JP2007047096A - Radioisotope manufacturing equipment and its installation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for weight reduction of the main heavy material, i.e. the shielding body of radioisotope manufacturing equipment for manufacturing nuclear medicine for injecting a patient in the PET diagnosis for examining for cancer and metabolism of brain and heart. fulfilling the requirement of the laws concerning prevention from radiation hazards due to radioisotopes and others. <P>SOLUTION: A radioisotope manufacturing equipment comprises an ion source (11) emitting ion beam [R], an accelerator (12) accelerating the ion beam [R] emitted from the ion source (11), a target (31), wherein material water for producing radioisotope when it is irradiated with the accelerated ion beam [R] is sealed, and a shielding body (20) arranged, by putting the target (31) in the center for shielding radiation generated from the target (31). The shielding body (20) has a substantially circular or polygonal higher hexagonal shape for the horizontal cross section passing the target (31) and a squeezed shape for the horizontal cross section, at both ends in the vertical directions. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a radioisotope production apparatus for producing a radiopharmaceutical to be injected into a patient in cancer screening and PET diagnosis for examining brain and heart metabolism, and is particularly harmful to the human body generated with ion beam irradiation. The present invention relates to a technique for shielding radiation.

¹⁸ F radioisotope (hereinafter referred to as F-18) using positron emission, diagnosis by tomography (hereinafter, PET (referred Positron Emission Tomography) Diagnostics) by implementing, it is possible effective cancer diagnosis It is known. For this reason, many PET diagnoses have begun to be used in the nuclear medicine field in Japan in addition to the United States and Europe.
By the way, when carrying out PET diagnosis, a radiopharmaceutical including F-18 injected into a patient irradiates a target enclosing ¹⁸ O water (hereinafter referred to as O-18 water (raw water)) with an ion beam. And ¹⁸ O (p, n) ¹⁸ F reaction.
Production of a radiopharmaceutical (F-18) for PET diagnosis so far has been performed by a radioisotope production apparatus using a cyclotron as an accelerator for outputting the ion beam. However, the conventional radioisotope production apparatus using this cyclotron is large in size (the cyclotron itself has a weight of about 20 tons and a shield installed around it is 40 to 50 tons). For this reason, when a radioisotope manufacturing apparatus using a cyclotron is to be accommodated in an existing facility, a large-scale remodeling work is required to greatly strengthen the building floor structure or widen the entrance. It was. Even if a shield can be installed around the cyclotron device, the shield cannot be additionally installed in the floor direction on the lower surface of the device (for example, Patent Document 1).

In recent years, radioisotope production apparatuses using linear accelerators (linacs) that do not require large-scale remodeling work as described above have become widespread.
The radioisotope manufacturing apparatus that uses this linac as an accelerator is significantly reduced in weight compared to the case where a cyclotron is used as an accelerator for the following two reasons. The first is that the linac body itself is smaller and lighter than the cyclotron. Second, when using a cyclotron to shield radiation harmful to the human body, the entire system including the target and the accelerator body must be shielded. However, when using a linac, the accelerator (linac) and target This is because the size of the structure of the shield can be greatly reduced because only the target can be separated and shielded.
JP 2004-294300 A (paragraph 0049)

Thus, as light-weight radioisotope production apparatuses using linacs as accelerators have become widespread, the demand for PET diagnosis has increased, and hospitals and medical centers that are newly considering the introduction of PET diagnosis apparatuses have increased. Then, the request | requirement of the further weight reduction became strong so that a PET diagnostic apparatus (and radioisotope manufacturing apparatus) can be easily installed in a general building. To this end, reducing the weight of the shield, which accounts for a significant proportion of the total weight of the PET diagnostic apparatus, is a shortcut for realizing the demand.
However, when such a requirement is realized, there is a possibility that a priority function that is originally required for a shield, such as shielding harmful radiation and securing surrounding safety, may be sacrificed.
Therefore, the present invention is reduced in weight while satisfying the standards of the Radiation Hazard Prevention Law by optimizing the material selection and dimensional shape of the shield, which is a major heavy object, in order to solve such problems. An object of the present invention is to provide a radioisotope production apparatus.

