Abstract:
A radiation therapy system according to the present invention includes a treatment system and an imaging system. The treatment system employs a first tungsten target to generate high power X-rays for treatment. The imaging system uses a second target to generate low power X-rays for imaging. The targets are arranged such that the resulting treatment and imaging beams are generally collinear.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to X-ray diagnostic imaging and, in particular, to X-ray diagnostic imaging in a radiation therapy treatment system. 
     2. Description of the Related Art 
     The use of linear accelerators in medicine is well known. Such linear accelerators are used for treating patients with radiation therapy, such as X-rays or electron beams. Such X-rays are created when high energy electrons are decelerated in a target material such as tungsten. 
     In such radiation therapy systems, it is desirable to obtain X-ray images for treatment diagnosis and treatment planning. Typically, radiation therapy systems use full energy electron beams to produce X-rays for diagnostic imaging. These high energy X-rays (about 2 MeV) produce washed out images that are difficult to interpret. 
     An alternative is to use low voltage sources, but typical low voltage sources are not collinear with the treatment beam. Consequently, the accuracy of the subsequent therapy relies on interpreting the relative position of the two beams. 
     As such, there is a need for a radiation therapy device that employs low power X-rays for imaging that are substantially aligned with treatment X-rays. 
     SUMMARY OF THE INVENTION 
     These and other drawbacks in the prior art are overcome in large part by a system and method according to the present invention. A diagnostic target is provided substantially adjacent a treatment target at an X-ray exit window or aperture in a linear accelerator. In a normal or treatment mode, a guide or bending magnet directs an electron beam toward the treatment target, generating X-rays directed at the patient. In a diagnostic mode, the guide magnet is turned off and the electron beam is directed at the diagnostic target such that diagnostic X-rays are directed at the patient. High energy X-rays are absorbed by head shielding. Low energy (about 500 keV) X-rays are used for diagnostic imaging. The high energy treatment beam and the low energy imaging beam are substantially collinear, thereby allowing use of the same beam shielding device hardware in both modes. 
     A radiation therapy system according to the present invention includes a treatment system and an imaging system. The treatment system employs a first tungsten target to generate high power X-rays for treatment. The imaging system uses a second target to generate low power X-rays for imaging. The targets are arranged such that the resulting treatment and imaging beams are collinear. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A better understanding of the invention is obtained when the following detailed description is considered in conjunction with the following drawings in which: 
     FIG. 1 is a diagram of a prior art radiation therapy system suitable for use with with a system in accordance with an implementation of the invention; 
     FIG. 2 is a block diagram of a radiation therapy system in accordance with an embodiment of the present invention; 
     FIG. 3 is a diagram illustrating beam direction according to an implementation of the invention; and 
     FIG. 4 is a flowchart illustrating a method according to an implementation of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1-4 illustrate an improved radiation therapy system with diagnostic imaging according to an implementation of the invention. A diagnostic target is provided substantially adjacent a treatment target at an X-ray exit window or aperture in a linear accelerator. In a normal or treatment mode, a guide magnet directs an electron beam toward the treatment target, generating X-rays directed at the patient. If electron beam treatment is desired, no treatment target is used in treatment mode. In a diagnostic mode, the guide magnet is turned off and the electron beam is directed at the diagnostic target such that diagnostic X-rays are directed at the patient. High energy X-rays are absorbed by head shielding. Low energy (about 500 keV) X-rays are used for diagnostic imaging. The high energy treatment beam and the low energy imaging beam are substantially collinear, thereby allowing use of the same beam shielding device hardware in both modes. 
     FIG. 1 illustrates a radiation emitting system  11 . The radiation emitting system  11  includes a radiation treatment device  2  of common design, which utilizes plates  4  and a control unit in a housing  9  along with a treatment processing unit  100  constructed in accordance with the present invention. The radiation treatment device  2  includes a gantry  6  which can be swiveled around a horizontal axis of rotation  8  in the course of therapeutic treatment. Plates  4  are fastened to a projection of gantry  6 . To generate the high-powered radiation required for the therapy, a linear accelerator is located in gantry  6 . The axis of the radiation bundle emitted from the linear accelerator and gantry  6  is designated  10 . Electron, photon, or any other detectable radiation can be used for the therapy. 
