Abstract:
A system and method for stereoscopically imaging a patient at multiple locations with a radiation treatment system using a common imaging center.

Description:
[0001]    This application is a continuation application of U.S. patent application Ser. No. 11/973,722, filed Oct. 9, 2007, which is a continuation application of U.S. patent application Ser. No. 11/170,832, filed Jun. 29, 2005, now U.S. Pat. No. 7,302,033, which are hereby incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates generally to image-guided radiation treatment systems and, in particular, to the geometry of imaging systems for guiding radiation treatment. 
       BACKGROUND 
       [0003]    Radiosurgery and radiotherapy are radiation treatment systems that use external radiation beams to treat pathological anatomies (e.g., tumors, lesions, vascular malformations, nerve disorders, etc.) by delivering a prescribed dose of radiation (e.g., X-rays or gamma rays) to the pathological anatomy while minimizing radiation exposure to surrounding tissue and critical anatomical structures (e.g., the spinal chord). Both radiosurgery and radiotherapy are designed to necrotize pathological anatomy while sparing healthy tissue and the critical structures. Radiotherapy is characterized by a low radiation dose per treatment and many treatments (e.g., 30 to 45 days of treatment). Radiosurgery is characterized by a relatively high radiation dose in one, or at most a few, treatments. In both radiotherapy and radiosurgery, the radiation dose is delivered to the site of the pathological anatomy from multiple angles. As the angle of each radiation beam is different, each beam intersects a target region occupied by the pathological anatomy, but passes through different areas of healthy tissue on its way to and from the target region. As a result, the cumulative radiation dose in the target region is high and the average radiation dose to healthy tissue and critical structures is low. 
         [0004]    Frame-based radiotherapy and radiosurgery treatment systems employ a rigid, invasive stereotactic frame to immobilize a patient during pre-treatment imaging for diagnosis and treatment-planning (e.g., using a CT scan or other 3-D imaging modality, such as MRI or PET), and also during subsequent radiation treatments. These systems are limited to intracranial treatments because the rigid frame must be attached to bony structures that have a fixed spatial relationship with target region, and the skull and brain are the only anatomical features that satisfy that criterion. 
         [0005]    In one type of frame-based radiosurgery system, a distributed radiation source (e.g., a cobalt 60 gamma ray source) is used to produce an approximately hemispherical distribution of simultaneous radiation beams though holes in a beam-forming assembly. The axes of the radiation beams are angled to intersect at a single point (treatment isocenter) and the beams together form an approximately spherical locus of high intensity radiation. The distributed radiation source requires heavy shielding, and as a result the equipment is heavy and immobile. Therefore, the system is limited to a single treatment isocenter. 
         [0006]    In another type of frame-based radiotherapy system, known as intensity modulated radiation therapy (IMRT), the radiation treatment source is an x-ray beam device (e.g., a linear accelerator) mounted in a gantry structure that rotates around the patient in a fixed plane of rotation. IMRT refers to the ability to shape the cross-sectional intensity of the radiation beam as it is moved around the patient, using multi-leaf collimators (to block portions of the beam) or compensator blocks (to attenuate portions of the beam). The axis of each beam intersects the center of rotation (the treatment isocenter) to deliver a dose distribution to the target region. Because the center of rotation of the gantry does not move, this type of system is also limited to a single treatment isocenter. 
         [0007]    Image-guided radiotherapy and radiosurgery systems (together, image-guided radiation treatment (IGRT) systems) eliminate the need for invasive frame fixation by tracking changes in patient position between the pre-treatment imaging phase and the treatment delivery phase (in-treatment phase). This correction is accomplished by acquiring real-time stereoscopic X-ray images during the treatment delivery phase and registering them with reference images, known as digitally reconstructed radiograms (DRRs), rendered from a pre-treatment CAT scan. A DRR is a synthetic X-ray produced by combining data from CAT scan slices and computing a two-dimensional (2-D) projection through the slices that approximates the geometry of the real-time imaging system. 
         [0008]    Gantry-based IGRT systems add an imaging x-ray source and a detector to the treatment system, located in the rotational plane of the LINAC (offset from the LINAC, e.g., by 90 degrees), and which rotate with the LINAC. The imaging x-ray beam passes through the same isocenter as the treatment beam, so the imaging isocenter coincides with the treatment isocenter, and both isocenters are fixed in space. 
