JP2012207966A - Radiation shield member of cyclotron for pet diagnosis and construction method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation shield member of a cyclotron for a PET (positron emission tomography) diagnosis capable of facilitating future dismantlement, removal, and disposal of the shield member and facilitating on-site installation work and dismantling and removal work.SOLUTION: The periphery and the upper part of a cyclotron 2 for producing radioisotopes is enclosed by a shield member body 4. A space 5 to be filled with water W is formed inside the shield member body 4 and the space 5 is filled with the water W. Lead plates 21a and 21b are stuck to at least a part of the surface of the shield member body 4.

Description

  The present invention relates to a radiation shielding member that shields radiation emitted from a cyclotron for PET (positron emission tomography) diagnosis, and a construction method thereof.

  In the medical field, PET (positron, emission, tomography) using a substance that emits positrons as a method of observing and diagnosing the internal state of the human body with images in recent years Attention has been focused on diagnostic imaging systems. The diagnostic imaging method (ie PET diagnosis) using the PET system is a method in which a radiopharmaceutical labeled with a radioisotope with a short half-life is administered to the human body. Detects tumors etc. dynamically. PET diagnosis is known to be effective for cancer diagnosis or brain function diagnosis.

  Radiopharmaceuticals used in PET diagnosis are produced using a synthesis apparatus using a short half-life radioisotope produced using a cyclotron as a raw material. The cyclotron produces radioactive isotopes by accelerating ions to high energy and irradiating the ions with a target. The synthesizer manufactures a radiopharmaceutical that can be administered to the human body using a radioisotope manufactured by a cyclotron as a raw material. Radiopharmaceuticals are labeled with radioisotopes.

Neutrons and secondary gamma rays are emitted during the operation of a cyclotron that produces radioisotopes. In particular, when producing ¹⁸ F, which is a raw material for ¹⁸ F-FDG (2- ¹⁸ F-fluoro-2-deoxy-D-glucose), a common radiopharmaceutical, many neutron rays and secondary gamma rays are used. Is released.

  In order to reduce the emission of neutrons and secondary gamma rays to below an allowable value, it is necessary to shield the six sides (four side walls, floor, ceiling) of the cyclotron room with a concrete wall having a thickness of 150 to 180 cm, for example. However, when there is a restriction on the space of the building or on the structure, a “self-shielding” shielding member is often installed in which the concrete wall is 50 to 60 cm thick and directly covers and shields the cyclotron itself.

  As a “self-shielding” shielding member, Patent Document 1 discloses a shielding member in which a cyclotron is covered with a box-shaped casing and a double door is attached to the front of the box-shaped casing. The walls and doors of the casing are manufactured by mixing boron (boron) and polyethylene in concrete and curing them. Boron and polyethylene are used for the purpose of neutron absorption, and concrete is used for the purpose of attenuation of neutrons and secondary gamma rays generated by neutron absorption of boron and polyethylene.

Japanese Patent Laying-Open No. 2009-53213 (see FIG. 1, paragraph 0022)

  Although the mass ratio of the boron compound in the concrete is as low as several percent, it is difficult to extract only the boron compound from the hardened concrete. For this reason, when dismantling and removing facilities, it is necessary to remove a large amount of shielding members including concrete. However, according to recent regulations on waste, it is necessary to treat boron as a poison, and it is impossible to dispose of a shielding member containing boron as general industrial waste when dismantling the facility.

  Further, the concrete of the shielding member is thick and its weight is considerably heavy. In order to mix and harden boron and polyethylene in concrete, most of the work is done at the factory, and the finished product is transported and carried to the site, where it is installed and assembled. For this reason, a large vehicle and a large heavy machine for carrying heavy objects are required, and there is a problem that time, labor, and cost for installation become large. There is a similar problem when dismantling the shielding member.

  Accordingly, the present invention provides a radiation shielding member for a PET diagnostic cyclotron and a method for constructing the same, which can easily dismantle and dispose of the shielding member in the future and can be easily installed and dismantled on site. Objective.

  In order to solve the above problems, one aspect of the present invention is a radiation shielding member that shields a cyclotron for PET (positron emission tomography) diagnosis, and surrounds and surrounds a cyclotron that produces a radioisotope, A shielding member body in which a space into which water can be poured is formed; water to be poured into the space of the shielding member body; and a lead plate attached to at least a part of the surface of the shielding member body. It is a radiation shielding member provided.

  Another aspect of the present invention is a method for constructing a radiation shielding member that shields a cyclotron for PET (positron emission tomography) diagnosis, and a step of preparing a shielding member body in which a space into which water can be injected is formed A step of installing the shielding member main body so as to surround the periphery and upper part of a cyclotron for producing a radioisotope, a step of injecting water into the shielding member main body, and lead on at least a part of the surface of the shielding member main body And a step of affixing a plate.

