width at the time of passing through the scatterer 23, the spread of the particle beam stop position (irradiation depth) in the affected area 41 is also small, for example, concentrated within a range of about several mm. ing. In this state, there is a region that cannot be irradiated to the affected part 41 having a further spread in the Z direction. Therefore, the particle beam 21 after passing through the scatterer 23 is transmitted through the ridge filter 25, so that the particle beam stop position in the affected area 41 is expanded in the Z direction, and the SOBP width is the maximum thickness 42 of the affected area. Is adjusted to be equal to In this adjustment, energy loss due to transmission through the range shifter 26, the collimator 27, and the energy compensator 28 is also taken into consideration.

  Next, the particle beam 21 passes through the range shifter 26, so that the maximum beam energy is adjusted based on the deepest position of the affected part 41. The irradiation field of the particle beam 21 after passing through the range shifter 26 is shaped by the collimator 27 into the same shape as that of the maximum area of the affected area 41 when viewed from the irradiation direction, and the normal area other than the affected area 41 is irradiated with the particle beam 21. It is adjusted not to be.

  Further, the particle beam 21 passes through an energy compensator 28 having different thicknesses depending on the irradiation direction, so that the particle beam stop position in the Z direction is affected in each irradiation direction due to the divergence angle of each particle beam. 41 is adjusted along a curved surface formed by connecting the deepest points. The thickness of the energy compensator 28 may be increased at the stop position of the particle beam 21, that is, the portion where the penetration depth is desired to be reduced. The energy compensator 28 prevents the particle beam 21 from penetrating the affected area 41 and reaching the normal tissue. The particle beam 21 adjusted in this way is incident from the body surface of the patient 40 and is irradiated to an affected part (tumor part) 41 which is an irradiated part.

  Next, the ridge filter 25 which is an energy distribution forming device will be described with reference to FIG. In FIG. 2, 25a is a virtual plane perpendicular to the Z direction. As described above, the ridge filter 25 is a device for converting the Bragg curve by the particle beam 21 into an enlarged Bragg curve having a predetermined SOBP width at the peak portion, and the SOBP width is usually the maximum thickness of the affected area. 42. The ridge filter 25 according to the first embodiment includes a first energy absorber and a second energy absorber disposed along a virtual plane 25a perpendicular to the Z direction.

  The first energy absorber has a staircase portion whose thickness changes stepwise in the X direction, and a flat portion, which is a constant thickness region of each staircase portion, maintains the thickness in the Y direction. It consists of a plurality of elongated rods 1. The plurality of rod-like bodies 1 constituting the first energy absorber are arranged in parallel with each other at a predetermined interval X0 in the X direction.

  The second energy absorber is composed of a plurality of structures arranged discretely and periodically in each of the X direction and the Y direction. In the first embodiment, the columnar body 3 is used as the structure. As shown in FIG. 2A, the columnar body 3 and the rod-shaped body 1 are arranged on the same plane by being fixed to the same base plate 5, and are arranged so as not to overlap in the Z direction.

  The ridge filter 25 includes each step portion of the rod-like body 1, the columnar body 3, and a portion where these are not disposed (hereinafter, referred to as “each portion of the ridge filter 25”). When the constituent materials of the rod-like body 1 and the columnar body 3 are the same, the area ratio of each part of the ridge filter 25 in a predetermined area on the same XY plane depends on the thickness of each part of the ridge filter. Usually, the area ratio decreases as the thickness increases.

  The columnar body 3 in the present first embodiment has a predetermined thickness B that is an energy absorption amount larger than the energy absorption amount of the particle beam by the step portion having the maximum thickness A of the rod-shaped body 1 (thickness). (See FIG. 6 for A and B). The predetermined thickness B is the minimum thickness of the second energy absorber. Thereby, the columnar body 3 can form an energy component lower than the energy component of the particle beam formed by the stepped portion having the maximum thickness A of the rod-shaped body 1.

  When the constituent materials of the rod-shaped body 1 and the columnar body 3 are the same, the minimum thickness B of the columnar body 3 is larger than the maximum thickness A of the rod-shaped body 1. However, the thickness of the columnar body 3 can be reduced by making the constituent material of the columnar body 3 a material having a higher density than the rod-shaped body 1. When the density of the rod-shaped body 1 is m1 and the density of the columnar body 3 is m2, the minimum thickness B of the columnar body 3 is the maximum value obtained by multiplying the maximum thickness A of the rod-shaped body 1 by m1 / m2. What is necessary is just to set larger than effective thickness. Thus, for example, when the material of the columnar body 3 is changed from aluminum to copper, the thickness can be reduced to about half. As a result, since the probability that the particle beam 21 incident on the columnar body 3 exits from the side surface of the columnar body 3 in the middle is reduced, the ridge filter 25 can be easily designed, and a highly accurate ridge filter can be obtained.

  Aluminum (Al), copper (Cu), or the like can be used as the material for the rod-like body 1 and the columnar body 3, but the material is not particularly limited, and other metals or alloys may be used. The base plate 5 can be a thin aluminum plate or plastic plate having a small energy absorption effect.

  As described above, the particle beam 21 that has reached the ridge filter 25 has already been enlarged to some extent by the wobbler magnet 22 and the scatterer 23, and the particle beam 21 on the virtual plane 25a on which the ridge filter 25 is disposed. The X-direction interval X0 of each rod-like body 1 is set to a sufficiently small value (for example, X0 is 10 mm or less for an irradiation field of 100 mm). Thereby, the area ratio of each part of the ridge filter 25 in a predetermined area (not shown) on the virtual plane 25a becomes substantially equal to the area ratio of each part in the entire ridge filter 25. Therefore, the particle beam 21 can transmit substantially uniformly through the portions having different thicknesses disposed on the entire surface of the ridge filter 25.

