Abstract:
A therapeutic apparatus ( 500, 600 ) comprising a radiotherapy apparatus ( 502 ) for treating a target zone ( 318, 536 ) and a magnetic resonance imaging system ( 510, 532, 44, 602 ) for acquiring magnetic resonance imaging data ( 624 ). The radiotherapy apparatus comprises a radiotherapy source ( 300, 302, 304, 504 ) for directing electromagnetic radiation ( 310, 312, 314, 508 ) into the target zone. The radiotherapy apparatus is adapted for rotating the radiotherapy source at least partially around the magnetic resonance magnet. The magnetic resonance imaging system further comprises a radio-frequency transceiver ( 532 ) adapted for simultaneously acquiring the magnetic resonance data from at least two transmit-and-receive channels ( 528, 530 ). The therapeutic apparatus further comprises a processor ( 614 ) and a memory ( 620 ) containing machine executable instructions ( 636, 638, 640, 642, 644 ) for the processor. Execution of the instructions causes the processor to: calibrate ( 100, 200 ) the transmit-and-receive channels; acquire ( 102, 202 ) the magnetic resonance data; reconstruct ( 104, 204 ) a magnetic resonance image ( 626 ); register ( 106, 206 ) a location ( 628 ) of the target zone in the image; and generate ( 108, 208 ) radiotherapy control signals ( 630 ) using the registered image.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to apparatuses for treating a target zone of a subject with radiotherapy, in particular the invention relates to radiotherapy apparatuses guided by magnetic resonance imaging. 
       BACKGROUND OF THE INVENTION 
       [0002]    In routine practice of Radiotherapy (RT), the subject is positioned relative to the stationary center of the rotating arc carrying the RT source. Positioning implies both height and lateral adjustment of the subject table. This positioning is required to optimize the dose in the lesion beyond variation that can be obtained by applying RT rays from different angles. 
         [0003]    Integration of MR and Linear Accelerators (LINAC) opens new horizons in Radiotherapy by improved lesion targeting, especially for moving organs. In a practical implementation proposal, the LINAC rotates around the subject to hit the gross target volume (GTV) and clinical target volume (CTV) from multiple angles while minimizing the radiation exposure for surrounding tissues. 
         [0004]    The combination of magnetic resonance apparatuses and LINAC radiotherapy sources is known. Typically a LINAC source is placed on a rotating gantry about the magnet and designing the magnet such that the LINAC rotates in a zero-field region of the magnet. Another particular feature of the concept is the use of a split gradient coil which prevents attenuation of the LINAC beam. 
         [0005]    U.S. Pat. No. 6,198,957 discloses a radiotherapy machine for beam treating a region of a subject combined with a magnetic resonance imaging system. The beam and the excitation coil assembly of the imaging system are arranged so that the beam is not incident on the coil assembly. 
         [0006]    While performing radiotherapy the radiotherapy source is typically moved to a variety of positions while irradiating a target zone. This is done to minimize the exposure portions of a subject which do not include the target zone to the effects of the radiation. Typically, this is done by rotating the radiotherapy source about an axis of rotation. 
       SUMMARY OF THE INVENTION 
       [0007]    The invention provides for a therapeutic apparatus, a computer program product, and a method of controlling a therapeutic apparatus in the independent claims. Embodiments are given in the dependent claims. 
         [0008]    A difficulty encountered in guiding radiotherapy treatments using magnetic resonance (MR) imaging is the limited space in magnets that are useful for clinical imaging, such as cylindrical superconducting magnets. For such magnets there is simply is not sufficient space in a magnet to position the target zone along the rotational axis of the radiotherapy source. 
         [0009]    Some embodiments of the invention address this problem by eliminating the use of a volume body coil from the magnetic resonance imaging system. The volume body coil is replaced by a least two transmit-and-receive-coils. This may have the advantage that the space normally used by a volume body coil is available for moving the subject within the magnet. This may allow more positioning of the subject such that a target zone is located at a rotational axis of a radiotherapy source. 
