Patent Grant
8106370
The present application includes subject matter related to subject matter disclosed in U.S. application Ser. No. 12/45,931 (Publ. No. 2010-0283371A1), which is entitled “ISOTOPE PRODUCTION SYSTEM AND CYCLOTRON HAVING REDUCED MAGNETIC STRAY FIELDS,” and also in U.S application Ser. No. 12/435,903 (Publ. No. 2010-0282978A1) entitled “ISOTOPE PRODUCTION SYSTEM AND CYCLOTRON,” filed contemporaneously with the present application, both of which are incorporated by reference in their entirety.
Embodiments of the invention relate generally to cyclotrons, and more particularly to cyclotrons used to produce radioisotopes.
Radioisotopes (also called radionuclides) have several applications in medical therapy, imaging, and research, as well as other applications that are not medically related. Systems that produce radioisotopes typically include a particle accelerator, such as a cyclotron, that accelerates a beam of charged particles and directs the beam into a target material to generate the isotopes. The cyclotron uses electrical and magnetic fields to accelerate and guide the particles along a spiral-like orbit within an acceleration chamber. When the cyclotron is in use, the acceleration chamber is evacuated to remove undesirable gas particles that can interact with the accelerated particles. For example, when the accelerated particles are negative hydrogen ions (H−), hydrogen gas molecules (H2) or water molecules within the acceleration chamber can strip the weakly bound electron from the hydrogen ion. When the ion is stripped of this electron it becomes a neutral particle that is no longer affected by the electrical and magnetic fields within the acceleration chamber. The neutral particle is irretrievably lost and may also cause other undesirable reactions within the acceleration chamber.
To maintain the evacuated state of the acceleration chamber, cyclotrons use vacuum systems that are fluidicly coupled to the chamber. However, conventional vacuum systems may have undesirable qualities or properties. For example, conventional vacuum systems can be large and require extensive space. This may be problematic, especially when the cyclotron and vacuum system must be used in a hospital room that was not originally designed for using large systems. Furthermore, existing vacuum systems typically have several interconnected components, such as a number of pumps (including different types of pumps), valves, pipes, and clamps. In order to effectively operate the vacuum system, it may be necessary to monitor each component (e.g., through sensors and gauges) and to individually control some of these components. Furthermore, with several interconnected components there may be more interfaces or regions where leaks may occur due to damaged or worn-out parts. This may lead to costly and time-consuming maintenance of the vacuum system.
In addition to the above, complex vacuum systems may require a cooling sub-system. For example, in one known vacuum system, several diffusion pumps are fluidicly coupled to the acceleration chamber. The diffusion pumps use a working fluid (e.g., oil) to generate a vacuum by boiling the oil to a vapor and directing the vapor through a jet assembly. However, the large amount of heat generated in the process must be removed from the vacuum system in order to condense and recover the oil. The cooling sub-system adds further complexity to the vacuum system.
Accordingly, there is a need for improved vacuum systems that remove undesirable gas particles from the acceleration chamber. There is also a need for vacuum systems that require less space, require less maintenance, are less complex, or are less costly than known vacuum systems.
In accordance with one embodiment, a cyclotron is provided that includes a magnet assembly to produce a magnetic field to direct charged particles along a desired path. The cyclotron also includes a magnet yoke that has a yoke body that surrounds an acceleration chamber. The magnet assembly is located in the yoke body. The yoke body forms a pump acceptance (PA) cavity that is fluidicly coupled to the acceleration chamber. The cyclotron also includes a vacuum pump that is configured to introduce a vacuum into the acceleration chamber. The vacuum pump is positioned in the PA cavity.
In accordance with another embodiment, an isotope production system is provided. The system includes a magnet assembly to produce a magnetic field to direct charged particles along a desired path. The system also includes a magnet yoke that has a yoke body that surrounds an acceleration chamber. The magnet assembly is located in the yoke body. The yoke body forms a pump acceptance (PA) cavity that is fluidicly coupled to the acceleration chamber. The system also includes a vacuum pump that is coupled to the PA cavity in the yoke body. The vacuum pump is configured to introduce a vacuum into the acceleration chamber. In addition, the system includes a target system that is positioned to receive the charged particles for generating isotopes.