         [0009]      FIG. 1  illustrates the configuration of an image-guided, robotic-based radiation treatment system  100 , such as the CYBERKNIFE® Radiosurgery System manufactured by Accuray, Inc. of California. In this system, the trajectories of the treatment x-ray beams are independent of the location of the imaging x-ray beams. In  FIG. 1 , the radiation treatment source is a LINAC  101  mounted on the end of a robotic arm  102  having multiple (e.g., 5 or more) degrees of freedom in order to position the LINAC  101  to irradiate a pathological anatomy (target region or volume) with beams delivered from many angles, in many planes, in an operating volume around the patient. Treatment may involve beam paths with a single isocenter, multiple isocenters, or with a non-isocentric approach (i.e., the beams need only intersect with the pathological target volume and do not necessarily converge on a single point, or isocenter, within the target). 
         [0010]    In  FIG. 1 , the imaging system includes X-ray sources  103 A and  103 B and X-ray detectors (imagers)  104 A and  104 B. Typically, the two x-ray sources  103 A and  103 B are mounted in fixed positions on the ceiling of an operating room and are aligned to project imaging x-ray beams from two different angular positions (e.g., separated by 90 degrees) to intersect at a machine isocenter  105  (where the patient will be located during treatment on a treatment couch  106 ) and to illuminate imaging surfaces (e.g., amorphous silicon detectors) of respective detectors  104 A and  104 B after passing through the patient.  FIG. 2  illustrates the geometry of radiation treatment system  100 . Typically, the x-ray detectors  104 A and  104 B are mounted on the floor  109  of the operating room at ninety degrees relative to each other and perpendicular to the axes  107 A and  107 B of their respective imaging x-ray beams. This orthogonal, stereoscopic imaging geometry is capable of great precision, reducing registration errors to sub-millimeter levels. However, there are some inherent limitations associated with this imaging geometry when installed in a typical operating room, which may have a ceiling no more than nine or ten feet high. 
         [0011]    As illustrated in  FIG. 2 , the LINAC  101  is highly maneuverable and relatively compact, but it still requires a minimum amount of separation between the patient  108  and the ceiling  110  of the operating room to deliver treatments from above the patient. There are also certain positions that the LINAC may be unable to occupy, either because the LINAC may block one of the imaging x-ray beams or because one of the x-ray detectors may block the radiation treatment beam. Furthermore, because the patient must be located at least some minimum distance from the ceiling to enable access from above, there may be insufficient room below the patient to deliver treatment from below, even if treatment from under the patient would be more beneficial (e.g., treating the spinal area while the patient is laying face up). Therefore, the location of the imaging center of the imaging system may need to be chosen as a compromise between treatment access and imaging access. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES  
         [0012]    The present invention is illustrated by way of example, and not by limitation, in the figures of the accompanying drawings in which: 
           [0013]      FIG. 1  illustrates a conventional image-guided radiation treatment system; 
           [0014]      FIG. 2  illustrates the geometry of a conventional image-guided radiation treatment system; 
           [0015]      FIG. 3A  illustrates an imaging system in one embodiment of imaging geometry; 
           [0016]      FIG. 3B  illustrates one application of the embodiment of  FIG. 3A ; 
           [0017]      FIG. 3C  illustrates another application of the embodiment of  FIG. 3A ; 
           [0018]      FIGS. 4A and 4B  illustrate an imaging system in a second embodiment of imaging geometry; 
           [0019]      FIG. 5  illustrates an imaging system in a third embodiment of imaging geometry; 
           [0020]      FIG. 6  illustrates an imaging system in a fourth embodiment of imaging geometry; 
           [0021]      FIG. 7  illustrates an imaging system in a fifth embodiment of imaging geometry; 
           [0022]      FIG. 8A  illustrates an imaging system in a sixth embodiment of imaging geometry; 
           [0023]      FIGS. 8B and 8C  illustrate a treatment delivery system incorporating the embodiment of  FIG. 8A . 