         [0010]    The invention disclosure describes a novel MRI guided Radiotherapy system that is compatible with state-of-the-art subject handling systems that are currently used with Linear Accelerator (LINAC) therapy systems. The following aspects of the system may enable free positioning of the subject with respect to the LINAC focal point and the acquisition of MRI data without the use of an in-built body coil in a manner that is compatible with the use of a state-of-the-art carbon fiber table top while avoiding physical interference of RF coils with the therapy beam. Embodiments of the inventions described herein may represent improvements upon the existing MR-LINAC system concept which utilizes a LINAC apparatus rotating about a common iso-center within a zero-field region of an MRI magnet. The key features may be:
       1) No built in body coil frees up space within the system bore that enable free 6 dimensional movement of the subject required for positioning target anatomies at the center of rotation of the LINAC beam as required for optimum therapeutic efficacy.   2) The magnet and gradient coil are designed to realize a ≧80 cm free bore in which the subject can be freely positioned. For an 80 cm bore inside the gradient coil it is expected that a 96 cm inner diameter magnet will suffice.   3) In place of the built in RF body coil, local transmit/receive RF coils or a split multi-element Tx/Rx array are used such that the subject can be surrounded by the elements while maintaining a suitable gap which avoids beam interference. Since the local coil arrays are placed on the table top, as opposed to surrounding it, the method is fully compatible with a carbon fiber table top. Since the coils are directly on the subject they are free to move with the subject and more efficient with respect to RF power demand.   4) The multi-element Tx/Rx array coils are used in transmit mode for MR excitation. By the use of RF shimming it is possible to focus the excitation at the target anatomy and also to focus the reception sensitivity of the coil to the same target anatomy thereby maximizing SNR.   5) Due to the extra large MR system bore it is possible to utilize existing LINAC subject positioning methods which enable 6 dimensional placement of the subject with target anatomy at system iso-center, as desired for optimum therapeutic efficacy.   6) To maximize the efficiency of the LINAC beam it is also proposed to optionally introduce an external recess in the magnet in order that the LINAC beam can be placed closer to the subject.       
 
         [0017]    A ‘computer-readable storage medium’ as used herein encompasses any tangible storage medium which may store instructions which are executable by a processor of a computing device. The computer-readable storage medium may be referred to as a ‘computer-readable non-transitory storage medium.’ The computer-readable storage medium may also be referred to as a ‘tangible computer readable medium.’ In some embodiments, a computer-readable storage medium may also be able to store data which is able to be accessed by the processor of the computing device. Examples of computer-readable storage media include, but are not limited to: a floppy disk, a magnetic hard disk drive, a solid state hard disk, flash memory, a USB thumb drive, Random Access Memory (RAM) memory, Read Only Memory (ROM) memory, an optical disk, a magneto-optical disk, and the register file of the processor. Examples of optical disks include Compact Disks (CD) and Digital Versatile Disks (DVD), for example CD-ROM, CD-RW, CD-R, DVD-ROM, DVD-RW, or DVD-R disks. The term computer readable-storage medium also refers to various types of recording media capable of being accessed by the computer device via a network or communication link. For example a data may be retrieved over a modem, over the internet, or over a local area network. 
         [0018]    ‘Computer memory’ or ‘memory’ is an example of a computer-readable storage medium. Computer memory is any memory which is directly accessible to a processor. Examples of computer memory include, but are not limited to: RAM memory, registers, and register files. 
         [0019]    ‘Computer storage’ or ‘storage’ is an example of a computer-readable storage medium. Computer storage is any non-volatile computer-readable storage medium. Examples of computer storage include, but are not limited to: a hard disk drive, a USB thumb drive, a floppy drive, a smart card, a DVD, a CD-ROM, and a solid state hard drive. In some embodiments computer storage may also be computer memory or vice versa. 
         [0020]    A ‘computing device’ or ‘computer system’ as used herein refers to any device comprising a processor. A ‘processor’ is an electronic component which is able to execute a program or machine executable instruction. References to the computing device comprising “a processor” should be interpreted as possibly containing more than one processor. The term computing device should also be interpreted to possibly refer to a collection or network of computing devices each comprising a processor. Many programs have their instructions performed by multiple processors that may be within the same computing device or which may even distributed across multiple computing device. 
         [0021]    A ‘user interface’ as used herein encompasses an interface which allows a user or operator to interact with a computer or computer system. A user interface may provide information or data to the operator and/or receive information or data from the operator. The display of data or information on a display or a graphical user interface is an example of providing information to an operator. The receiving of data through a keyboard, mouse, trackball, touchpad, pointing stick, graphics tablet, joystick, gamepad, webcam, headset, gear sticks, steering wheel, pedals, wired glove, dance pad, remote control, and accelerometer are all examples of receiving information or data from an operator. 
         [0022]    Magnetic Resonance (MR) data is defined herein as being the recorded measurements of radio frequency signals emitted by atomic spins by the antenna of a Magnetic resonance apparatus during a magnetic resonance imaging scan. A Magnetic Resonance Imaging (MRI) image is defined herein as being the reconstructed two or three dimensional visualization of anatomic data contained within the magnetic resonance data. This visualization can be performed using a computer. 
         [0023]    A ‘volume body coil’ or ‘body coil’ as used herein encompasses a radiofrequency antenna used to excite or manipulate the orientation of magnetic spins as preparation for the acquisition of magnetic resonance data. 
         [0024]    A ‘transmit-and-receive channel’ as used herein encompasses an antenna which is used to both excite or manipulate the orientation of magnetic spins as preparation for the acquisition of magnetic resonance data and for the acquisition of magnetic resonance data. 
