Abstract:
A method of compensating for breathing and other motions of a patient during treatment includes periodically generating internal positional data about an internal target region. The method further includes generating external positional data about external motion of the patient&#39;s body using an external sensor and generating a correlation between one or more positions of the internal target region and one or more positions of an external region using the external positional data of the external sensor and the internal positional data of the internal target region. The method further includes predicting the position of the internal target region at some later time based on the correlation model.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/306,951, filed Nov. 29, 2011 and entitled “Frameless Radiosurgery Treatment System and Method,” which is a continuation of U.S. patent application Ser. No. 12/356,442, filed Jan. 20, 2009 and entitled “Frameless Radiosurgery Treatment System and Method,” issued Dec. 27, 2011 as U.S. Pat. No. 8,086,299, which is a continuation of U.S. patent application Ser. No. 10/919,765, filed Aug. 17, 2004 and entitled “Frameless Radiosurgery Treatment System and Method,” now abandoned, which is a continuation of U.S. patent application Ser. No. 09/663,104, filed Sep. 15, 2000 and entitled “Frameless Radiosurgery Treatment System and Method,” issued Aug. 17, 2004 as U.S. Pat. No. 6,778,850, which is a continuation in part of U.S. patent application Ser No. 09/270,404, filed Mar. 16, 1999 and entitled “Apparatus and Method for Compensating for Respiratory and Patient Motion During Treatment,” issued Nov. 7, 2000 as U.S. Pat. No. 6,144,875, all of which are owned by the same assignee as the present application and all of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    This invention relates generally to a system and method for treating a patient and in particular to a system and method for controlling a treatment to administer a precise dose to a patient. In more detail, the invention relates to an apparatus and method for performing accurate surgical procedures on a particular target region within a patient utilizing previously obtained reference data indicating the position of the target region with respect to its surrounding which may contain certain reference points. 
         [0003]    In order to control a surgical procedure, such as radiosurgery, many different prior techniques have been used including the manual targeting of the treatment. Many of the prior techniques are not sufficiently accurate so that healthy tissue surrounding the target region is often unnecessarily irradiated and damaged or killed. Other techniques are clumsy and cannot be used for particular types of treatments. For example, one prior technique involved frame-based stereotaxy that was often used for body parts and regions that could be easily physically immobilized. For example, the frame based stereotaxy was often used to immobilize the head of the patient so that a target region in the brain, such as a brain tumor, could be irradiated by the radiosurgical beam. To do so, the patient was positioned on a treatment bed and then his/her head was immobilized by a frame that was securely attached to the person&#39;s head with some attachment means and that was also securely attached to an immovable object such as a treatment table. Thus, during the treatment, the patient was not able to move his/her head at all which permitted an accurate targeting of the treatment. The problem is that a frame-based system cannot be used for fractionated treatment in which repeated smaller does are given to the patient over some predetermined period of time, such as a couple of weeks or a month. A fractionated treatment plan is often desirable since it permits larger overall doses of treatment, such as radiation, to be applied to the target region while still permitting the healthy tissue to heal. Clearly, it is extremely difficult to leave the frame secured to the patient&#39;s head for that period of time. In addition, it is impossible to remove the frame and later reposition the frame in the exact same location for the next treatment. Thus, the frame based stereotaxy provides the desired accuracy, but cannot be used with various desirable treatment schedules. 
         [0004]    Another typical positioning system is a frameless stereotaxy system wherein a physical frame attached to the patient is not necessary. An example of a frameless stereotaxy system is disclosed in U.S. Pat. No. 5,207,223 which is owned by the same assignee as the present application and is incorporated herein by reference. In general, a preoperative imaging of the region surrounding the target region is completed, such as by computer tomography. Then, during the treatment, a stereo image is generated, such as by X-ray imaging. The stereo image is then correlated to the preoperative image in order to locate the target region accurately. Then, a radiation source located on a robot is automatically positioned based on the correlation between the preoperative scans and the stereo images in order to accurately treat the target region without -unnecessarily damaging the healthy tissue surrounding the target region. 
