Abstract:
The invention relates to a radiotherapy system for directing a treatment beam onto an isocenter ( 14 ) in a patient ( 13 ), especially for tumor treatment in radiotherapy. Said radiotherapy system comprises a base ( 15 ) on which the patient ( 13 ) rests and a radiation device, more particularly, a linear accelerator ( 1 ) that generates a treatment beam ( 12 ). According to the invention, the direction of the treatment beam ( 12 ) can be regulated by means of a hexapod ( 3, 4, 5, 6, 7, 8, 9, 10 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is a continuation of and claims priority of International patent application Serial No. PCT/EP02/14163, filed Dec. 12, 2002 and published as WO 2003/053520 A2, the content of which is hereby incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a radiotherapy system. 
       BACKGROUND ART 
       [0003]    Known radiotherapy systems consist at least of one base on which the patient rests, namely the so-called patient&#39;s berth, and a radiation apparatus, in particular a so-called linear accelerator. The linear accelerator is usually fastened to a frame, the so-called gantry. The gantry is usually provided with a movable configuration, i.e. it is rotatable about the patient situated on the berth. The radiation field produced in the linear accelerator is focused in a focusing instrument, namely the so-called collimator, and optionally shaped, i.e. the shape of the radiation field is adjusted to the shape of the tumor, thus enabling a purposeful irradiation. 
         [0004]    One problem encountered in radiotherapy is to position the tumor and thus the patient relative to the radiation source in such way that the ray or the radiation field hits the tumor as precisely as possible and avoids adjacent tissue. Principally there are two possibilities which can also be combined. On the one hand, the radiation source can remain stationary and the patient and thus the tumor can be moved relative to the same. On the other hand, the patient can be fixed and the radiation source can be moved. In order to change the position of the patient, various systems are known which are all based on the fact that the patient who is fastened to the berth is moved in such a way that the position of the berth is adjusted. 
         [0005]    DE 197 28 788 describes a method for the positioning of patients relative to the treatment device. The patient&#39;s actual position is determined here by means of CCD cameras and image processing and morphing and compared with a previously determined desired position. Thereupon the servomotors of the berth are triggered which bring the patient back to the set position. This triggering is performed in the second or tenths of second cycle in order to also allow responding to the breathing action of the patient. 
         [0006]    A method is further known from DE 198 05 917 with which the position of patients can be recognized during radiotherapy and the patient can be positioned accordingly. For this purpose the surface structure of the patient&#39;s body is detected with at least two sensors and compared with a set image, as a result of which deviations of the current position of the patient from the desired position can be recognized. Thereupon it is possible to optionally perform a correction of the positional deviation. 
         [0007]    In the adjustment of the radiation source it is also known that the same can occur by rotation of the gantry. U.S. Pat. No. 6,052,436 further shows an apparatus for radiotherapy in which two guide rails are fixed over the patient on which a linear accelerator with attached collimator can be moved. As a result of slots in the guide rails, the plates of the collimator are moved in such a way that the radiation window changes following the motion of the linear accelerator, such that the shape of the radiation window is adjusted to the shape of the tumor. 
         [0008]    Despite the known solutions, the problem remains that the positioning of the patient or, in other words, the isocenter of the tumor relative to the radiation source is still relatively imprecise. Moreover, the known radiation systems come with the disadvantage that the radiation source is adjustable only within limits relative to the patient, as a result of which the irradiation from unusual angles is made more difficult or complex apparatuses are necessary. 
       SUMMARY OF THE INVENTION 
       [0009]    It is the object of the present invention to provide a radiation therapy system which avoids the aforementioned disadvantages. A system is to be provided with which the radiation source can be set relative to the patient in the quickest and most precise manner in order to achieve an optimal treatment of the tumor. 
         [0010]    This object is achieved by a radiotherapy system pursuant to claim  1 . Advantageous embodiments are the subject matter of the subclaims. 
         [0011]    The radiation therapy system in accordance with the invention consists at least of a base on which the patient rests and a radiation apparatus, especially a linear accelerator, which generates a treatment beam. The term “treatment beam” shall designate all types of radiation produced by the linear accelerator, i.e. both photon as well as electron rays. Moreover, the term shall not only comprise point-like ray beams, but also so-called radiation fields. 
         [0012]    It is provided for according to the invention that the base on which the patient rests is adjustable by means of at least one hexapod. The term “hexapod” designates an apparatus which works according to the so-called Stewart principle (D. Stewart, “A Platform With Six Degrees of Freedom”), UK Institution of Mechanical Engineers Proceedings, 1965-66, Vol. 180, Pt 1, No 15). A hexapod comprises six struts or stays, especially hydraulic cylinders or electric spindles, which each extend between an upper and a lower platform. One of the two platforms is fixed or stationary, whereas the other is moved by change in the length of the struts, stays or spindles. The hexapod allows a combined translational and rotary movement along or about the six coordinates (X, Y, Z, theta-X, theta-Y, theta-Z). As a result, a hexapod has six degrees of freedom. 
         [0013]    The use of a hexapod for adjusting the base on which the patient rests therefore allows its rapid and precise alignment. This means in practical operation that by rotating the gantry there is a rough alignment and the fine adjustment can then occur especially by means of the hexapod, such that the treatment beam is aligned with the assistance of the hexapod. This allows an especially rapid and precise adjustment. The use of the hexapod for adjusting the base on which the patient rests further allows that there is low need for space in comparison with other adjusting possibilities (such as so-called compound tables). The hexapod further has a relatively small overall size. 