           [0024]      FIGS. 9A and 9B  illustrate an imaging system in a seventh embodiment of imaging geometry; 
           [0025]      FIG. 10  is a flowchart illustrating a method in one embodiment of imaging geometry; 
           [0026]      FIG. 11  illustrates a system in which embodiments of imaging geometry may be practiced; and 
           [0027]      FIG. 12  is a flowchart illustrating a method in one embodiment of imaging geometry. 
       
    
    
     DETAILED DESCRIPTION  
       [0028]    Apparatus and methods for imaging geometry in radiation treatment systems are described. In the following description, numerous specific details are set forth such as examples of specific components, devices, methods, etc., in order to provide a thorough understanding of embodiments of the present invention. It will be apparent, however, to one skilled in the art that these specific details need not be employed to practice embodiments of the present invention. In other instances, well-known materials or methods have not been described in detail in order to avoid unnecessarily obscuring embodiments of the present invention. The term “coupled” as used herein, may mean directly coupled or indirectly coupled through one or more intervening components or systems. The term “X-Ray image” as used herein may mean a visible X-ray image (e.g., displayed on a video screen) or a digital representation of an X-ray image (e.g., a file corresponding to the pixel output of an X-ray detector). The terms “in-treatment image” or “real-time image” as used herein may refer to images captured at any point in time during a treatment delivery phase of a radiosurgery or radiotherapy procedure, which may include times when the radiation source is either on or off. The term IGR as used herein may refer to image-guided radiation therapy, image-guided radiosurgery, or both. 
         [0029]      FIG. 3A  illustrates an imaging system  300  in one embodiment of an imaging geometry associated with a robotic-based IGRT system such as the CYBERKNIFE® Radiosurgery System, manufactured by Accuray, Inc. of California. Imaging system  300  includes a first pair of x-ray sources  301 A and  301 B to generate a first x-ray beam  302 A and a second x-ray beam  302 B, where the axis  303 A of the first x-ray beam and the axis  303 B of the second x-ray beam define a first imaging plane. Imaging system  300  may also include a second pair of x-ray sources  301 C and  301 D to generate a third x-ray beam  302 C and a fourth x-ray beam  302 D, where the axis  303 C of the third x-ray beam and the axis  303 D of the fourth x-ray beam define a second imaging plane. The first x-ray beam  302 A and the second x-ray beam  302 B may be disposed to intersect at a first angle β 1  at a first imaging center  304 . The third x-ray beam  302 C and the fourth x-ray beam  302 D may be disposed to intersect at a second angle β 2  at a second imaging center  305 . Imaging system  300  may also include a first pair of x-ray detectors  306 A and  306 B in the first imaging plane to detect the first x-ray beam  302 A and the second x-ray beam  302 B, and a second pair of x-ray detectors  306 C and  306 D in the second imaging plane to detect the third x-ray beam  302 C and the fourth x-ray beam  302 D. 
         [0030]    Thus, as illustrated in  FIG. 3A , the imaging geometry of imaging system  300  may provide two imaging centers  304  and  305  located at different elevations. X-ray sources  301 A and  301 B may be located above the imaging centers and x-ray sources  301 C and  301 D may be located below the imaging centers. Angles β 1  and β 2  may be selected (e.g., by changing the separation between the x-ray sources and/or the x-ray detectors) to determine the location of the imaging centers with respect to one another and with respect to the x-ray sources and x-ray detectors. In particular, angles β 1  and β 2  may be selected to be equal angles (e.g., 90 degrees) such that the intersection of x-ray beam  302 A and x-ray beam  302 B is symmetrical with the intersection of x-ray beams  302 C and  302 D. 