         [0005]    The current frameless stereotaxic techniques have some limitations which limit their effectiveness. First, most surgical operation rooms have limited workspace and the current stereotaxic frameless systems require a large space due to the movement of the robot supporting the surgical radiation beam and the two beam imagers Second, the cost of having two beam generators and two imagers is very high making the treatment system very expensive These systems also typically require some form of implanted fiducials, such as markers that are viewable using an X-ray, to track soft tissue targets. Finally, for most current frameless systems, breathing and other patient motion may interfere with the target region identification and tracking due to a degradation of the images. Thus, it is desirable to provide a frameless radiosurgery treatment system and method that overcomes the above limitations and problems and it is to this end that the present application is directed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a diagram illustrating a typical frameless radiosurgical treatment system; 
           [0007]      FIG. 2  is a diagram illustrating the diagnostic and treatment beams of the system shown in  FIG. 1 ; 
           [0008]      FIG. 3  is a block diagram illustrating the treatment system of  FIG. 1 ; 
           [0009]      FIG. 4  is a diagram illustrating a preferred embodiment of the frameless treatment system in accordance with the invention; 
           [0010]      FIG. 5  is a block diagram illustrating more of the details of the treatment system of  FIG. 4 ; 
           [0011]      FIG. 6  is a flowchart illustrating a method for treatment in accordance with the invention using the system of  FIG. 4 ; 
           [0012]      FIG. 7  is a diagram illustration a respiration cycle of a patient; 
           [0013]      FIG. 8  is a flowchart illustrating a method for treating a patient with respiration tracking in accordance with the invention; 
           [0014]      FIG. 9  is a diagram illustrating a second embodiment of the frameless treatment system in accordance with the invention; 
           [0015]      FIG. 10  is a flowchart illustrating a method for treatment in accordance with the invention using the system of  FIG. 9 ; 
           [0016]      FIG. 11  is a diagram illustrating a third embodiment of the frameless treatment system in accordance with the invention; 
           [0017]      FIG. 12  is a flowchart illustrating a method for treatment in accordance with the invention using the system of  FIGS. 11 ; and 
           [0018]      FIG. 13  illustrates the deformation of the pre-treatment and/or intra-treatment data to establish optimal correspondence to infer better target positions. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    The invention is particularly applicable to a radiosurgical treatment system and method and it is in this context that the invention will be described. It will be appreciated, however, that the system and method in accordance with the invention has greater utility, such as to other types of treatments wherein it is necessary to accurately position a treatment at a target, region within the patient in order to avoid damaging healthy tissue such as to other types of medical procedures with other types of medical instruments, such as positioning biopsy needles, ablative, ultrasound or other focused energy treatments, positioning a laser beam for laser beam treatment or positioning radioactive seeds for brachytherapy. Prior to describing the invention, a typical radiosurgery device will be described to provide a better understanding of the invention. 
         [0020]      FIGS. 1-3  are diagram illustrating an example of a stereotaxic radiation treatment device  10 . The radiation treatment device  10  may include a data processor  12 , such as a microprocessor, and a disc or tape storage unit  13  (shown in  FIG. 3 ) which may store a three dimensional image of a patient  14 . The three dimensional image may be loaded into the data processor, if not already there, to compare the three dimensional image to images generated during the surgical procedure. The three dimensional image may be generated by various conventional techniques such as computer aided tomography (CAT) scan or magnetic resonance imaging (MR). The radiation treatment device  10  may also include a beaming apparatus  20  which, when activated, emits a collimated surgical ionizing beam directed at a target region  18  (shown in  FIG. 2 ). The collimated surgical ionizing beam may have sufficient strength to cause the target region to become necrotic. A variety of different beaming apparatus may be used which generate an ionizing radiation or heavy particle beam such as a linear accelerator and preferably an x-ray linear accelerator. Such an x-ray beaming apparatus is commercially available. The beaming apparatus may be activated by the operator throwing a switch  23  at a control console  24  connected to the beaming apparatus  20  by a cable  22 . 
         [0021]    The radiation treatment device  10  may also include an apparatus for passing a first diagnostic beam  26  and a second diagnostic beam  28  through the region previously imaged by the three-dimensional image. The diagnostic beams are positioned at a predetermined non-zero angle with respect to each other, such as being orthogonal as shown in  FIG. 2 . The diagnostic beams may be generated by a first x-ray generator  30  and a second x-ray generator  32 , respectively. A first and second image receiver  34 ,  36  or a single receiver may receive the diagnostic beams  26 ,  28  to generate an image from the diagnostic beams which is fed into the microprocessor  12  (as shown in  FIG. 4 ) so that the diagnostic images may be compared to the three-dimensional image. 