         [0014]    It is preferably provided that at least one sensor is provided on the hexapod and/or the linear accelerator and/or the collimator with which the position of the patient can be detected. 
         [0015]    Preferably, two sensors are provided. It can also be provided that only one sensor is provided on the hexapod or linear accelerator or collimator and the other at any other desirable point in the treatment room. This ensures a precise determination of the position of the patient because at least two images are provided and can be compared with each other. 
         [0016]    An especially preferable embodiment of the invention provides that the hexapod can be controlled in such a way that the treatment beam can be guided according to the shape of the tumor. Such a control can provide for example that by means of methods which produce a three-dimensional picture such as computer tomography (CT), it is possible to detect the shape of the tumor and the position of the tumor in the patient. On the basis of such data, the treatment beam is thus aligned and moved by means of the hexapod and the beam guide elements as set by the same that the treatment beam follows the shape of the tumor. It is ensured in this way that the tumor is irradiated fully and it is prevented at the same time that adjacent tissue is affected by the irradiation. Moreover, the guidance of the treatment beam along the shape of the tumor ensures that it is possible to work with the lowest possible dose because any factors of uncertainty concerning the tumor size for example can be excluded and its purposeful irradiation is ensured. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The invention is explained and described in closer detail by reference to the enclosed drawing, wherein: 
           [0018]      FIG. 1  shows a radiotherapy system in accordance with the invention in a schematic representation. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0019]    As is shown in the (only)  FIG. 1 , the radiotherapy system in accordance with the invention comprises a linear accelerator  1 . The linear accelerator  1  can assume any desirable shape. It can be arranged as a device standing on the floor, but also as a device mounted on the ceiling. The linear accelerator  1  will usually be fastened to a frame, the so-called gantry. The radiation required for the treatment will be produced in the known manner in the linear accelerator. The treatment beam  12 , which is indicated by a respective arrow, thus passes the head  2  of the linear accelerator  1  and a collimator  11 . Instead of the collimator  11  it is possible to provide any other desirable focusing or beam guide element, depending on the desired application. 
         [0020]    It is provided for in accordance with the invention that a hexapod is provided beneath the base  15  on which the patient rests. The hexapod comprises two platforms  3  and  10 , with the platform  3  being fastened to a secure fixing, and the movable platform  10  is fastened to the base  15 . 
         [0021]    It is preferably provided that the platform  3  is fixedly connected, and thus forms the platform of the hexapod which is fixed in its position. Platform  10  is adjustable by changing the length of the struts  4 ,  5 ,  6 ,  7 ,  8  and  9 , with the term “struts” also relating to similarly acting stays or spindles or general translational drives. The struts  4 ,  5 ,  6 ,  7 ,  8  and/or  9  are longitudinally adjustable along their longitudinal axis, as is indicated by arrow  18 . By changing the length of at least one strut  4 ,  5 ,  6 ,  7 ,  8  and/or  9  the adjustable platform  10  is thus changed in its position and thus the base  15  is co-moved accordingly. This again changes the irradiation angle of the treatment beam  12  relative to the patient. The treatment beam  12  can thus be aligned in such a way that as precisely as possible it meets the isocenter  14  in the patient who is strapped to the base  15 . Such an isocenter  14  is understood as being a tumor for example which is to be treated by means of radiotherapy. 
         [0022]    Preferably, a sensor system is provided with which the position of patient  13  can be fixed to the base  15 . Sensors  20  and  21  can be provided, for example. Scanning systems can be used as sensors  20  and  21  which continuously scan the body and thus the position of patient  13  or which scan the surface shape of patient  13 . The sensors  20  and  21  are oriented towards the patient  13 , as is indicated by the dot-dash lines  22  and  23 . The sensors  20  and  21  are thus used to detect the position of patient  13  on the base  15  and thus to check continually whether the isocenter  14  and the treatment beam  12  are aligned optimally with respect to each other, meaning whether the treatment beam  12  meets the isocenter  14  precisely. If deviations are determined then it is aforementioned hexapod is controlled in such a way that the treatment beam  12  is readjusted and the same meets the isocenter  14  again precisely. 
         [0023]    As an alternative it could also be provided that in the case of a deviation from the actual position of patient  13  from the scheduled position, the radiation system is cut off in order to prevent any damage to ambient tissue.  FIG. 1  schematically shows a control unit  30  which is connected with the hexapod via the one signal output  31  each. The control unit  30  can further comprise different inputs, e.g. the inputs  32  and  33  of sensors  20  and  21 . Moreover, the control unit  30  can also comprise signal inputs of imaging devices such as a CT. It is provided that the control unit  30  triggers each strut  4 ,  5 ,  6 ,  7 ,  8 ,  9  of the hexapod permanently and separately in order to achieve the most precise possible alignment of the treatment beam  12  in all six degrees of freedom. 
         [0024]    Thus, the base  15  on which the patient  13  rests is provided with an adjustable configuration. This adjustability is achieved in such a way that a hexapod is provided with which the base  15  can be adjusted. The provision of a hexapod for changing the position of the base  15  offers the advantage that the hexapod ensures an adjustability in six degrees of freedom. The base  15  and thus the patient  13  can be brought into any position in a continuous manner and with low need for space. Moreover, a hexapod ensures a highly precise and rapid adjustability of the base  15 .