         [0031]    Two imaging centers, such as imaging centers  304  and  305 , may establish multiple treatment frames of reference and enable image-guided radiation treatment from above a patient and from below a patient. For example, as illustrated in  FIG. 3B , x-ray sources  301 A and  301 B, and x-ray detectors  306 C and  306 D may be mounted on the ceiling  307  of an operating room. X-ray sources  301 C and  301 D, and x-ray detectors  306 A and  306 B may be mounted on the floor  308  of the operating room. If a patient  309  is positioned (e.g., by moving the patient on a robotic couch, such as treatment couch  310 ) near the first machine center  304 , the patient may be imaged while a robotically controlled LINAC  311  administers radiation treatment from a region  312  above the patient. Region  312  may include a predefined set of treatment nodes or locations where LINAC  311  may be positioned to deliver radiation treatment from one or more angles. For example, region  312  may include 100 nodes and LINAC  311  may be positioned at 12 different angles at each node to deliver a total of 1200 individual treatment beams. In one embodiment, in the case of intracranial radiation treatment, for example, region  312  may be an approximately hemispherical region centered on the head of patient  309  with a radius from approximately 650 millimeters to approximately 800 millimeters. In an alternative embodiment, in the case of radiation treatment to the body of patient  309 , region  312  may be an approximately cylindrical with a radius from approximately 900 mm to 1000 mm. Conversely, as illustrated in  FIG. 3C , if the patient  309  is positioned near the second machine center  305 , the patient may be imaged while the robotically controlled LINAC  311  administers radiation treatment from a region  313  below the patient which may mirror the same general dimensions as region  312 . 
         [0032]      FIG. 3A  illustrates an imaging system  300  where the first imaging plane and the second imaging plane are coplanar planes. Other configurations of the first imaging plane and the second imaging plane may be advantageous (e.g., to best utilize limited floor space in an operating room or to reduce the number of blocked treatment nodes).  FIG. 4A  illustrates an alternative embodiment of a system  400  where the first imaging plane  314  is rotated at an angle γ with respect to the second imaging plane  315 . In one embodiment, as illustrated in  FIG. 4B  as a top down view of system  400 , γ may be a ninety degree angle.  FIG. 4B  illustrates how treatment couch  310  may be positioned at multiple angles with respect to LINAC  311  on robotic arm  318 , with respect to image planes  314  and  315 , and also with respect to machine centers  304  and  305 . It will be appreciated that the positioning flexibility provided by the configuration of system  400  may eliminate the problem of blocked treatment nodes described above. 
         [0033]    Returning now to  FIG. 3A , it will be observed that x-ray detector  306 A may be disposed at an imaging angle θ 1  with respect to the axis  303 A of x-ray beam  302 A. Likewise, x-ray detectors  306 B,  306 C and  306 D may be disposed at imaging angles θ 2 , θ 3  and θ 4  with respect to the axes  303 B,  303 C and  303 D of x-ray beams  302 B,  302 C and  302 D. In one embodiment, imaging angles θ 1  through θ 4  may be ninety degree angles, such that the imaging surfaces of x-ray detectors  306 A through  306 D are all perpendicular to the axes of their respective x-ray beams. In another embodiment, imaging angles θ 1  through θ 4  may be acute angles selected to dispose x-ray detectors  306 A and  306 B along a baseline  316  in the first imaging plane  314 , and to dispose x-ray detectors  306 C and  306 D along a topline  317  in the second imaging plane  315 . In one embodiment, baseline  316  and topline  317  may correspond to the ceiling  307  and the floor  308  of  FIGS. 3B and 3C . 
         [0034]    In one embodiment of imaging geometry, as illustrated in  FIG. 5 , an imaging system  500  may include three x-ray sources and three x-ray detectors. In FIG.  5 , a first x-ray source  501 A may project an x-ray beam  502 A, having an axis  503 A, onto an imaging surface  508 A of a first x-ray detector  506 A. A second x-ray source  501 B may project an x-ray beam  502 B, having an axis  503 B, onto an imaging surface  508 B of a second x-ray detector  506 B. X-ray beam  502 B may be disposed to intersect x-ray beam  502 A such that axis  503 B intersects axis  503 A at a first imaging center  504  at an angle α 1 . A third x-ray source  501 C may project a third x-ray beam, having an axis  503 C, onto an imaging surface  508 C of a third x-ray detector  506 C. X-ray beam  502 C may be disposed to intersect x-ray beam  502 A such that axis  503 C intersects axis  503 A at a second imaging center  505  at a second angle α 2 . X-ray beam  502 C may also be disposed to intersect x-ray beam  502 B such that axis  503 C intersects axis  503 B at a third imaging center  507  at an angle α 3 . 