         [0025]    In one aspect the invention provides for a therapeutic apparatus comprising a radiotherapy apparatus for treating a target zone of a subject. The radiotherapy apparatus comprises a radiotherapy source for directing electromagnetic radiation into the target zone. The electromagnetic radiation may be high energy photons generated for example but not limited to: an x-ray source, a LINAC x-ray source, and a radioisotope gamma radiation source. A radioisotope gamma radiation source as used herein encompasses a radiation source for generating gamma radiation that uses a radioisotope. 
         [0026]    The therapeutic apparatus further comprises a magnetic resonance imaging system for acquiring magnetic resonance imaging data from an imaging zone. The target zone is within the imaging zone. The magnetic resonance imaging system comprises a magnet for generating a magnetic field within the imaging zone. The radiotherapy apparatus is adapted for rotating the radiotherapy source at least partially around the magnet. The magnetic resonance imaging system further comprises a radio-frequency transceiver adapted for simultaneously acquiring the magnetic resonance data from at least two transmit-and-receive channels. As used herein a channel refers to an antenna. The channels may comprise multiple coils or antenna elements. 
         [0027]    The therapeutic apparatus further comprises a processor for controlling the therapeutic apparatus. A processor as used herein encompasses a computer system with one or more processors and it may also encompass computer systems with multiple processors. The therapeutic apparatus further comprises a memory containing machine executable instructions for execution by the processor. 
         [0028]    Execution of the instructions causes the processor to perform a pre-scan calibration of the at least two transmit-and-receive channels using the magnetic resonance imaging system. During the pre-scan calibration magnetic resonance data is acquired for each of the at least two transmit-and-receive channels. The individual transmit-and-receive channels could for example be placed on the subject in different positions. They may be placed such that the radiotherapy apparatus does not direct the electromagnetic radiation into the transmit-and-receive channels. By performing a pre-scan calibration of the at least two transmit-and-receive channels their placement is not critical. The pre-scan calibration may be used for determining the phases and amplitudes for transmitting and receiving radio signals from magnetic spins in the imaging zone. 
         [0029]    Execution of the instructions further causes the processor to acquire the magnetic resonance data in accordance with the pre-scan calibration using the at least two transmit-and-receive channels. This may include the phase and amplitudes of individual coil elements of each of the transmit-and-receive channels and also the phase and amplitude corrections for received radio signals by each coil or element of the at least two transmit-and-receive channels. Execution of the instructions further causes the processor to reconstruct a magnetic resonance image from the magnetic resonance data. It is understood herein that a magnetic resonance image may refer to multiple magnetic resonance images. For instance the magnetic resonance data may be acquired primarily from a particular volume. A series of magnetic resonance images may be constructed to represent the volume from which the magnetic resonance data is primarily acquired. The magnetic resonance image is typically reconstructed using Fourier techniques. For this reason volumes outside of the image may also contribute to the magnetic resonance image due to the Fourier techniques. 
         [0030]    Execution of the instructions further causes the processor to generate radiotherapy control signals in accordance with the location of the target zone. The radiotherapy control signals cause the radiotherapy source to irradiate the target zone. The radiotherapy control signals may also cause the radiotherapy source to be positioned by the radiotherapy apparatus. The radiotherapy apparatus may for instance contain a ring or other positioning mechanisms or elements for physically moving the radiotherapy source. In this case the radiotherapy control signals control both whether the radiotherapy source is generating radiation and the position of the radiotherapy source. 
         [0031]    Execution of the instructions further cause the processor to send the radiotherapy control signals to the radiotherapy system. Sending the radiotherapy control signals may be performed in different ways depending upon the embodiment. For instance the processor may send control signals to a separate controller or a computer which controls the radiotherapy apparatus. In other embodiments a hardware interface is used such that the processor controls and sends control signals to the radiotherapy system directly. 
         [0032]    In another embodiment the radiotherapy apparatus contains a rotation mechanism for rotating the radiotherapy source around a rotational axis. In another embodiment the radiotherapy source directs the radiation through the rotational axis. In another embodiment the magnetic resonance imaging system has an axis. In another embodiment the rotational axis of the radiotherapy apparatus and the axis of the magnet of the magnetic resonance imaging system are coaxial. 
         [0033]    In another embodiment the therapeutic apparatus further comprises a subject support. The subject support comprises a mechanical positioning system for positioning the subject within the magnet. In different embodiments the subject support is capable of moving with a varying number of degrees of freedom. In some embodiments a mechanical positioning system has six degrees of freedom. The support may move in three spatial directions and also be able to rotate about an axis for each of those directions. This embodiment allows the free placement of a subject such that the target zone is treated optimally. 
         [0034]    In another embodiment the radiotherapy source rotates about an axis of rotation. Execution of the instructions further causes the processor to generate positioning control signals that cause the mechanical positioning system to move the target zone to the axis of rotation. The positioning control signals are generated in accordance with the location of the target zone in the registered magnetic resonance image. Execution of the instructions further cause the processor to send the positioning control signals to the mechanical positioning system. This embodiment is advantageous because if the radiotherapy source rotates about an axis of rotation and the target zone is placed in the axis of rotation then the radiotherapy source will always be in a position to irradiate the target zone. This may minimize the amount of electromagnetic radiation which is directed into regions of the subject which are not part of the target zone. 