         [0022]    The radiation treatment device  10  may also include a device for adjusting the relative positions of the beaming apparatus  20  and/or the patient  14  so that the ionizing beam is continuously focused on the target region  18 . In the radiation treatment device shown in  FIG. 1 , the positions of the beaming apparatus and the patient may be altered with six degrees of freedom by a gantry  40  and a moveable operating table  38  with a tilting top  44 . The positions of the beaming apparatus relative to the patient may also be accomplished by using a processor controllable robotic arm mechanism that permits the beaming apparatus to be moved freely about the patient&#39;s body including up, down, longitudinally along or laterally along the body of the patient. 
         [0023]      FIG. 3  is a block diagram of the radiation treatment device  10  including the microprocessor  12 , the tape drive  13 , the beaming apparatus  20 , the robotic ann.  46  or the gantry  40 , the x-ray cameras  30 ,  32 ,  34  and  36 , and the operator control console  24  as described above. In addition, the device  10  may include safety interlocks  50  to ensure that the beaming apparatus is not activated accidentally. The device  10  may also include an operator display  48  for tracking the progress of the treatment and controlling the treatment. Any further details of the radiosurgery device may be found in U.S. Pat. No. 5,207,223 which is owned by the assignee of this application and which is incorporated herein by reference. 
         [0024]    The above system is well suited for the treatment of stationary target regions (e.g., stationary with respect to bony structures that can be seen on an image) wherein respiratory motion or pulsation motion do not affect the accuracy of the treatment beam. The drawback of the above system is that anatomic sites subject to respiratory motion are difficult to treat. In accordance with the invention, the frameless treatment system may improve upon the system shown in  FIGS. 1-3 . The frameless treatment system and method in accordance with the invention with the above advantages will now be described. 
         [0025]      FIG. 4  is a diagram illustrating a preferred embodiment of the frameless treatment system  180  in accordance with the invention. This embodiment of the invention is particular applicable to the targeting of a target region without embedded markers wherein there is no surrounding region that can be easily located (e.g., no bones are present) and respiration motion may affect the position of the target region. An example of a target region for this embodiment is a lung tumor. 
         [0026]    The treatment system  180  may include a patient treatment table or couch  102  on which a patient  103  may rest during the treatment. The treatment system may also include a diagnostic beam recording device  104  that may be located underneath the treatment table and underneath the patient and one or more diagnostic beam generators  106  (one is shown in this example). The recording device  104  may record the images generated when the diagnostic beam device is energized at one or more different predetermined positions. The recording device  104  may be any device that can be used to capture the image generated by the diagnostic beams. In a preferred embodiment, the recording device  104  may be the amorphous silicon plate that captures the x-ray beams being generated by the diagnostic beam generators  106 . The recording device  104  may be connected to a computer that controls the operation of the recording device and the diagnostic beam generator. The recording device in this embodiment may also have a first portion  105  and a second portion  107  wherein the first diagnostic beam is captured by the first portion and the second diagnostic beam is captured by the second portion. Thus, the diagnostic beams may be simultaneously energized or may be sequentially energized. A recording medium with one or more diagnostic beams is also shown in U.S. Pat. No. 5,207,223 to Adler which is owned by the same assignee as the present invention. 
         [0027]    The robot and the treatment beam generator (shown in  FIG. 5 ) are not shown in  FIG. 4 . The system may further include a track  152  in which the diagnostic beam generator moves so that the diagnostic beam generator may be moved to different positions (see the diagnostic beam generator  106  in a first position  154  and the other positions shown by the phantom pictures of the generator) wherein the diagnostic beam generator is at a different non-zero angle with respect to the other positions. Thus, in this embodiment, the diagnostic beam generator  106  is moved from the first position  154  to other positions at periodic times in order to generate the images of the target region as described above. In addition to the elements shown in  FIG. 5 , the system may also include a controller, to position of the diagnostic beam generator, that may be controlled by the computer. 
         [0028]    In addition to the above, this system  180  may also include an external marker tracking device  182  that may include one or more external marker tracking generators  184  that generate one or more external marker tracking beams  184 , such as infrared beams or passive markers whose position is detectable with optical cameras. The system may also include one or more external markers  188  attached to the patient that measure the external movement of the patient during respiratory motion as described in more detail in the co-pending application that was incorporated by reference. Now, the system will be described in more detail. 