  In order to solve the above-described problems, a radioisotope manufacturing apparatus according to the present invention includes an ion source that emits an ion beam, an accelerator that accelerates the ion beam emitted from the ion source, and the accelerated ion beam. Is provided with a target in which raw material water that generates a radioisotope is enclosed, and a shield that shields radiation generated from the target by placing the target substantially at the center, The horizontal cross section passing through the target has a substantially circular shape or a polygonal shape of hexagon or more, and the horizontal cross sections at both ends in the vertical direction have a narrowed shape.

  By having the configuration according to the present invention, generally, the radiation generated from the target is radiated in a spherical shape around the target, and the horizontal cross section of the shield has a polygonal shape of hexagon or more. It is obvious that there are fewer wasted parts in the horizontal cross section required to attenuate the radiation to the allowable dose of the radiation damage prevention method, compared to the case of less than hexagon (for example, square). Similarly, when examining the vertical cross section of the shield containing the vertically long target box inside, it can be said that there are few wasted parts to attenuate to the allowable dose because the horizontal cross sections at both ends in the vertical direction are narrowed. . In this way, the shield is reduced in weight by the amount that the portion through which the radiation passes after being attenuated to the allowable dose is reduced.

  According to the present invention, the shield, which is a major heavy object, is reduced in weight while satisfying the standards of the Radiation Hazard Prevention Law, so that a radioisotope manufacturing apparatus that satisfies both safety requirements and installation simplicity requirements simultaneously. Is provided.

A radioisotope production apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings as appropriate.
As shown in FIG. 1, the radioisotope production apparatus 10 of the present embodiment includes an ion source 11, a high-frequency quadrupole linear accelerator (hereinafter referred to as RFQ) 12a, a drift tube linear accelerator (hereinafter referred to as “RFD”). DTL: Drift Tube Linac) 12b and the shield 20. In addition, the linear accelerator (linac) 12 in this invention is formed by the combination of this RFQ12a and DTL12b.
Moreover, this radioisotope manufacturing apparatus 10 is installed inside the management area U surrounded by the concrete wall T as shown in FIG.

The ion source 11 serves to ionize a source material (in this case, hydrogen) to be an ion and extract it as a positive ion beam R, and a magnet (not shown) that selectively extracts only desired ions by mass is provided around the ion source 11. In addition, an electrostatic lens (not shown) for shaping the ion beam R, an ion beam generator, and the like are provided.
As the ion source 11, a hot cathode type duoplasmatron type ion source or a PIG type ion source can be used. A microwave discharge ion source that can generate a large current with a long lifetime can also be used.

The RFQ 12a is provided at the subsequent stage of the ion source 11, and accelerates the ion beam R emitted from the ion source 11 until it reaches a predetermined energy. A vacuum chamber having a wavy quadrupole electrode is provided inside the RFQ 12a. The quadrupole electrode forms a quadrupole electric field in a direction perpendicular to the traveling direction of the ion beam R, and the ion beam R is accelerated while being focused.
In place of the RFQ 12a used here, a multi-electrode type high-frequency accelerator having an even number of magnetic poles of six or more poles may be used, and other high-frequency accelerators may be used.

The DTL 12b receives the ion beam R accelerated by the RFQ 12a and further accelerates it. A plurality of drift tubes 14 are arranged in the axial direction at the center inside the DTL 12b. A quadrupole electromagnet (not shown) is incorporated in the drift tube 14, and the ion beam R is converged when passing through the drift tube 14. The ion beam R is accelerated between the drift tubes 14 and 14.
Such RFQ 12a and DTL 12b are combined to function as a linear accelerator (linac) 12 that finally generates an ion beam R having a high energy of about 7 MeV.

The shield 20 includes a main frame portion 21, an opening / closing door 22 (22a, 22b), a lower frame portion 23, an upper frame portion 24, a top plate portion 25, a bottom plate portion 26, and a target box 27. The horizontal section shows an octagon (see FIG. 2). The shield 20 serves to shield radiation harmful to the human body that is generated when the target 31 is irradiated with the ion beam R.
When the open / close door 22 (22a, 22b) of the shield 20 is opened, the XX cross section shown in FIG. 2 shows the outer shell of the shield 20 as shown in FIG. The outer shell shielding part (gamma ray shielding part) M having a thickness of 5 mm and the inner shielding part (neutron shielding part) P provided so as to fill the inside thereof.
Similarly, when the YY cross section shown in FIG. 3A is viewed, as shown in FIG. 3B, the shield 20 has an outer shell constituted by an outer shell shielding portion (gamma ray shielding portion) M. The inside is constituted by an inner shielding part (neutron shielding part) P.