  The columnar body 3 according to the first embodiment is provided in place of the staircase portion of the rod-shaped body 1 whose area ratio in a predetermined area on the virtual plane 25a is smaller than the predetermined ratio in design. An energy component corresponding to the energy component of the particle beam formed by the portion is formed. That is, in the rod-like body 1, the processing width is increased by replacing the stepped portion, which requires high machining accuracy because of its small width, with the columnar body 3 that is a discrete structure. This eliminates the need for high-precision processing. The predetermined ratio here is appropriately determined depending on the material strength of the rod-shaped body 1 and the processing accuracy of the apparatus when the rod-shaped body 1 is manufactured.

  The columnar body 3 which is one form of the structure constituting the second energy absorber is one or more types depending on which step portion of the rod-shaped body 1 which is the first energy absorber is replaced with the columnar body 3. Consists of columnar bodies of different thickness. In FIG. 2, 31 (31a, 31b, 31c) is a columnar body having a first thickness, 32 (32a, 32b, 32c) is a columnar body having a second thickness, and 33 (33a, 33b, 33c). Is a columnar body having a third thickness. In the example illustrated in FIG. 2, the columnar body 3 includes a plurality of three types of columnar bodies 31, 32, and 33 having different thicknesses in the Y direction.

The three types of columnar bodies ₃₁ , ₃₂ , ₃₃ are arranged on a straight line parallel to the Y direction at predetermined intervals ΔY ₃₁ , ΔY ₃₂ , ΔY ₃₃ in the Y direction for each type. Further, the columnar bodies 3a, 3b, 3c periodically arranged in the Y direction are arranged between the adjacent rod-like bodies 1 in the X direction. Note that ΔY ₃₁ , ΔY ₃₂ , and ΔY ₃₃ do not necessarily have the same value. In this case, the number of the three types of columnar bodies 31, 32, and 33 arranged in a predetermined range in the Y direction is not the same. Further, all of the three types of columnar bodies 31, 32, 33 may not necessarily be arranged on a straight line parallel to the Y direction, and the relative positions in the X direction between the adjacent rod-shaped bodies 1. The relationship may be arbitrary. Such an arrangement example is shown in FIGS.

FIG. 3 is a plan view of a portion including a part of the second energy absorber of the ridge filter 25 as viewed from the upstream side in the particle beam irradiation direction. Three types of columnar bodies 31, 32, and 33 having different thicknesses are periodically arranged in the X direction and the Y direction for each type. In FIG. 3A, an example in which three types of columnar bodies ₃₁ , ₃₂ , and ₃₃ are arranged at substantially the same intervals ΔY ₃₁ , ΔY ₃₂ , and ΔY ₃₃ in the Y direction at different X-direction positions (X coordinates). Show. FIG. 3B shows an example in which three types of columnar bodies ₃₁ , ₃₂ and ₃₃ are arranged at different intervals ΔY ₃₁ , ΔY ₃₂ and ΔY ₃₃ in the Y direction at different X coordinates.

  Next, the calculation method of the space | interval (DELTA) Y of the Y direction of a 2nd energy absorber is demonstrated using FIG.4 and FIG.5. FIG. 4 schematically shows the spread of the dose distribution on the irradiation plane by the particle beam transmitted through the columnar body 3 as the second energy absorber. The columnar bodies A to D shown here are obtained by selecting two adjacent ones having the same thickness from the columnar bodies 3 in the X and Y directions. Assume that A and B, C and D are arranged along the Y direction, and A and D, and B and C are arranged along the X direction, respectively. Moreover, 41a has shown the irradiation plane of the affected part.

  In the first embodiment, the interval ΔY in the Y direction of the portion having the same thickness of the columnar body 3 is set to the interval X0 in the X direction of the rod-shaped body 1 or an interval smaller than X0. In FIG. 4, the interval ΔY in the Y direction of the columnar bodies 3 is set to the same value as X0, and the interval in the X direction is also set to X0. Here, the distance X0 in the X direction of the rod-shaped body 1 is determined by the conventional design method, and the particle beam that has passed through each step portion of the rod-shaped body 1 and the particles that have passed through the ridge filter 25 without passing through the energy absorber. Any of the line beams is determined so that a uniform distribution is formed on the irradiation plane 41a. Therefore, the remaining examination item is whether or not the particle beam of energy corresponding to the thickness of the columnar body 3 forms a uniform distribution on the irradiation plane 41a after passing through the columnar body 3. This will be discussed below.

  Since the particle beam incident on the ridge filter 25 has a predetermined divergence angle, when an absorber is arranged at the position of the ridge filter 25 in the X direction at an interval X0, the dose distribution of the particle beam after passing through the absorber. Are located at an interval of X1, which is a value larger than X0 on the irradiation plane 41a. If the enlargement factor at this time is α, X1 is α × X0. The same applies to the Y direction. Therefore, when each columnar body A to D is projected onto the predetermined irradiation plane 41a according to the divergence angle of the particle beam, the interval in the Y direction is Y1, and the particle beam beam on the irradiation plane 41a after passing through each columnar body A to D is Assuming that the center position is a to d shown in FIG. 4, when ΔY is made equal to X0, Y1 becomes X1 which is the same as the X direction, and the line connecting abcd becomes a square. The enlargement ratio α can be obtained by design calculation or actual measurement.