         [0035]    In another embodiment the radiotherapy source directs electromagnetic radiation through the rotational axis. 
         [0036]    In another embodiment the therapeutic apparatus comprises the at least two transmit-and-receive channels. The at least two transmit-and-receive channels are part of the therapeutic apparatus in this embodiment. 
         [0037]    In another embodiment each of the transmit-and-receive channels has multiple coil elements. Execution of the instructions further causes the processor to calibrate the send amplitudes and phases and the receive amplitudes and phases for the multiple coil elements during the pre-scan calibration. This may be performed by acquiring magnetic resonance data which each coil element for each of the transmit-and-receive channels and then performing a fitting procedure to determine the best amplitudes and phases to use for both sending signals and receiving signals using the transmit-and-receive channels. 
         [0038]    In another embodiment the at least two transmit-and-receive channels comprise flexible coil elements. This embodiment is particularly advantageous because the transmit-and-receive channels can then be placed directly on the subject. As they may then conform to the outer shape of the subject, the at least two transmit-and-receive channels will occupy less space. This allows more room in the magnet and allows for more freedom in controlling the positioning of the subject, for instance if the therapeutic apparatus comprises a subject support then the subject support will have more space in which to move the subject. 
         [0039]    In another embodiment execution of the instructions further causes the processor to repeatedly acquire the magnetic resonance data, repeatedly reconstruct the magnetic resonance image, and repeatedly register the location of the target zone during irradiation of the target zone. Execution of the instructions further cause the processor to repeatedly generate and send repeatedly updated radiotherapy control signals. The updated radiotherapy control signals compensate for motion of the subject between subsequent acquisitions of the magnetic resonance data. Execution of the instructions further causes the processor to repeatedly send the updated radiotherapy control signals to the radiotherapy source during irradiation of the target zone. In some embodiments the positioning control signals may also be repeatedly generated and repeatedly sent to the mechanical positioning system. 
         [0040]    Repeatedly acquiring the magnetic resonance data and then compensating for motion of the subject either internal or external may be beneficial because the target zone is irradiated more accurately and there is a reduced chance that portions of the subject which are not part of the target zone are irradiated by mistake. 
         [0041]    In another embodiment the radiotherapy source comprises an adjustable beam collimator. The adjustable beam collimator may for instance be a multi leaf collimator. The updated radiotherapy control signals comprise commands for controlling the beam collimator. For instance the beam collimator may move a series of plates or other material which attenuates the magnetic radiation generated by the radiotherapy source. By adjusting the plates the magnetic radiation beam directed at the target signal may be controlled. This is advantageous because the path of the beam may be controlled without moving the radiotherapy source rotationally or in some embodiments moving the mechanical positioning system. 
         [0042]    In another embodiment a radio-frequency excitation field manipulating the orientation of the magnetic spins in an imaging zone is generated exclusively by the at least two transmit-and-receive channels. This embodiment may be particularly advantageous because a radio-frequency volume body coil is not used for creating the radio-frequency excitation field. This provides more space within the imaging zone of the magnet for moving the subject. 
         [0043]    In another embodiment the magnetic resonance imaging system does not comprise a radio-frequency volume body coil. 
         [0044]    In another embodiment the magnet is a cylindrical superconducting magnet. The magnet has a recess in an outer wall. The radiotherapy apparatus is adapted for rotating the radiotherapy source around or about the recess. At least a portion of the radiotherapy source is within the recess. This embodiment is advantageous because the radiotherapy source is positioned closer to the subject. This may have the benefit of positioning the radiotherapy source within a low magnet field zone of the magnet. It may also have the advantage that a less accurate adjustable beam collimator is needed for accurately controlling the electromagnetic radiation directed into the target zone. This may reduce the cost of the therapeutic apparatus. 
         [0045]    In another embodiment the radiotherapy apparatus comprises a light source for illuminating a portion of the subject that is descriptive of the path of radiation generated by the radiotherapy source. This embodiment is advantageous because an operator or healthcare provider positioning a subject in the therapeutic apparatus can see if anything will block the path of the electromagnetic radiation generated by the radiotherapy source. For instance the at least two transmit-and-receive channels can be positioned on the subject and then checked with the light source to see if the radiation beam will hit the receive channels. If the light does contact the receive channels then the at least two transmit-and-receive channels can be repositioned. 
         [0046]    In another embodiment the radiotherapy source is a LINAC x-ray source. In another embodiment the radiotherapy source is an x-ray tube. In another embodiment the radiotherapy source is a radioisotope gamma radiation source. 
