Patent Application
20080315113
This application claims the benefit of DE 10 2007 028 646.7 filed Jun. 21, 2007, which is hereby incorporated by reference.
The present embodiments relate to a beam guidance magnet.
A beam guidance magnet is used to deflect a beam along a curved beam path.
Curved beam guidance magnets are used in particle accelerator systems for deflecting and/or focusing a beam of charged particles, such as electrons or ions. The particles are accelerated to high kinetic energies in the particle accelerator system and are used in medical therapy, such as cancer therapy. German Patent Application DE 199 04 675 A1 and U.S. Pat. No. 4,870,287 A disclose a radiation treatment system for medical therapy. The radiation treatment system includes a particle source and an accelerator for generating a high-energy particle beam. The high-energy particle beam is aimed at a region to be irradiated, such as a tumor, of a test subject. The radiation dose in the surrounding area, which is the area not to be treated, of the body (patient) should be kept as slight as possible (minimized). To keep the radiation dose slight in the region not to be treated, the region to be treated is irradiated from various directions. The particle beam is shot (directed) along an axis, predetermined by the accelerator, into a so-called “gantry,” which is rotatable about the axis predetermined by the particle beam.
The “gantry” is an arrangement of various beam guidance magnets, with which the particle beam can be deflected multiple times out of its original direction, so that after leaving the gantry, it strikes the region to be irradiated at a certain angle. Typically, the particle beam strikes the region to be irradiated at an angle of 45° to 90°, relative to the axis of rotation of the gantry. The beam guidance magnets are disposed on a frame, which is part of the gantry, in such a way that the particle beam emerging from the gantry always passes through a certain region, the so-called “isocenter”. A region to be treated can be irradiated from a plurality of sides. In a region lateral to the particle beam, the isocenter has an area of 20×20 cm, for example. The radiation dose in the region surrounding the isocenter may be distributed over a large volume, and the radiation exposure outside the isocenter may be relatively slight (minimized).
For irradiating a spatially extensive tumor or growth, a variation in the angle at which the particle beam strikes the region to be irradiated, a variation of the kinetic energy of the particles, and a variation of the lateral location coordinates at the point struck by the particle beam are desirable. For varying the lateral location coordinates of the particle beam at the site of the isocenter, scanner magnets are typically integrated with the gantry. With the aid of the scanner magnets, the particle beam can be deflected in a horizontal or vertical plane, by small angles. The deflections of the particle beam caused by the scanner magnets are compensated for in such a way that the particle beam leaves the gantry in beams into the isocenter that are to be made virtually parallel. The magnets following the scanner magnets in the beam direction compensate for the deflections.
For varying the kinetic energy of the particles, the particles originating at the particle source are shot (directed) into a gantry at different kinetic energies. Depending on the desired kinetic energy of the particles shot into the gantry, the individual magnets of the gantry are excited to suitable energies.
Because of the aforementioned conditions placed on the magnets of a gantry, ion-optical demands are made in terms of the construction of the beam guidance magnets. Coil designs are optimized in view of the criteria.
The magnetic flux density increases to very high values at the end regions of a beam guidance magnet. The end regions may be arches of the curved primary and/or correction coils. Accordingly, the magnetic flux density increases because of the small radii of curvature. If the coils of the beam guidance magnets are made in superconducting fashion, this technical problem is exacerbated, since the magnetic fields that occur in the end regions of the coils can be greater than the critical magnetic flux density of the superconductor material.
German Patent Application DL 199 04 675 A1 discloses reducing the supercritical magnetic flux densities in the end region of the individual coils of a beam guidance magnet. For example, German Patent Application DE 199 04 675 A1 discloses bending the end parts of the primary coils upward relative to the beam guidance plane by more than 90°. The end parts extend into the field range of the respective curved end part of the respective associated secondary coil.
German Patent Application DE 199 04 675 A1 discloses a beam guidance magnet that can avoid the occurrence of supercritical magnetic fields in the curved end parts of the secondary coils. Magnetic fields in the curved end parts of the secondary coils can be avoided that exceed maximum limit values, which are predetermined by the material used to construct the beam guidance magnet. Particularly in a beam guidance magnet with superconducting coils, exposing the superconductor material to a supercritical magnetic field, which causes the superconductor material above this supercritical magnetic field to lose its superconducting properties, can be avoided. The critical magnetic field of the corresponding superconductor material is dependent on the current carried by the superconducting material. In accordance with the aforementioned provisions, a predetermined current-carrying capacity of the superconductor material can expose the material solely to a suitably subcritical magnetic field. The beam guidance magnet is improved with regard to its reliability, without requiring oversizing of its conductor material.
