Abstract:
The invention relates to a gantry system for a particle therapy facility, having a beam guidance gantry which has elements for beam guidance, and having a measurement gantry which has a device for beam monitoring. The measurement gantry and beam guidance gantry are thus of a mutually independent design and are, in particular, arranged in a mutually concentric manner. A gantry system of this kind is inter alia less susceptible to mechanical deviations during rotation of the beam guidance gantry.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   The present application claims the benefit of the provisional patent application filed on Aug. 5, 2005, and assigned application No. 60/705,824. The present application also claims priority of German application No. 10 2005 037 018.7 filed on Aug. 5, 2005. Both of the applications are incorporated by reference herein in their entirety. 

   FIELD OF THE INVENTION 
   The invention relates to a gantry system for a particle therapy facility, having a beam guidance gantry which has elements for beam guidance. 
   BACKGROUND OF THE INVENTION 
   In particle therapy, gantry systems are used to irradiate patients from different directions with particles, that is to say protons, carbon ions or oxygen ions, for example. For this purpose the gantry comprises a plurality of deflection magnets which rotate about the axis of rotation of the gantry system. Beam monitoring elements are usually arranged at a beam exit. These elements supply, for example, information concerning the site and intensity of the particle beam and are used for the output of controlled variables which notify a control system of the site and number of particles administered and of the amount of energy used. This is necessary especially in the case of radiation therapy using a scan system, since here the proton beam scans over the tissue to be irradiated in the form of what is called a pencil beam. Examples of gantry systems are known, for example, from EP 1 396 278 A2, EP 1 479 411 B1 and EP 1 402 923 A1. 
   In known gantry arrangements the particle beam is directed onto a stationary treatment target known as the isocenter. The irradiation angle can be freely adjusted such that a patient awaiting treatment can be irradiated from different directions in the same treatment position. Owing to the high particle energies of some 100 MeV, correspondingly large deflection magnets are required for beam guidance. These magnets are arranged on a frame and can rotate on circular paths with relatively large radii of, for example, some meters about an axis of rotation which extends through the isocenter. The problem thus arises, in particular, that the gantry system, which has been dimensioned with a view to adequate rigidity, nevertheless, depending on the angle of rotation, undergoes different displacements or distortions or deformations such that, for example, the positions of the deflection and beam-forming magnets vary. This has a disadvantageous effect on precision during guidance of the particle beam and thus on accuracy of aim and reproducibility. 
   The problem of the considerable structural dead weight has a heightened effect in the case of gantry systems for heavy ions (carbon ions), since here the magnets and the beam guidance elements arranged between the magnets are substantially heavier. 
   SUMMARY OF THE INVENTION 
   An object of the invention is to provide a gantry system which enables accurate radiation therapy to be administered irrespective of the displacements or distortions or deformations of the gantry. 
   This object is achieved as claimed in the invention by virtue of a gantry system for a particle therapy facility as claimed in the independent claim, which system comprises a beam guidance gantry which has elements for beam guidance, and a measurement gantry which has a device for beam monitoring. The device thus measures at least one beam parameter of the administered beam, the beam parameter being provided for control of the particle therapy facility. 
   The device for the output of the parameter is preferably provided on a control system of the particle therapy facility. As part of the beam monitoring apparatus, the device can thereby provide feedback for the administration of radiation therapy. 
   For an irradiation procedure the measurement gantry is preferably first rotated into an angular position intended to form the basis for the radiation therapy. In this position, a measuring unit of the device for measuring particles is then exposed to radiation after the beam guidance gantry has been correspondingly rotated. This enables beam parameters, in particular the site and/or the energy and/or the number of administered particles of the beam to be measured. 
   One advantage of an embodiment of the invention is that the effects of displacements or distortions or deformations caused by the weight load of the beam guidance elements such as deflection magnets or quadrupole magnets were restricted to the beam guidance gantry. The measurement gantry, which is of a stand-alone and substantially lighter and smaller design, is, by contrast, not subjected to stress and distorted. This has the further advantage that the device for beam monitoring can be positioned very accurately relative to the isocenter independently of the beam guidance gantry. 