     During the treatment, the radiation beam is trained on a zone  12  of an object  13 , for example, a patient who is to be treated, and who lies at the isocenter of the gantry rotation. The rotational axis  8  of the gantry  6 , the rotational axis  14  of a treatment table  16 , and the beam axis  10  all preferably intersect in the isocenter. In addition, an imaging unit  17  may be provided for diagnostic or setup purposes. The construction of such a radiation treatment device is described in general in a brochure “Digital Systems for Radiation Oncology”, Siemens Medical Laboratories, Inc. A91004-M2630-B358-01 -4A00, September 1991. An exemplary radiation treatment system is the Primus system, available from Siemens Medical Systems, Inc., Concord, Calif. The imaging unit may be the Beamview system, also available from Siemens Medical Systems, Inc., Concord, Calif. 
     FIG. 2 shows a portion of an illustrative radiation treatment device  2  and portions of treatment processing unit  100  in more detail. An electron beam  1  is generated in an electron accelerator  20 . The accelerator  20  includes an electron gun  21 , a wave guide  22 , and an evacuated envelope or guide magnet housing  23 . A trigger system  3  generates injector trigger signals and supplies them to injector  5 . Based on these injector trigger signals, injector  5  generates injector pulses which are fed to electron gun  21  in accelerator  20  for generating electron beam  1 . Electron beam  1  is accelerated and guided by wave guide  22 . For this purpose, a high frequency (HF) source (not shown) is provided which supplies radio frequency (RF) signals for the generation of an electromagnetic field supplied to wave guide  22 . The electrons injected by injector  5  and emitted by electron gun  21  are accelerated by this electromagnetic field in wave guide  22  and exit at the end opposite to electron gun  21  as electron beam  1 . Electron beam  1  then enters a guide magnet  23 , and from there is guided through a window  7  along axis  10 . After passing through a first scattering foil  15 , the beam goes through a passageway  51  of a shield block  50  and encounters a second scattering foil  17 . Next, the beam is sent through a measuring chamber  60 , in which the dose is ascertained. If the scattering foils are replaced by a target, the radiation beam is an X-ray beam. Finally, aperture plate arrangement  4  includes a pair of plates  41  and  42 . Of course, this is just one example of a beam-shielding arrangement that can be used in the invention. The invention is suitable in other arrangements, as is well appreciated by those skilled in the art. For example, the beam shielding arrangement may be a multi-leaf collimator employing a plurality of thin leaves. 
     Plate arrangement or beam shielding device  4  may be embodied as one or more pairs of aperture plates  41  and  42  and additional pairs of aperture plates (not shown) arranged perpendicular to plates  41  and  42 . in order to change the size of the irradiated field, the aperture plates can be moved with respect to axis  10  by a drive unit  43  which is indicated in FIG. 2 only with respect to plate  41 . Drive unit  43  comprises an electric motor which is coupled to plates  41  and  42  and which is controlled by a motor controller  40 . Position sensors  44  and  45  are also coupled to plates  41  and  42 , respectively, for sensing their positions. The plate arrangement  4  is employed both in the treatment mode and in the imaging mode, as will be explained in greater detail below. 
     The area of a patient that is irradiated is known as the field. As is well known, plates  4  are substantially impervious to the emitted radiation. They are mounted between the radiation source and patient in order to delimit the field. Areas of the body, for example, healthy tissue, are therefore subjected to as little radiation as possible, and preferably to none at all. Preferably, with at least one of the plate movable, the distribution of radiation over the field need not be uniform (one region can be given a higher dose than another); further, with the gantry able to be rotated, different beam angles and radiation distributions are allowed without having to move the patient around. 