German Patent Application DE 199 04 675 A1 discloses a beam guidance magnet that can reduce the field to which the curved end parts of the secondary coils are exposed. In addition to the ion-optical demands to be made of the beam guidance magnet, however, limits can be set on an embodiment of the end parts of the primary coils of the proposed beam guidance magnet. For ion-optical reasons, for example, optimal field compensation for the end parts of the primary coils may not be achieved. The proposed beam guidance magnet can keep a stray field as small as possible in a patient room.
The present embodiments may obviate one or more of the drawbacks or limitations inherent in the related art. For example, in one embodiment, a beam guidance magnet reduces the aforementioned problems.
German Patent Application 10 2007 025 584.7, which was filed Jun. 1, 2007 and not published prior to the priority date of the present application and is entitled “Strahlführungsmagnet zur Ablenkung eines Strahls elektrisch geladener Teilchen längs einer gekrümmten Teilchenbahn und Bestrahlungsanlage mit einem solchen Magneten” [“Beam Guidance Magnet for Deflecting a Beam of Electrically Charged Particles Along a Curved Particle Path, and Radiation Treatment System Having Such a Magnet”], discloses a beam guidance magnet for deflecting a beam of electrically charged particles along a curved particle path that defines a beam guidance plane. The beam guidance magnet includes a coil system, which does not include ferromagnetic material that affects the beam guidance. The coil system has curved individual coils stretched out along the particle path. The individual coils are disposed in pairs in mirror symmetry to the beam guidance plane. The coil system includes at least two primary coils with side parts elongated in the direction of the particle path and with end parts bent upward relative to the beam guidance plane. The coil system includes two at least largely flat secondary coils, curved in bananalike (crescentlike) shape, between the end parts of the primary coils and having side parts, elongated in the direction of the particle path, and curved end parts.
In one present embodiment, a beam guidance magnet includes supplementary coils, which are disposed in the field region of the respective curved end parts of the secondary coils. The beam of electrically charged particles may be deflected into an elongated patient room, with compensation coils located on both sides of the elongated patient room.
The supplementary coils may reduce the field to which the curved end parts of the primary coils are exposed. The supplementary coils may, for example, be controlled separately from the remaining coil system of the beam guidance magnet, so that optimal compensation of the magnetic fields can be achieved. Ion-optical demands of the beam guidance magnet may be taken into account, without dispensing with a suitable field compensation in the region of the curved end regions of the primary coils. The stray field of the beam guidance magnet in the patient room may be actively compensated for in the compensation coils disposed on both sides of an elongated patient room. For various medical and technical reasons, low exposure of the patient room to the stray field of the beam guidance magnet is desirable. The field of use for the beam guidance magnet expands, for example, to patients who have electromagnetically sensitive devices implanted in their body.
The supplementary coils may extend in one or more planes parallel to the beam guidance plane. The supplementary coils may be arranged (disposed) in one or more planes parallel to the beam guidance plane. The supplementary coils arranged (disposed) in one or more planes parallel to the beam guidance plane may compensate for the stray field of the beam guidance magnet.
The compensation coils may extend in a plane or planes that are parallel to the beam guidance plane. Because the compensation coils are disposed parallel to the beam guidance plane, especially effective field compensation in the patient room may be attained.
The end parts of the primary coils may be bent (curved) upward in such a way that in projection into the beam guidance plane, the end parts of the primary coils and the curved end parts of the secondary coils overlap. An overlap of the end parts of the primary coils and of the curved end parts of the secondary coils in projection into the beam guidance plane may generate a region in the applicable area of the overlap with effective compensation of the magnetic fields.
The end parts of the primary coils may be bent upward by approximately 180° relative to the beam guidance plane. The end parts of the primary coils may (e.g., at least approximately) be located in a plane that is at least approximately parallel to a plane, which is defined by the respective curved end part of the associated secondary coil. If the end parts of the primary coil are bent upward by approximately 180° relative to the beam guidance plane, then the magnetic field generated by the end parts of the primary coil has (e.g., virtually, solely) a magnetic field component that is exactly opposite in its direction to the magnetic field, which is generated by the curved end parts of the associated secondary coil. The magnetic field generated by the end parts of the primary coil may compensate for the magnetic fields of the end parts of the primary coils and the end parts of the secondary coils.
The coil system may include first and second coil systems for generating a first and second dipole moment. The first coil system may include at least the two primary coils with the bent-upward end parts as first primary coils and the two at least largely flat secondary coils. The secondary coils may enclose an inner region in which at least one largely flat correction coil curved in banana-like (crescent-like) shape is disposed. The second coil system may include two second primary coils curved in banana-like (crescent-like) shape, which are each disposed in the region of the beam guidance plane between the first primary coils and have one elongated second side part near the particle path and one elongated second side part remote from the particle path. When viewed in cross section, the side parts may have a greater length perpendicular to the beam guidance plane than parallel to the beam guidance plane. The first and second coil systems may be excited such that the first and second dipole moments point in opposite directions or at least approximately opposite directions. A beam guidance magnet with a coil system may include a reduced stray field. A beam guidance magnet with a reduced stray field may be powerful beam guidance magnets, in which the occurrence of high magnetic fields in the curved end parts of the secondary coils is especially dominant. For powerful beam guidance magnets, the high magnetic fields occurring at the curved end parts of the secondary coils can be compensated for with the coil system.