         [0029]      FIG. 5  is a block diagram illustrating more of the details of the treatment system  100  of  FIG. 4 . In particular, the system  100  may include a computer  110  that controls the operation of the various elements of the system including the beam generators  106 ,  108  as well as the image recorder  104 . The system may also include a treatment beam device  112 , such as a linear accelerator (LINAC) in this embodiment, that generates a treatment beam and a robot  114  that positions the treatment beam (a LINAC manipulator in this embodiment) that are both controlled by the computer  110  that may be a multi-processor computer in this embodiment. The computer may issue control commands and receive back status commands from the treatment beam generator  112 , the robot  114  and the beam generators  106 ,  108 . For the image recorder  104 , the computer may issue control signals to control the operation of the image recorder as described above and may receive image data from the image recorder. 
         [0030]    The system may also include safety interlocks  116  that ensures that the diagnostic beams and the treatment beam cannot be activated (the beams are only energized when a status signal is received by the computer) unless all people other than the patient are out of the treatment room due to the radiation danger. The system may also include a tape drive  118  for storing the images generated by the image recorder, the pre-operative CT three-dimensional images and any treatment planning software that may perform the comparison of the images and control the movement of the treatment beam. The system may further include an operator control console  120  and an operator display  122  that permit a user of the system, such as a surgeon, to interact with and operate the system and monitor the treatment. The treatment planning software in the computer may compare the pre-operative image to the images from the diagnostic beam generators to determine how to control the treatment robot and therefore the treatment beam during the treatment. The computer, based on the comparison and the surgeon&#39;s manual commands, may then control the treatment beam in order to deliver the appropriate dose to the patient without damaging the healthy tissue surrounding the target region. Now, a method of treatment using the preferred embodiment will be described. 
         [0031]      FIG. 6  is a flowchart illustrating a method  200  for treatment in accordance with the invention using the system of  FIG. 4 . In step  202 , a three-dimensional mapping of a region of the patient including the target region is generated prior to the treatment. The three-dimensional mapping may be done using typical equipment such as computer tomography, magnetic resonance tomography or the like. The three-dimensional mapping of the region is stored in the storage device  118 . The mapping shows the relative locations of the target region with respect to other surrounding regions that may be seen in the mapping to locate the target region relative to the surrounding regions. For example, the target region may be a lung tumor. 
         [0032]    On the day of treatment, the patient may be positioned on the treatment bed as shown in  FIG. 9 . The respiratory cycle of the patient may then be determined in step  203  and at various different times during the treatment. The respiratory cycle may be determined by monitoring chest wall surface movement with optical or ultrasound digitizers, and/or by using a strain gauge, by the measurement of the airflow exiting the patient or by other well known methods. In step  204 , the system may determine if the treatment can begin based on the status of the safety interlocks. If it is not safe to begin the treatment, then the method loops back to test the safety interlocks until a safe condition is indicated. 
         [0033]    In step  206 , a diagnostic beam generator is positioned along the track in the appropriate position and energized by the computer in order to generate an image on the recording device. In a preferred embodiment, the diagnostic beam generator is an x-ray generators and the image recorder is an amorphous silicon imager that generates an image in response to x-rays as is well known. The image generated by the first diagnostic beam in the image recorder may then be downloaded by the computer to the storage device attached to the computer in step  208  and the image recorder may be reset. Each image is acquired at the same phase of the respiratory cycle  20  as described below with respect to  FIGS. 7 and 8 . 
         [0034]    In step  210 , the method determines if there are any other positions for the diagnostic beam. If there are other positions for the diagnostic beam, the method loops back to step  206  to energize that generator at the other position, generate an image and download the image to the storage device. In this embodiment, the movement of the diagnostic beam generator along the track generates multiple images wherein each image is at a non-zero angle with respect to the other images and acquired during the same phase of the respiratory cycle. In accordance with the invention, the method sequentially energizes the diagnostic beam generator at different positions to generate the images in a sequential manner. In accordance with the invention, repeated sequence of images from the diagnostic beam generator may be generated at periodic times so that the location of the target region at different times may be determined. 