  Still another embodiment of the present invention is a method for constructing a radiation shielding member for shielding a cyclotron for PET (positron emission tomography) diagnosis, wherein a space into which water can be injected is formed, and at least one surface of the surface is formed. Preparing a shielding member main body to which a lead plate is attached to a part, installing the shielding member main body so as to surround the periphery and upper part of a cyclotron for producing a radioisotope, and water in the space of the shielding member main body And a step of injecting the radiation shielding member.

  According to the present invention, neutrons can be decelerated and absorbed by water injected into the shielding member body, and secondary gamma rays can be attenuated by a lead plate attached to the shielding member body. Since radiation is shielded without using boron, future dismantling and disposal of the shielding member can be easily realized. Also, if the secondary gamma rays are absorbed only by the water injected into the shielding member body, it is necessary to increase the thickness of the water. It becomes a big restriction of. The radiation shielding member can be downsized by attenuating secondary gamma rays with a lead plate attached to the shielding member body.

  Furthermore, since the structure is such that water is poured into the shielding member main body and the lead plate is attached to the necessary portion, transportation, loading, installation, and assembly may be performed on the shielding member main body and the lead plate. Since water can be easily supplied from the local water supply, vehicles and heavy machinery can be small, and installation work on the site can be greatly simplified. The dismantling and removal work of the shielding member is also greatly simplified.

The top view of the radiation shielding member of one embodiment of the present invention Vertical sectional view of the radiation shielding member Process diagram of construction method of radiation shielding member ((a) in the figure shows the construction method of the radiation shielding member of one embodiment of the present invention, and (b) in the figure shows a comparative example) Graph showing attenuation rate of neutron and secondary gamma ray ((a) in the figure shows a comparative example in the case of water only, and (b) in the figure shows self-shielding of the present invention in which a lead plate is pasted in addition to water injection) Indicate)

  Hereinafter, a radiation shielding member according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows a plan view of the radiation shielding member 1, and FIG. 2 shows a vertical sectional view of the radiation shielding member 1.

A radiation shielding member 1 according to an embodiment of the present invention covers a cyclotron 2 for PET diagnosis and shields radiation emitted from the cyclotron 2. The cyclotron 2 accelerates ions to high energy and irradiates the ions with a target to produce radioisotopes used for PET diagnosis, for example, ¹¹ C, ¹³ N, ¹⁵ O, and ¹⁸ F. Since all of these radioisotopes have a short half-life (2-110 minutes), they are manufactured at a PET facility in a hospital. During operation of the cyclotron 2, neutrons and secondary gamma rays are emitted. In order to prevent radiation emission in the hospital, the cyclotron 2 is covered with a self-shielding radiation shielding member.

  As shown in FIG. 2, the radiation shielding member 1 includes a shielding member main body 4 having a cylindrical side wall portion 4a and a circular ceiling portion 4b. A space 5 into which water can be injected is formed in the side wall portion 4 a and the ceiling portion 4 b of the shielding member body 4. The side wall 4 a of the shielding member main body 4 includes a cylindrical inner steel plate 6, a cylindrical outer steel plate 7, and a bottom steel plate 8 coupled to the bottom of the inner steel plate 6 and the bottom of the outer steel plate 7. A lower steel plate 9 constituting the lower surface of the ceiling portion 4b is joined to the upper portion of the inner steel plate 6 of the side wall portion 4a. The upper side steel plate 10 which comprises the upper surface of the ceiling part 4b is couple | bonded with the upper part of the outer side steel plate 7 of the side wall part 4a. The space 5 into which water is injected extends from the side wall portion of the shielding member body 4 to the ceiling portion.

  As shown in FIG. 1, the shielding member main body 4 is formed by joining divided bodies 4-1 and 4-2 divided into left and right with the center line of the cyclotron 2 as a boundary. The two divided bodies 4-1 and 4-2 are divided at the center of the ceiling portion 4b. As shown in FIG. 2, the end steel plate 11-1 constituting the mating surface of the two divided bodies 4-1 and 4-2 is coupled to the lower steel plate 9 and the upper steel plate 10 on the left ceiling portion 4 b. The An end steel plate 11-2 constituting the mating surface is coupled to the lower steel plate 9 and the upper steel plate 10 on the right ceiling 4b.

  As shown in FIG. 2, the end steel plate 11-1 of the left divided body 4-1 and the end steel plate 11-2 of the right divided body 4-2 are not formed flat but formed in an uneven shape. The On the lower side of the left end steel plate 11-1, a convex portion 13-1 projecting stepwise toward the right divided body 4-1 is formed. A concave portion 13-2 corresponding to the convex portion 13-1 of the left end steel plate 11-1 is formed in the right end steel plate 11-2. This is to prevent radiation from leaking from the mating surfaces.