In accordance with yet another embodiment, a cyclotron is provided that includes a magnet yoke having a yoke body. The yoke body includes a pair of poles that are located opposite to one another across a mid-plane of the yoke body. The poles have a first spatial region therebetween where charged particles are directed along a desired path. The cyclotron also includes a pair of magnet coils that are located within the yoke body opposite to one another across the mid-plane. Each magnet coil surrounds a corresponding pole. The magnet coils have a second spatial region therebetween that surrounds the first spatial region. The first and second spatial regions collectively form an acceleration chamber of the magnet yoke. Also, the cyclotron includes a vacuum pump that is fluidicly coupled to the acceleration chamber and configured to maintain a vacuum within the first and second spatial regions.
To generate isotopes, the particle beam 112 is directed by the cyclotron 102 through the extraction system 115 along a beam transport path 117 and into the target system 114 so that the particle beam 112 is incident upon the target material 116 located at a corresponding target area 120. The system 100 may have multiple target areas 120A-C where separate target materials 116A-C are located. A shifting device or system (not shown) may be used to shift the target areas 120A-C with respect to the particle beam 112 so that the particle beam 112 is incident upon a different target material 116. A vacuum may be maintained during the shifting process as well. Alternatively, the cyclotron 102 and the extraction system 115 may not direct the particle beam 112 along only one path, but may direct the particle beam 112 along a unique path for each different target area 120A-C.
Examples of isotope production systems and/or cyclotrons having one or more of the sub-systems described above are described in U.S. Pat. Nos. 6,392,246; 6,417,634; 6,433,495; and 7,122,966 and in U.S. Patent Application Publication No. 2005/0283199, all of which are incorporated by reference in their entirety. Additional examples are also provided in U.S. Pat. Nos. 5,521,469; 6,057,655; and in U.S. Patent Application Publication Nos. 2008/0067413 and 2008/0258653, all of which are incorporated by reference in their entirety.
The system 100 is configured to produce radioisotopes (also called radionuclides) that may be used in medical imaging, research, and therapy, but also for other applications that are not medically related, such as scientific research or analysis. When used for medical purposes, such as in Nuclear Medicine (NM) imaging or Positron Emission Tomography (PET) imaging, the radioisotopes may also be called tracers. By way of example, the system 100 may generate protons to make 18F− isotopes in liquid form, 11C isotopes as CO2, and 13N isotopes as NH3. The target material 116 used to make these isotopes may be enriched 180 water, natural 14N2 gas, and 16O-water. The system 100 may also generate deuterons in order to produce 15O gases (oxygen, carbon dioxide, and carbon monoxide) and 15O labeled water.
In some embodiments, the system 100 uses 1H− technology and brings the charged particles to a low energy (e.g., about 7.8 MeV) with a beam current of approximately 10-30 μA. In such embodiments, the negative hydrogen ions are accelerated and guided through the cyclotron 102 and into the extraction system 115. The negative hydrogen ions may then hit a stripping foil (not shown) of the extraction system 115 thereby removing the pair of electrons and making the particle a positive ion, 1H+. However, in alternative embodiments, the charged particles may be positive ions, such as 1H+, 2H+, and 3He+. In such alternative embodiments, the extraction system 115 may include an electrostatic deflector that creates an electric field that guides the particle beam toward the target material 116.
The system 100 may include a cooling system 122 that transports a cooling or working fluid to various components of the different systems in order to absorb heat generated by the respective components. The system 100 may also include a control system 118 that may be used by a technician to control the operation of the various systems and components. The control system 118 may include one or more user-interfaces that are located proximate to or remotely from the cyclotron 102 and the target system 114. Although not shown in
The system 100 may produce the isotopes in predetermined amounts or batches, such as individual doses for use in medical imaging or therapy. A production capacity for the system 100 for the exemplary isotope forms listed above may be 50 mCi in less than about ten minutes at 20 μA for 18F−; 300 mCi in about thirty minutes at 30 μA for 11CO2; and 100 mCi in less than about ten minutes at 20 μA for 13NH3.