   A further advantage is that, owing to the smaller mass, the measurement gantry can be positioned more quickly and more accurately. If the measurement gantry is also arranged inside the beam guidance gantry, rotation of the beam guidance gantry does not put at risk a patient and/or operating personnel located inside the measurement gantry. It is thus possible for patient positioning, for example, and, if the measurement gantry also has an imaging device, position verification to be started without, at that time, the beam guidance gantry already being rotated into the angular position later required. If the measurement gantry also comprises a laser system for patient positioning and/or an imaging position verification system, etc. as already mentioned above, these systems are also independent of the angle of rotation, that is to say, they supply information that is not conditional on the position of the beam guidance gantry. 
   A further advantage relating to the beam guidance gantry is that said gantry becomes less expensive since the positioning accuracy and any positioning errors can be corrected by the independently arranged beam monitoring apparatus. 
   A further advantage is that the measurement gantry and beam guidance gantry can be designed independently in respect of energy supply, signal processing and the installation of components. 
   A further advantage is that all the enclosures visible in a patient room can be fitted on the measurement gantry. 
   In an advantageous embodiment of the gantry system, the measurement gantry comprises apparatus for verifying the patient&#39;s position and/or a patient positioning device and/or a laser positioning device. The patient&#39;s position is verified shortly before exposure to radiation with, for example, the aid of pairs of x-ray sources and x-ray detectors arranged at an angle. A patient positioning device comprises, for example, a video camera system which matches the patient&#39;s position to a required position. A laser positioning device comprises, for example, a laser cross formed by a plurality of laser beams. 
   An advantage of such embodiments is that an imaging device can be positioned more quickly relative to the patient for patient position verification, since the rotation of the measurement gantry with the imaging devices is independent of the rotation of the beam guidance gantry. A further advantage is the fact that, during the imaging process, the drive and bearing of the beam guidance gantry are not under stress. The independent rotatability of the measurement gantry also, for example, permits orthogonal imaging relative to the irradiation angle. In the case of a continuous, rapid rotation of the measurement gantry, said independent rotatability also permits the capture, from different angles, of a plurality of fluoroscopic images from which, for example, 3D image data sets can be obtained for matching with CT position planning data. 
   In further embodiments of the gantry system, the measurement gantry and the beam guidance gantry can be installed independently of each other and/or they can be adjusted in their angular position independently of each other and/or they are mechanically, thermally and/or vibrationally separate. 
   Further advantageous embodiments of the invention are characterized by the features of the subclaims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An explanation follows of two exemplary embodiments of the invention with reference to  FIGS. 1 to 3 , in which: 
       FIG. 1  is a diagrammatic representation of a first embodiment of a concentric gantry system in a vertical sectional drawing through its axis of rotation, 
       FIG. 2  is a front view of the gantry in  FIG. 1 , and 
       FIG. 3  is a diagrammatic representation of a second embodiment of a concentric gantry system in a vertical sectional drawing through its axis of rotation. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows a gantry system  1  in a vertical sectional drawing along an axis of rotation  3 . The object of the gantry system  1  is to be able to guide a particle beam  5  such that a patient  7  having tissue that is to be irradiated, for example having a brain tumor, can undergo radiation therapy from any direction of incidence. For this purpose, the patient  7  is positioned, for example on a patient bed  9 , with the tissue to be irradiated in an isocenter  11  of the gantry system  1 . The isocenter  11  preferably lies on the axis of rotation  3 . The direction of incidence can be at any angle to the axis of rotation  3 . For illustrative purposes, an angle of 90° was selected in  FIG. 1 . When the gantry system  1  rotates, the direction of incidence rotates about the axis of rotation  3 . 
   In the exemplary embodiment shown in  FIG. 1 , the particle beam is guided by the beam guidance gantry  12  from the beam entry into the gantry system  1  to the patient  7 . The particle beam  5  enters the gantry system  1  on the axis of rotation  3 . The particle beam  5  is deflected from the axis of rotation  3  by a first deflection magnet  13 A before it is deflected by further deflection magnets  13 B and  13 C such that it passes, for example, radially through the isocenter  11 . Further beam guidance elements  15 , for example quadrupole magnets, raster scan magnets, etc. are arranged between the deflection magnets  13 A,  13 B,  13 C. The deflection magnets  13 A,  13 B,  13 C and the beam guidance elements  15 , together with a support structure  16 , form the beam guidance gantry  12 . A bearing device is used for rotation of the beam guidance gantry  12 . The bearing device comprises a first bearing  17  which is arranged in an axial direction, where possible at the level of the centre of gravity of the beam guidance gantry  12 , and also comprises a bearing  19  which is arranged in the region of the beam incoupling. The bearings  17  and  19  are supported on a base  20 . The bearing  17  is preferably in the form of a bearing ring. 
   Owing to the weight of the beam guidance gantry there is the possibility of distortions which cannot be completely prevented even by a very rigidly designed support structure  16  and which lead to positional variations, for example of the beam guidance elements  15 , and thus to beam displacement. 
   Arranged concentrically with the beam guidance gantry  12  inside the beam guidance gantry  12  is a measurement gantry  21 . The measurement gantry  21  can rotate independently of the beam guidance gantry  12 . This is made possible by bearings  23 , which are arranged in the direction of the axis of rotation at the level of the bearing  17  of the beam guidance gantry  12 . The bearings  17  and  19  are supported on the base. The bearings  23  are likewise supported on the base  20 , indirectly via the bearing  17 . 
   In the region of the beam exit  25  of the beam guidance gantry, the measurement gantry  21  has a device  27  for beam monitoring. Apparatus for laser positioning and/or for patient position verification can also be fitted there. The weight of the measurement gantry  21  is much less overall, with the result that deformations depending on the angular position can be very largely prevented. The physical positions of the components supported by the measurement gantry are accordingly reproducible, that is to say, for example the distance to the isocenter  11  is not dependent on the angle of rotation. 
   The device  27  for beam monitoring measures at least one beam parameter of the administered beam, for example the beam position, the beam intensity and/or the beam energy; the beam parameter or parameters are provided for control of the particle therapy facility and are thus an essential constituent in the administration of radiation therapy. The beam guidance gantry and the measurement gantry thus cooperate during radiation therapy in order to administer a beam with the appropriate parameters. The measurement gantry enables the administered dose and the position of the administered beam to be actively measured. The feedback of this information to, for example, a control unit of the particle therapy facility is required for the irradiation procedure so that, for example, the desired dose can be administered very precisely. This measurement of “primary” parameters of the beam differs from the measurement of radioactive secondary products, for example with a PET machine which, following administration, supplies information concerning the site of the administered dose and cannot be used for control of the particle therapy facility. This latter machine is used far more for quality assurance than for the controlled administration of the irradiation procedure. 
   The gantry system  1  is preferably designed so that, for radiation therapy, the measurement gantry  21  can be rotated into an angular position in which a measuring unit of the device is penetrated by the particle beam when the beam guidance gantry  12  is correspondingly rotated, in order to measure, in particular, the site and/or the energy and/or the number of administered particles of the beam. 
   Accordingly, the measuring unit of the device  27  has, for example, a location detector (e.g. multichannel plates) for defining position and/or a dosimeter for measuring intensity. 
   To illustrate the structure in  FIG. 1 , reference is made to  FIG. 2 , which is a front view of the gantry system  1  in the direction of the axis of rotation. Visible there are the patient  7  in the isocenter  11  of the gantry system  1 , the beam exit  25  and an outer gantry ring  31  of the beam guidance gantry  12 , as well as the measurement gantry  21  arranged therein with the device  27  for beam monitoring. Also visible there are two flat panel detectors  33 , which are arranged on both sides of the device  27  for beam monitoring and are used for position verification. The x-ray sources required for this purpose are located opposite the patient and are integrated into the measurement gantry  21  and not visible in  FIG. 2 . 
     FIG. 3  shows a further exemplary embodiment of a concentric gantry system  41 , the beam guidance gantry  12 ′ having the components referred to in  FIG. 1 , for example deflection magnets  13 A′,  13 B′,  13 C′, bearings  17 ′ and  19 ′, beam exit  25 ′, etc. 
   Unlike the embodiment shown in  FIG. 1 , a measurement gantry  42  is not supported indirectly via the beam guidance gantry  12 ′. Instead there is provided a bearing  43  which is itself arranged on a base  47  of the particle therapy facility. The bearing  43  and the bearings  17 ′ and  19 ′ are thus mechanically separate. This embodiment facilitates complete mechanical, thermal and/or vibrational separation of the measurement gantry and beam guidance gantry  12 ′ and  42 . The measurement gantry  42  again comprises means  45  for imaging, beam monitoring and/or laser positioning.