Radiation shield structure

Abstract

To provide a radiation shield structure that can greatly reduce the leakage dose at a doorway.SOLUTION: A maze 24 has, in a direction separating from a radiation generator 12, a side end part 26 of a maze inner wall 22, a first leg 30 that is a passage extending in a thickness direction of the maze inner wall 20 from an opening 28 formed between a radiation shield wall 14 and the first leg, a second leg 32 that is a passage connected with the first leg 30 at an angle and extending along the maze inner wall 20 and a maze outer wall 22, and a third leg 34 that is a passage connected with an end of the second leg 32 close to a doorway 18 at an angle and extending in the thickness direction of the maze outer wall 22 from the end in a direction separating from the radiation generator 12. A length L3 of the passage of the third leg 34 is set on the basis of a length L2 and a shape of the second leg 32 and the maximum dose used in the radiation generator 12.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a radiation shielding structure having a maze at the entrance and exit of, for example, a medical radiation irradiation room. [Background technology]

[0002] Conventionally, in radiation facilities such as medical linac rooms, a maze structure is provided between the irradiation room where radiation is irradiated and the entrance / exit to prevent radiation from leaking outside, and a shielding door is installed at the entrance / exit (see, for example, Patent Document 1). The maze in a linac room often has a two-legged structure.

[0003] 5(1) and (2) show an example of a conventional linac room equipped with a two-legged maze. As shown in these figures, the linac room 1 has an irradiation room 4 that is substantially rectangular in plan view and surrounded by a radiation shielding wall 3 with an iron plate 2 built in, and a two-legged maze 6 that is connected to an entrance 5 of the irradiation room 4. A linac device 7 that emits radiation is provided in the approximate center of the irradiation room 4, from which a usable wire weight C is formed. The maze 6 has a first leg A and a second leg B, and is provided along the maze inner wall 8. The maze inner wall 8 is a wall that protrudes from one radiation shielding wall 3 toward the opposing radiation shielding wall 3 so as to separate the irradiation room 4 from the entrance 5, and an opening 9 that connects the irradiation room 4 to the maze 6 is formed between the protruding end of the maze inner wall 8 and the opposing radiation shielding wall 3.

[0004] The first leg A of the maze 6 is provided on the side closer to the irradiation chamber 4, and the second leg B is provided on the side closer to the entrance / exit 5. The first leg A is short in length because its purpose is to connect the second leg B. In the example of FIG. 5, the length of the first leg A is approximately the same as the sum of the thickness of the maze inner wall 8 and the maze width. The second leg B is installed at a right angle or at a slight angle outward from the first leg A along the maze inner wall 8, and has a length approximately the same as the width of the irradiation chamber 4. The entrance / exit 5 is installed at the end of the second leg B or at a right angle near the end of the second leg B.

[0005] A shielding door 5A containing two layers of shielding plates made of lead and polyethylene is installed at the entrance 5. If there is a duct penetration hole in the hanging wall (not shown) of the entrance 5, a shielding shelf containing two layers of shielding plates made of lead and polyethylene is installed at the top of the maze 6 close to the entrance 5. The standard thicknesses of the lead and polyethylene are about 1 cm and 10 cm, respectively, but this varies depending on the energy of the linac device 7, the maximum usable dose, and the structure of the linac room 1. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2018-179851 A Summary of the Invention [Problem to be solved by the invention]

[0007] Most of the radiation entering the first leg A of the maze 6 from the irradiation room 4 is scattered by the walls and floor of the first leg A, and some of it enters the second leg B. The scattered radiation that enters the second leg B travels along the straight wall of the second leg B while being collimated, and reaches the entrance 5. Near the end of the second leg B, the radiation dose was not below the legal limit, so it was necessary to install a shielding door 5A to attenuate the radiation and make it below the legal limit. Since the shielding door 5A is heavy, an expensive electric drive device of the overhead suspension type was required. In addition, regular maintenance including adjustment and an auxiliary function to open and close it manually in the event of a power outage or malfunction were also required.