The first and second coil systems may be excited in such a way that in the outside region of the beam guidance magnet, the sum of the dipole moments of the first and second coil systems is minimized. Minimizing the stray field of a beam guidance magnet improves electromagnetic compatibility. The high magnetic fields in the curved end parts of the secondary coils may be minimized.
The beam of electrically charged particles may be deflected along a curved particle path into an isocenter. The sum of the dipole moments of the first and second coil systems may be minimized at least at the site of the isocenter. If a beam guidance magnet is used for therapeutic purposes, then the region to be treated may be located at the site of the isocenter. The beam guidance magnet, because of its reduced stray field, may be accessible to (used for) medical applications in which an electromagnetically sensitive device, such as a pacemaker, is located at or in the vicinity of the isocenter. For therapeutic purposes, such as ion therapy, powerful magnets are typically used. Powerful magnets have elevated magnetic fields in the curved end parts of the secondary coils. For a powerful beam guidance magnet, the elevated magnetic fields in the curved end parts of the secondary coils may be reduced.
The individual coils of the first and second coil systems may be connected electrically in series. The number of windings of the individual coils may be dimensioned such that the sum of the dipole moments of the first and second coil systems is minimized. The individual coils of the first and second coil systems may be connected electrically in series, and the surface area enclosed by the second primary coils in the beam guidance plane may be dimensioned such that the sum of the dipole moments of the first and second coil systems is minimized. A beam guidance magnet may be improved with regard to a minimized stray field and with regard to the occurrence of maximum magnetic field exposures.
The conductors of the individual coils may have metal low-temperature superconductor material (“LTC superconductor material”) or metal oxide high-temperature superconductor material (“HTC superconductor material”). The metal oxide high-temperature superconductor material may be kept at (maintained) an operating temperature between 10K and 40K, preferably at an operating temperature between 20K and 30K. If a beam guidance magnet is made with superconducting coils, then the problem of the occurrence of supercritical magnetic fields in the curved end parts of the secondary coils is especially critical. A superconductor material, above a material-specific critical magnetic field, loses its superconducting properties. If the occurrence of supercritical magnetic fields can be avoided, then the beam guidance magnet may be improved in terms of its reliability.
A radiation treatment system may have a fixed particle source that generates a beam of electrically charged particles. The radiation treatment system may have a gantry system, which is rotatable about an axis of rotation and has a plurality of deflection and/or focusing magnets for deflecting and/or focusing the particle beam into an isocenter. At least one of the deflection and/or focusing magnets is a beam guidance magnet in accordance with one of embodiments disclosed herein.
The radiation treatment system may include a beam guidance magnet in accordance with one of the aforementioned embodiments as the deflection and/or focusing magnet through which the particle beam passes last before reaching the isocenter. The deflection and/or focusing magnet of a radiation treatment system through which the particle beam passes last before reaching the isocenter is typically a high-power beam guidance magnet. The beam guidance magnet may reduce the occurrence of superelevated magnetic fields in the curved end parts of the secondary coils.
The radiation treatment system may have a beam guidance magnet whose stray field is minimized in a patient room, preferably at least at the site of the isocenter. Minimizing the stray field of the beam guidance magnet in the patient room, preferably at the site of the isocenter, may improve the electromagnetic compatibility of the radiation treatment system. The beam guidance magnet of the radiation treatment system may reduce the occurrence of supercritical magnetic fields in the curved end parts of the secondary coils.
The particle beam may be a beam comprising C6+ particles. C6+ particles may be used for cancer therapy. Such radiation treatment systems used in medical technology are radiation treatment systems with high-power deflection and/or focusing magnets. A radiation treatment system with high-power deflection and/or focusing magnets may include at least one beam guidance magnet that reduces the superelevated magnetic fields in the curved end parts of the secondary coils.
The gantry system may deflect the particle beam 101 into the isocenter 103. The isocenter 103 is the region in which the particle beam 101 intersects the axis of rotation A of the gantry. Upon a rotation of the gantry system about the axis of rotation A, the particle beam 101 always (or almost always) passes through the isocenter 103.
A gantry system may be used for medical therapy. A region to be treated, such as a tumor or growth that is to be irradiated, will be located in the region of the isocenter 103. A beam of C6+ ions may be used for medical treatment.
The deflection and/or focusing magnets 105 of a radiation treatment system 100 may have magnetic windings that are made from normally conducting material, or from superconductor material.
