JP7175184B2 - Radiation reduction structure - Google Patents

Description

The present invention provides a radiation reduction structure that reduces the radiation controlled area in a space (for example, a space such as a seismic isolation layer) provided outside a radiation irradiation room in which a radiation generator is installed.

For example, in an irradiation chamber for radiation such as X-rays, a structure is adopted to reduce leakage of radiation from the irradiation chamber to the outside.

For example, Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2004-45338) discloses a technique for reducing the dose of radiation that leaks to the outside after being reflected from an object to be irradiated in an irradiation chamber by providing a curved portion (12) in the passage. disclosed.
JP-A-2004-45338

In the radiation irradiation room where radiation generators such as electron linacs (linear accelerators) are installed, concrete and iron are used to suppress the leakage of radiation outside the controlled area and to keep the effective dose at the boundary of the controlled area below the value stipulated by law. A thick shielding wall using

By the way, due to the spread of seismic isolation structures, the number of cases where the radiation irradiation room is built directly above the seismic isolation layer is increasing. When the radiation irradiation room is set up directly above the seismic isolation layer, part of the seismic isolation layer (near the area immediately below the radiation irradiation room) is designated as a radiation controlled area, and no one is allowed to enter the controlled area while the radiation generator is in operation. It is conceivable that the restriction will lower the shielding performance of the floor of the irradiation room and lower the construction cost compared to the case where the radiation control area is not provided in the seismic isolation layer.

As described above, for facilities with a radiation controlled area in the seismic isolation layer directly below the radiation irradiation room, if people enter the controlled area due to maintenance of the seismic isolation layer, etc., the operating status and schedule of the radiation generator will be adjusted. There is a need to. Therefore, it is desirable that the radiation controlled area in the seismic isolation layer is as small as possible. there were.

The present invention is intended to solve the above problems, and a radiation shielding structure according to the present invention is provided around an installation space in which a radiation generator that emits radiation in an irradiation direction is installed, and the radiation generator emits radiation. a first shielding structure that shields the generated radiation;
a second shielding structure provided below the first shielding structure, the radiation reducing structure comprising:
A seismic isolation device is provided between the first shielding structure and the second shielding structure,
The second shielding structure faces the first shielding structure with a space therebetween,
It is characterized in that a concave portion recessed downstream in the irradiation direction is provided at a location located downstream in the irradiation direction with respect to the irradiation section of the radiation generator .

Further, in the radiation shielding structure according to the present invention, the concave portion has a shape in which the opening portion is sunken .

Moreover, the radiation shielding structure according to the present invention is characterized in that a person can pass between the first shielding structure and the second shielding structure .

In the radiation reduction structure according to the present invention, at least a portion of the second shielding structure corresponding to the radiation irradiation range has a recessed structure portion recessed from other portions. According to such a radiation reduction structure, For example, it is possible to reduce the controlled area in the seismic isolation layer provided under the radiation irradiation room.

It is a figure which shows an example of the radiation irradiation room 2 which has a seismic isolation layer in the lower part which is one of the application places of the radiation reduction structure 1 which concerns on embodiment of this invention. It is a figure explaining the radiation reduction structure 1 which concerns on embodiment of this invention. It is a figure explaining the effect by the radiation reduction structure 1 which concerns on embodiment of this invention. It is a schematic diagram explaining the outline|summary of the radiation reduction structure 1 which concerns on the 2nd Embodiment of this invention. It is a figure explaining other examples of application of radiation reduction structure 1 concerning an embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an example of a radiation irradiation room 2 having a seismic isolation layer underneath, which is one of the applications of the radiation reduction structure 1 according to the embodiment of the present invention.

A radiation generator is installed in the radiation irradiation room 2 . In this embodiment, only the radiation source 3 in such a radiation generator is shown. An example of a radiation generator is an electron linac (linear accelerator) that emits X-rays. However, the radiation-reducing structure 1 according to the present invention can also be compatible with radiation sources that irradiate radiation such as α-rays, β-rays, γ-rays, and ions, including those that irradiate X-rays as the radiation source 3. It is possible.

Here, the radiation irradiation room 2, which is the space in which the radiation generator is installed, is defined as an installation space A. As shown in FIG. Moreover, the radiation source 3 shall irradiate the radiation irradiation range R with radiation. In the radiation irradiation room 2, a treatment table 5 is placed within a radiation irradiation range R, and it is assumed that a patient (not shown) receives radiation treatment on the treatment table 5. FIG.