  As shown in FIG. 1, the divided body 4-1 (having four wheels) is linearly movable on two parallel rails 16, and the divided body 4-2 is similarly parallel. It is provided on the two rails 16 so as to be linearly movable. Wheels 19-1 and 19-2 that are rotationally driven by electric motors 18-1 and 18-2 as drive sources are attached to the respective divided bodies 4-1 and 4-2. When the electric motors 18-1 and 18-2 rotate the wheels 19-1 and 19-2, the divided bodies 4-1 and 4-2 linearly move in one direction along the rail 16. When the two divided bodies 4-1 and 4-2 are brought close to each other by the electric motors 18-1 and 18-2, the shielding member main body 4 is closed, and the entire periphery and the upper part of the cyclotron 2 are covered. When the two divided bodies 4-1 and 4-2 are separated by the electric motors 18-1 and 18-2, the shielding member main body 4 is opened, and the cyclotron 2 appears from the inside. Since the shielding member main body 4 is opened and closed by linearly moving the divided bodies 4-1 and 4-2 by the electric motors 18-1 and 18-2, the heavy shielding member main body 4 can be easily opened and closed. In addition to the electric motors 18-1 and 18-2, a hydraulic motor or the like may be used as the drive source.

  Water W is poured and filled into the space 5 of the shielding member main body 4. The water W is filled not only in the side wall part 4a of the shielding member body 4 but also in the ceiling part 4b. In order to prevent the steel shielding member main body 4 from rusting, the inner surface of the shielding member main body 4 is subjected to rust prevention treatment. For example, a rust preventive agent is painted or a resin is coated. As the water W, tap water that has been deoxygenated using an oxygen scavenger or a deaerator is used. At the time of maintenance of the facility every several years, the sterilization treatment by the sterilization lamp or the exchange of the water W is performed, and the soundness of the water W and the steel shielding member main body 4 is maintained.

  Lead plates 21 a and 21 b are attached to at least a part of the outer surface of the shielding member body 4. It is not necessary to stick the lead plates 21a and 21b to the entire outer surface of the shielding member body 4, and only the direction of generation of neutrons and the location (evaluation point) accessed by a person. The lead plates 21a and 21b have a thickness of 2 to 3 cm. In this embodiment, a lead plate 21a is attached in a ring shape around the side wall portion 4a of the shielding member body 4 in accordance with the height of the neutron generation source 22, and the upper surface of the ceiling portion 4b of the shielding member body 4 is more than a cyclotron. A large circular lead plate 21b is attached.

  The water W in the shielding member body 4 is used for neutron deceleration, absorption, and secondary gamma ray attenuation. Lead plates 21a and 21b are used to attenuate some secondary gamma rays that cannot be attenuated by water W. Water W is an effective shielding member against neutrons and secondary gamma rays. However, secondary gamma rays cannot be reduced sufficiently when used as a self-shield for the cyclotron 2. In order to attenuate secondary gamma rays, it is necessary to increase the thickness of the water W, and the radiation shielding member 1 becomes larger than the case where it is entirely made of concrete. This is a great restriction on the layout plan. Therefore, by sticking the lead plates 21a and 21b having a thickness of 2 to 3 cm to the outer surface of the shielding member main body 4, the remaining secondary gamma rays are attenuated to obtain a predetermined level of shielding effect as a whole.

  Fig.3 (a) shows an example of the construction method of the radiation shielding member of this invention. First, the divided bodies 4-1 and 4-2 having the above structure are manufactured in a factory. Next, the divided bodies 4-1 and 4-2 manufactured at the factory are transported from the factory to the site by a truck, and are lowered from the truck to the vicinity of the carry-in entrance by a small crane 24. At this stage, since water is not injected into the divided bodies 4-1, 4-2, the weight of the divided bodies 4-1, 4-2 is light. This makes it possible to work with trucks and small cranes. Next, the divided bodies 4-1 and 4-2 are horizontally pulled by a winch, a chill roller 25 and the like, and are carried into the cyclotron chamber 26 in the building. Then, after installing the two division bodies 4-1 and 4-2 so as to surround the cyclotron 2, the water hose 27 is connected to the division bodies 4-1 and 4-2, and the division bodies 4-1 and 4-2. Water W is injected into the space 5. Finally, lead plates 21a and 21b are affixed to a part of the outer surfaces of the divided bodies 4-1 and 4-2. The lead plates 21a and 21b may be attached to the divided bodies 4-1 and 4-2 at the factory when the divided bodies 4-1 and 4-2 are manufactured. -2 may be affixed before injecting water.