  Two opening / closing doors 22 (22a, 22b) are attached to the main frame portion 21 so as to be freely opened and closed. When the opening / closing door 22 is closed, the both ends of the top-and-bottom direction move horizontally toward the end. The cross section is narrowed. At the center position of the horizontal section, an elongated target box 27 is arranged with its longitudinal direction aligned with the vertical axis of the shield 20.

  The upper frame portion 24 and the lower frame portion 23 are respectively provided at both ends where the cross section of the main frame portion 21 is narrowed. The heights of the upper frame portion 24 and the lower frame portion 23 are shown in FIG. 3A, where u is the shortest distance from the upper and lower end surfaces of the target box 27 to the top plate portion 25 and the bottom plate portion 26. If r is the shortest distance from the side wall surface of the target box 27 in the horizontal section of the shield 20 shown in 3 (b) to the side wall surface of the shield 20, u and r are set to approximate values. The

  As described above, the reason why the upper frame portion 24 and the lower frame portion 23 are provided and the top and bottom directions of the shield 20 protrude is the reason for the target box 27 where the target stage portion 30 described later is disposed. This is because the radiation is not attenuated inside because it is just a space. If such a shape in which the top and bottom directions of the shield 20 protrude is used, the radiation radiated in the longitudinal direction of the elongated target box 27 is effectively attenuated.

The top plate portion 25 and the bottom plate portion 26 are provided so as to close both open ends of the upper frame portion 24 and the lower frame portion 23, respectively.
In the drawings, the horizontal cross section of the shield 20 is an octagon, but the horizontal cross section is not limited to this, and the horizontal cross section arbitrarily includes a substantially circular or hexagonal or more polygonal shape.

The inner shielding part (neutron shielding part) P is formed by laminating a plurality of sheet-like parts having a thickness of about 10 cm, and surrounds the outer periphery of the target box 27 without a gap. The material is polyethylene blended with boron.
The inner shielding part (neutron shielding part) P converts neutrons (energy of about 1 MeV) emitted when the ion beam R (energy of about 7 MeV) is incident on the raw water (18-O concentrated water) to hydrogen It exhibits the function of shielding by utilizing deceleration / absorption due to elastic scattering.
The outer shell shielding portion (gamma ray shielding portion) M arranged in the outer shell of the neutron shielding portion P is mainly composed of iron or lead, and when the ion beam R is incident thereon. It functions to shield the emitted secondary gamma rays. It should be noted that the effect of attenuating the secondary gamma rays is higher for a material having a larger atomic number (that is, a higher density and consequently heavier).

  FIG. 4 is a perspective view showing a state in which the opening / closing door 22 of the shield 20 is opened. Thus, when the opening / closing door 22 is opened, the internal space of the target box 27 can be seen. A beam passage hole 27a is opened in the target box 27, and the ion beam R (see FIG. 1) incident through the beam incident duct 28 shown in FIG. 3B is passed through the beam passage hole 27a. 31 is irradiated. When the target 31 is maintained, the open / close doors 22a and 22b closed as shown in FIG. 2 are released as shown in FIG.

In the internal space of the target box 27, a target stage unit 30 as shown in FIG. The target stage unit 30 includes a target 31 (31a, 31b, 31c), a guide 33, and a rail 34.
The targets 31 (31a, 31b, 31c) are all the same, and are attached to the guide 33 so as to be detachable by switching the release lever 32.
The guide 33 is moved in the vertical direction along the longitudinal direction of the rail 34 by a control device (not shown). In this way, by moving the guide 33, any one of the targets 31 (31a, 31b, 31c) is aligned with the position of the beam passage hole 27a (see FIG. 3B), and the ion beam R Can be irradiated.