Between the end parts 205, 206 of each of the primary coils 201, 202 is a respective largely flat secondary coil 207 curved in a banana-like (crescent-like) shape. The secondary coils 207 have side parts 208, elongated in the direction of the particle path, and curved end parts 209, 210.
The bent-upward end parts 205, 206 of the primary coils 201, 202 are bent upward out of the beam guidance plane in such a way that bent-upward end parts 205, 206 extend into the field range of the associated end parts 209, 210 of the secondary coils 207. In the exemplary embodiment shown in
The beam guidance magnet 200 may be free of ferromagnetic material that affects the beam guidance. The beam guidance magnet 20 may not include magnetic field-forming material, such as iron yokes.
The end parts 205, 206 of the primary coils 201, 202 may be bent upward by more than 90° out of the beam guidance plane. The end parts 205, 206 of the primary coils 201, 202 may be bent upward at least approximately 180° relative to the beam guidance plane. The end regions 205, 206 of the primary coils 201, 202 may be located in a plane that is at least approximately parallel to the beam guidance plane. If the end parts 205, 260 of the primary coils 201, 202 are bent upward by more than 90° from the beam guidance plane, then the magnetic field generated by the end parts 205, 206 has a magnetic field component that is perpendicular to the beam guidance plane. The magnetic field component that is perpendicular to the beam guidance plane compensates at least partially for the magnetic field generated by the curved end parts 209, 210 of the secondary coils 207. If the end parts 205, 260 of the primary coils 201, 202 are bent upward by approximately 180° from the beam guidance plane, then the magnetic field generated by the end parts 205, 206 has a magnetic field component that is perpendicular to the beam guidance plane. Since the magnetic field component, which is perpendicular to the beam guidance plane and is generated by the end parts 205, 260 of the primary coils 201, 202, has a direction which is the direction of the magnetic field that is generated by the curved end parts 209, 210 of the secondary coils 207, the corresponding magnetic fields compensate for one another at least partially.
The beam guidance magnet 200 may have individual coils whose conductors are made at least predominantly from metal low-temperature superconductor material (“LTC superconductor material”). The beam guidance magnet 200 may have individual coils whose conductors have metal oxide high-temperature superconducting material (“HTC superconductor material”). The high-temperature superconductor material may include, for example, yttrium barium copper oxide “YBCO”. The operating temperature of conductors of the individual coils comprising a high-temperature superconductor material may be between approximately 10K and 40K, and preferably between 20K and 30K. A beam guidance magnet 200 that is equipped with superconducting individual coils may include a cooling system for cooling the superconducting individual coils.
The first and second coil systems may be excited such that the dipole moment of the first coil system and the dipole moment of the second coil system at least approximately compensate for one another. The first and second coil systems may be excited such that in the remote field of the beam guidance magnet 300, the sum of the dipole moments of the first coil system and second coil system is minimized. A quadrupole moment, viewed from the site where of its generation, drops off faster than a dipole moment. Since the dipole moments of the first and second coil system at least partially compensate for one another, the beam guidance magnet 300 of the exemplary embodiment shown in
The beam guidance magnet 300 of the exemplary embodiment shown in
The beam guidance magnet 300 in the exemplary embodiment shown in
The dipole moments generated by the first and second coil systems may compensate for one another. The individual coils of the first and second coil systems may be connected electrically in series, and the number of windings in the individual coils of the first and second coil systems may be dimensioned such that the sum of the dipole moments of the first and second coil systems is minimized. Alternatively, the individual coils of the first and second coil systems can be connected electrically in series, and the second primary coils 203 may enclose an area inside the beam guidance plane that is dimensioned such that the sum of the dipole moments of the first and second coil systems is minimized.
The second coil system includes two second primary coils 302, 303, which are each curved in banana-like shape and are disposed in the region of the beam guidance plane between the first primary coils 201. The two second primary coils 302, 303 each have one partial piece 401 near the particle path and one side part 304, 305 remote from the particle path. As shown in
The coil system shown in
The end parts 205, 206 of the primary coils 201, 202 may be bent upward in such a way that the end parts 205, 206 overlap with the curved end parts 209, 210 of the secondary coils 207 in the projection into the beam guidance plane.
With the beam guidance magnet 200 shown in
The supplementary coils 501 and/or the compensation coils 403 may be made from normally conducting material or from superconductor material and can be triggerable or excitable individually or jointly with the rest of the coil system of the beam guidance magnet 200.
Various embodiments described herein can be used alone or in combination with one another. The forgoing detailed description has described only a few of the many possible implementations of the present invention. For this reason, this detailed description is intended by way of illustration, and not by way of limitation. It is only the following claims, including all equivalents that are intended to define the scope of this invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 028 646.7 | Jun 2007 | DE | national |