  Next, the 1 / e divergence angle due to scattering of the particle beam from the columnar body 3 of the particle beam transmitted through the columnar body 3 is θ_1 / e, and the distance between the plane on which the columnar body 3 is arranged and the irradiation plane 41a is L. , The ratio of Y1 (= X1) to the scattering radius R1, which is the product of the 1 / e divergence angle (θ_1 / e) of the particle beam transmitted through the columnar body 3 and L, is less than 1.7 or 1.7. X0 is set to have a value. The 1 / e divergence angle of the particle beam is an angle at which the particle number is 1 / 2.718 with the particle beam irradiation direction as an axis and the angular distribution of the number of particles on a plane orthogonal to the direction as a Gaussian distribution. . This 1 / e divergence angle can be obtained by design calculation for simulating the behavior of the particle beam, or by actually measuring the particle beam distribution corresponding to the thickness of each part after passing through each part of the ridge filter 25. Normally, the thickness of each energy absorber is sufficiently small with respect to the distance L, so the effect due to the difference in the thickness of the energy absorber can be ignored.

As already explained, the following formula 1 is established.
R1 = θ_1 / e × L (Formula 1)
In the irradiation plane 41a, the contribution of the particle beam that has passed through the columnar bodies A and B at the midpoint M2 between the projection positions a and b of the columnar bodies A and B, that is, the total number T2 of scattered particles is the sum of the particle beams in the irradiation plane 41a. From the scattering radius R1 and the projected length X1 of the arrangement pitch X0 on the irradiation plane 41a, it can be estimated by Equation 2. In FIG. 4, since ΔY is set equal to X0, the distance between projections on the irradiation plane 41a of the columnar bodies A and B can be set to X1.
T2 = 2 × exp (− (0.5 × X1 / R1) ² ) (Formula 2)

Next, the total number T4 of scattering particles at the intermediate point M4 between the projection positions a, b, c, and d of the columnar bodies A, B, C, and D is obtained. Here, since ΔY is set to the same value as X0, the projections of the columnar bodies A, B, C, and D on the irradiation plane 41a form a square. Therefore, the distances from the projection positions a, b, c, d of the respective columnar bodies A, B, C, D to the intermediate point M4 are (0.5 × 1.414 × X1), and the scattering particles at the intermediate point M4 The total number T4 can be estimated by Equation 3.
T4 = 4 × exp (− (0.5 × 1.414 × X1 / R1) ² ) (Formula 3)

  FIG. 5 is a plot of Equation 2 and Equation 3 above as a function of X1 / R1. In FIG. 5, the vertical axis indicates the relative value of the total number of scattered particles T2 and T4 at the intermediate points M2 and M4, and the horizontal axis indicates X1 / R1. Further, when the value of the vertical axis is 1, it indicates that the numbers of scattered particle beams at the projection positions of the respective columnar bodies A, B, C, and D are equal.

  As shown in FIG. 5, the total number T2 and T4 of the scattering particles at the intermediate points M2 and M4 change with X1 / R1. In the vicinity of X1 / R1 = 1.665 (= 2 × √ln (2), hereinafter referred to as about 1.7), the contribution of the particle beam that has passed through the columnar bodies A, B, C, and D at the midpoint M4 The total is equal to the contribution of the particle beam at the projection position of the irradiation plane 31a of each columnar body A, B, C, D. That is, on the irradiation plane 41a, the distribution obtained by synthesizing the contributions of the scattered particle beams from the columnar bodies A, B, C, and D becomes substantially flat. Strictly speaking, when the contributions from all the columnar bodies 3 included in the extent of the Gaussian distribution are summed, the uniformity is further improved.

  Next, in the case where X1 is smaller than 1.7 × R1 (X1 / R1 <1.7), the value on the vertical axis becomes larger than 1 from FIG. 5, and the uniformity seems to deteriorate. However, as described above, strictly speaking, it is necessary to sum up the contributions from all the columnar bodies 3 included in the range of the spread of the Gaussian distribution. When X1 is smaller than 1.7 × R1, the contribution from the other columnar bodies 3 is increased, so that uniformity is maintained.

  Similarly, even if one of the X and Y directions has an interval equal to 1.7 × R1, and the other interval is smaller than that, uniformity is maintained. That is, if the intervals in the X and Y directions of the columnar body 3 are X0 and ΔY, respectively, and the intervals when projected onto the irradiation plane 41a are X1 and Y1, respectively, 1.7 × for each of X1 and Y1. By determining it to be equal to or smaller than R1, the uniformity of the particle beam transmitted through the columnar body 3 on the irradiation plane 41a is ensured.

  By the way, as the thickness of the absorber increases, the degree of scattering in the absorber increases, and as a result, the 1 / e divergence angle also increases. Now, the interval X0 in the X direction of the rod-shaped body 1 is sufficiently different from the particle beam transmitted through each stepped portion of the rod-shaped body 1 through the corresponding stepped portion of the adjacent rod-shaped body 1 on the irradiation plane 41a. It was selected so as to constitute an overlapping and uniform distribution. In the case of a particle beam transmitted through a columnar body 3 having a thickness greater than that of the rod-shaped body 1, the 1 / e divergence angle of the Gaussian distribution is larger than the 1 / e divergence angle in the case of a particle beam transmitted through the rod-shaped body 1. Therefore, even if the columnar bodies 3 are arranged at intervals larger than X0, the uniformity of the particle beam transmitted through the columnar bodies 3 on the irradiation plane 41a is ensured.