         [0047]    In another embodiment the radiotherapy source is a LINAC for generating x-ray or gamma radiation. The magnet is adapted for generating a low magnetic field zone which encircles the magnet. The radiotherapy apparatus is adapted such that the radiotherapy source rotates about the magnet within the low magnetic field zone. The magnetic field strength within the low magnetic field zone is below an operational threshold of the LINAC source. The operational threshold defines a magnetic field strength which prevents the LINAC source from functioning properly. In modern cylindrical bore magnetic resonance imaging magnets there are typically several compensation coils. The compensation coils generate a magnetic field which is opposed to coils used to generate the main magnetic field. This results in an area outside of the cylindrical magnet approximately in the mid-plane which is doughnut-shaped and has a low magnetic field. The low magnetic field zone may be this doughnut-shaped zone surrounding the cylindrical magnet with compensation coils. 
         [0048]    In another embodiment the operational threshold is below 50 gauss, preferably below 10 gauss. 
         [0049]    In another aspect the invention provides for a computer program product comprising machine executable instructions for execution by a processor of a radiotherapy apparatus. For instance the computer program product may be stored on a computer-readable storage medium. The therapeutic apparatus comprises a radiotherapy apparatus for treating a target zone of a subject. The radiotherapy apparatus comprises a radiotherapy source for directing electromagnetic radiation into the target zone. 
         [0050]    The therapeutic apparatus further comprises a magnetic resonance imaging system for acquiring magnetic resonance imaging data from an imaging zone. The target zone is within the imaging zone. The magnetic resonance imaging zone comprises a magnet for generating a magnetic field within the imaging zone. The radiotherapy apparatus is adapted for rotating the radiotherapy source at least partially around the magnet. The magnetic resonance imaging system further comprises a radio-frequency transceiver adapted for simultaneously acquiring the magnetic resonance data from at least two transmit-and-receive channels. Execution of the instructions causes the processor to perform a pre-scan calibration of the at least two transmit-and-receive channels using the magnetic resonance imaging system. 
         [0051]    Execution of the instructions further causes the processor to acquire the magnetic resonance data in accordance with the pre-scan calibration using the at least two transmit-and-receive channels. Execution of the instructions further causes the processor to reconstruct a magnetic resonance image from the magnetic resonance data. Execution of the instructions further causes the processor to register a location of the target zone in the magnetic resonance image. Execution of the instructions further causes the processor to generate radiotherapy control signals in accordance with the location of the target zone. The radiotherapy control signals cause the radiotherapy source to irradiate the target zone. Execution of the instructions further causes the processor to send the radiotherapy control signals to the radiotherapy system. 
         [0052]    The invention also provides for a computer-readable storage medium containing a computer program product according to an embodiment of the invention. 
         [0053]    The invention also provides for a method of controlling a therapeutic apparatus. The method and embodiments of the method herein may also be implemented as a computer-implemented method. The therapeutic apparatus comprises a radiotherapy apparatus for treating a target zone of a subject. The radiotherapy apparatus comprises a radiotherapy source for directing electromagnetic radiation into the target zone. 
         [0054]    The therapeutic apparatus further comprises a magnetic resonance imaging system for acquiring magnetic resonance imaging data from an imaging zone. The target zone is within the imaging zone. The magnetic resonance imaging system comprises a magnet for generating a magnetic field within the imaging zone. The radiotherapy apparatus is adapted for rotating the radiotherapy source at least partially around the magnet. The magnetic resonance imaging system further comprises a radio-frequency transceiver adapted for simultaneously acquiring the magnetic resonance data from at least two transmit-and-receive channels. 
         [0055]    The method comprises the step of performing a pre-scan calibration of the at least two transmit-and-receive channels using the magnetic resonance imaging system. The method further comprises the step of acquiring the magnetic resonance data in accordance with the pre-scan calibration using the at least two transmit-and-receive channels. The method further comprises the step of reconstructing a magnetic resonance image from the magnetic resonance data. The method further comprises the step of registering a location of the target zone in the magnetic resonance image. The method further comprises the step of generating radiotherapy control signals in accordance with the location of the target zone. The radiotherapy control signals cause the radiotherapy source to irradiate the target zone. The method further comprises the step of sending the radiotherapy control signals to the radiotherapy system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0056]    In the following preferred embodiments of the invention will be described, by way of example only, and with reference to the drawings in which: 
           [0057]      FIG. 1  shows a flow diagram which illustrates a method according to an embodiment of the invention; 
           [0058]      FIG. 2  shows a flow diagram which illustrates a method according to a further embodiment of the invention; 
           [0059]      FIG. 3  shows a diagraph which illustrates the positioning of a radiotherapy source relative to a target zone of a subject; 
           [0060]      FIG. 4  shows a diagraph which further illustrates the positioning of a radiotherapy source relative to a target zone of a subject; 
           [0061]      FIG. 5  shows a diagraph which further illustrates the positioning of a radiotherapy source relative to a target zone of a subject; 
           [0062]      FIG. 6  shows a diagram which illustrates a therapeutic apparatus according to an embodiment of the invention; and 
           [0063]      FIG. 7  shows a diagram which illustrates a therapeutic apparatus according to a further embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0064]    Like numbered elements in these figures are either equivalent elements or perform the same function. Elements which have been discussed previously will not necessarily be discussed in later figures if the function is equivalent. 