         [0035]    In one embodiment, imaging surface  508 A may be disposed at an imaging angle φ 1  with respect to axis  503 A, imaging surface  508 B may be disposed at an imaging angle φ 2  with respect to axis  503 B, and imaging surface  508 C may be disposed at an imaging angle φ 3  with respect to axis  503 C. In one embodiment, angles φ 1 , φ 2 , and φ 3  may be right angles. In other embodiments, one or more of angles φ 1 , φ 2 , and φ 3  may be selected such that imaging surfaces  508 A,  508 B and  508 C are parallel to a baseline  509 . 
         [0036]    In one embodiment, x-ray source  501 A and x-ray detector  506 A may each be configured to move horizontally, together or independently, in order to adjust the points of intersection of the first x-ray beam  502 A with the second x-ray beam  502 B and the third x-ray beam  502 C, in order to adjust the locations of the first imaging center  504  and the second imaging center  505 , and/or the separation Δ between the first imaging center  504  and the second imaging center  505 . 
         [0037]      FIG. 6  illustrates an imaging system  600  in yet another embodiment of imaging geometry. Imaging system  600  includes a first pair of x-ray sources  601 A and  601 B at a separation δ 1  to project a first x-ray beam  602 A and a second x-ray beam  602 B to intersect at an angle ρ 1  at a first imaging center  604 , located at a height h 1  above the x-ray sources. Imaging system  600  may also include a second pair of x-ray sources  601 C and  601 D at a separation δ 2  to project a third x-ray beam  602 C and a fourth x-ray beam  602 D to intersect at an angle ρ 2  at a second imaging center  605 , located at a height h 2  above the x-ray sources. Separations δ 1 , δ 2  and δ 3  may be selected to adjust the angles ρ 1  and ρ 2 , and the locations of imaging centers  604  and  605 . As illustrated in  FIG. 6 , imaging center  604  is enclosed by an imaging volume V 1 , subtended by x-ray beams  602 A and  602 B. Imaging center  605  is enclosed by an imaging volume V 2 , subtended by x-ray beams  602 C and  602 D. Volumes V 1  and V 2  may also be adjusted by selecting separations δ 1 , δ 2 , and δ 3 . Although not illustrated, it will be appreciated that the geometry of  FIG. 6  may be inverted. That is, the locations of the x-ray sources and x-ray detectors may be reversed. 
         [0038]      FIG. 7  illustrates a system  700  in another embodiment of imaging geometry. System  700  includes a single pair of movable x-ray sources which may be configured to maintain alignment with x-ray detectors  606 A and  606 B when x-ray sources  701 A and  701 B are at either separation δ 1  or δ 2 . Methods for maintaining angular alignments through linear displacements are known in the art and will not be described, herein. Thus, it will be appreciated that imaging system  700  may provide the same functionality as imaging system  600  with only two x-ray sources. 
         [0039]      FIG. 8A  illustrates an imaging system  800  in another embodiment of imaging geometry. Imaging system  800  includes two pairs of x-ray sources  801 A and  801 B, and  801 C and  801 D mounted below a floorline  808  and covered by an x-ray transparent material  809 . It will be appreciated that mounting the x-ray sources below the floorline may maximize the space available within an operating theater to position a LINAC, such as LINAC  311  for treatment. X-ray sources  801 A and  801 B may project x-ray beams  802 A and  802 B that intersect at imaging center  804  and illuminate x-ray detectors  806 A and  806 B, respectively. X-ray sources  801 C and  801 D may project x-ray beams  802 C and  802 D that intersect at imaging center  805  and illuminate x-ray detectors  806 A and  806 B, respectively. 
         [0040]      FIGS. 8B and 8C  illustrate an example of a radiation treatment delivery system  825  incorporating the imaging system of  FIG. 8A . Radiation treatment delivery system  825  includes a LINAC  311  mounted on a robotic arm  810 . The system also includes a robotic arm assembly  811 , with multiple degrees of freedom of motion (e.g., five or more) to position treatment couch  310  at multiple positions relative to imaging centers  804  and  805 .  FIG. 8B  illustrates treatment couch  310  positioned in proximity to imaging center  804 , and  FIG. 8C  illustrates treatment couch  310  positioned in proximity to imaging center  805 . 