  The raw material water (O-18 concentrated water) necessary for obtaining a radioisotope (F-18) necessary for one PET diagnosis is sealed inside one target 31, and the target 31 is ionized. When irradiated with the beam R, O-18 undergoes a nuclear reaction and F-18 is generated. Once the target 31a is irradiated with the ion beam R and a predetermined yield of radioisotope (F-18) is obtained, the target stage unit 30 is moved to irradiate the next target 31b. Thus, it is possible to produce a desired radioisotope (for example, C-11, O-15, etc.).

  As shown in FIG. 6, a cable lead-out hole 29 a for pulling out the power supply cable of the target stage unit 30 (FIG. 5) and the like to the outside of the shield 20 is provided on the lower surface of the target box 27. The cable pipe 29 that communicates from the cable lead-out hole 29a on the lower surface of the target box 27 to the cable lead-out hole 29b provided in the lower frame portion 23 is provided meandering as shown in the figure. This is to prevent the radiation from going straight and leaking out of the cable extraction hole 29a.

  The cable pipe 29 is disposed so as to be exposed when the upper cover 23a of the lower frame portion 23 is removed and a part of the neutron shielding portion P disposed below is removed. Thus, the cable pipe 29 can be easily exposed from the outside of the shield 20, and the power supply cable or the like passing through the cable pipe 29 can be easily routed, so that the maintenance work is facilitated.

(Description of operation)
Next, the operation of the radioisotope production apparatus 10 configured as described above will be described with reference to FIGS. 1 and 2, and the target 31 in which the raw material water is sealed will be ionized with reference to FIG. 7. The process in which the radiation (neutron, secondary gamma ray) emitted when the beam R is irradiated is attenuated by the shield 20 and reaches the reference value of the allowable dose will be verified.

First, before operating the radioisotope production apparatus 10, a target 31 filled with raw material water (O-18) is attached to the target stage 30 (FIG. 5) inside the shield 20 in advance, and the door is opened and closed. Close 22 securely.
When an operation switch (not shown) is operated, predetermined high-frequency power is supplied to the RFQ 12a and DTL 12b, and an electric field is formed in each RFQ 12a and DTL 12b. Thereafter, predetermined power is supplied to the ion source 11. As a result, the ion beam R emitted from the ion beam generator (not shown) of the ion source 11 is accelerated by the RFQ 12a until it reaches a predetermined energy. The accelerated ion beam R is emitted from the RFQ 12a, is incident on the subsequent DTL 12b, and is further accelerated by the DTL 12b.
The ion beam R accelerated to high energy in this way is irradiated to the raw water (O-18 water) in the target 31. When the O-18 is irradiated with the ion beam R, F-18 is generated by the nuclear reaction, and at the same time, radiation (neutron, secondary gamma ray) is emitted around the target 31.

As shown in FIG. 7, this radiation attenuates and the dose becomes 100 μSv / w or less, which is an allowable dose rate, outside the management area U. FIG. 7 shows that a polyethylene blended with 30% B ₂ O ₃ as a neutron shielding part (inner shielding part) P is arranged so that the thickness in the radiation traveling direction becomes 62 cm, and a gamma ray shielding part (outer shell shielding) Part) The result of analysis under the condition that an iron plate having a thickness of 5 cm is arranged as M, and the management area U is separated by a concrete wall (thickness of 30 cm) at a distance of 200 cm from the target 31 is shown.

As shown in FIG. 7, neutrons emitted from the target 31 are rapidly attenuated in the neutron shielding part P as indicated by a broken line, and then pass through the outer shell shielding part M and the air layer (management area U). Thus, it is further attenuated by the shielding effect of the concrete wall T (only due to diffusion), and is attenuated to about 1/3 of the allowable dose rate outside the management area U.
On the other hand, the secondary gamma rays are not so attenuated in the neutron shielding part P as shown by the alternate long and short dash line, and the intensity is reversed to the intensity of the neutrons near the center of the neutron shielding part P.
The secondary gamma rays that have passed through the neutron shielding part P are greatly attenuated by the outer shell shielding part M. After that, secondary gamma rays pass through the air layer (management area U) in the same manner as neutrons, and are further attenuated by the shielding effect of the concrete wall T.
In this way, the dose of radiation harmful to the human body that is generated when the radioisotope (F-18) is produced by irradiating the ion beam R is an allowable dose (100 μSv / w or less).

  Next, when the desired yield of F-18 is obtained, the emission of the ion beam R is stopped, the open / close door 22 of the shield 20 is opened, and the target 31 is removed. The concentrated water containing F-18 is taken out from the target 31 and F-18 is extracted. In addition, since the remaining raw material water (O-18 concentrated water) which did not carry out a nuclear reaction is very expensive, it collect | recovers, returns in the target 31, and is reused.

(Dimensions of shield structure)
Next, the optimum dimensions of the outer shell shielding part M constituting the outer shell of the shield 20 and the neutron shielding part P constituting the inner side thereof will be examined.
First, the neutron shielding part P has a thickness so as to attenuate the neutrons outside the control area U to less than half of the allowable dose reference value (100 μSv / w in FIG. 7) (about 30 μSv / w in FIG. 7). (62 cm with 30% B ₂ O ₃ blended polyethylene). The outer shell shielding portion M has a thickness such that the dose of secondary gamma rays is less than the allowable dose (100 μSv / w in FIG. 7) in terms of total intensity including neutron rays (5 cm for iron).

In summary, the procedure for determining the structure of the shield 20 of the radioisotope manufacturing apparatus 10 is as follows.
(1) A neutron energy intensity distribution corresponding to the irradiation ion beam energy from the target 31 is given.
(2) The thickness of the neutron shielding part P is determined so that the neutron intensity is sufficiently smaller (1 / 2-1 / 10 or less) than the dose tolerance standard at the point considered.
(3) The gamma ray shielding material necessary for shielding secondary gamma rays generated by neutron attenuation at the neutron shielding part P is selected, and the total dose rate of gamma rays and neutrons is the allowable dose rate at the point of consideration. The thickness of the outer shell shielding part M is determined so as to be less than.

(Installation method of shield 20)
A method for installing the shield will be described with reference to FIG.
First, as shown to Fig.8 (a), the baseplate part 26 is arrange | positioned on the floor surface used as the installation place of the management area U partitioned off by the concrete wall T. FIG. And the lower frame part 23 is arrange | positioned on it. Next, as shown in FIG. 8B, a sheet-like neutron shielding part P is laminated and spread on the inner side of the lower frame part 23, and the main frame part 21 is installed on the upper part of the lower frame part 23. To do.

  Next, as shown in FIG. 8C, the target box 27 is installed inside the main frame portion 21 and the neutron shielding portion P is stacked and spread. Next, as shown in FIG. 8D, the upper frame portion 24 is installed on the upper portion of the main frame portion 21 and the neutron shielding portion P is stacked and spread. Next, as shown in FIG. 8 (e), the top plate portion 25 is installed on the upper portion of the main frame portion 21 and the opening / closing door 22 is attached.

  As described above, the outer shell shielding portion M (see FIG. 3A) of the shield 20 includes the bottom plate portion 26, the lower frame portion 23, the main frame portion 21, the upper frame portion 24, the top plate portion 25, and the open / close door 22. Since it has the structure divided | segmented into (3), the shield 20 can be assembled | assembled sequentially from the downward direction inside the management area U with a crane or a jack. And the sheet-like neutron shielding part P is piled up and spread | arranged inside the outer shell shielding part M assembled in this way. This work can be performed manually without using heavy machinery. As described above, the shield 20 used in the present invention is characterized in that it has excellent carry-in properties and is very simple to install as compared with the conventional type in which the finished product is arranged as it is.

Next, regarding the configuration of the shield 20 used in the present invention, as shown in FIG. 9, the shielding properties and the total weight were evaluated for materials other than those used in the above-described embodiment.
The shielding characteristics of neutrons generated here are analyzed using the ANISN code (Engle Jr WW, AUser Manual for ANISN: One Dimensional Discrete Ordinates Transport Code with Anisotropic Scattering, Oak Ridge National Laboratory, K1-1613 (1967)). ing.

According to the evaluation results, the polyethylene with 10% B ₂ O ₃ has the best neutron shielding performance, followed by polyethylene with 20% B ₂ O _3, polyethylene with 30% B ₂ O ₃ , and high-density polyethylene. Results were obtained. This is because boron-containing polyethylene has a lower source exponential density of hydrogen as the boron content increases, so the shielding performance of fast neutrons deteriorates, but the shielding effect of thermal neutron capture by boron exceeds this, This is probably because the shielding performance is higher than that of high density polyethylene.

Further, considering the total weight of the shield 20 based on the radiation attenuation characteristic shown in FIG. 7, the thickness of the neutron shielding portion P is increased to increase the attenuation of neutrons, thereby increasing the specific gravity. The thickness of the configured outer shell shielding part M can be reduced. If the shield 20 is configured in accordance with this policy, when polyethylene containing 30% B ₂ O ₃ is used as the neutron shielding part P, if the thickness is increased from 61 cm to 66 cm, the thickness of the outer shell shielding part M is 3 cm. Therefore, the front weight of the shield 20 can be reduced to 73% (2.37 tons / 3.26 tons), which is more suitable for installation in an existing building.

It is a side view of the radioisotope manufacturing apparatus which concerns on embodiment of this invention. It is a top view of the radioisotope manufacturing apparatus which concerns on embodiment of this invention. (A) It is front sectional drawing which shows an open / close door in the shielding body used by this embodiment. (B) It is the same top view. It is a perspective view which shows an open / close door in the shielding body used by this embodiment. It is a perspective view of the target stage arrange | positioned inside a shield. It is an exploded view at the time of performing piping maintenance in the shield used in this embodiment. It is a graph which shows the attenuation | damping characteristic of a radiation when the radiation which generate | occur | produces from a target is shielded by the shielding body used by this embodiment. (A)-(e) is a figure which shows the installation method of the shield used by this embodiment. It is a table | surface which shows the shielding evaluation result of the radiation around the target by a shield.

Explanation of symbols

10 Radioisotope production equipment 11 Ion source 12 Accelerator (Linear accelerator (LINAC))
DESCRIPTION OF SYMBOLS 20 Shield 21 Main frame part 22 Open / close door 23 Lower frame part 23a Top cover 24 Upper frame part 25 Top plate part 26 Bottom plate part 27 Target box 27a Beam passage hole 29 Cable piping 29a Cable extraction hole 30 Target stage part 31 (31a, 31b, 31c) Target M Outer shell shielding part (gamma ray shielding part)
P Inner shield (neutron shield)
R ion beam T concrete wall U controlled area

Claims (7)

An ion source that emits an ion beam;
An accelerator for accelerating the ion beam emitted from the ion source;
A target in which raw water for generating a radioisotope is encapsulated when irradiated with the accelerated ion beam;
A shield that places the target substantially at the center and shields radiation generated from the target;
The radioisotope characterized in that the shield has a substantially circular or hexagonal or more polygonal horizontal cross section passing through the target, and the horizontal cross sections at both ends in the vertical direction are narrowed. Manufacturing equipment. The shield is
A main frame part in which an opening and closing door for taking out the target is provided separably;
A lower frame portion disposed at a lower end of the main frame portion;
The radioisotope manufacturing apparatus according to claim 1, wherein an upper frame portion disposed at an upper end of the main frame portion is configured to be separable. The shield is
The outer shell is constituted by an outer shell shielding part having a wall thickness, and the inner part is constituted by an inner shielding part formed by laminating a plurality of sheets. The radioisotope production apparatus described. The outer shell shielding part is mainly composed of iron or lead,
The radioisotope manufacturing apparatus according to claim 3, wherein the inner shield is a polyethylene containing boron. The inner shielding portion is set to have a radial thickness centered on the target such that the neutron dose of the radiation is less than half of the allowable dose outside the management area,
The thickness of the outer shell shielding part is set so that the total radiation including the dose of the neutron is equal to or less than an allowable dose outside the management area. Item 5. The radioactive isotope production apparatus according to Item 4. The shield is
In the interior, a target box for storing the target,
The target box and cable piping communicating with the outside of the shield,
6. The structure according to claim 3, wherein a part of the outer shell shielding part and the inner shell shielding part are removable so that the cable pipe is exposed to the outside. The radioisotope production apparatus described in the item. In the radioisotope production apparatus according to claim 2,
An installation method of a radioisotope manufacturing apparatus, wherein the shield is assembled in the order of the lower frame portion, the main frame portion, and the upper frame portion at an installation location.

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