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 . fig3 a 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 . thus , as illustrated in fig3 a , 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 . 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 fig3 b , 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 fig3 c , 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 . fig3 a 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 ). fig4 a 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 fig4 b as a top down view of system 400 , γ may be a ninety degree angle . fig4 b illustrates how treatment couch 310 may be positioned at multiple angles with respect to linac 311 on robotic arm 320 , 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 . returning now to fig3 a , 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 fig3 b and 3c . in one embodiment of imaging geometry , as illustrated in fig5 , an imaging system 500 may include three x - ray sources and three x - ray detectors . in fig5 , 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 . 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 . 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 a between the first imaging center 504 and the second imaging center 505 . fig6 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 fig6 , 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 fig6 may be inverted . that is , the locations of the x - ray sources and x - ray detectors may be reversed . fig7 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 . fig8 a 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 . fig8 b and 8c illustrate an example of a radiation treatment delivery system 825 incorporating the imaging system of fig8 a . 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 . fig8 b illustrates treatment couch 310 positioned in proximity to imaging center 804 , and fig8 c illustrates treatment couch 310 positioned in proximity to imaging center 805 . fig9 a 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 fig9 a , 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 fig9 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 . fig9 b 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 . fig1 is a flowchart illustrating a method 925 in one embodiment of an imaging geometry . with reference to fig3 a - 3c and 4 a , the method includes establishing a first imaging center 304 at a first location hi 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 ). 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 , 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 . fig1 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 fig1 , system 4000 may include a diagnostic imaging system 1000 , a treatment planning system 2000 and a treatment delivery system 3000 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . fig1 is a flowchart illustrating a method 950 in one embodiment of imaging geometry . with reference , again , to fig3 b 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 . 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 , 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 ). 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 .
a system and method for stereoscopically imaging a patient at multiple locations in a radiation treatment system with a variable imaging geometry to enable the delivery of radiation treatments from multiple ranges of treatment angles without obstructing the imaging system or the radiation treatment .