  When dismantling and removing the PET facility, first, the water W filled in the divided bodies 4-1 and 4-2 is extracted, and a process for detoxifying the water W is performed. The divided bodies 4-1 and 4-2 from which the water W has been removed are lighter in weight. For this reason, it becomes possible to transport using a small crane or a truck. The divided bodies 4-1 and 4-2 from which the water W has been removed are discarded as general industrial waste.

  FIG. 3B shows a comparative example when the divided bodies 4-1 and 4-2 are made of concrete. If the divided bodies 4-1 and 4-2 are made of concrete, the weight thereof is considerably increased. After the concrete is hardened at the factory, if you try to transport the divided bodies 4-1 and 4-2 to the site, you will need a heavy trailer for transportation, and you will need a large crane 28 to unload from the heavy trailer. turn into.

  FIG. 4A shows a calculation result of the radiation dose when water W is injected into the shielding member main body 4 and the lead plates 21a and 21b are not attached to the shielding member main body 4. FIG. FIG. 4B shows a calculation result when water W is injected into the shielding member body 4 and the lead plates 21 a and 21 b are attached to the shielding member body 4. The radiation doses of neutrons and gamma rays emitted from the generation source are reduced at the self-shielding portion which is the shielding member body 4 and further reduced at the wall portion of the cyclotron chamber 26, and become a low level at the evaluation point. As shown in FIG. 4A, even in the case of only water, the radiation dose of neutrons can be sufficiently reduced at the self-shielding portion. However, the radiation dose of secondary gamma rays cannot be reduced sufficiently. As shown in FIG. 4B, by adhering lead plates 21a and 21b having a thickness of 3 cm, the radiation dose of secondary gamma rays can be rapidly reduced at the portions of the lead plates 21a and 21b.

  Note that the present invention is not limited to being embodied in the above-described embodiment, and can be variously modified without changing the gist of the present invention.

  For example, the shape of the shielding member main body is not limited to the above embodiment, and can be variously changed according to the shape and size of the cyclotron, the size of the cyclotron chamber, and the like.

  For example, the shielding member main body may be an integral one that is not divided, or may be divided into three or more parts. The shape of the shielding member is not limited to a cylindrical shape, and may be a rectangular parallelepiped shape. You may provide a door in a shielding member main body.

  Further, the lead plate may be attached not to the outer surface of the shielding member body but to the inner surface facing the cycloton.

DESCRIPTION OF SYMBOLS 1 ... Radiation shielding member 2 ... Cyclotron 4 ... Shielding member main body 4-1, 4-2 ... Divided body 5 ... Space 21a, 21b ... Lead plate W ... Water

Claims (6)

A radiation shielding member for shielding a cyclotron for PET (positron emission tomography) diagnosis,
A shielding member body that surrounds and surrounds a cyclotron that produces a radioisotope, and that has a space into which water can be injected.
Water injected into the space of the shielding member body;
A radiation shielding member comprising: a lead plate attached to at least a part of the surface of the shielding member main body. The shielding member main body is formed by combining two or more divided bodies.
At least one of the divided bodies is provided to be linearly movable in one direction,
The radiation shielding member according to claim 1, wherein the shielding member main body opens and closes by linearly moving at least one of the divided bodies in the one direction using a driving source. The shielding member main body is made of metal, and the inner surface that comes into contact with the water is rust-proofed.
The radiation shielding member according to claim 1, wherein the water is deoxygenated tap water. The shielding member body includes a side wall that surrounds the cyclotron, and a ceiling that covers the top of the cyclotron.
The space of the shielding member body is formed on both the side wall portion and the ceiling portion of the shielding member body,
The radiation shielding member according to claim 1, wherein the lead plate is attached to at least a part of an outer surface of the side wall part and at least a part of an upper surface of the ceiling part. A method of constructing a radiation shielding member for shielding a cyclotron for PET (positron emission tomography) diagnosis,
Preparing a shielding member body in which a space into which water can be poured is formed;
Installing the shielding member body so as to surround the periphery and upper part of a cyclotron for producing a radioisotope, and
Injecting water into the shielding member body;
And a step of attaching a lead plate to at least a part of the surface of the shielding member body. A method of constructing a radiation shielding member for shielding a cyclotron for PET (positron emission tomography) diagnosis,
A step of preparing a shielding member body in which a space into which water can be injected is formed and a lead plate is attached to at least a part of the surface;
Installing the shielding member body so as to surround the periphery and upper part of a cyclotron for producing a radioisotope, and
And a step of injecting water into the space of the shielding member main body.

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