         [0065]      FIG. 1  shows a full flow diagram which illustrates an embodiment of a method according to the invention. In step  100  a pre-scan calibration of the at least two transmit-and-receive channels is performed. In step  102  magnetic resonance data is acquired. The magnetic resonance data is acquired using a calibration that was determined in step  100 . Next in step  104  a magnetic resonance image is reconstructed from the magnetic resonance data. The magnetic resonance image may be one or a collection of magnetic resonance images. In step  106  the location of the target zone is registered in the magnetic resonance image. In step  108  radiotherapy control signals are generated. In step  110  the radiotherapy control signals are sent to the radiotherapy system. Sending the radiotherapy control signals to the radiotherapy system causes the radiotherapy system to perform a therapeutic operation on the subject. 
         [0066]      FIG. 2  shows a flow diagram which illustrates a method according to a further embodiment of the invention. In step  100  a pre-scan calibration is performed for the at least two transmit-and-receive channels. In step  2  magnetic resonance data is acquired. In step  204  a magnetic resonance image is reconstructed from the magnetic resonance data. In step  206  a location of the target zone in the magnetic resonance image is registered. Step  206  is equivalent to step  106  in  FIG. 1 . The registration may be performed by any number of known registration techniques. For instance a deformable model may be fit to one or more magnetic resonance images. Also specialized algorithms which detect anatomical features in the magnetic resonance may be used also. The located anatomical features or the deformable model may be used to fine the location of the target zone. In step  208  radiotherapy control signals are generated. In step  210  positioning control signals are generated. 
         [0067]    The radiotherapy control signals and the positioning control signals are generated in conjunction with each other. As both sets of control signals are needed to position the target zone such that the radiotherapy source is able to irradiate it. Next in step  212  the radiotherapy control signals are sent to the radiotherapy system. In step  214  positioning control signals are sent to the mechanical positioning system. In this flow diagram there is an arrow that looks back from step  214  to step  202 . This indicates that during process of the target zone magnetic resonance data may be repeatedly acquired and used to repeatedly generate radiotherapy control signals and positioning control signals. This may be repeated repeatedly until the therapy ends in step  216 . 
         [0068]      FIG. 3  shows a cross-sectional view of some components of a therapeutic apparatus. Shown are a radiotherapy source in a first position  300 , a second position  302 , and a third position  304 . The dashed line labeled  306  shows the path of rotation of the radiotherapy source  300 ,  302 ,  304 . The point labeled  308  indicates the axis of rotation  308 . The region labeled  310  is the radiation beam generated by the radiotherapy source in the first position  300 . The region labeled  312  shows the path of the radiation beam generated by the radiotherapy source in the second position  302 . The region labeled  314  shows a path of the radiation beam when the radiotherapy source in the third position  304 . Sitting in the center of the diagram is a subject  316  with a target zone  318  that is off axis with regard to the axis of rotation  308 . The lines  320  indicate the angular range of the radiotherapy source  302  where the radiotherapy source  302  will be able to irradiate the target zone  318  with radiation. 
         [0069]    In this Fig. it is quite clear that the treatment options are very limited. In addition regions of the subject  316  which are not for the target zone  318  will be irradiated also. If for instance the radiation beam is used to kill a cancer located in the target zone  318  it is very likely that a large amount of healthy tissue surrounding the target zone  318  would also be killed or damaged. If the subject  316  is within a magnetic resonance imaging system without much clearance then it is clear that it will not be feasible to have the target zone  318  located at the axis of rotation  308 . 
         [0070]      FIG. 4  shows a diagram which is identical to  FIG. 3  except the subject  316  has been moved such that the target zone  318  is now located at the axis of rotation  308 . In examining this Fig. it is clear that the target zone  308  will be treated regardless of what position the radiotherapy source  300 ,  302 ,  304  is in.  FIG. 4  illustrates the benefit of being able to move a subject within a magnetic resonance imaging system for positioning the target zone  318  on the axis of rotation  308 . 
         [0071]      FIG. 5  shows an embodiment of a therapeutic apparatus  500  according to an embodiment of the invention. In  FIG. 5  there is a radiotherapy apparatus  502 . Within the radiotherapy apparatus  502  is a radiotherapy source  504 . Below the radiotherapy source  504  is an adjustable beam collimator  506 . The radiotherapy source  504  generates a radiation beam  508 . The therapeutic apparatus  500  also comprises a magnetic resonance imaging system. The radiotherapy apparatus  502  forms a ring around a magnet  510  of the magnetic resonance imaging system. The magnet is a superconducting magnet with a cryostat  512 . There are superconducting coils  514  for generating a magnetic field for the magnet. There are superconducting shield coils  516  which generate a low magnetic field region  518 . The radiotherapy source  504  is shown as being located within the low field region  518 . The low field region  518  forms a doughnut surrounding the cylindrical magnet  510 . 
