Radiation shielding wall

Abstract

To provide a radiation shielding wall using a metal shielding body capable of suppressing excessive use of a metal shielding material.SOLUTION: A radiation shielding wall 5 is provided around an irradiation room 1 in which a medical LINAC is installed, and includes a plate-shaped metal shielding body 10 arranged in areas of a ceiling, walls, and a floor where a useful beam of radiation radiated by the medical LINAC is radiated, and a concrete shielding part 40 that covers the metal shielding body 10. The metal shielding body 10 increases in a width perpendicular to the central axis of the useful beam around the central axis according to a distance from an isocenter IC. The metal shielding body 10 may also gradually increase in the width perpendicular to the central axis of the useful beam according to the distance from the isocenter IC, using a rectangular partial metal shielding body.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a radiation shielding wall using a metal shield that can reduce the use of excessive metal shielding material. [Background technology]

[0002] Radiation irradiation rooms, which contain radiation generating devices such as electron linacs (linear accelerators) used in cancer treatment, are surrounded by thick shielding walls made of concrete or metal shields such as iron to block radiation.

[0003] In medical linacs, photons or electron beams are generated as a point source at the metal target position, and the maximum size of the irradiation field is 40 × 40 cm at the isocenter, 100 cm away. 2 It is also possible to irradiate from 360° directions around the isocenter.

[0004] The metal shield is installed on the ceiling, walls, and / or floor of the irradiation room. When considering the ceiling, walls, and floor separately, the conventional shape of the metal shield is a rectangular parallelepiped (see Patent Document 1).

[0005] The width of the metal shield is set to sufficiently cover the width of the radiation beam when it reaches the shielding iron plate. In order to reduce the weight and cost of the shielding iron plate, the cross-sectional shape of the shielding is designed (see Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6384713 [Patent Document 2] Patent No. 6839572 Summary of the Invention [Problem to be solved by the invention]

[0007] Meanwhile, metal shields installed on the ceiling, walls, floor, etc. of the irradiation room are rectangular plate-like members with the rotation direction of the useful beam centered on the isocenter as the longitudinal direction, but for example, the irradiation width of the useful beam for a metal shield installed on the ceiling is larger at both ends (the joints between the ceiling and the wall) than at the center in the rotation direction of the useful beam (see Figures 2 and 3). Since conventional metal shields use the irradiation width of the useful beam on both ends as the standard, the width of the metal shield near the isocenter, where the irradiation width is smallest, is unnecessarily large, and excessive metal shielding material is placed.

[0008] The present invention has been made in consideration of the above, and has an object to provide a radiation shielding wall using a metal shield that can reduce the use of excessive metal shielding material. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems and achieve the object, the present invention provides a radiation shielding wall provided around an irradiation room in which a medical linac is installed, comprising a plate-shaped metal shielding body arranged in the areas of the ceiling, wall, and floor where the useful beam of radiation irradiated by the medical linac is irradiated, and a concrete shielding section covering the metal shielding body, wherein the metal shielding body has a width perpendicular to the central axis of the useful beam, the width increasing around the central axis depending on the distance from the isocenter.

[0010] In the present invention, the thickness of the metal shield is reduced in accordance with the distance from the isocenter.

[0011] In addition, in the above-mentioned invention, the metal shielding is a rectangular partial metal shielding whose width perpendicular to the plane of rotation of the central axis of the useful beam is gradually increased depending on the distance from the isocenter.

[0012] In addition, in the above-mentioned invention, the partial metal shielding is arranged so that the partial metal shielding located at the position closest to the isocenter is placed at the center, and other partial metal shields whose widths increase as the distance from the isocenter increases are arranged to sandwich the partial metal shielding.

[0013] In the above-mentioned invention, the bonding surface of the partial metal shield is inclined with respect to a plane of the partial metal shield.

[0014] In addition, in the above-mentioned invention, the partial metal shielding is formed by stacking a plurality of metal shielding plates in stages toward the outside of the irradiation chamber, so that the bonding surfaces of the partial metal shielding are formed at an angle in stages.

[0015] In addition, the present invention is characterized in that, in the above-mentioned invention, the metal shielding plates on the same plane are arranged adjacent to each other with a gap, and another metal shielding plate arranged on a lower metal shielding plate is arranged so as to straddle other metal shielding plates of the same plane arranged adjacent to both sides of the same plane of the lower metal shielding plate. Effect of the Invention

[0016] According to the present invention, it is possible to provide a radiation shielding wall using a metal shield that can reduce the use of excessive metal shielding material. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a perspective view showing the structure of a radiation-shielding wall according to the present embodiment. [Diagram 2] FIG. 2 is a cross-sectional view of the radiation shielding wall shown in FIG. 1 taken along line AA. [Diagram 3] FIG. 3 is a cross-sectional view of the radiation shielding wall 5 shown in FIG. 1 taken along line BB. [Figure 4] FIG. 4 is a diagram showing the configuration of a radiation shielding wall according to the first modification. [Diagram 5] FIG. 5 is a diagram showing the configuration of a radiation shielding wall according to the second modification. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a perspective view of the structure of a radiation shielding wall 5 according to the present embodiment, seen through the transparent view. FIG. 2 is a cross-sectional view of the radiation shielding wall 5 shown in FIG. 1 taken along line AA. FIG. 3 is a cross-sectional view of the radiation shielding wall 5 shown in FIG. 1 taken along line BB. FIG. 1 does not show the configuration related to entering and leaving the irradiation room 1 in which the head unit 50 of the medical linac is installed. FIG. 2 and FIG. 3 also show the state of the utilized beam of radiation accompanying the rotation of the head unit 50. FIG. 2 and FIG. 3 show only the metal shielding body 20 installed on the ceiling out of the metal shielding body 10.

[0019] The head unit 50 shown in Fig. 1 is provided with a target T. The head unit 50 generates bremsstrahlung radiation by colliding electrons accelerated by an accelerator with an energy of, for example, 10 MeV with the target T. The radiation generated by the target T is focused by a metal collimator or the like and is used for treatment at the position of the isocenter IC. It is assumed that a patient is laid on the treatment table 3 so that the affected area of ​​the patient overlaps with the isocenter IC.

[0020] The head unit 50 is configured to be rotatable 360° in the θA direction or the θB direction on the YZ plane around the isocenter IC, and radiation can be irradiated to the isocenter IC from any position on the rotation orbit of the head unit 50. A radiation shielding wall 5 is provided around the irradiation chamber 1 to block radiation emitted from the head unit 50. This radiation shielding wall 5 has a metal shielding body 10 made of a metal such as iron, and a concrete shielding section 40 made of concrete to cover this metal shielding body 10.

[0021] As shown in FIG. 1, the head unit 50 rotates 360° while irradiating radiation, so the metal shield 10 is plate-shaped and is arranged in a square shape on the ceiling, wall, and floor to be irradiated with radiation. Here, in this embodiment, as shown in FIG. 2 and FIG. 3, for example, the irradiation width of the useful beam on the metal shield 20, which is the metal shield 10 on the ceiling, is larger at both ends (the joints between the ceiling and the wall) than at the center in the useful beam rotation direction, so as shown in FIG. 1, the metal shield 20 is designed to increase the width perpendicular to the central axis CS of the useful beam around the central axis CS according to the distance from the isocenter IC. Similarly, for the metal shield 10 installed on the wall, the width of the central part of the wall increases toward the joints between the wall and the ceiling and the joints between the wall and the floor. Similarly, for the metal shield 10 installed on the floor, the width of the central part of the floor increases toward the joints between the floor and the wall.

[0022] As shown in Figures 2 and 3, if the irradiation angle of the useful beam with target T as its vertex is 2θ, the distance from isocenter IC to the ceiling is Hcm, the concrete thickness on the irradiation room 1 side of the ceiling is Dcm, the thickness of metal shielding 20 on the ceiling is Tcm, and the distance d between the center of isocenter IC and target T is 100cm, when the useful beam of radiation is irradiated perpendicularly to the ceiling (in the +Z direction), the irradiation width (single width) W1 of the useful beam on the top surface of metal shielding 20 is expressed by the following equation (1). W1 = (H + D + T + 100) × tan θ … (1)

[0023] On the other hand, when the useful beam of radiation is irradiated to the junction between the ceiling and the wall, assuming that the distance from the isocenter IC to the wall is L cm, the useful beam is irradiated to the intersection point of the extension of the inner wall surface of the wall and the top surface of the metal shielding 20, and the irradiation width (single width) W2 on the top surface of the metal shielding 20 is expressed by the following equation (2). W2=(√((H+D+T) 2 +L 2 ))+100)×tan θ …(2)

[0024] As a result, the irradiation width W2 is always larger than the irradiation width W1. Specifically, if H=200cm, D=30cm, T=40cm, L=400cm, and θ=11.31°, then W1=74cm and W2=117cm, and W2 is 1.57 times larger than W1. Therefore, if the metal shielding 20 is a rectangular plate and the width of the short side direction (±X direction) of the metal shielding 20 is set based on the maximum irradiation width (=W2), an excessive amount of metal shielding material will be used directly above the isocenter IC (+Z direction), where the irradiation width (=W1) is the smallest.

[0025] Therefore, in this embodiment, the width of the metal shield 20 in the short side direction is set to a value according to the irradiation width of the metal shield 20 with the rotation of the useful beam. As a result, the width in the short side direction directly above the metal shield 20 is minimum, and the width increases toward both ends in the longitudinal direction, changing so that the width is maximum at both ends in the longitudinal direction. This makes it possible to avoid using unnecessary metal shielding material. Note that this is not limited to the metal shield 20, but also applies to the metal shields 10 provided on the walls and floors, whose width in the short side direction increases as the distance from the isocenter IC increases.

[0026] In addition, the greater the distance from the isocenter IC, the greater the irradiation width, and the lower the radiation density and intensity. In the above description, the metal shield 10 is plate-shaped, but the thickness of the metal shield 10 may be set to be thinner as the distance from the isocenter IC increases. This also avoids the use of unnecessary metal shielding material.

[0027] The width in the short direction and the thickness in the long direction of the metal shield 10 are designed to have an appropriate margin depending on the intensity of radiation.

[0028] <Variation 1> Fig. 4 is a diagram showing the configuration of the radiation shielding wall of the first modified example. Fig. 4 shows only a portion of the metal shielding 10 corresponding to the metal shielding 20. Fig. 4(a) is a plan view of the metal shielding 21 seen from the +Z direction, Fig. 4(b) is a back view of the metal shielding 21 seen from the -Z direction, and Fig. 4(c) is a cross section of the radiation shielding wall having the metal shielding 21, which is a cross section passing through the central axis C of the metal shielding 21 seen from the -X direction. Note that Fig. 4 describes only the metal shielding 21 on the ceiling, but the metal shielding 21 placed on the wall or floor can also have a similar configuration.

[0029] In the above embodiment, the metal shield 20 is designed to increase the width perpendicular to the plane of rotation of the central axis CS of the useful beam around the central axis CS according to the distance from the isocenter IC. However, as shown in FIG. 4, in this modification 1, the metal shield 21 is formed by combining rectangular partial metal shields 22-24 whose width perpendicular to the plane of rotation of the central axis CS of the useful beam increases stepwise according to the distance from the isocenter IC. The metal shield 21 is made up of three (odd number) partial metal shields 22-24, with the width WB of the partial metal shield 24 at the shortest distance from the isocenter IC being the smallest, and the width WA of the partial metal shields 22, 23 at both ends on the wall side being the largest. The widths WA, WB are the widths centered on the central axis C of the metal shield 21 and perpendicular to the plane of rotation of the central axis CS of the useful beam. In addition, in FIG. 4, the metal shield 21 is made up of three partial metal shields 22 to 24, but it is also possible to set the width in finer steps by using an odd number of partial metal shields, three or more.

[0030] In other words, the partial metal shields are arranged so that the partial metal shield located at the position closest to the isocenter is placed at the center, and other partial metal shields whose widths increase as the distance from the isocenter increases are arranged on either side of the central partial metal shield.

[0031] Here, the two plate-like partial metal shields that shield radiation are arranged adjacent to each other along the same plane, and the surfaces of the partial metal shields that face and contact each other are not perpendicular to the plane of the partial metal shields. More specifically, the partial metal shield 24 that tapers toward the isocenter IC is arranged between the partial metal shields 22 and 23, and the facing surfaces of the partial metal shield 24 and the partial metal shield 22, and the partial metal shield 24 and the partial metal shield 23 are brought into contact with each other, and these contact surfaces are used as bonding surfaces.

[0032] In order to suppress leakage from the joints, the joint surfaces of the partial metal shields 22 to 24 are inclined with respect to the plane of the partial metal shields 22 to 24. Here, the inclined surfaces of the joint surfaces are formed to widen toward the outside (+Z direction) so that concrete, which will be poured later, can be filled in without gaps.

[0033] In the present first modification, since the metal shield 21 is composed of rectangular partial metal shields 22 to 24, the metal shield 21 can be easily formed.

[0034] <Variation 2> Fig. 5 is a diagram showing the configuration of a radiation shielding wall according to Modification 2. Fig. 5 shows only a portion of the metal shielding 10 corresponding to the metal shielding 20. Fig. 5(a) is a plan view of the metal shielding 31 seen from the +Z direction, Fig. 5(b) is a back view of the metal shielding 31 seen from the -Z direction, and Fig. 5(c) is a cross section of the radiation shielding wall having the metal shielding 31, showing a cross section passing through the central axis C of the metal shielding 31 seen from the -X direction. Note that Fig. 5 describes only the metal shielding 31 on the ceiling, but the metal shielding 31 placed on the wall or floor can also have a similar configuration.

[0035] As shown in Figure 5, in this variant example 2, partial metal shields 32 to 34 are provided which correspond respectively to the partial metal shields 22 to 24 in variant example 1, and each partial metal shield 32 to 34 is formed by stacking a plurality of metal shielding plates in stages facing the outside of the irradiation chamber 1, so that the bonding surfaces of the partial metal shields are formed at an angle in stages.

[0036] The partial metal shield 32 has five metal shielding plates 32a to 32e stacked toward the outside. The partial metal shield 33 has five metal shielding plates 33a to 33e stacked toward the outside. The partial metal shield 34 has five metal shielding plates 34a to 34e stacked toward the outside. At this time, the metal shielding plate arranged on the central metal shielding plate is arranged so as to straddle the metal shielding plates arranged adjacent to both sides of the lower metal shielding plate. For example, the metal shielding plate 34b arranged on the metal shielding plate 34a is arranged so as to straddle the metal shielding plates 32a and 33a. As a result, the gaps between the metal shielding plates on the same surface become gradually inclined between the partial metal shielding 34 and the partial metal shielding 32, and between the partial metal shielding 34 and the partial metal shielding 33, and radiation leakage through the gaps can be prevented.

[0037] In this second variant, the partial metal shields 32 to 34 are each made up of five metal shielding plates, so that when assembling the metal shield 31, it is only necessary to transport and assemble the lighter metal shielding plates, thereby improving workability.

[0038] In the above-mentioned modified examples 1 and 2, since a joint is provided, an auxiliary shield may be provided outside the joint to further suppress leakage.

[0039] In addition, in the above-mentioned modified examples 1 and 2, it is assumed that the useful beam of the irradiation radiation rotates. However, this is not limited to the above. The useful beam may not rotate, and metal shielding may be provided only in the areas of the ceiling, walls, and floor where the useful beam is irradiated.

[0040] Note that the configurations illustrated in the above embodiments and modifications are merely functional schematics and do not necessarily have to be physically configured as illustrated. In other words, the distribution and integration of each device and component is not limited to that illustrated, and all or part of them can be functionally or physically distributed and integrated in any unit depending on various usage conditions, etc. [Explanation of symbols]

[0041] 1 Irradiation room 3 Treatment table 5 Radiation shielding wall 10,20,21,31 Metal shield 22~24,32~34 Partial metal shield 32a~32e, 33a~33e, 34a~34e Metal shielding plate 40 Concrete shield 50 Head C,CS center axis d Distance IC Isocenter T Target W1, W2 Irradiation width WA,WB Width

Claims

1. A radiation shielding wall provided around an irradiation room in which a medical linear accelerator is installed, A plate-shaped metal shielding member is disposed in the area of ​​a ceiling, a wall, and a floor where a useful beam of radiation emitted by the medical linear accelerator is irradiated; a concrete shielding portion covering the metal shielding body; Equipped with A radiation shielding wall, characterized in that the metal shield has a width perpendicular to the central axis of the useful beam that increases around the central axis depending on the distance from the isocenter.

2. 2. The radiation shielding wall according to claim 1, wherein the thickness of the metal shielding is decreased according to the distance from the isocenter.

3. 2. The radiation shielding wall according to claim 1, wherein the metal shielding is a rectangular partial metal shield having a width that is increased stepwise in a direction perpendicular to the plane of rotation of the central axis of the useful beam depending on the distance from the isocenter.

4. The radiation shielding wall according to claim 3, characterized in that the partial metal shielding is arranged so that a partial metal shield arranged at a position farthest from the isocenter is placed at the center, and other partial metal shields whose widths become wider as the distance from the isocenter increases are placed on either side of the partial metal shielding.

5. The radiation shielding wall according to claim 4 , wherein the bonding surface of the partial metal shield is oblique to a plane of the partial metal shield.

6. The radiation shielding wall according to claim 5, wherein the partial metal shielding is formed by stacking a plurality of metal shielding plates in stages toward the outside of the irradiation chamber, so that the bonding surfaces of the partial metal shielding are formed at an angle in stages.

7. The metal shielding plates are arranged adjacent to each other on the same plane with a gap therebetween, The radiation shielding wall according to claim 6, characterized in that the other metal shielding plate arranged on the lower metal shielding plate is arranged so as to straddle other other metal shielding plates of the same surface arranged adjacent to both sides of the same surface of the lower metal shielding plate.

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