[0008] If there are ducts or sleeve through-holes in the hanging wall of the entrance 5, radiation will leak through them. In this case, since the radiation dose near the end of the second leg B was not below the legal limit, it was necessary to install a shielding shelf with the same shielding ability as the shielding door 5A on the top of the maze 6 for shielding. In addition, the shielding shelf is heavy, so it had to be firmly fixed with metal fittings, etc. to prevent it from falling in the event of an earthquake, etc.

[0009] If the radiation leakage at the entrance / exit 5 is below the legal limit, the shielding door and shelf will not be necessary, and it will be possible to reduce the manufacturing, installation and maintenance costs. For this reason, there has been a demand for technology that can significantly reduce the radiation leakage at the entrance / exit.

[0010] The present invention has been made in consideration of the above, and has an object to provide a radiation shielding structure that can significantly reduce the amount of leakage radiation at an entrance / exit. [Means for solving the problem]

[0011] In order to solve the above problems and achieve the object, the radiation shielding structure according to the present invention is a radiation shielding structure including: a storage chamber that stores a radiation generating device and is surrounded by a radiation shielding wall; a maze inner wall that is provided between the radiation generating device and the entrance / exit of the storage chamber in order to prevent radiation from the radiation generating device from directly reaching the entrance / exit of the storage chamber; and a maze that is partitioned and formed by a maze outer wall that is disposed opposite to the entrance / exit side of the maze inner wall and is connected to the entrance / exit, The radiation generating device has a first leg which is a passage extending from an opening formed between the shielding walls in the thickness direction of the inner maze wall, a second leg which is a passage connected at an angle to the first leg and extending along the inner maze wall and the outer maze wall, and a third leg which is a passage connected at an angle to the end side of the second leg closer to the entrance / exit and extending from the end side in the thickness direction of the outer maze wall toward a side away from the radiation generating device, and the length of the passage of the third leg is set based on the length and shape of the passage of the second leg and the maximum usage dose of the radiation generating device.

[0012] Further, another radiation shielding structure according to the present invention is characterized in that in the above-mentioned invention, the entrance and the maze do not have a shielding door and a shielding shelf for shielding against radiation. Effect of the Invention

[0013] According to the radiation shielding structure of the present invention, there is provided a radiation shielding structure including: a storage chamber that stores a radiation generating device and is surrounded by a radiation shielding wall; a maze inner wall that is provided between the radiation generating device and the entrance / exit in order to prevent radiation from the radiation generating device from directly reaching the entrance / exit of the storage chamber; and a maze that is partitioned and formed by a maze outer wall that is arranged opposite to the entrance / exit side of the maze inner wall and is connected to the entrance / exit, and the maze extends from a side end of the maze inner wall and an opening formed between the radiation shielding walls toward a side away from the radiation generating device through a thickness of the maze inner wall. the first leg being a passage extending in the thickness direction of the maze outer wall; the second leg being connected at an angle to the first leg and being a passage extending along the inner wall and the outer wall of the maze; and the third leg being connected at an angle to the end side of the second leg closer to the entrance / exit and being a passage extending from the end side in the thickness direction of the maze outer wall toward the side away from the radiation generating device, the length of the passage of the third leg being set based on the length and shape of the passage of the second leg and the maximum usage dose of the radiation generating device, thereby achieving the effect of significantly reducing the leakage dose at the entrance / exit.

[0014] In addition, according to another radiation shielding structure of the present invention, since the entrance / exit and maze do not have shielding doors and shielding shelves that shield against radiation, it is possible to reduce the manufacturing costs, installation costs, and maintenance costs of the shielding doors and shielding shelves. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a cross-sectional plan view showing an embodiment of a radiation shielding structure according to the present invention. [Diagram 2] FIG. 2 is a contour diagram showing an example of a calculation result of a leakage dose (dose rate). [Diagram 3] FIG. 3 is an explanatory diagram of the dimensions of the radiation shielding structure according to the present invention. [Figure 4] FIG. 4 is a contour diagram showing an example of a calculation result of a leakage dose (dose rate). [Diagram 5] FIG. 5 is a cross-sectional plan view showing an example of a conventional radiation shielding structure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the radiation shielding structure according to the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to these preferred embodiments.