  Therefore, if the columnar bodies 3 are arranged at the interval X0, the condition that X1 is equal to about 1.7 × R1 (X1 / R1 = 1.7) or smaller (X1 / R1 <1.7). Are considered secured. This is common to the X and Y directions, and the interval between the columnar bodies 3 can be arbitrarily set in the Y direction. Therefore, if the interval ΔY between the columnar bodies 3 in the Y direction is equal to or smaller than X0, irradiation is performed. The uniformity of the particle beam is maintained on the plane 41a.

  Hereinafter, a procedure for determining the thickness and area ratio of each part of the ridge filter 25 so that the particle beam after passing through the ridge filter 25 has a predetermined energy distribution will be described according to Step 1 to Step 5. The predetermined energy distribution refers to an energy distribution in which the absorbed dose of the affected area 41 is uniform in a region from the deepest part to the shallowest part of the affected part 41 when irradiated with the particle beam of the energy distribution.

  First, as a first step, the energy of the particle beam incident on the ridge filter 25 and a Bragg curve corresponding to the energy are determined. These can be grasped beforehand by design calculation or actual measurement.

  Next, as a second step, a necessary SOBP width is set for the particle beam that has passed through the ridge filter 25. Here, the spread in the Z direction (depth direction) of the affected area 41 of the patient 40 is measured and evaluated in advance, and the required SOBP width, that is, the maximum thickness 42 of the affected area is obtained from the depths of the shallowest part and the deepest part. (See FIG. 1).

In the third step, a plurality of composite Bragg curves g _j (z) and their ratios S _j (j = 1 to _m ) for obtaining a necessary SOBP width are determined. A library made up of a plurality of Bragg curves used for this work is stored in advance in a storage device. Let the Bragg curve of this library be f _i (z) (an integer satisfying 1 ≦ i ≦ n). Here, z represents the depth of the affected part 41 with respect to the particle beam irradiation direction. This Bragg curve f _i (z) is a Bragg curve formed by a particle beam transmitted through the absorber when the particle beam before entering the ridge filter 25 is incident on an energy absorber having a common area and a thickness t _i. And This can be determined by simulation or actual measurement. If the thickness t _i = Δt × (i−1), f ₁ (z) is a Bragg curve by a particle beam that has passed through a zero-thickness absorber, and passes through a thick absorber by Δt as i increases. It represents the Bragg curve by the particle beam.

Also, assuming that the depths of the shallowest part and the deepest part of the SOBP width obtained in the second step are _Dmin and _Dmax , Bragg having peaks at positions _Dmin and _Dmax from the Bragg curve in the library. Let the curves be f _i (z) (i = min, max), respectively. Note that min is usually equal to 1, so that min = 1 in the following. If there is no Bragg curve with the matching peak position, it is supplemented by simulation calculation, or interpolation is performed by interpolating or extrapolating the Bragg curve of the neighboring number. Alternatively, approximation may be performed by simply shifting the peak position using a Bragg curve of a neighboring number.

Spread out Bragg curve F (z) is expressed by equation 4 below W _i as a load factor.
F (z) = W 1 · f 1 (z) + W 2 · f 2 (z) + W 3 · f 3 (z)
+ ... W _i · f _i (z) + ··· + W _max · f _max (z) (Formula 4)
Here, W _i (i = 1 to max) is within a range of z corresponding to the SOBP width of F (z) (that is, D _min ≦ z ≦ D _max ), and variation of F (z) is preset. It is determined to be smaller than the above value. This operation can be easily performed by using a computer.

When the variation in F (z) does not become small, the Bragg curve f ′ _i (z) (i = 1 to n ′ (> n) corresponding to a finer absorber thickness difference (Δt ′ <Δt). ) was _prepared, and to perform the same operation using instead of _{f i (z) f 'i} (z). This f ′ _i (z) can be obtained by simulation calculation or actual measurement in the same manner as f _i (z), but is obtained by interpolation or extrapolation of neighboring f _i (z) or simple shift approximation of peak positions. You can also

In this work, the number of Bragg curves used for synthesizing the enlarged Bragg curve is equal to the number of types of thicknesses of the energy absorbers arranged in the ridge filter 25, so that the number of Bragg curves used for synthesis is smaller. Is good. Therefore, the product of the peak heights of W _i and f _i (z) whose contribution is smaller than others may be omitted, and the variation of F (z) within the SOBP range may be recalculated. is there. In this way, the final remaining f _i (z), t _i , and W _i (i may be discontinuous) are renumbered with sequential numbers, respectively, g _j (z), H _j, and _S j; and (j = 1~m m ≦ n) . Each Bragg curve shown in FIG. 12 is equivalent to _{S j × g j (z)} .

Further, in the fourth step, the Bragg curve group g _j (z) determined in the third step, the absorber thickness H _j corresponding to each of them, and the load coefficient S _j (j = 1 to m; m ≦ n), the thickness H _j of the absorber constituting the ridge filter 25 and the area ratio S _j are selected. At this time, as a general rule, those having a large area ratio are absorbers in the form of rod-shaped bodies 1, and those having a small area ratio are discrete columnar bodies 3 in both the X and Y directions. It should be noted that the criteria for determining the size of the area ratio is set in advance in consideration of the machining accuracy of the assumed machining apparatus.

Finally, as a fifth step, after determining the thickness H _j and the area ratio S _j of each part of the ridge filter 25, the enlarged Bragg curve of the particle beam after passing through the ridge filter 25 is calculated based on the configuration, It is confirmed whether or not a predetermined SOBP width is realized. Note that the arrangement period in the X and Y directions at this time can be determined from the divergence angle of the particle beam, which can be grasped in advance by calculation or the like. When there is an error in the SOBP width, the final condition is determined by iterative calculation while correcting the given absorber condition.

Next, a specific operation in the fourth step will be described using the ridge filter 25 in the first embodiment as an example. FIG. 6 is a partially enlarged cross-sectional view in the XZ plane of the ridge filter 25 according to the first embodiment, and the rod-like body 1 has seven step portions whose thickness changes stepwise in the X direction. Yes. In the figure, 11 is the first step, 12 is the second step,..., 16 is the sixth step, and 17 is the seventh step. In the figure, H _i and X _i (i = 1 to 7) respectively indicate the thickness of the i-th step and the width in the X direction (in the case of i = 2, 3, and 7). Shows). Further, the thicknesses of the columnar bodies ₃₁ , ₃₂ , and ₃₃ arranged alternately with the rod-shaped body 1 are H ₃₁ , H ₃₂ , and H ₃₃ (only the columnar body 33 is shown in the figure).

The ridge filter 25 according to the first embodiment has a total of 11 different thickness portions including a zero-thickness portion, the first to seventh step portions of the rod-like body 1, and the columnar bodies 31, 32, and 33. Therefore, it is selected corresponding to 11 Bragg curves. Of the 11 Bragg curves, the portions corresponding to the three Bragg curves having a particularly small load coefficient (area ratio) _Sj are realized as the columnar bodies 31, 32, and 33, and the other seven Bragg curves are supported. The portion is realized as seven steps 11, 12... 17 of the rod-shaped body 1. Further, the remaining one Bragg curve is a Bragg curve 101 as shown in FIG. 12 and corresponds to the zero-thickness portion of the ridge filter 25.

Here, as shown in FIG. 2A, the area occupied by one period of the energy absorbers periodically arranged on the virtual plane 25a when viewed from the irradiation direction of the particle beam 21 is X0 × Y0. . In this area (X0 × Y0), the area ΔS _i occupied by the step portion of the i-th stage having the thickness H _i of the rod-like body 1 can be expressed by the following equation (5) (where i is 1 to 6): ).
ΔS _i = (X _i −X _{i + 1} ) × Y 0 (Formula 5)
Further, the area ΔS ₇ of the virtual plane 25a occupied by the seventh stepped portion 17 having the thickness H ₇ can be expressed by the following Expression 6.
ΔS ₇ = _{X 7} × Y0 (Equation 6)
Further, in the cross-sectional shapes of the columnar bodies 31, 32, and 33 on the XY plane, the areas of the portions clogged with the constituent materials are denoted by ΔS ₃₁ , ΔS ₃₂ , and ΔS ₃₃ , respectively.

Assuming that the intervals in the Y direction of the columnar bodies _{31, 32} , ₃₃ are ΔY31 _, ΔY32, ΔY33, the total area occupied by the columnar bodies 31 arranged in the Y direction in the area (X0 × Y0) is ΔS. ₃₁ is indicated by × (Y0 / ΔY _31), likewise, the total area occupied by the columnar body 32 arranged in the Y direction _{ΔS 32 × (Y0 / ΔY 32} ), occupied by columnar body 33 arranged in the Y direction The total area is indicated by ΔS ₃₃ × (Y 0 / ΔY ₃₃ ). In the following description, assuming that ΔY _31, ΔY ₃₂ , and ΔY ₃₃ are all equal ΔY, the number Ny of columnar bodies having the same height that can be arranged in a line along the Y direction is obtained by Ny = Y0 ÷ ΔY. .

As shown in FIG. 6, when considering the thickness of the base plate 5, the ridge filter 25 has a portion where the thickness is zero. Assuming that the area occupied by this portion is ΔS ₀ , the following expression 7 is obtained for the area occupied by one period on the virtual plane 25 a of the ridge filter 25.
X0 × Y0 = ΔS ₀
+ ΔS ₁ + ΔS ₂ + ΔS ₃
+ ΔS ₄ + ΔS ₅ + ΔS ₆ + ΔS ₇
+ Ny × (ΔS ₃₁ + ΔS ₃₂ + ΔS ₃₃ ) (Formula 7)

From Equation 7, the area ratio of each portion having a different thickness of the ridge filter 25, for example, in the case of the 7th stage of the stepped portion 17 is _{ΔS 7 / (X0 × Y0)} , in the case of columnar body 31 (Ny × ΔS ₃₁ ) / (X 0 × Y 0). In addition, as described above, the area ratio of the area ΔS _i occupied by each part having a thickness corresponding to each Bragg curve is equal to the load coefficient rate W _{j of} each of the 11 Bragg curves. The area ΔS _i occupied by each part in the period can be respectively determined.

In order to obtain a uniform SOBP distribution over the range of the maximum thickness 42 of the affected area, the portion having the largest beam energy E _j after passing through the ridge filter 25, that is, the portion of the ridge filter 25 where the thickness is zero is shown. It is necessary to maximize the load coefficient rate W _j of the Bragg curve corresponding to the area ΔS ₀ , and the area ratio is usually about 30% of the whole. Further, since the load coefficient rate W _j of the Bragg curve corresponding to the columnar bodies 31, 32, 33 having a large thickness in the portion where the beam energy E _j is small, that is, the ridge filter 25 is small, the columnar bodies 31, 32, 33 The occupied area ratio becomes small, and it becomes several percent or less of the whole.

As described above, in the fourth step, as the absorbent body having the thickness H _j corresponding to each of the eleven Bragg curves determined in the third step, the seven-step staircase portion 11 of the rod-shaped body 1 is provided. 12 and 17 and the columnar bodies 31 to 33 are selected, and the load coefficient ratio W _j when the enlarged Bragg curve is synthesized in the third step is used as the respective area ratios, thereby designing each part of the ridge filter 25. Is what you do. Further, in the confirmation work in the fifth step, when there is an error in SOBP width, by finely adjusting the diameter of the X-direction width X _i and columnar body 31 to 33 of each step portion, modifies the SOBP width be able to.

Hereinafter, in the ridge filter 25 according to the first embodiment, an effect obtained by replacing a predetermined stepped portion of the rod-shaped body 1 with a plurality of columnar bodies 3 will be specifically described. While the staircase portion of the rod-shaped body 1 is continuous in the Y direction, the plurality of columnar bodies 3 are discretely arranged in the Y direction. In order to obtain a uniform SOBP distribution in the ridge filter 25, as described above, the area ΔS ₀ of the minimum thickness portion is maximized, and the area ΔS _j gradually decreases as the thickness H _j increases. For this reason, the cross-sectional shape of the rod-shaped body 1 of the ridge filter 25 is usually a mountain shape as shown in FIG.

In addition, when the required SOBP width is large, the number of necessary steps (the number of types of thickness) increases, and the area occupied by the thick portion becomes very small. When the energy absorber is composed only of the rod-like body 1 as in the conventional ridge filter 50 shown in FIG. 11, the X-direction width ΔX _j (ΔX _j = X _j −X _{j + 1} ) of the staircase portion is 0.1 mm. In some cases, high processing accuracy was required.

Therefore, in the first embodiment, when the area ΔS _{j of the j-th} step portion of the rod-like body 1 is smaller than the predetermined ratio by design, or when the rod-like body 1 is formed as one step, its X-direction width ΔX _j Is designed to be smaller than a predetermined value (for example, 0.1 mm to 1 mm), the staircase portion is replaced with a plurality of columnar bodies 3 that can be easily processed.

If the columnar body 3 has a cylindrical, the value of the diameter R is, compared to the same area in the X-direction width [Delta] X _j in the case of forming a stage of the staircase portion of the rod-shaped body 1, gamma fold increase. γ is determined from the following equations 8-12.
ΔX _j × Y0 = Ny × πR ² (Formula 8)
When the interval ΔY in the Y direction of the columnar body 3 is made equal to the interval X0 in the X direction of the rod-like body 1, Ny = Y0 / X0, and Expression 8 is expressed as Expression 9 below.

ΔX _j × Y0 = (Y0 / X0) × πR ²
ΔX _j = πR ² / X0 (Formula 9)
R = (X0 × ΔX _j /3.14) ^1/2 (Formula 10)
γ = R / ΔX _j
= (X0 / 3.14 / ΔX _j ) ^1/2 (Formula 11)
Here, assuming that X0 = 10 mm and ΔX _j = 0.1 mm,
γ = (10 / 3.14 / 0.1) ^1/2
= 5.6 (Formula 12)

Thus, when the stepped portion of the X-direction width [Delta] X j ₌ 0.1 mm in the rod-shaped body 1 was replaced by a columnar body 3, the diameter of the columnar body 3 necessary, be about 5.6 times larger than [Delta] X _j. For this reason, when the ridge filter 25 having a large SOBP width is produced, an enlarged Bragg curve having a large SOBP width is required without requiring high processing accuracy compared to the case of producing a ridge filter 50 composed only of the rod-like body 1. Can be formed with high accuracy.

  In addition, since the external dimensions in the XY direction of the columnar body 3 are usually several mm or less, the particle beam 21 incident on the columnar body 3 has a certain probability before the columnar body 3 completely transmits the side surface of the columnar body 3. (Outside) will go out. For this reason, the ratio of the particle beam 21 that actually permeates the columnar body 3 is smaller than the ratio determined by the area ratio of the columnar body 3 on the XY plane. It is desirable to calculate this ratio in advance using, for example, a Monte Carlo code or the like, and to reflect the result in the calculation when determining the area ratio of each part of the ridge filter 25.

  In addition, the cross-sectional shape of the rod-like body 1 in the XZ direction is generally a triangle, but it does not necessarily have left-right symmetry and may have a staircase structure only on one side. Moreover, like the rod-shaped body 1a shown to Fig.7 (a), one slope has the seven-step staircase parts 11-17, and the other slope has the five-step staircase parts 11, 12, 14, 16, 17 It may be designed to have

The columnar body 3 is provided in place of the staircase portion of the rod-shaped body 1 whose area ratio in the predetermined area of the virtual plane 25a is smaller than the predetermined ratio in design, and the staircase portion is a staircase portion having the maximum thickness. Not necessarily. For example, as in the rod-shaped body 1b shown in FIG. 7B, the X-direction width (ΔX ₃ = X ₃ −X ₄ ) of the _third stepped portion 13 from the bottom is very small, and high machining accuracy is required. In this case, the staircase portion 13 can be replaced with a columnar body 3 that forms the same energy component. In the first embodiment, the cross-sectional shape of the columnar bodies 31, 32, and 33 in the XY plane is circular, but may be any shape such as an ellipse, a triangle, a quadrangle, and a rectangle.