         [0035]    The series of diagnostic beam images may be processed using a CT-like algorithm to generate a 3-D image of the patient during the treatment. Once the series of diagnostic images are processed into a 3-D image, the 3-D image is compared to the three-dimensional preoperative mapping as is well known to determine the location of the target region at the particular time in step  212 . In step  214 , the targeting of the treatment beam is adjusted based on the comparison so that the treatment beam is always focused on the target region. If there are repeated diagnostic images generated, after each new set of images is generated, the images are compared to the mapping and the treatment beam targeting is adjusted to compensate for changes in the position of the target region. In this manner, the target region is accurately tracked so that the treatment beam is focused on the target region. 
         [0036]    In some cases, the placement of certain structures is visible in the intra-treatment 3-D reconstruction, but the target region or critical region is either not visible at all, not clearly visible, or is visible but difficult to segment automatically by computer. In this case, the system may comprise the step of deforming the intra-treatment images in such a way that the positions of the clearly visible structures best match the pre-operative image data. From this, the exact deformation pattern of the entire anatomical area can be inferred. The exact position of the target and/or healthy critical tissue visible in the pre-operative image data, but not clearly visible in the intra-treatment data may be inferred as described in more detail with reference to  FIG. 13 . 
         [0037]      FIG. 7  is a chart  260  illustrating a typical respiration cycle for a human being wherein the respiration cycle is represented by a sine wave. The y-axis of the chart is the movement of the chest wall thus showing that the chest wall moves out and in during the respiration cycle. A first point  262  in the respiration cycle with maximum expansion of the chest and a second point  264  in the respiration cycle with no chest movement are shown. The respiration cycle may be determined using the various techniques described above. In accordance with the invention, the energizing of the diagnostic beams and the treatment beam may be periodically timed so that the energizing occurs at the corresponding points in the respiration cycle such as at the first point or the second point. In addition, the energizing of the beams may occur at more than one time during the respiration cycle. Thus, the accuracy of the treatment is improved since the beams are energized at the same time in the respiration cycle. 
         [0038]      FIG. 8  is a flowchart illustration of a method  270  for energizing a diagnostic or treatment beam based on the respiration cycle in accordance with the invention. In step  272 , the treatment is started and the respiration cycle of the patient is determined. In step  274 , the system determines if at predetermined point in the respiration cycle has occurred and waits until the predetermined point has occurred. Once the predetermined point in the respiration cycle is reached, the system may energize the beam in step  276 . Now, a second embodiment of the invention will be described. 
         [0039]      FIG. 9  is a diagram illustrating a second embodiment of the frameless treatment system  150  in accordance with the invention. This embodiment of the invention is particular applicable to fiducial-less targeting of a target region wherein a surrounding region can be located, but the surrounding region does not have a fixed relationship with the target region (e.g., no bones are present) and respiration motion does not affect the position of the target region. An example of a target region for this embodiment is the prostate. 
         [0040]    The system  150  may include the same elements as the prior embodiment as designated by like reference numerals such as the treatment table  102 , the image recorder  104  and the diagnostic beam generator  106 . As with the prior embodiment, the robot and the treatment beam generator are not shown. In this embodiment, a single diagnostic beam generator  106  may be used to further reduce the cost of the treatment system. In this embodiment, the system may further include a track  152  in which the diagnostic beam generator moves so that the diagnostic beam generator may be moved to different positions (see the diagnostic beam generator  106  in a first position  154  and the other positions shown by the phantom pictures of the generator) wherein the diagnostic beam generator is at a different non-zero angle with respect to the other positions. Thus, in this embodiment, the diagnostic beam generator  106  is moved from the first position  154  to other positions at periodic times in order to generate the images of the target region as described above. The embodiment may have similar elements as those shown in  FIG. 5  and may also include a controller, to position the diagnostic beam generator, that may be controlled by the computer. Now, the method of treatment using the second embodiment will be described. 
         [0041]      FIG. 10  is a flowchart illustrating a method  160  for treatment in accordance with the invention using the system of  FIG. 9 . In step  162 , a three-dimensional mapping of a region of the patient including the target region is generated prior to the treatment. The three-dimensional mapping may be done using typical equipment such as computer tomography or the like. The three-dimensional mapping of the region is stored in the storage device  118 . The mapping shows the location of the target region with respect to other surrounding regions that may be seen in the mapping to locate the target region relative to the surrounding regions. For example, the target region may be a prostate tumor and the other surrounding regions may be the bladder. On the day of treatment, the patient may be positioned on the treatment bed as shown in  FIG. 7 . In step  164 , the system may determine if the treatment can begin based on the status of the safety interlocks. If it is not safe to begin the treatment, then the method loops back to test the safety interlocks until a safe condition is indicated. 