Below the installation space A, a first shielding structure B is arranged to shield the radiation generated by the radiation source 3 . As the first shielding structure B, concrete, iron, or the like is generally used. Outside the first shielding structure B, a space such as a seismic isolation layer in which the seismic isolation device 7 is housed is arranged. A space such as this seismic isolation layer is defined as an outer space C. As shown in FIG. A second shielding structure D is provided around the outside space C to serve as a base for the seismic isolation device 7 and also function as a radiation shield.

The radiation reduction structure 1 according to the present invention includes an installation space A in which a radiation source 3 is arranged, a first shielding structure B, a mainly hollow outer space C, and a second shielding structure in order away from the installation space A. It is assumed that the structure D is applied to the laid out structure.

Under the above premise, in the radiation reduction structure 1 according to the present invention, the effective dose in the outer space C is reduced by providing the concave structure 10 in the second shielding structure D. A structure according to the present invention having such a concave structure 10 will be described based on differences from the conventional structure shown in FIG.

2A and 2B are diagrams for explaining a radiation reduction structure 1 according to an embodiment of the present invention, FIG. 2A shows the structure around a conventional radiation irradiation chamber 2, and FIG. The structure around a radiation irradiation room 2 to which such a radiation reduction structure 1 is applied is shown. Note that the seismic isolation device 7 is omitted from the drawing.

In the radiation reduction structure 1 according to the present invention, as shown in FIG. 2(B), at least a portion corresponding to the radiation irradiation range R (a portion indicated by a double-headed arrow) in the second shielding structure D is It is characterized by having a concave structure 10 which is recessed. The recessed structure 10, in which the second shielding structure D is recessed from other parts, refers to a structure having a bottom surface lower than the bottom surface of a normal floor.

When radiation is emitted from the installation space A by the radiation source 3, part of the radiation transmitted through the first shielding structure B is scattered within the first shielding structure B and spreads to the outer space C, but the first shielding structure Radiation transmitted through the structure B passes through the recessed structure 10, which is a recess in the floor of the second shielding structure D, and reaches the lower bottom surface. Further, part of the radiation reaching the floor is repeatedly reflected inside the concave structure 10 and attenuated, so that the dose in the outer space C can be reduced.

A scaffolding can be provided in the recessed structure 10 by installing a grating or the like through which radiation can pass relatively easily.

The effect of reducing the effective dose by the concave structure portion 10 of the radiation reducing structure 1 according to the present invention was evaluated by simulation using Monte Carlo calculation. A three-dimensional Monte Carlo calculation code MCNP5 was used as the calculation code.

In the calculation, the distance from the bottom surface of the first shielding structure B of the radiation source 3 was 2.295 m. The first shielding structure B was made of ordinary concrete. Also, the thickness of the first shielding structure B was set to 1.6 m, and the height of the outer space C was set to 1.0 m.

A conical X-ray beam was emitted from the radiation source 3 so that the irradiation area was 0.16 m ² at a point 1.0 m away from the radiation source, and the absorbed dose to water at the point was 360 Gy/h. Illuminated downward.

On the floor of the second shielding structure D, as a shielding structure, a recessed structure 10 having a diameter of 3 m and a depth of 0.4 m was provided as a shielding structure.

In the outer space C, at a height of 0.5 m above the floor of the second shielding structure D, and at a horizontal distance (H) of 4 to 9 m from the axis of the X-ray beam (the position indicated by the x mark). Then, the effective dose in the case where the recessed structure 10 was not provided in the conventional case and in the case where the recessed structure 10 of the radiation reduction structure 1 according to the present invention was provided was obtained by Monte Carlo calculation for every 1 m at the distance H. . The results are shown in FIG.

As shown in FIG. 3, when the effective dose was calculated for each 1 m by Monte Carlo calculation in each case, the radiation reduction structure 1 according to the present invention with the recessed structure 10 had It was confirmed that the effective dose was reduced by 20% on average compared to .

As described above, in the radiation reducing structure 1 according to the present invention, at least the portion corresponding to the radiation irradiation range of the second shielding structure D has the recessed structure portion 10 that is recessed from other portions. According to the radiation reduction structure 1, for example, the controlled area in the seismic isolation layer provided under the radiation irradiation room can be reduced.

Next, another embodiment of the present invention will be described. FIG. 4 is a schematic diagram for explaining the outline of the radiation reduction structure 1 according to the second embodiment of the present invention. In the embodiment shown in FIG. 4, the recessed structure 10 has an area (S ₁ ) larger than the area (S ₀ ) of the opening 12 of the recessed structure 10 on the far side (vertically downward side), where S ₁ > S ₀ ).

In the case of the second embodiment as described above, the radiation transmitted through the first shielding structure B reaches the deeper space through the opening 12 of the recessed structure 10 . When the cross section 15 is sufficiently wide, the radiation is repeatedly reflected and attenuated inside, and the dose in the outer space C can be reduced. In the case of the second embodiment, compared to the previous first embodiment, the space on the far side of the opening 12 is wider, and the area (S 1 ) of the cross section 15 is larger than the area (S ₁ ) of the opening 12 . ₀ ), a greater dose reduction effect in the outer space C can be expected.

Also for the second embodiment, the effective dose was determined by Monte Carlo calculation. In FIG. 4, the diameter of the circular opening 12 in plan view was set to 4.0 m, and the diameter of the circular cross section 15 in plan view was set to 6.0 m.

A recessed structure 10 is provided at a height of 0.5 m above the floor of the second shielding structure D and a horizontal distance (H) of 4 to 9 m from the axis of the X-ray beam (position indicated by x). In the case of the conventional case where the radiation reduction structure 1 according to the second embodiment is not provided, and in the case where the recessed structure portion 10 of the radiation reduction structure 1 according to the second embodiment is provided, the effective dose was obtained by Monte Carlo calculation every 1 m at the distance H. As a result, it was confirmed that when the concave structure 10 of the radiation reducing structure 1 according to the second embodiment was present, the effective dose was reduced by 37% on average compared to the case without the concave structure 10 .

If the area where the effective dose in the outer space C is 130 μSv/3 months, which is 1/10 of the effective dose limit of 1300 μSv/3 months at the boundary of the controlled area, is defined as a controlled area by enclosing it with a square in plan view, it will be as follows. .
・In the case shown in FIG. 2A where there is no concave structure 10, the shortest distance from the center axis of the X-ray beam to the controlled area boundary is 6.3 m, the area of the square is 159 m ² , and the area ratio is 100% (this case).
- In the case of having the recessed structure 10 according to the first embodiment shown in ^FIG . Area ratio is 85%.
- In the case of having the recessed structure 10 according to the ^second embodiment shown in FIG. 73%.

As described above, according to the radiation reduction structure 1 according to the second embodiment, the area of the controlled area could be reduced by 27% without the recessed structure 10 .

Next, an example in which the radiation reduction structure 1 according to the present invention is applied to another situation will be shown. FIG. 5 is a diagram illustrating another application example of the radiation reduction structure 1 according to the embodiment of the present invention. FIG. 5 shows a plan view of the structure around the radiation irradiation chamber 2. As shown in FIG.

In the application examples of the present invention described so far, the installation space A for the radiation source 3, the first shielding structure B, the outer space C, and the second shielding structure D are arranged in this order vertically downward. On the other hand, in the example of application shown in FIG. C corresponds to the space used as passage 20 . Even in such a case, a recessed structure 10 that is recessed from the other portions is provided in the portion corresponding to the radiation irradiation range R in the second shielding structure D. As shown in FIG. In such an application example shown in FIG. 5, it is possible to reduce the effective dose in the passage 20, and the like.

As described above, in the radiation reduction structure according to the present invention, at least a portion of the second shielding structure corresponding to the radiation irradiation range has a concave structure recessed from other portions. For example, it is possible to reduce the controlled area in the seismic isolation layer provided under the radiation irradiation room.

Reference Signs List 1... Radiation reduction structure 2... Radiation irradiation room 3... Radiation source 5... Treatment table 7... Seismic isolation device 10... Concave structure 12... Opening 15... Cross section 20 Passage A Installation space B First shielding structure C Outer space D Second shielding structure R Radiation irradiation range H X-ray Horizontal distance from beam center axis

Claims (3)

a first shielding structure provided around an installation space in which a radiation generator that emits radiation in an irradiation direction is installed and shields radiation generated by the radiation generator;
a second shielding structure provided below the first shielding structure, the radiation reducing structure comprising:
A seismic isolation device is provided between the first shielding structure and the second shielding structure,
The second shielding structure faces the first shielding structure with a space therebetween,
A radiation reducing structure characterized by having a concave portion recessed downstream in the irradiation direction at a location located downstream in the irradiation direction with respect to an irradiation section of the radiation generator . 2. The radiation reducing structure according to claim 1, wherein the concave portion has a constricted opening. 3. The radiation reduction structure according to claim 1 , wherein a person can pass between said first shielding structure and said second shielding structure.

Images