         [0041]      FIGS. 9A and 9B  illustrate an imaging system  900  in a further embodiment of imaging geometry. Imaging system  900  includes a pair of movable x-ray sources  901 A and  901 B which may be linearly translated to change the separation between the x-ray sources from σ 1  to σ 1 ′. Imaging system  900  may also include a pair of movable x-ray detectors  906 A and  906 B which may be linearly translated to change the separation between the x-ray detectors from σ 2  to σ 2 ′. In  FIG. 9A , x-ray beams  902 A and  902 B intersect at image center  904 . At the position of the x-ray sources and x-ray detectors illustrated in  FIG. 9   a , it can be seen that treatment cannot be provided by LINAC  911  (shown in dotted line) because positioning the LINAC as shown will block x-ray beam  902 B and prevent imaging system  900  from obtaining a stereoscopic image.  FIG. 9B  illustrates imaging system  900  with x-ray sources  901 A and  901 B, and x-ray detectors  906 A and  906 B, repositioned to generate x-ray beams that intersect at imaging center  904  without being blocked by LINAC  911 . 
         [0042]      FIG. 10  is a flowchart illustrating a method  925  in one embodiment of an imaging geometry. With reference to  FIGS. 3A-3C  and  4 A, the method includes establishing a first imaging center  304  at a first location h 1  to enable radiation treatment of a target anatomy  309  from a first region  312  in a treatment frame of reference (step  1001 ). The method also includes establishing a second imaging center  305  at a second location h 2  to enable radiation treatment of the target anatomy  309  from a second region  313  in the treatment frame of reference (step  1002 ). 
         [0043]    In one embodiment, establishing the first imaging center (step  1001 ) may include generating a first imaging beam  302 A having a first axis  303 A, and a second imaging beam  302 B having a second axis  303 B, the first axis and the second axis defining a first image plane  314 , the second imaging beam disposed at a first angle β 1  with respect to the first imaging beam to intersect the first imaging beam at the first location. In one embodiment, establishing the second imaging center (step  1002 ) may include generating a third imaging beam  302 C having a third axis  303 C, and a fourth imaging beam  302 D having a fourth axis  303 D, the third axis and the fourth axis defining a second image plane  315 , the fourth imaging beam disposed at a second angle β 2  with respect to the third imaging beam to intersect the third imaging beam at the first location. 
         [0044]      FIG. 11  illustrates one embodiment of systems that may be used in performing radiation treatment in which features of the present invention may be implemented. As described below and illustrated in  FIG. 10 , system  4000  may include a diagnostic imaging system  1000 , a treatment planning system  2000  and a treatment delivery system  3000 . 
         [0045]    Diagnostic imaging system  1000  may be any system capable of producing medical diagnostic images of a volume of interest (VOI) in a patient that may be used for subsequent medical diagnosis, treatment planning and/or treatment delivery. For example, diagnostic imaging system  1000  may be a computed tomography (CT) system, a magnetic resonance imaging (MRI) system, a positron emission tomography (PET) system, a single photon emission CT (SPECT), an ultrasound system or the like. For ease of discussion, diagnostic imaging system  1000  may be discussed below at times in relation to a CT x-ray imaging modality. However, other imaging modalities such as those above may also be used. 
         [0046]    Diagnostic imaging system  1000  includes an imaging source  1010  to generate an imaging beam (e.g., x-rays, ultrasonic waves, radio frequency waves, etc.) and an imaging detector  1020  to detect and receive the beam generated by imaging source  1010 , or a secondary beam or emission stimulated by the beam from the imaging source (e.g., in an MRI or PET scan). In one embodiment, diagnostic imaging system  1000  may include two or more diagnostic X-ray sources and two or more corresponding imaging detectors. For example, two x-ray sources may be disposed around a patient to be imaged, fixed at an angular separation from each other (e.g., 90 degrees, 45 degrees, etc.) and aimed through the patient toward (an) imaging detector(s) which may be diametrically opposed to the x-ray sources. A single large imaging detector, or multiple imaging detectors, can also be used that would be illuminated by each x-ray imaging source. Alternatively, other numbers and configurations of imaging sources and imaging detectors may be used. 