[0017] 1, a radiation shielding structure 10 according to an embodiment of the present invention includes a storage room 16 that contains a radiation generating device 12 and is surrounded by a radiation shielding wall 14, a maze inner wall 20 provided between the radiation generating device 12 and the entrance / exit 18 to prevent radiation from the radiation generating device 12 from directly reaching the entrance / exit 18 of the storage room 16, and a tripod-structured maze 24 that is partitioned by a maze outer wall 22 arranged opposite the entrance / exit 18 side of the maze inner wall 20 and is connected to the entrance / exit 18. A shielding door having a radiation shielding function is not provided at the entrance / exit 18, but may be provided.

[0018] The radiation shielding structure 10 is assumed to be a linac room. The radiation generating device 12 is a linac device that emits radiation to form a useful beam C, and is provided approximately in the center of a storage room 16. The storage room 16 is an irradiation room that is approximately rectangular in plan view. The radiation shielding wall 14 is provided at a position including the vertical width direction Z of the storage room 16, which is made of concrete, and the horizontal width direction Y perpendicular to the vertical width direction Z.

[0019] The maze inner wall 20 is a wall that protrudes in the width direction Y from an end of one radiation shielding wall 14A extending in the vertical width direction Z toward the other opposing radiation shielding wall 14B so as to separate the storage chamber 16 from the entrance / exit 18, and an opening 28 that connects the storage chamber 16 to the maze 24 is formed between the protruding end 26 (side end) of the maze inner wall 20 and the other opposing radiation shielding wall 14B. A hanging wall (not shown) or the like is provided in the opening 28.

[0020] The maze outer wall 22 is formed of the radiation shielding wall 14 extending in the width direction Y from the end of the other radiation shielding wall 14B on the entrance / exit 18 side along the outside of the maze inner wall 20. The thickness of the maze outer wall 22 is approximately the same as the thickness of the radiation shielding wall 14B.

[0021] Maze 24 has first leg 30 , second leg 32 and third leg 34 and is disposed along inner maze wall 20 and outer maze wall 22 .

[0022] The first leg 30 is a passage that extends from the opening 28 in the thickness direction (vertical width direction Z) of the maze inner wall 20 and abuts the maze outer wall 22. The first leg 30 is short in length because its purpose is to connect to the second leg 32. The length L1 of the passage of the first leg 30 is equal to the sum of the thickness of the maze inner wall 20 and the maze width of the second leg 32. The maze width of the first leg 30 is constant.

[0023] The second leg 32 is a passage that is connected to the end of the first leg 30 at a right angle to the passage direction of the first leg 30 in a plan view, and extends in the width direction Y along the maze inner wall 20 and the maze outer wall 22. The length L2 of the passage of the second leg 32 is equal to the sum of the length L from the position where the protruding end 26 of the maze inner wall 20 is orthogonally projected onto the maze outer wall 22 to the end 36 of the maze outer wall 22 facing the third leg 34, and the maze width of the third leg 34. The maze width of the second leg 32 is constant.

[0024] The third leg 34 is a passageway that is connected to the end side of the second leg 32 close to the entrance 18 at a right angle in the passage direction of the second leg 32 in a plan view, and extends from the end side of the second leg 32 toward the entrance 18 in the thickness direction (vertical width direction Z) of the maze outer wall 22. The third leg 34 is not limited to being connected to the end (terminal end) of the second leg 32 close to the entrance 18, but may be connected near the terminal end of the second leg 32. The third leg 34 is provided between the side end surface 38 of the maze outer wall 22 and the radiation shielding wall 40 facing it, and along the radiation shielding wall 42. The radiation shielding wall 42 is a radiation shielding wall that is thinner than the other radiation shielding walls 14, is connected flush with the side end surface 38 of the maze outer wall 22 and the inner surface of the radiation shielding wall 40, and extends in the vertical width direction Z toward the entrance 18. The radiation shielding wall 40 extends in the vertical width direction Z with a constant thickness from the end of the second leg 32. The length L3 of the passage of the third leg 34 is the length from the end 36 (corner) on the inner side in the thickness direction of the side end face 38 of the maze outer wall 22 to the entrance 18. The maze width of the third leg 34 is constant.