         [0072]    The magnet  510  is shown as resting on the floor  520 . Adjacent to the magnet  520  is a six-dimensional positioning system  522  for a subject support  524 . A subject  526  is shown as reposing on the subject support  524 . On either side of the radiation beam  508  is shown a first transmit-and-receive channel  528  and a second transmit-and-receive channel  530 . Both the first  528 , and second transmit-and-receive channels are connected to a transceiver  532 . The transceiver in this embodiment is shown as two separate transceivers  532  but may also be a single unit which both channels  528 ,  530  are connected to. Between the first  528  and second  530  transmit-and-receive channels is imaging zone  534 . The target zone  536  of the subject  526  is shown as being located within the imaging zone  534 . The space within the magnet  510  for receiving the subject  526  is the bore  538  of the magnet. The rotational axis  542  is also the axis of symmetry for the magnet  510  in this example. 
         [0073]    In this example the magnet has a large bore. For some embodiments, a six-dimensional positioning system  522  is beneficial if the magnet has a bore of 80 cm or greater. This allows the target zone  536  to be positioned efficiently such that the target zone  536  is accessible by the radiation beam  508  and is positioned on the rotational axis  542 . The dashed line pointed to by arrow  542  is the rotational axis. In this embodiment the magnet  510  has a recess  540  which allows the radiotherapy source  504  to be positioned closer to the subject  526 . Also shown within the bore  538  of the magnet  510  is a magnetic field gradient coil  544 . The magnet field gradient coil  544  is shown as being a split type with a gap  546  in the magnet field gradient coil. The gap  546  may be a region with a reduced number or no conductors from the coil. In this example the gradient coil  544  is shown as one assembly. However, typically magnet field gradient coils contain three separate gradient systems for spatially encoding spins within the imaging zone  534 . 
         [0074]    Embodiments constructed in accordance with  FIG. 5  may have several features. The first feature (1) is to eliminate the volume RF body coil. This frees up space which can be used to enable a larger degree of subject positioning. 
         [0075]    The next feature (2) specifies an inner system bore size of at least 80 cm. By eliminating the RF body coil this saves approximately 6 cm of subject bore and consequently this results in a smaller magnet and gradient coil bore thereby reducing cost and power requirements. 
         [0076]    The third feature (3) is to always use local and multi-element RF transmit (Tx) receive (Rx) coils. Local Tx/Rx coil can be placed around the subject for maximum sensitivity and are always placed on top of the table thereby avoiding the problems associated with using a carbon fiber table top. From the RF perspective, local coils can be made compatible with continued use of a carbon fiber tabletop as preferred for LINAC therapy. 
         [0077]    The next feature (4) uses multiple groups of multi-element multi-channel Tx/Rx coils which can be placed around the subject while avoiding the path of the LINAC therapy beam. Due to the multi-channel transmit capability it is now possible to focus the transmit and receive field to the target anatomy thereby obtaining maximum efficiency/sensitivity despite the physical gap allowed for the therapy beam. 
         [0078]    By widening the magnet bore and enabling re-use of the carbon fiber table top it is now possible (5) to use subject table technology that can position the subject accurately at MRI and therapy iso-center. 
         [0079]    The final feature of this innovation (6) is to recess the outer canister of the magnet thereby enabling closer proximity of the LINAC gantry to the subject for better efficiency of the LINAC beam. 
         [0080]      FIG. 6  shows a further embodiment of a therapeutic apparatus  600  according to an embodiment of the invention. The therapeutic apparatus shown in  FIG. 6  is essentially equivalent to that shown in  FIG. 5 . In the embodiment shown in  FIG. 6  there is no recess shown in the magnet  510  as is shown in  FIG. 5 . However a recess could easily be incorporated into the embodiment shown in  FIG. 6  also. Also in comparison to  FIG. 5  there is no gap in the magnetic field gradient coil  544 . However, such a magnetic field gradient coil could also be incorporated into the embodiment shown in  FIG. 6 . The magnetic field gradient coil  544  is shown as being connected to a magnetic field gradient coil power supply which is adapted for supplying current to the magnetic field gradient coil. 
         [0081]    In the embodiment shown in  FIG. 6  a single transceiver  532  is connected to the first  528  and second  530  transmit-and-receive channels. There is a computer system  610  with a processor  614  for controlling the operation and function of the therapeutic apparatus  600 . Connected to the processor  614  is a hardware interface  612  which interfaces to the magnet field gradient power supply  602 , the radio-frequency transceiver  532  and the radiotherapy apparatus  502 . 