         [0047]    The imaging source  1010  and the imaging detector  1020  are coupled to a digital processing system  1030  to control the imaging operation and process image data. Diagnostic imaging system  1000  includes a bus or other means  1035  for transferring data and commands among digital processing system  1030 , imaging source  1010  and imaging detector  1020 . Digital processing system  1030  may include one or more general-purpose processors (e.g., a microprocessor), special purpose processor such as a digital signal processor (DSP) or other type of device such as a controller or field programmable gate array (FPGA). Digital processing system  1030  may also include other components (not shown) such as memory, storage devices, network adapters and the like. Digital processing system  1030  may be configured to generate digital diagnostic images in a standard format, such as the DICOM (Digital Imaging and Communications in Medicine) format, for example. In other embodiments, digital processing system  1030  may generate other standard or non-standard digital image formats. Digital processing system  1030  may transmit diagnostic image files (e.g., the aforementioned DICOM formatted files) to treatment planning system  2000  over a data link  1500 , which may be, for example, a direct link, a local area network (LAN) link or a wide area network (WAN) link such as the Internet. In addition, the information transferred between systems may either be pulled or pushed across the communication medium connecting the systems, such as in a remote diagnosis or treatment planning configuration. In remote diagnosis or treatment planning, a user may utilize embodiments of the present invention to diagnose or treatment plan despite the existence of a physical separation between the system user and the patient. 
         [0048]    Treatment planning system  2000  includes a processing device  2010  to receive and process image data. Processing device  2010  may represent one or more general-purpose processors (e.g., a microprocessor), special purpose processor such as a digital signal processor (DSP) or other type of device such as a controller or field programmable gate array (FPGA). Processing device  2010  may be configured to execute instructions for performing treatment planning operations discussed herein. 
         [0049]    Treatment planning system  2000  may also include system memory  2020  that may include a random access memory (RAM), or other dynamic storage devices, coupled to processing device  2010  by bus  2055 , for storing information and instructions to be executed by processing device  2010 . System memory  2020  also may be used for storing temporary variables or other intermediate information during execution of instructions by processing device  2010 . System memory  2020  may also include a read only memory (ROM) and/or other static storage device coupled to bus  2055  for storing static information and instructions for processing device  2010 . 
         [0050]    Treatment planning system  2000  may also include storage device  2030 , representing one or more storage devices (e.g., a magnetic disk drive or optical disk drive) coupled to bus  2055  for storing information and instructions. Storage device  2030  may be used for storing instructions for performing the treatment planning steps discussed herein. 
         [0051]    Processing device  2010  may also be coupled to a display device  2040 , such as a cathode ray tube (CRT) or liquid crystal display (LCD), for displaying information (e.g., a 2D or 3D representation of the VOI) to the user. An input device  2050 , such as a keyboard, may be coupled to processing device  2010  for communicating information and/or command selections to processing device  2010 . One or more other user input devices (e.g., a mouse, a trackball or cursor direction keys) may also be used to communicate directional information, to select commands for processing device  2010  and to control cursor movements on display  2040 . 
         [0052]    It will be appreciated that treatment planning system  2000  represents only one example of a treatment planning system, which may have many different configurations and architectures, which may include more components or fewer components than treatment planning system  2000  and which may be employed with the present invention. For example, some systems often have multiple buses, such as a peripheral bus, a dedicated cache bus, etc. The treatment planning system  2000  may also include MIRIT (Medical Image Review and Import Tool) to support DICOM import (so images can be fused and targets delineated on different systems and then imported into the treatment planning system for planning and dose calculations), expanded image fusion capabilities that allow the user to treatment plan and view dose distributions on any one of various imaging modalities (e.g., MRI, CT, PET, etc.). Treatment planning systems are known in the art; accordingly, a more detailed discussion is not provided. 
         [0053]    Treatment planning system  2000  may share its database (e.g., data stored in storage device  2030 ) with a treatment delivery system, such as treatment delivery system  3000 , so that it may not be necessary to export from the treatment planning system prior to treatment delivery. Treatment planning system  2000  may be linked to treatment delivery system  3000  via a data link  2500 , which may be a direct link, a LAN link or a WAN link as discussed above with respect to data link  1500 . It should be noted that when data links  1500  and  2500  are implemented as LAN or WAN connections, any of diagnostic imaging system  1000 , treatment planning system  2000  and/or treatment delivery system  3000  may be in decentralized locations such that the systems may be physically remote from each other. Alternatively, any of diagnostic imaging system  1000 , treatment planning system  2000  and/or treatment delivery system  3000  may be integrated with each other in one or more systems. 