     The central treatment processing or control unit  100  (FIG. 1) is usually located apart from radiation treatment device  2  in a different room to protect the therapist from radiation. Treatment processing unit  100  includes an output device, such as at least one visual display unit or monitor  70 , and an input device, such as a keyboard  19 , although data can be input also through data carriers, such as data storage devices. The treatment processing unit  100  is typically operated by the therapist who administers actual delivery of a radiation treatment as prescribed by an oncologist. By utilizing keyboard  19 , or other input device, the therapist enters into a control unit  76  of the treatment processing unit  100  the data that defines the radiation to be delivered to the patient, for example, according to the prescription of the oncologist. The program can also be input via another input device, such as a data storage device, through data transmission. On the screen of a monitor  70 , various data can be displayed before and during the treatment. 
     Central processing unit  18  (FIG.  2 ), included in treatment processing unit  100 , is connected with the input device, e.g., keyboard  19 , for inputting the prescribed delivery of the radiation treatment and with a dose control unit  61  that generates the desired values of radiation for the controlling trigger system  3 . Trigger system  3  suitably adapts the pulse repetition frequency or other parameters to change the radiation output. A digital dosimetry system is particularly advantageous in order to more easily control the digital output of central processing unit  18 . Central processing unit  18  suitably includes a control unit  76  for controlling execution of the treatment program in conjunction with memory  77  and a combination circuit  78  which suitably receives signals from the control unit  76  and memory  77  for combination to produce a set signal, S, that identifies a dose rate for dose rate control unit  61  in accordance with the present invention. 
     In addition, as will be explained in greater detail below, the CPU  18  generates control signals to turn off the guide magnet and redirect the electron beam using in-plane steering coils (not shown) through a diagnostic target  102  for diagnostic imaging using the imaging unit  17 . 
     More particularly, an imaging unit  17  is provided such that an image detector  69  is positioned in opposition to the treatment head and the diagnostic target  102 . The image detector is coupled to an imaging station  80 , which includes a video control unit  71  for capturing video images and controlling imaging operation, and a display  72  for displaying the resulting images. In one implementation, the video control unit  71  is implemented as a video camera, video capture board, and various processing circuitry. In this implementation, the image detector  69  is a metal foil scintillation detector. Alternatively, the image detector  69  may be implemented as a flat panel detector comprising one or more arrays of photosensitive cells. 
     The use of the diagnostic target is illustrated in greater detail with reference to FIG.  3 . As shown, the guide magnet housing  23  includes the guide magnet  300 , and the diagnostic target  102 . In a first mode, the CPU  18  supplies control signals to cause the guide magnet  300  to be activated and the X-ray beam  100  to be generated, as described above. In a diagnostic mode, the CPU  18  generates control signals to turn off the guide magnet  300  and engage in-plane steering coils (not shown) the steer the beam  200  into the diagnostic target  102 . Forward or high energy X-rays area absorbed by the head shielding. Ninety degree, 500 keV X-rays are used to obtain clearer pictures. 
     Turning now to FIG. 4, a flowchart illustrating operation of an implementation of the invention is shown. In a step  400 , the CPU  18  sends control signals to turn off the guide magnet  300 . In a step  402 , the in-plane steering coils are used to guide the electron beam  200  to the diagnostic target. The diagnostic target, which may be formed of copper or tungsten, for example, is positioned such that low energy 90 degree X-rays are provided for imaging. In a step  404 , the resulting 90 degree X-rays are used to obtain one or more images. Once the desired images have been obtained, the CPU sends control signals to turn on the guide magnet  300 , in a step  406 . In a step  408 , the electron beam  100  is guided to impinge on a treatment target (if desired) and the treatment beam is generated in step  410 . 
     The invention described in the above detailed description is not intended to be limited to the specific form set forth herein, but is intended to cover such alternatives, modifications and equivalents as can reasonably be included within the spirit and scope of the appended claims.