         [0082]    The hardware interface  612  is also connected to an optional light source  604 . The light source has a light collimator  606  and is mounted onto an edge of the magnet  510 . The light source can be controlled by the processor  614  such that when the subject  526  is retracted from the magnet  510  the light source can show where the radiation beam  508  will impinge on the subject  526 . This could be used for instance to determine if the radiation will hit either the first  528  or second  530  transmit-and-receive channel. The light source  604  is mounted on the outside of the magnet  510  because an operator or healthcare professional placing the transmit-and-receive channels  528 ,  530  would not be able to see them within the bore  538  of the magnet  510 . The light source  604  could for instance be mounted on a rail which goes along the outside edge of the magnet  510 . This could be used to circle the subject  526  and show where the radiation beam  508  will hit the subject  526  when the subject  526  is placed into the bore  538  of the magnet  510 . 
         [0083]    The processor  614  is further connected to a user interface  616  which allows an operator to control the functionality of the therapeutic apparatus  600 . The processor  614  is also connected to computer storage  618  and computer memory  620 . The computer storage  618  is shown as containing a treatment plan  622 . The treatment plan  622  contains instructions or details for performing therapy on the target zone  536 . The treatment plan may contain anatomical instructions and durations or times and energies of radiation  508  to be impinged on the target zone  536 . Also shown in the computer storage is magnetic resonance data  624  acquired using the therapeutic apparatus  600 . Also shown within the computer storage  618  is a magnetic resonance image  626  which has been reconstructed from the magnetic resonance data  624 . Further shown within the computer storage  618  is a registered location of a target zone  628 . The registered location  628  is a description in terms of the therapeutic apparatus&#39; internal coordinates of the location of the target zone  536 . 
         [0084]    The computer storage  618  is further shown as containing radiotherapy control signals  630  and positioning control signals  632 . The radiotherapy control signals  630  are for controlling the radiotherapy apparatus  502  and the positioning control signals  632  are for controlling the subject support  524  and the six-dimensional positioning system  522 . Further shown within the computer memory  618  is a channel calibration  634 . The channel calibration  634  contains phase and/or amplitude calibrations for the sending and/or receiving of radio-frequency signals using the two channels. The transmit-and-receive channels may contain individual antenna or coil elements. The channel calibration  634  contains phase and/or amplitude calibrations for these individual coil or antenna elements. The computer memory  620  is shown as containing a therapeutic control system module  636 . The therapeutic control system module  636  is executable code for controlling the operation and function of the therapeutic system. Further, in some embodiments it may convert the treatment plan  622  into radiotherapy control signals  630  and positioning control signals  632 . 
         [0085]    The computer memory  620  is further shown as containing an image reconstruction module  638 . The image reconstruction module  638  contains executable code for transforming the magnetic resonance data  624  into a magnetic resonance image  626 . The computer memory  620  is further shown as containing an image registration module  640 . The image registration module  640  contains computer executable code for performing a registration on the magnetic resonance image  626  and generating the registered location of the target zone  628 . The computer memory  620  is further shown as containing a planning module  642 . The planning module may use the image registration module  642  and the treatment plan  622  to generate the radiotherapy control signals  630  and/or the positioning control signals  632 . The computer memory  620  is further shown as containing a pre-calibration module  644 . The pre-calibration module  644  contains computer executable code for performing and generating the channel calibration  634 . Functions not discussed in modules  638 ,  640 ,  642 , and  644  are performed by the therapeutic control system module  636 . 
         [0086]    While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. 
         [0087]    Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
         
           
               300  radiotherapy source in first position 
               302  radiotherapy source in second position 
               304  radiotherapy source in third position 
               306  path of rotation 
               308  axis of rotation 
               310  radiation beam in first position 
               312  radiation beam in second position 
               314  radiation beam in third position 
               316  subject 
               318  target zone 
               320  angular zone 
               500  therapeutic apparatus 
               502  radiotherapy apparatus 
               504  radiotherapy source 
               506  adjustable beam collimator 
               508  radiation beam 
               510  magnet 
               512  cryostat 
               514  superconducting coil 
               516  shield coil 
               518  low field region 
               520  floor 
               522  six dimensional positioning system 
               524  subject support 
               526  subject 
               528  first transmit-and-receive channel 
               530  second transmit-and-receive channel 
               532  transceiver 
               534  imaging zone 
               536  target zone 
               538  bore of magnet 
               540  recess 
               542  rotational axis 
               544  magnetic field gradient coil 
               546  gap in magnetic field gradient coil 
               600  therapeutic apparatus 
               602  magnetic field gradient coil power supply 
               604  light source 
               606  light collimator 
               610  computer system 
               612  hardware interface 
               614  processor 
               616  user interface 
               618  computer storage 
               620  computer memory 
               622  treatment plan 
               624  magnetic resonance data 
               626  magnetic resonance image 
               628  registered location of target zone 
               630  radiotherapy control signals 
               632  positioning control signals 
               634  channel calibration 
               636  therapeutic control system module 
               638  image reconstruction module 
               640  image registration module 
               642  planning module 
               644  pre-calibration module