[0025] The length L3 of the passage of the third leg 34 is set based on the length L2 and arrangement of the passage of the second leg 32, and the maximum usable dose of the radiation generating device 12. By adjusting the length L3, the leakage dose from the entrance / exit 18 at the end of the third leg 34 can be adjusted to a desired dose. By shortening L3, the leakage dose increases, and by lengthening L3, the leakage dose decreases. The attenuation rate of the third leg 34 is 1 / (L3) depending on the length L3 [m]. 2 Follow the rules.

[0026] Figure 2 shows an example of a contour diagram of the leakage dose calculated by changing the length L2 (L) of the passage of the second leg 32. Figure 2 (1) shows the case of L = 270 cm, and (2) shows the case of L = 300 cm. As shown in this figure, the radiation entering the third leg 34, which is installed perpendicular to the second leg 32, is mainly scattered on the wall surface around the end of the second leg 32, so it is understood that the radiation is considerably less than the radiation at the end of the second leg 32.

[0027] The concrete thickness of the radiation shielding wall 42 and the ceiling wall facing the third leg 34 is sufficient at about 30 cm, and does not need to be thicker than that. Therefore, there is no need to make the radiation shielding wall 42 thicker.

[0028] By appropriately setting the lengths L2 and L3 of the second leg 32 and the third leg 34, the leakage dose at the end of the third leg 34 can be kept below the legal limit. This allows the leakage dose at the entrance 18 to be significantly reduced. This eliminates the need to install a shielding door and a shielding shelf to shield radiation at the entrance 18. Since the installation of the shielding door and the shielding shelf is no longer necessary, the manufacturing costs, installation costs, and maintenance costs of the shielding door and the shielding shelf can be reduced. The door installed at the entrance 18 can be a general inward-opening door, an inner single-leaf door, a sliding door, or the like. The duct and sleeve installed near the end of the third leg 34 can be freely installed without taking measures against radiation leakage. In addition, since the entrance 18 is farther away from the target of the linear accelerator device (radiation generating device 12), the thickness of the maze inner wall 20 can be made thinner. Under standard operating conditions of the linac device, the length L3 of the third leg 34, which makes it unnecessary to install a shielding door and a shielding shelf as shown in FIG. 2, is considered to be about 300 cm.

[0029] (Example) Next, an embodiment of the present invention will be described. The value of L3 shown in this embodiment is for the maximum dose of the linac device being 60,000 [Gy / 3 months]. Since L3 varies depending on the maximum dose of the actual linac device, MD, it is possible to obtain L3 for MD by multiplying L3 by the value of MD / 60,000.

[0030] FIG. 3 is a diagram for explaining the dimensions of the maze periphery of this embodiment. As shown in this figure, in order to minimize the leakage dose from the entrance 18 at the end of the third leg 34, it is important to maximize the length L2 of the second leg 32 as much as possible. In this case, a wall thickness of 50 cm or more is sufficient for the end of the second leg 32. The distance (length) L from the first leg 30 to the third leg 34 is obtained by subtracting the opening width (maze width) W3 of the third leg 34 from the length L2 of the second leg 32. It is desirable to set L to 150 cm or more. The length L3 of the third leg 34 can be roughly determined by this L. The length L3a of the radiation shielding wall 42 of the extension part of the third leg 34 is calculated by subtracting L3 from the thickness D of the maze outer wall 22. mo It can be found by subtracting

[0031] Figure 4 shows an example of contour diagrams of leakage dose calculated by changing L2, the length of the passage of the second leg 32, from 150 to 500 cm. Figure 4 (1) shows the case where L = 150 cm, (2) shows the case where L = 200 cm, (3) shows the case where L = 250 cm, (4) shows the case where L = 300 cm, (5) shows the case where L = 350 cm, (6) shows the case where L = 400 cm, (7) shows the case where L = 450 cm, and (8) shows the case where L = 500 cm.