  Furthermore, the rod-shaped body 1 and the columnar body 3 may be disposed on different planes by changing the Z-direction coordinates without being disposed on the same plane. Specifically, using two base plates 5, the rod-like body 1 and the columnar body 3 are formed on different base plates 5. In order to reduce the energy loss and scattering of the particle beam due to the use of two base plates 5, a frame-shaped base plate 5b (see FIG. 11) may be used. Thus, by arranging the rod-shaped body 1 and the columnar body 3 on different base plates 5, a plurality of types of them can be prepared and used in different combinations, so that the ridge filter 25 with high versatility is obtained.

  In the case where the ridge filter 25 is arranged separately on two planes, the area ratio of each part of the ridge filter 25 is strictly considered to be projected on one of the planes in consideration of the spread of the particle beam 21. However, as long as these two planes are not separated greatly, even if they are handled in the same manner as when they are on the same plane, there is no big problem in calculating the area ratio. Therefore, as described above, the influence of the spread of the particle beam 21 on the area ratio of the absorber thickness may be ignored.

  As described above, according to the first embodiment, the manufacturing can be performed without requiring high processing accuracy compared to the case of forming the conventional ridge filter 50 (FIG. 11) composed only of the rod-like body 1. It is easy and the processing time is shortened, and the manufacturing cost can be reduced. Furthermore, the particle beam irradiation system provided with the particle beam irradiation means 20 including the ridge filter 25 according to the first embodiment can form a highly accurate energy distribution.

Embodiment 2. FIG.
In the first embodiment, the columnar body 3 constituting the second energy absorber of the ridge filter 25 is a cylinder, and three types of columnar bodies 31, 32, and 33 having different thicknesses have a predetermined interval in the Y direction. An example in which they are placed discretely has been described. In the second embodiment, another configuration example of the second energy absorber will be described with reference to FIGS. In the drawings, the same or corresponding parts are denoted by the same reference numerals.

  In the second energy absorber according to the second embodiment, a plurality of types of structures having different thicknesses are integrally formed as one structure, which is discretely and periodically in each of the X direction and the Y direction. It is arranged. As a form of such a structure, FIGS. 8 and 9 show a step-like structure whose thickness changes stepwise in the Y direction. FIG. 10 shows a pyramid-like structure whose thickness changes stepwise in all directions orthogonal to the Z direction as another form included in the step-like structure.

  The ridge filter 250 shown in FIG. 8 includes a second energy absorber 31d having a first thickness, a second thickness 32d, and a third thickness 33d having a stepped structure. The body 3d is integrated together. The structural body 3d is disposed on the same base plate 5 as the rod-shaped body 1.

  The ridge filter 251 shown in FIG. 9 has a step-like structure in which a portion 31e having a first thickness, a portion 32e having a second thickness, and a portion 33e having a third thickness of the second energy absorber. The body 3e is integrated together. The plurality of structures 3e arranged in the Y direction are connected to each other at the bottom portion, and both ends thereof are supported by the frame-shaped base plate 5b. Note that by using such a frame-shaped base plate 5b, the maximum energy of the particle beam can be increased, and the scattering of the particle beam can be reduced.

  Further, the ridge filter 252 shown in FIG. 10 includes a portion 31f having the first thickness, a portion 32f having the second thickness, and a portion 33f having the third thickness of the second energy absorber. The pyramid-like structures 3f are integrated together.

  In the examples shown in FIGS. 8 to 10, in any case, the number of arrangements of the structures 3d, 3e, and 3f, which are the second energy absorbers, can be reduced. This also improves the stability. Furthermore, especially in the case of the structure 3f shown in FIG. 10, the ratio of the particle beam which leaks from the side surface of the structure can be reduced. This facilitates the design of the ridge filter. In any example, the material constituting the structures 3d, 3e, and 3f is made of a material having a higher density than the material constituting the rod-like body 1, so that the overall height of the structures 3d, 3e, and 3f can be reduced. Can be small. Thereby, all of the above effects are further improved.

  As described above, according to the second embodiment, in addition to the same effects as those of the first embodiment, the installation stability is improved, and the design and manufacture of the ridge filter is further facilitated. In addition, according to the particle beam irradiation system according to the present invention that employs the energy distribution forming apparatus according to the first embodiment and the second embodiment, the irradiated portion (affected portion) having a spread in the depth direction is used. The particle beam irradiation can be performed with a more uniform dose.

  The energy distribution forming device and the particle beam irradiation system using the same according to the present invention can be used as a particle beam cancer treatment device.

It is a longitudinal cross-sectional view which shows the particle beam irradiation means of the particle beam irradiation system which concerns on Embodiment 1 of this invention. It is the perspective view and partial expanded sectional view which show the energy distribution formation apparatus which concerns on Embodiment 1 of this invention. It is a top view which shows the other example of arrangement | positioning of the 2nd energy absorber in the energy distribution formation apparatus which concerns on Embodiment 1 of this invention. It is a schematic diagram which shows the breadth of dose distribution on the irradiation plane by the particle beam which permeate | transmitted the 2nd energy absorber of the energy distribution formation apparatus which concerns on Embodiment 1 of this invention. It is a figure which shows the relationship between X1 / R1 and the total number of scattering particles in the intermediate points M2 and M4 of the energy distribution formation apparatus which concerns on Embodiment 1 of this invention. It is a partial expanded sectional view of the energy distribution formation apparatus which concerns on Embodiment 1 of this invention. It is a partial expanded sectional view which shows the other structure of the energy distribution formation apparatus which concerns on Embodiment 1 of this invention. It is a perspective view which shows the structure of the energy distribution formation apparatus which concerns on Embodiment 2 of this invention. It is a perspective view which shows the other structure of the energy distribution formation apparatus which concerns on Embodiment 2 of this invention. It is a perspective view which shows the other structure of the energy distribution formation apparatus which concerns on Embodiment 2 of this invention. It is a perspective view which shows the conventional energy distribution formation apparatus. It is a figure explaining composition of an expansion Bragg curve.