         [0042]    In step  166 , a diagnostic beam generator is positioned along the track in the appropriate position and energized by the computer in order to generate an image on the recording device. In a preferred embodiment, the diagnostic beam generators is an x-ray generator and the image recorder is an amorphous silicon imager that generates an image in response to x-rays as is well known. The image generated by the first diagnostic beam in the image recorder may then be downloaded by the computer to the storage device attached to the computer in step  168  and the image recorder may be reset. In step  170 , the method determines if there are any other positions for the diagnostic beam. If there are other positions for the diagnostic beam, the method loops back to step  166  to energize that generator at the other position, generate an image and download the image to the storage device. In this embodiment, the movement of the diagnostic beam generator along the track generates multiple images wherein each image is at a non-zero angle with respect to the other images. In accordance with the invention, the method sequentially energizes the diagnostic beam generator at different positions to generate the images in a time sequential manner. In accordance with the invention, repeated sequence of images from the diagnostic beam generator may be generated at periodic times so that the location of the target region at different times may be determined. The 2-D images generated by the diagnostic beams are processed to yield a CT-like image which may then be compared to the pre-operative 3-D mapping. 
         [0043]    Once the diagnostic images are generated, the two or more images are compared to the three-dimensional pre-operative mapping as is well known to determine the location of the target region at the particular time in step  172 . The comparison may again include the step of deformation as described above. In step  174 , the targeting of the treatment beam is adjusted based on the comparison so that the treatment beam is always focused on the target region. If there are repeated diagnostic images generated, after each new set of images is generated, the images are compared to the mapping and the treatment beam targeting is adjusted to compensate for changes in the position of the target region. In this manner, the target region is accurately tracked so that the treatment beam is focused on the target region. 
         [0044]      FIG. 11  is a diagram illustrating another embodiment of the frameless treatment system  100  in accordance with the invention that may be particularly suited for treating target regions that have a fixed relationship to a fixed reference point, such as bones. Thus, this embodiment of the invention may be used for treating, for example, the spine of a patient or the brain of the patient since these target regions are near or surrounded by bones. The other embodiments of the invention described below may be particularly suited for the treatment of other target regions. In this figure, only one detector under the patient couch is used. The two diagnostic beams in this case may either be activated sequentially or the two beams may be activated simultaneously while projecting their respective images to a different portion of the single detector plate/camera. The simultaneous activation of the diagnostic beams is particularly useful when time-stamps are needed so that the exact time of a given 3-D position is known. 
         [0045]    The treatment system  100  may include a patient treatment table or couch  102  on which a patient  103  may rest during the treatment. In the example shown, the brain of the patient is being treated. The treatment system may also include a diagnostic beam recording device  104  that may be located underneath the treatment table and underneath the patient and one or more diagnostic beam generators  106 ,  108  (two are shown in this example). The recording device  104  may record the images generated when each diagnostic beam device  106 ,  108  is energized. The recording device  104  may be any device that can be used to capture the image generated by the diagnostic beams. In a preferred embodiment, the recording device  104  may be the amorphous silicon plate that captures the x-ray beams being generated by the diagnostic beam generators  106 ,  108 . The recording device  104  may be connected to a computer that controls the operation of the recording device and the diagnostic beam generators. The recording device in this embodiment may have a first portion  105  and a second portion  107  wherein the first diagnostic beam is captured by the first portion and the second diagnostic beam is captured by the second portion. Thus, the diagnostic beams may be simultaneously energized or may be sequentially energized. 
         [0046]    In accordance with the invention, the diagnostic beam generators  106 ,  108  may be controlled by the computer to be energized at different predetermined time intervals or simultaneously so that each diagnostic beam generator is producing an image on the recording device at a different time or simultaneously. In addition, the diagnostic beam generators are located at different positions so that the diagnostic beams pass through the patient at different non-zero angles so that the angle between the two diagnostic beams is also non-zero which permits a two-dimensional image of the target region to be generated from the two images. 
