Patent Publication Number: US-2011057124-A1

Title: Radiation therapy apparatus and method for monitoring an irradiation

Description:
This application claims the benefit of DE 10 2009 040 389.2 filed Sep. 7, 2009, which is hereby incorporated by reference. 
     BACKGROUND 
     The present embodiments relate to a radiation therapy apparatus. 
     Particle therapy, which is a special form of radiation therapy, has gained increasing importance over the last few years. Particle therapy enables methods for treating tissue (e.g., tumor diseases) to be implemented. Irradiation methods, like those used in particle therapy, are also used in non-therapeutic fields. Research work for product development is within the scope of particle therapy, the research work being implemented, for example, on non-living phantoms or bodies or being the irradiation of materials. 
     Charged particles such as protons, carbon ions or other charged particles, for example, are accelerated to high energies, shaped to form a particle beam and fed to one or several irradiation rooms by way of a high energy beam transportation system. The object to be irradiated with a target volume is irradiated in one of these irradiation rooms with the particle beam. 
     The interaction of the particle beam with the material of the target object to be irradiated produces unstable cores, both in the particles of the particle beam and also in the material of the target object. Positron emission tomography (PET) systems, with which the break-up of these unstable cores may be detected, are known. 
     SUMMARY AND DESCRIPTION 
     The present embodiments may obviate one or more of the drawbacks or limitations in the related art. For example, in one embodiment, a radiation therapy apparatus that enables a simple and cost-effective monitoring of the break-ups of unstable cores may be provided. 
     In one embodiment, a radiation therapy apparatus includes a source for providing a therapy beam, which may be directed from the source onto a target object to be irradiated, and an imaging apparatus including an x-ray source and an x-ray detector. The x-ray source and the x-ray detector may be arranged such that diagnostic x-rays may be directed from the x-ray source, through the target object to be irradiated and onto the x-ray detector. The radiation therapy apparatus also includes a control apparatus (e.g., a controller) for the imaging apparatus. The control apparatus is configured to read out the x-ray detector during an irradiation of the target object with the therapy beam. As a result, a recording of photons that are produced within the target object as a result of the interaction of the therapy beam with the target object may be implemented. 
     In the case of radiation therapy apparatuses, a patient or another target object to be irradiated is accurately positioned spatially with respect to the therapy beam in order to provide the desired irradiation. An imaging apparatus that enables the internal structure of the target volume to be irradiated to be mapped in the target object may be used. The position of the target volume may be determined immediately prior to the start of an irradiation and if necessary, may be corrected accordingly. The imaging apparatus may also be used during the irradiation, in order to detect and monitor the position of the target volume (e.g., during a fluoroscopy-type operation). 
     An already existing imaging apparatus may also be used for another purpose, to record the radioactive break-ups that are produced in the target volume as a result of the interaction of the therapy beam with the material of the target volume by way of the photons emitted therefrom. As the photons generated in this way in the target volume act as a measure for the dose deposited in the target volume, a monitoring of the dose deposition implemented with the therapy beam may be implemented in this way. Additional devices such as, for example, an additional PET system or a SPECT system are not needed. Accordingly, costs and space requirements are reduced. In particular, the photons recorded in this way are evaluated and may be used to control the radiation therapy apparatus (e.g., even during an irradiation session or for subsequent irradiation sessions). 
     In one embodiment, the radiation therapy apparatus also includes an evaluation apparatus (e.g., a computing unit) that is configured to reconstruct a dose distribution deposited in the target object by the therapy beam at least partially from the photons recorded with the x-ray detector. The deposited dose distribution may, in this way, already be determined at least partially during an irradiation or after an irradiation, so that the irradiation success may be monitored. If the x-ray radiation detector is moved about the target object, for example, a dose distribution may be determined in three dimensions from the recorded photons. However, conclusions may be drawn as to the range of the therapy beam and/or a lateral extension of the deposited dose even with a stationary detector, which only records data from one specific direction, 
     In one embodiment, the control apparatus is configured to read out the x-ray detector without simultaneously activating the x-ray source. The imaging apparatus may thus be operated in two different modes. In a first mode of operation, the imaging apparatus is operated such that the x-ray detector interacts with the x-ray source and is read out while the x-ray source is activated. By contrast, in a second mode of operation, the x-ray detector may only be used to detect the photons generated in the target object. 
     In one embodiment, the imaging apparatus may be arranged at different positions relative to the target object. This enables the photons generated in the target object to be recorded from different angles of view or enables a suitable position of the x-ray detector relative to the target object and the beam exit to be selected. Accordingly, the information content of the recording may be improved. This may be useful, for example, with a reconstruction of the deposited dose distribution. The imaging apparatus may be arranged, for example, on a positioning apparatus (e.g., on a robot arm), with which the imaging apparatus may be moved to different positions. The imaging apparatus may be controlled, for example, such that the position of the imaging apparatus for recording the photons generated by the therapy beam may be changed during an irradiation of the target volume, in order, for example, to obtain three-dimensional information about the deposited dose distribution. 