Explanation of symbols

1, 1a, 1b first energy absorber (rod-like body),
3, 3a, 3b, 3c second energy absorber (columnar body),
3d, 3e, 3f second energy absorber (structure),
5 Base plate, 5b Frame-shaped base plate,
20 particle beam irradiation means, 21 particle beam, 22 wobbler electromagnet, 23 scatterer,
24 dose monitor, 25 ridge filter, 25a virtual plane, 26 range shifter,
27 collimator, 28 energy compensator,
31, 31a, 31b, 31c A columnar body having a first thickness,
31d, 31e, 31f portions having a first thickness,
32, 32a, 32b, 32c a columnar body having a second thickness;
32d, 32e, 32f portions having a second thickness,
33, 33a, 33b, 33c a columnar body having a third thickness,
33d, 33e, 33f portions having a third thickness,
40 patients, 41 affected area (tumor area), 41a irradiation plane, 42 maximum thickness of affected area,
50 Conventional ridge filter,
100 Enlarged Bragg curve, 101, 102, 103 Bragg curve,
250, 251, 252 Ridge filter.

Claims (14)

When the particle beam irradiation direction is the Z direction, the two directions orthogonal to the Z direction and the two directions orthogonal to each other are the X direction and the Y direction, respectively, and the length in the Z direction is the thickness,
A first energy absorber and a second energy absorber disposed along a plane perpendicular to the Z direction,
The first energy absorber has a step portion whose thickness changes stepwise in the X direction, and a flat portion that is a constant thickness region of each step portion maintains the thickness. A plurality of rod-shaped bodies extending in the Y direction, and the plurality of rod-shaped bodies are arranged in parallel to each other at a predetermined interval X0 in the X direction;
The second energy absorber has a plurality of structures having a predetermined thickness B that provides an energy absorption amount larger than the energy absorption amount of the particle beam by the stepped portion having the maximum thickness A of the first energy absorber. The plurality of structures are arranged discretely and periodically in each of the X direction and the Y direction, and are arranged so as not to overlap the first energy absorber in the Z direction. Energy distribution forming device.   2. The energy distribution according to claim 1, wherein the rod-shaped body and the structure are disposed on the same plane, and the structure is disposed between the rod-shaped bodies adjacent to each other in the X direction. Forming equipment.   The energy distribution forming apparatus according to claim 1, wherein the rod-like body and the structure are arranged on different planes.   The energy distribution forming device according to any one of claims 1 to 3, wherein the structures are arranged in the X direction at the predetermined interval X0.   When the density of the rod-shaped body is m1 and the density of the structure is m2, the predetermined thickness B of the structure is a value obtained by multiplying the maximum thickness A of the rod-shaped body by m1 / m2. The energy distribution forming apparatus according to any one of claims 1 to 4, wherein the energy distribution forming apparatus is larger than a maximum effective thickness.   6. The energy distribution forming apparatus according to claim 5, wherein the predetermined thickness B is a minimum thickness of the structure.   The said structure is a columnar body of the same thickness, The energy distribution formation apparatus of any one of Claims 1-6 characterized by the above-mentioned.   The structure includes a plurality of types of columnar bodies having different thicknesses, and the plurality of types of columnar bodies are periodically arranged in the X direction and the Y direction for each type. The energy distribution formation apparatus of any one of Claims 1-6.   The energy distribution forming device according to any one of claims 1 to 6, wherein the structure is a step-like structure whose thickness changes stepwise in the Y direction.   The energy distribution forming device according to claim 9, wherein the step-like structure is a pyramid-like structure whose thickness changes stepwise in all directions orthogonal to the Z direction.   When the rod-like body and the structure are projected along a particle beam on the same plane perpendicular to the Z direction, the same structure projected in a predetermined range including the particle beam irradiation field on the same plane 11. The energy according to claim 7, wherein an area ratio of a portion having a thickness is smaller than an area ratio of each stepped portion of the rod-shaped body projected in the range. Distribution forming device.   The part having the same thickness of the plurality of structures is arranged in the Y direction at the interval X0 or at an interval smaller than the interval X0. An energy distribution forming device according to claim 1.   The interval in the Y direction of the portions having the same thickness of the plurality of structures is Y1 when the interval in the Y direction is projected onto a predetermined irradiation plane according to the divergence angle of the particle beam. When the distance between the arranged plane and the irradiation plane is L, the 1 / e divergence angle of the particle beam transmitted through the structure (the angular distribution of the particle number on the plane orthogonal to the particle number and the particle beam irradiation direction) The ratio of Y1 to the scattering radius R1, which is the product of L and Gaussian distribution and the number of particles is 1 / 2.718) and L, is determined to have a value smaller than 1.7 or 1.7 The energy distribution forming device according to claim 12, wherein:   Particle beam generating means, particle beam accelerating means for accelerating the particle beam generated from the particle beam generating means, particle beam transport means for guiding the particle beam accelerated by the particle beam accelerating means to a predetermined position, and the predetermined beam The particle beam irradiation system provided with the particle beam irradiation means containing the energy distribution formation apparatus as described in any one of Claims 1-13 installed in the position of.

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