Also, the system 100 may use a reduced amount of space with respect to known isotope production systems such that the system 100 has a size, shape, and weight that would allow the system 100 to be held within a confined space. For example, the system 100 may fit within pre-existing rooms that were not originally built for particle accelerators, such as in a hospital or clinical setting. As such, the cyclotron 102, the extraction system 115, the target system 114, and one or more components of the cooling system 122 may be held within a common housing 124 that is sized and shaped to be fitted into a confined space. As one example, the total volume used by the housing 124 may be 2 m3. Possible dimensions of the housing 124 may include a maximum width of 2.2 m, a maximum height of 1.7 m, and a maximum depth of 1.2 m. The combined weight of the housing and systems therein may be approximately 10000 kg. The housing 124 may be fabricated from polyethylene (PE) and lead and have a thickness configured to attenuate neutron flux and gamma rays from the cyclotron 102. For example, the housing 124 may have a thickness (measured between an inner surface that surrounds the cyclotron 102 and an outer surface of the housing 124) of at least about 100 mm along predetermined portions of the housing 124 that attenuate the neutron flux.
The system 100 may be configured to accelerate the charged particles to a predetermined energy level. For example, some embodiments described herein accelerate the charged particles to an energy of approximately 18 MeV or less. In other embodiments, the system 100 accelerates the charged particles to an energy of approximately 16.5 MeV or less. In particular embodiments, the system 100 accelerates the charged particles to an energy of approximately 9.6 MeV or less. In more particular embodiments, the system 100 accelerates the charged particles to an energy of approximately 7.8 MeV or less.
As shown in
The yoke sections 228 and 230 include poles 248 and 250, respectively, that oppose each other across the mid-plane 232 within the acceleration chamber 206. The poles 248 and 250 may be separated from each other by a pole gap G. The pole 248 includes a pole top 252 and the pole 250 includes a pole top 254 that faces the pole top 252. The poles 248 and 250 and the pole gap G are sized and shaped to produce a desired magnetic field when the cyclotron 200 is in operation. For example, in some embodiments, the pole gap G may be 3 cm.
The cyclotron 200 also includes a magnet assembly 260 located within or proximate to the acceleration chamber 206. The magnet assembly 260 is configured to facilitate producing the magnetic field with the poles 248 and 250 to direct charged particles along a desired path. The magnet assembly 260 includes an opposing pair of magnet coils 264 and 266 that are spaced apart from each other across the mid-plane 232 at a distance D1. The magnet coils 264 and 266 may be, for example, copper alloy resistive coils. Alternatively, the magnet coils 264 and 266 may be an aluminum alloy. The magnet coils may be substantially circular and extend about the central axis 236. The yoke sections 228 and 230 may form magnet coil cavities 268 and 270, respectively, that are sized and shaped to receive the corresponding magnet coils 264 and 266, respectively. Also shown in
The acceleration chamber 206 is configured to allow charged particles, such as 1H− ions, to be accelerated therein along a predetermined curved path that wraps in a spiral manner about the central axis 236 and remains substantially along the mid-plane 232. The charged particles are initially positioned proximate to the central region 238. When the cyclotron 200 is activated, the path of the charged particles may orbit around the central axis 236. In the illustrated embodiment, the cyclotron 200 is an isochronous cyclotron and, as such, the orbit of the charged particles has portions that curve about the central axis 236 and portions that are more linear. However, embodiments described herein are not limited to isochronous cyclotrons, but also includes other types of cyclotrons and particle accelerators. As shown in
The acceleration chamber 206 may be in an evacuated state before and during the forming of the particle beam 112. For example, before the particle beam is created, a pressure of the acceleration chamber 206 may be approximately 1×10−7 millibars. When the particle beam is activated and H2 gas is flowing through an ion source (not shown) located at the central region 238, the pressure of the acceleration chamber 206 may be approximately 2×10−5 millibar. As such, the cyclotron 200 may include a vacuum pump 276 that may be proximate to the mid-plane 232. The vacuum pump 276 may include a portion that projects radially outward from the end 214 of the yoke body 204. As will discussed in greater detail below, the vacuum pump 276 may include a pump that is configured to evacuate the acceleration chamber 206.