     In one embodiment, the radiation therapy apparatus includes at least one further imaging apparatus, which includes a further x-ray source and a further x-ray detector. The further imaging apparatus may also be configured and used like the first imaging apparatus. Alternatively, the first imaging apparatus may be operated in the first mode of operation, and the second imaging apparatus may be operated in the second mode of operation, so that a monitoring of the dose deposition and the position of the target volume in the target object may be implemented at the same time. 
     In one embodiment, the x-ray detector includes an adjustment apparatus for modifying the photons striking the x-ray detector. The adjustment apparatus may be positioned reversibly in front of the x-ray detector and in an automatically controlled fashion. The x-ray detector may be operated for instance in a first, conventional imaging mode without the adjustment apparatus, while the adjustment apparatus in the second operating mode filters and/or modifies the photons generated in the target object by interaction with the therapy beam before the photons strike the x-ray detector. 
     A method for monitoring an irradiation of a target object includes irradiating the target object with a therapy beam and generating photons in the target object as a result of the interaction of the therapy beam with the target object. The method includes recording the photons using an imaging apparatus that includes an x-ray source and an x-ray detector for x-raying the target object with an x-ray beam. The method also includes evaluating the recorded photons. 
     The methods of the present embodiments are suitable both within the scope of an irradiation of a patient and also within the scope of an irradiation of a non-human or non-animal body (e.g., when irradiating a phantom for test, research and/or calibration purposes). 
     In one embodiment, the photons are recorded with the x-ray detector at a point in time at which the x-ray source is not activated. 
     The recorded photons are evaluated such that a dose distribution deposited in the target object by the therapy beam is at least partially reconstructed from the recorded photons. 
     The x-ray detector may be moved to a different position during the recording of the photons. 
     To record the photons, an adjustment apparatus for modifying the photons striking the x-ray detector may be arranged upstream of the x-ray detector. The adjustment apparatus may be positioned reversibly upstream of the x-ray detector and in an automatically controlled fashion. 
     The x-ray detector may be operated in an imaging mode, in which the x-ray detector interacts with the x-ray source in order to record image data of an object to be irradiated. The x-ray detector may also be operated in a therapy monitoring mode, in which the x-ray detector records the photons produced in the body by interaction with the therapy beam without interaction with the x-ray source. 
     The preceding and subsequent description of the individual features relates both to the apparatus embodiments and the method embodiments, without this being explicitly explained in detail in each case; the individual features disclosed here may also be of significance to the present embodiments in other combinations than those shown. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a particle therapy system; 
         FIG. 2  shows one embodiment of a radiation therapy apparatus that is operated in the imaging mode; 
         FIG. 3  shows one embodiment of the radiation therapy apparatus of  FIG. 2  in the therapy monitoring mode; 
         FIG. 4  shows one embodiment of a radiation therapy apparatus including two imaging apparatuses; and 
         FIG. 5  shows a flow chart of monitoring an irradiation of a target object according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a schematic overview of the design of a particle therapy system  10 . In a particle therapy system  10 , an irradiation of a body (e.g., a tumor-diseased tissue) takes place using a particle beam. 
     Ions such as, for example, protons, helium ions, carbon ions or other particle types such as pions may be used as particles. Particles of this type may be generated in a particle source  11 . If, as shown in  FIG. 1 , two particle sources  11  that generate two different ion types exist, the two different ion types may be switched between within a short time interval. A switching magnet  12  is used, for example, to switch between the two different ion types. The switching magnet is arranged between the ion sources  11  and a preaccelerator  13 . In one embodiment, the particle therapy system  10  may be operated with protons and carbon ions at the same time. 
     The ions generated by the ion source  11  or one of the ion sources  11  and selected with the switching magnet  12  are accelerated in the preaccelerator  13  to a first energy level. The preaccelerator  13  is a linear accelerator (LINAC), for example. The particles are fed into an accelerator  15  (e.g., a synchrotron or cyclotron). The particles are accelerated to high energies (e.g., as used for irradiation) in the accelerator  15 . After the particles leave the accelerator  15 , a high energy beam transportation system  17  guides the particle beam to one or several irradiation rooms  19 . In an irradiation room  19 , the accelerated particles are directed at a body to be irradiated. Depending on the embodiment, this takes place from a fixed direction (e.g., in “fixed beam” rooms) or from different directions by way of a moveable gantry, which may be rotated about an axis  22 . 
     The design shown in  FIG. 1  corresponds to a known particle therapy system  10 . A particle therapy system  10  of this type may be developed such that the present embodiments may be used. 
     The present embodiments may however also be used in other particle therapy systems than those shown here. Radiation therapy systems operating with x-rays may also be used, provided the x-ray beams are created such that further photons develop in the target object as a result of interaction. 
     The present embodiments are described in more detail with the aid of the following  FIGS. 2 to 4 . 
       FIG. 2  shows a schematic representation of the design of an irradiation room  19 , in which a particle beam may escape from a nozzle  23  and strike a target object  25  to be irradiated. 
     An imaging apparatus  27  is also arranged in the room. In the embodiment shown in  FIG. 2 , the imaging apparatus is a C-arm  29  with an x-ray detector  31  and an x-ray source  33 . The C-arm  29  may be moved by way of a robot arm  25  suspended from the ceiling. 
       FIG. 2  shows the imaging apparatus  27  in the imaging mode. In the imaging mode, the x-ray source  33  is activated, and an image of the interior of the target object  25  to be irradiated may be recorded. This may take place, for example, prior to an irradiation session for the precise positioning of the target object  25  or also during the irradiation for recording and monitoring the current position of the target object  25 . This is illustrated in  FIG. 2  with diagnostic x-rays  37 , which start from the x-ray source  33  and strike the x-ray detector  31 . An adjustment apparatus  39 , which may be moved in a controlled fashion upstream of the x-ray detector  31 , is located in a position not in the radiation path of the diagnostic x-rays  37 . 
       FIG. 2  illustrates a control apparatus  41  for controlling the imaging apparatus  27 . The components of the imaging apparatus  27  may be positioned and activated with the control apparatus.  FIG. 2  also illustrates an evaluation apparatus  43 , with which the measurement data generated by the imaging apparatus  27  may be evaluated and further processed. 
       FIG. 3  shows the imaging apparatus  27  in a therapy monitoring mode. A particle beam  45  is activated, and radioactive isotopes are produced inside the target object  25  by interaction with the particle beam  45 . The radioactive isotopes break up, and photons  47  are generated and emitted from the target object  25 . The control apparatus  41  controls the imaging apparatus  27  such that the x-ray detector  31  is read out without activating the x-ray source  33 . Information about the photons  47  produced in the target object  25  (e.g., spatial distribution and/or intensity of the photons  47 ) may be determined in this way. The evaluation apparatus  41  may at least partially reconstruct the deposited dose distribution  49  in the target object  25  from this determined information. 
     In the therapy mode, the adjustment apparatus  39  is arranged upstream of the x-ray detector  31 . A scatter grid or an absorber plate may be used, for example, as an adjustment apparatus  39 , so those photons that are not to be guided back for an interaction of the therapy beam  45  with the target beam  25  or strike the x-ray detector  31  from a “false” direction, may be filtered in an improved fashion. The therapy mode may be a single photon emission computed tomography (SPECT) recording mode. 
     By moving the imaging apparatus  27  during the irradiation and/or immediately after the irradiation, an improvement in the reconstruction of the recorded photons may be achieved, since photons  47  may be recorded from different directions. The movement is illustrated in  FIG. 3  by the double arrow. 
     The recording of the photons  47  produced in the target object enables, for example, a subsequent evaluation of the deposited dose  49 . The recording of the photons  47  may also be used online during an irradiation in order, for example, to halt an irradiation if a dose deposition is determined outside of a planned region. 
       FIG. 4  shows one embodiment of a radiation therapy apparatus with a first imaging apparatus  27  and a second imaging apparatus  51  configured similarly. Both imaging apparatuses  27 ,  51  may be used and operated in the manner described above with the aid of  FIG. 2  and  FIG. 3 . 
       FIG. 5  illustrates a flow chart of monitoring an irradiation of a target object. 
     At act  61 , a target object to be irradiated is positioned in an irradiation room for irradiation purposes, with an imaging mode of the imaging apparatus being activated. The imaging apparatus is used to produce an image of the inside of the target object, which is used when locating the correct position and during the positioning of the target object relative to the therapy beam (act  63 ). 
     The imaging apparatus is switched from the imaging mode into a therapy monitoring mode (act  65 ). The irradiation is started (act  67 ). During the irradiation, the imaging apparatus may be moved to different positions (act  69 ) in order to be able to record photons from more than one direction. Photons, which are produced in the target volume by interaction of the therapy beam with the target volume, are recorded with the x-ray detector (act  71 ) during the irradiation and immediately after the irradiation. 
     The recorded photons may be used to control the irradiation system. The recorded photons may however also be used to at least partially reconstruct the dose distribution deposited by the therapy beam (act  73 ). 
     While the present invention has been described above by reference to various embodiments, it should be understood that many changes and modifications can be made to the described embodiments. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description.