[0032] 4(1) to (6), when L is 150 cm or more and 400 cm or less, the length L3 of the passage of the third leg 34 can be roughly calculated by subtracting L from 600 cm. That is, L3 can be determined as 600-L [cm].

[0033] Furthermore, as shown in Figure 4 (7), when L is 450 cm, the approximate value of the length L3 of the passage of the third leg 34 can be obtained by subtracting L from 630. That is, L3 can be determined as 630-L [cm].

[0034] Also, as shown in Fig. 4(8), when L is 500 cm or more, the approximate value of the length L3 of the passage of the third leg 34 can be set to 150 cm. That is, it can be determined that L3 is approximately 150 cm.

[0035] As described above, the radiation shielding structure according to the present invention is a radiation shielding structure including: a storage chamber that stores a radiation generating device and is surrounded by a radiation shielding wall; a maze inner wall that is provided between the radiation generating device and the entrance / exit in order to prevent radiation from the radiation generating device from directly reaching the entrance / exit of the storage chamber; and a maze that is partitioned by a maze outer wall that is disposed opposite to the entrance / exit side of the maze inner wall and is connected to the entrance / exit, and the maze extends from a side end of the maze inner wall and an opening formed between the radiation shielding wall toward a side away from the radiation generating device. the first leg being a passageway extending in the thickness direction of the inner wall of the maze; the second leg being connected at an angle to the first leg and extending along the inner wall of the maze and the outer wall of the maze; and the third leg being connected at an angle to the end side of the second leg closer to the entrance / exit and extending in the thickness direction of the outer wall of the maze from the end side toward the side away from the radiation generating device, the length of the passageway of the third leg being set based on the length and shape of the passageway of the second leg and the maximum usage dose of the radiation generating device, thereby significantly reducing the leakage dose at the entrance / exit.

[0036] In addition, according to another radiation shielding structure of the present invention, since the entrance / exit and maze do not have shielding doors and shielding shelves that shield against radiation, the manufacturing costs, installation costs, and maintenance costs of the shielding doors and shielding shelves can be reduced. [Industrial Applicability]

[0037] INDUSTRIAL APPLICABILITY As described above, the radiation shielding structure according to the present invention is useful for radiation utilization facilities equipped with a maze, such as medical radiation irradiation rooms, and is particularly suitable for significantly reducing the amount of leakage radiation at entrances and exits. [Explanation of symbols]

[0038] 10 Radiation shielding structure 12 Radiation Generator 14, 14A, 14B, 40, 42 Radiation shielding wall 16 Containment Room 18 Entrance / exit 20 Maze inner wall 22 Maze outer wall 24 Maze 26 Projecting end (side end) 28 Opening 30 1st leg 32 Second leg 34 Third leg 36 End 38 Side end face Y Width direction Z vertical width direction

Claims

1. A radiation shielding structure comprising: a storage chamber that stores a radiation generating device and is surrounded by a radiation shielding wall; a maze inner wall that is provided between the radiation generating device and the entrance / exit of the storage chamber in order to prevent radiation from the radiation generating device from directly reaching the entrance / exit of the storage chamber; and a maze that is partitioned by a maze outer wall that is disposed opposite the entrance / exit side of the maze inner wall and is connected to the entrance / exit, the maze has a first leg which is a passage extending from a side end of the maze inner wall and an opening formed between the radiation shielding walls in a thickness direction of the maze inner wall toward a side away from the radiation generating device, a second leg which is a passage connected to the first leg at an angle and extends along the maze inner wall and the maze outer wall, and a third leg which is connected to an end side of the second leg close to the entrance at an angle and extends from the end side in a thickness direction of the maze outer wall toward a side away from the radiation generating device, A radiation shielding structure, characterized in that the length of the passage of the third leg is set based on the length and shape of the passage of the second leg and the maximum usable dose of the radiation generating device.

2. 2. The radiation shielding structure according to claim 1, wherein said entrance and said maze do not have a shielding door or a shielding shelf for shielding radiation.

Images