In some embodiments, the yoke sections 228 and 230 may be moveable toward and away from each other so that the acceleration chamber 206 may be accessed (e.g., for repair or maintenance). For example, the yoke sections 228 and 230 may be joined by a hinge (not shown) that extends alongside the yoke sections 228 and 230. Either or both of the yoke sections 228 and 230 may be opened by pivoting the corresponding yoke section(s) about an axis of the hinge. As another example, the yoke sections 228 and 230 may be separated from each other by laterally moving one of the yoke sections linearly away from the other. However, in alternative embodiments, the yoke sections 228 and 230 may be integrally formed or remain sealed together when the acceleration chamber 206 is accessed (e.g., through a hole or opening of the magnet yoke 202 that leads into the acceleration chamber 206). In alternative embodiments, the yoke body 204 may have sections that are not evenly divided and/or may include more than two sections. For example, the yoke body may have three sections as shown in
The acceleration chamber 206 may have a shape that extends along and is substantially symmetrical about the mid-plane 232. For instance, the acceleration chamber 206 may be substantially disc-shaped and include an inner spatial region 241 defined between the pole tops 252 and 254 and an outer spatial region 243 defined between the chamber walls 272 and 274. The orbit of the particles during operation of the cyclotron 200 may be within the spatial region 241. The acceleration chamber 206 may also include passages that lead radially outward away from the spatial region 243, such as a passage P1 (shown in
Also shown in
Furthermore, the poles 248 and 250 (or, more specifically, the pole tops 252 and 254) may be separated by the spatial region 241 therebetween where the charged particles are directed along the desired path. The magnet coils 264 and 266 may also be separated by the spatial region 243. In particular, the chamber walls 272 and 274 may have the spatial region 243 therebetween. Furthermore, a periphery of the spatial region 243 may be defined by a wall surface 354 that also defines a periphery of the acceleration chamber 206. The wall surface 354 may extend circumferentially about the central axis 236. As shown, the spatial region 241 extends a distance equal to a pole gap G (
As shown in
The vacuum pump 276 is positioned within a pump acceptance (PA) cavity 282 formed by the yoke body 204. The PA cavity 282 is fluidicly coupled to the acceleration chamber 206 and opens onto the spatial region 243 of the acceleration chamber 206 and may include a passage Pi. When positioned within the PA cavity 282, at least a portion of the vacuum pump 276 is within the envelope 207 of the yoke body 204 (
The vacuum pump 276 includes a tank wall 280 and a vacuum or pump assembly 283 held therein. The tank wall 280 is sized and shaped to fit within the PA cavity 282 and hold the pump assembly 283 therein. For example, the tank wall 280 may have a substantially circular cross-section as the tank wall 280 extends from the cyclotron 200 to the platform 220. Alternatively, the tank wall 280 may have other cross-sectional shapes. The tank wall 280 may provide enough space therein for the pump assembly 283 to operate effectively. The wall surface 354 may define an opening 356 and the yoke sections 228 and 230 may form corresponding rim portions 286 and 288 that are proximate to the port 278. The rim portions 286 and 288 may define the passage P1 that extends from the opening 356 to the port 278. The port 278 opens onto the passage P1 and the acceleration chamber 206 and has a diameter D2. The opening 356 has a diameter D5. The diameters D2 and D5 may be configured so that the cyclotron 200 operates at a desired efficiency in producing the radioisotopes. For example, the diameters D2 and D5 may be based upon a size and shape of the acceleration chamber 206, including the pole gap G, and an operating conductance of the pump assembly 283. As a specific example, the diameter D2 may be about 250 mm to about 300 mm.
The pump assembly 283 may include one or more pumping devices 284 that effectively evacuates the acceleration chamber 206 so that the cyclotron 200 has a desired operating efficiency in producing the radioisotopes. The pump assembly 283 may include a one or more momentum-transfer type pumps, positive displacement type pumps, and/or other types of pumps. For example, the pump assembly 283 may include a diffusion pump, an ion pump, a cryogenic pump, a rotary vane or roughing pump, and/or a turbomolecular pump. The pump assembly 283 may also include a plurality of one type of pump or a combination of pumps using different types. The pump assembly 283 may also have a hybrid pump that uses different features or sub-systems of the aforementioned pumps. As shown in
Furthermore, the pump assembly 283 may include other components for removing the gas particles, such as additional pumps, tanks or chambers, conduits, liners, valves including ventilation valves, gauges, seals, oil, and exhaust pipes. In addition, the pump assembly 283 may include or be connected to a cooling system. Also, the entire pump assembly 283 may fit within the PA cavity 282 (i.e., within the envelope 207) or, alternatively, only one or more of the components may be located within the PA cavity 282. In the exemplary embodiment, the pump assembly 283 includes at least one momentum-transfer type vacuum pump (e.g., diffusion pump, or turbomolecular pump) that is located at least partially within the PA cavity 282.
Also shown, the vacuum pump 276 may be communicatively coupled to a pressure sensor 312 within the acceleration chamber 206. When the acceleration chamber 206 reaches a predetermined pressure, the pumping device 284 may be automatically activated or automatically shut-off. Although not shown, there may be additional sensors within the acceleration chamber 206 or PA cavity 282.
As shown, the pole 248 is located within the open-sided cavity 320. The ring portion 321 and the pole 248 are concentric with each other and have the central axis 236 extending therethrough. The pole 248 and the inner surface 322 define at least a portion of the coil cavity 268 therebetween. In some embodiments, the yoke section 228 includes a mating surface 324 that extends along the ring portion 321 and parallel to the plane defined by the radial lines 237 and 239. The mating surface 324 is configured to mate with an opposing mating surface (not shown) of the yoke section 230 when the yoke sections 228 and 230 are mated together along the mid-plane 232 (
Also shown, the yoke section 228 may include a yoke recess 330 that partially defines the passage P1 and the PA cavity 282 (
In one embodiment, all or a portion of the surface 322 and any other surface that may interact with the particles is plated with copper. The copper-plated surfaces are configured to reduce the influence of a porous iron surface. In one embodiment, interior surfaces of the vacuum pump 276 may include copper plating. The copper-plated interior surfaces may also be configured to reduce the surface resistively.
Although not shown, there may be additional holes, openings, or passages extending through the radial thickness T2 of the yoke section 228. For example, there may be an RF feed-through and other electrical connections that extend through the radial thickness T2. There may also be a beam exit channel where the particle beam exits the cyclotron 200 (
In the illustrated embodiment, the cyclotron 200 is an isochronous cyclotron where the pole top 252 of the magnet pole 248 forms an arrangement of sectors including hills 331-334 and valleys 336-339. As will be discussed in greater detail below, the hills 331-334 and the valleys 336-339 interact with corresponding hills and valleys of the pole 250 (
The pole top 254 of the pole 250 includes hills 431-434 and valleys 436-439. The yoke section 230 also includes radio frequency (RF) electrodes 440 and 442 that extend radially inward toward each other and toward a center 444 of the pole 250. The RF electrodes 440 and 442 include hollow dees 441 and 443, respectively, that extend from stems 445 and 447, respectively. The dees 441 and 443 are located within the valleys 436 and 438, respectively. The stems 445 and 447 may be coupled to an inner surface 422 of the ring portion 421. Also shown, the yoke section 230 may include a plurality of interception panels 471-474 arranged about the pole 250 and inner surface 422. The interception panels 471-474 are positioned to intercept lost particles within the acceleration chamber 206. The interception panels 471-474 may comprise aluminum. The yoke section 230 may also include beam scrapers 481-484 that may also comprise aluminum.
The RF electrodes 440 and 442 may form an RF electrode system, such as the electrical field system 106 described with reference to
Returning to
Also shown, the yoke section 528 of the cyclotron 502 may be moveable between open and closed positions. (
Furthermore, the vacuum pump 576 may be located within a pump chamber 562 of the ring section 529 and the housing 524. The pump chamber 562 may be accessed when the partition 552 and the yoke section 528 are in the open position. As shown, the vacuum pump 576 is located below a central region 538 of the acceleration chamber 533 such that a vertical axis extending through a center of the port 578 from a horizontal support 520 would intersect the central region 538. Also shown, the yoke section 528 and ring section 529 may have a shield recess 560. The beam path 536 extends through the shield recess 560.
Embodiments described herein are not intended to be limited to generating radioisotopes for medical uses, but may also generate other isotopes and use other target materials. Furthermore, in the illustrated embodiment the cyclotron 200 is a vertically-oriented isochronous cyclotron. However, alternative embodiments may include other kinds of cyclotrons and other orientations (e.g., horizontal).
It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. While the dimensions and types of materials described herein are intended to define the parameters of the invention, they are by no means limiting and are exemplary embodiments. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. §112, sixth paragraph, unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
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