         [0054]    Treatment delivery system  3000  includes a therapeutic and/or surgical radiation source  3010  (e.g., LINAC  311 ) to administer a prescribed radiation dose to a target volume in conformance with a treatment plan. Treatment delivery system  3000  may also include an imaging system  3020  to capture intra-treatment images of a patient volume (including the target volume) for registration or correlation with the diagnostic images described above in order to position the patient with respect to the radiation source. Imaging system  3020  may include any of the imaging systems and imaging geometries described above (e.g., systems  300 ,  400 ,  500 ,  600 ,  700 ,  800  and  900 ). Treatment delivery system  3000  may also include a digital processing system  3030  to control radiation source  3010 , imaging system  3020  and a patient support device such as a treatment couch  3040 . Digital processing system  3030  may include one or more general-purpose processors (e.g., a microprocessor), special purpose processor such as a digital signal processor (DSP) or other type of device such as a controller or field programmable gate array (FPGA). Digital processing system  3030  may also include other components (not shown) such as memory, storage devices, network adapters and the like. Digital processing system  3030  may be coupled to radiation source  3010 , imaging system  3020  and treatment couch  3040  by a bus  3045  or other type of control and communication interface. 
         [0055]    Digital processing system  3030  may implement algorithms to register images obtained from imaging system  3020  with pre-operative treatment planning images in order to align the patient on the treatment couch  3040  within the treatment delivery system  3000 , and to precisely position the radiation source with respect to the target volume. 
         [0056]    The treatment couch  3040  may be coupled to a robotic arm (not shown) having multiple (e.g., 5 or more) degrees of freedom. The couch arm may have five rotational degrees of freedom and one substantially vertical, linear degree of freedom. Alternatively, the couch arm may have six rotational degrees of freedom and one substantially vertical, linear degree of freedom or at least four rotational degrees of freedom. The couch arm may be vertically mounted to a column or wall, or horizontally mounted to pedestal, floor, or ceiling. Alternatively, the treatment couch  3040  may be a component of another mechanical mechanism, such as the Axum® treatment couch developed by Accuray, Inc. of California, or be another type of conventional treatment table known to those of ordinary skill in the art. 
         [0057]      FIG. 12  is a flowchart illustrating a method  950  in one embodiment of imaging geometry. With reference, again, to  FIGS. 3B and 3C , the method begins at step  951  by generating a first imaging beam  302 A. At step  952 , a second imaging beam  302 B is generated to intersect the first imaging beam at a first imaging center  304 . At step  953 , a patient  309  is positioned at approximately the first imaging center. At step  954 , a first image is generated with the first imaging beam and a second image is generated with the second imaging beam. At step  955 , the first image and the second image are registered with a first set of pre-treatment reference images. At step  956 , the registration result is used to position a radiation treatment source (e.g., the LINAC  311 ). At step  957 , radiation treatment is delivered to a target anatomy in the patient  309  from a first range of angles  312 . At step  958 , a third imaging beam  303 C is generated. At step  959 , a fourth imaging beam  302 D is generated to intersect the third imaging beam at a second imaging center  305 . At step  960 , the patient  309  is positioned at approximately the second imaging center. At step  961 , a third image is generated with the third imaging beam and a fourth image is generated with the fourth imaging beam. At step  962 , the third image and the fourth image are registered with a second set of pre-treatment reference images. At step  963 , the registration result is used to position the radiation treatment source (e.g., the LINAC  311 ). At step  964 , radiation treatment is delivered to the target anatomy in the patient  309  from a second range of angles  313 . 
         [0058]    It should be noted that the methods and apparatus described herein are not limited to use only with medical diagnostic imaging and treatment. In alternative embodiments, the methods and apparatus herein may be used in applications outside of the medical technology field, such as industrial imaging and non-destructive testing of materials (e.g., motor blocks in the automotive industry, airframes in the aviation industry, and welds in the construction industry and drill cores in the petroleum industry) and seismic surveying. In such applications, for example, “treatment” may refer generally to the application of radiation beam(s). 
         [0059]    While some specific embodiments of the invention have been shown the invention is not to be limited to these embodiments. The invention is to be understood as not limited by the specific embodiments described herein, but only by scope of the appended claims.