         [0047]    In operation, the first diagnostic beam generator  106  may be energized to emit a diagnostic beam that passes through the target region and generates an image on the recording device. The image developed by the recording device is then downloaded to the computer and the recording device is erased. Next, the second diagnostic beam  108  is energized and an image generated by the second diagnostic beam is received by the recording device. This image is also downloaded to the computer where it is stored with the first image. By comparing these diagnostic images in combination with the pre-operative 3-D CT scan or the like, the treatment beam (not shown) of the treatment system may be accurately targeted at the target region. For purposes of illustration, the treatment beam generator and the treatment beam robot are not shown in  FIG. 11 . The operation of this embodiment of the treatment system is described in more detail below with reference to  FIG. 12 . 
         [0048]      FIG. 12  is a flowchart illustrating a method  130  for treatment in accordance with the invention using the system of  FIG. 11 . In particular, in step  132 , a three-dimensional mapping of a region of the patient including the target region is generated prior to the treatment. The three-dimensional mapping may be done using typical equipment such as computer tomography or the like. The three-dimensional mapping of the region is stored in the storage device  118 . The mapping shows the location of the target region with respect to other surrounding regions that may be seen in the mapping and appear on X-ray images made with the image recorder. For example, the target region may be a brain tumor and the other surrounding regions may be the skull bones. On the day of treatment, the patient may be positioned on the treatment bed as shown in  FIG. 4 . In step  134 , the system may determine if the treatment can begin based on the status of the safety interlocks. If it is not safe to begin the treatment, then the method loops back to test the safety interlocks until a safe condition is indicated. 
         [0049]    In step  136  when the treatment begins, a first diagnostic beam generator is energized by the computer in order to generate an image on the recording device. In a preferred embodiment, the diagnostic beam generators are x-ray generators and the image recorder is an amorphous silicon imager that generates an image in response to x-rays as is well known. The image generated by the first diagnostic beam in the image recorder may then be downloaded by the computer to the storage device attached to the computer in step  138  and the image recorder may be reset. In step  140 , the method determines if there are any other diagnostic beams to be energized. If there are other diagnostic beams to energize, the method loops back to step  136  to energize that generator, generate an image and download the image to the storage device. In this embodiment, there may be two diagnostic beam generators that are at a predetermined non-zero angle with respect to each other. In accordance with the invention, the method sequentially energizes the diagnostic beam generators to generate the images from each of the diagnostic beams in a time sequential manner. In accordance with the invention, repeated pairs of images from the diagnostic beam generators may be generated at periodic times so that the location of the target region at different times may be determined. 
         [0050]    Once the diagnostic images are generated, the two images are compared to the three-dimensional pre-operative mapping as is well known to determine the location of the target region at the particular time in step  142 . In step  144 , the targeting of the treatment beam is adjusted based on the comparison so that the treatment beam is always focused on the target region. If there are repeated diagnostic images generated, after each new set of images is generated, the images are compared to the mapping and the treatment beam targeting is adjusted to compensate for changes in the position of the target region. In this manner, the target region is accurately tracked so that the treatment beam is focused on the target region. 
         [0051]      FIG. 13  illustrates a pre-operative image  250  and intra-treatment image data  252  generated by the diagnostic beams. As shown, the intra-treatment images generated by the diagnostic beams are less clear and it is difficult to make out all of the structures or even the target region in the image. The pre-operative image  250 , on the other hand, is very clear and each structure of the body can be clearly seen. Therefore, in order to make it possible to infer the position of the target region from the intra-treatment images shown, the intra-treatment image is deformed, using various well known deformation techniques such as linear interpolation or warping, to form a deformed image  254  until the intra-treatment images and its structures form the best match with the pre-operative images. Once the deformation is completed, the position of the target region may be inferred from the position of the structures. This deformation technique may be used with all of the embodiments of the invention described above. 
         [0052]    Although the above embodiments show a single diagnostic beam source being used, the invention is not limited to a single diagnostic beam source. In fact, the system may use five fixed sources that generate the diagnostic beams and two or more moving sources that generate the diagnostic beams. For the fixed sources, they may be activated at specific time points throughout the respiration cycle. More detailed information about the deformation model corresponding to respiratory motion may then be obtained as set forth in the U.S. patent application Ser. No. 09/270,404. 
         [0053]    While the foregoing has been with reference to particular embodiments of the invention, it will be appreciated by those skilled in the art that changes in these embodiments may be made without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims.