Patent Publication Number: US-2006004281-A1

Title: Vest-based respiration monitoring system

Description:
This application claims the benefit of U.S. Provisional Patent Application No. 60/584,304 entitled “VEST-BASED RESPIRATION MONITORING SYSTEM,” filed Jun. 30, 2004, the contents of which are incorporated by reference herein. 
    
    
     TECHNICAL FIELD  
      This invention relates to the field of radiation treatment, and in particular, to a system of tracking the movement of a pathological anatomy during respiration.  
     BACKGROUND  
      Tumors and lesions are types of pathological anatomies characterized by abnormal growth of tissue resulting from the uncontrolled, progressive multiplication of cells, while serving no physiological function. As an alternative to invasive surgery, pathological anatomies can now be treated non-invasively, for example, by external beam radiation therapy. In one type of external beam radiation therapy, an external radiation source is used to direct a sequence of x-ray beams at a tumor site from multiple angles, with the patient positioned so the tumor is at the center of rotation (isocenter) of the beam. As the angle of the radiation source is changed, every beam passes through the tumor site, but passes through a different area of healthy tissue on its way to the tumor. As a result, the cumulative radiation dose at the tumor is high and the average radiation dose to healthy tissue is low. The term radiotherapy refers to a procedure in which radiation is applied to a target region for therapeutic, rather than necrotic, purposes. The amount of radiation utilized in radiotherapy treatment sessions is typically about an order of magnitude smaller, as compared to the amount used in a radiosurgery session. Radiotherapy is typically characterized by a low dose per treatment (e.g., 100-200 centi-Grays (cGy)), short treatment times (e.g., 10 to 30 minutes per treatment) and hyperfractionation (e.g., 30 to 45 days of treatment). For convenience, the term “radiation treatment” is used herein to mean radiosurgery and/or radiotherapy unless otherwise noted by the magnitude of the radiation.  
      One challenge facing the delivery of radiation to treat pathological anatomies is identifying the target (i.e. tumor location within a patient). The most common technique currently used to identify and target a tumor location for treatment involves a diagnostic x-ray or fluoroscopy system to image the patient&#39;s body to detect the position of the tumor. This technique assumes that the tumor is stationary. Even if a patient is kept motionless, radiation treatment requires additional methods to account for movement due to respiration, in particular when treating a tumor located near the lungs. Breath hold and respiratory gating are two primary methods used to compensate for target movement during respiration while a patient is receiving conventional radiation treatments.  
      Breath hold requires the patient to hold their breath at the same point in their breathing cycle and only treats the tumor when the tumor is stationary. A respirometer is often used to measure the tidal volume and ensure the breath is being held at the same location in the breathing cycle during each irradiation. This method takes longer than a standard treatment and often requires training the patient to hold their breath in a repeatable manner.  
      Respiratory gating is the process of turning on the radiation beam as a function of a patient&#39;s breathing cycle. When using a respiratory gating technique, treatment is synchronized to the individual&#39;s breathing pattern, limiting the radiation beam delivery to only one specific part of the breathing cycle and targeting the tumor only when it is in the optimum range. This treatment method may be much quicker than the breath hold method but requires the patient to have many sessions of training to breath in the same manner for long periods of time. This training requires many days of practice before treatment can begin. This system may also require healthy tissue to be irradiated before and after the tumor passes into view to ensure complete coverage of the tumor. This can add an additional margin of 5-10 mm on top of the margin normally used during treatment.  
      Attempts have been made to avoid the burdens placed on a patient from breath hold and respiratory gating techniques. In another method to track the movement of a tumor in real time during respiration, a combination of internal imaging markers and external position markers has been used to detect the movement of a tumor. In particular, fiducial markers are placed near a tumor to monitor the tumor location. The position of the fiducial markers is coordinated with the external position markers to track the movement of the tumor during respiration. External position markers are used because the fiducial markers are typically monitored with x-ray imaging. Because it may be unsafe to expose the patient continuously to x-rays to monitor the fiducials, the position of the markers can be used to predict the position of the fiducial markers between the longer periods of x-ray images. One type of external position markers integrates light emitting diodes (LEDs) into a vest that is worn by the patient. The flashing LEDs are detected by a camera system to track movement.  FIG. 1  illustrates a typical configuration of a real time tracking vest for radiation treatment. The LEDs are positioned on the vest while the fiducials are planted within the patient near the tumor. One problem with LED-based vests is that in the internal images, typically generated by x-ray imaging, to display the position of the fiducial marker, the wires routed along the vests for the LEDs are also displayed. The wiring for the LEDs are metallic (typically copper wire) so the x-ray imaging detects both the fiducial marker and the wiring making the two not easily discemable. Because the image of the target region containing the tumor cannot be clearly visualized by the operator, planning and executing a successful radiation treatment plan may be difficult.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings.  
       FIG. 1  illustrates a typical configuration of a real time tracking vest for radiation treatment.  
       FIG. 2  illustrates one part of an external motion tracking system for use during radiation treatment.  
       FIG. 3A  is an oblique-front view of a fiber optic beacon.  
       FIG. 3B  is an oblique top view of a fiber optic beacon.  
       FIG. 3C  is a top view of a fiber optic beacon.  
       FIG. 3D  is bottom view of a fiber optic beacon.  
       FIG. 3E  is a side view of a fiber optic beacon.  
       FIG. 3F  is a front view of a fiber optic beacon.  
       FIG. 3G  is perspective side view of a fiber optic beacon.  
       FIG. 4  illustrates a fiber optic cable bundle having a quick connector.  
       FIG. 5A  shows a front view of a respiration monitoring vest.  
       FIG. 5B  shows a back view of a respiration monitoring vest.  
       FIG. 6  illustrates one embodiment of a configuration for respiration tracking system during radiation treatment.  
       FIG. 7  illustrates a cross-sectional view of a chest region during respiration and various elements of the internal imaging and respiration monitoring system working together to track motion of a patient.  
       FIG. 8  illustrates one configuration of a magnetic motion tracking system.  
       FIG. 9  illustrates a top view of a patient and showing the position of pathological anatomy that is targeted for radiation treatment.  
       FIG. 10  illustrates a side view of the magnetic motion tracking configuration for a patient lying treatment couch.  
       FIG. 11  illustrates respiration monitoring system that includes the use of LED as beacons for motion tracking.  
       FIG. 12  illustrates another respiration monitoring system that includes the use of LED as beacons for motion tracking.  
       FIG. 13  is a flowchart describing one method for motion tracking during respiration.  
       FIG. 14  illustrates one embodiment of systems that may be used to perform radiation treatment in which features of the present invention may be implemented.  
       FIG. 15  illustrates one embodiment of a treatment delivery system.  
    
    
     DETAILED DESCRIPTION  
      In the following description, numerous specific details are set forth such as examples of specific systems, components, methods, etc. in order to provide a thorough understanding 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 the present invention. In other instances, well-known components or methods have not been described in detail in order to avoid unnecessarily obscuring the present invention. It is understood that the figures herein are not necessarily drawn to scale, and the relative dimensions of the physical structure should not be inferred from the relative dimensions shown in the drawings.  
      Embodiments of a method and apparatus to track the movement of a pathological anatomy during respiration are described. In one embodiment, a combination of a first reference object placed outside of a patient and a second reference object placed within a patient (e.g., fiducial markers) is used to track the movement of a pathological anatomy during respiration. The second reference object serves as a marker for an internal image of a treatment area that includes the pathological anatomy. The position of the first reference object and the second reference object can be correlated to determine a position of pathological anatomy in real-time. By accurately and clearly following the movement of the pathological anatomy in real-time, a radiation treatment can be performed while a patient is breathing normally. One advantage of the motion tracking system described herein is that the first reference object does not appear in the internal image of the treatment area, thereby avoiding any confusion as to the identity and location of the second reference object. In one embodiment, an internal imaging system and an external motion tracking system are integrated with a radiation treatment system to track movement of a pathological anatomy (in real-time or near real-time) during radiation treatment.  
      The term “real-time” refers to a time scale that is substantially simultaneous to the actual radiation treatment delivery session, for example, at a rate approximately equal to or greater than 1 Hertz (Hz). The term “near real-time” refers to a time scale that is slower than real-time, for example, by about one or more orders of magnitude less than the time scale of real-time. As an example, the time scale for acquiring x-ray images, which may range from about a fraction of a second to about several seconds may be considered near real-time.  
      According to one aspect of the present invention, the external motion tracking system generally includes a reference object adapted to be tightly attached to a patient&#39;s upper body and a tracking system for tracking the movement of the reference object in real-time. The tracking system includes a detecting system for detecting the position of the reference object and a computer system for control of the detecting system and/or the reference object, and for calculating the position of the reference object in a coordinate system. The movement of the reference object is correlated with the respiratory movement of the patient. The positions of the reference object recorded by the tracking system are transmitted to a treatment system, which uses this information to determine a real-time position of the treatment target, for example a pathological anatomy. The treatment system then synchronizes the treatment to the moving pathological anatomy, thus enabling the radiation treatment system to administer treatment to the pathological anatomy in a dynamical and highly accurate manner.  
      In one embodiment, fiducial markers are used for the internal imaging of a pathological anatomy and the reference object is part of an external tracking system that includes a vest to be worn by the patient during radiation treatment. In one embodiment, the reference object is a fiber optic beacon disposed on the vest and connected to a light emitting source via a fiber optic cable. The light emitted from the beacon through the fiber optic cable is detected by a camera system to track movement. No element of the fiber optic system (e.g., fiber optic cable, fiber optic beacon) is displayed on the internal image of a treatment area, because substantially no metallic materials are part of the fiber optic system. The only markers displayed on the internal image generated by x-ray imaging are the fiducial markers, which track the position of the pathological anatomy. If elements of both the fiber optic system and the fiducial markers were displayed on the internal image, it may not be possible to distinguish between the two easily.  
      In an alternative embodiment, the reference object is a magnetic sensor disposed on the vest, with the patient wearing the vest and placed in an electromagnetic field created by a transmitter. The magnetic sensor is connected to a digital processing system that can determine the position and orientation of the patient. Similar to the fiber optic system, elements of a magnetic sensor system is not displayed on the internal image generated by x-ray imaging. In yet another embodiment, the reference object can be an LED beacon having a connecting wire that is thin enough such that the wire is easily discernable from the fiducial marker. Alternatively, the layout of the wire leading to an LED can be configured as so that there is no overlap with the fiducial marker. For example, the wire is positioned so that it does not rest directly over a fiducial marker planted near a target region within the patient.  
       FIG. 2  illustrates one part of an external motion tracking system  200  for use during radiation treatment. Tracking system  200  includes a vest  30  that is tightly secured to the torso of the patient as shown.  FIG. 2  illustrates a front view of vest  30 , which in one embodiment, is made from material such as spandex, lycra, and the like that conforms to the shape of the patient&#39;s body without pleat or spacing between the patient&#39;s body and vest  30 . One or more fiber optic beacons (e.g., beacon  11 , beacon  12 , and beacon  13 ) are secured to an outer surface of vest  30 . In one embodiment, the fiber optic beacons are secured to vest  30  with one or strips of small hooks or loops such as strip  31 , strip  32 , and strip  33 . The strips may be include any type of hook and loop fasteners known in the art, for example VELCRO® strips made by Velcro Industries B.V. For example, a bottom surface of fiber optic beacon  11  may include a series of hooks and strip may include a series of loops to secure fiber optic beacon  11  to vest  30 . Each fiber optic beacon is connected to a light source with a fiber optic cable as shown. Beacon  11  is connected via cable  16 , beacon  32  is connected via cable  17 , and beacon  13  is connected via cable  18 . In one embodiment, the fiber optic cables, beacons and vest  30  are made from plastic or other types of polymers exhibiting material properties of plastic, thereby eliminating metal from the treatment field, so that the x-ray system can clearly image any implanted fiducials with no artifacts created during a CT scan around the radiation treatment region. In one particular embodiment, fiber optic beacons  11 - 13 , fiber optic cables  16 - 18 , and vest  30  are made from a radiolucent material to allow for artifact free x-ray images during radiation treatment. Vest  30  of  FIG. 2  has been illustrated and described with three fiber optic beacons, but the external motion tracking system is not limited to three fiber optic beacons. In alternative embodiments, vest  30  may include less than three or more than three fiber optic beacons.  
       FIGS. 3A-3G  illustrate different views of fiber optic beacon  12 . As the three fiber optic beacons are substantially similar in form and function, a detailed description is provided with respect to one fiber optic beacon for clarity.  FIG. 3A  is an oblique-front view and  FIG. 3B  is an oblique top view of fiber optic beacon  12 .  FIG. 3C  is a top view and  FIG. 3D  is bottom view of fiber optic beacon  12 .  FIG. 3E  is a side view,  FIG. 3F  is a front view, and  FIG. 3G  is perspective side view of fiber optic beacon  12 . As shown in the figures, the fiber optic beacon  12  is constructed with a dome shape. An elongated fiber optic cable  16  extends between two ends, a first end  10  adapted to be connected to a breakout box (not shown), and a second end  20  secured to beacon  12  and extending through beacon  12  to at least an outer surface  14 , as illustrated in  FIGS. 3A, 3B , and  3 G. As shown in  FIG. 3D , the bottom surface  15  of the beacon  12  is provided with a piece of fabric of small hook and loop fasteners. The portion near the second end  20  of the fiber optic cable  16  is received in a channel defined in the beacon  12 , as shown in the perspective side view in  FIG. 3G . The angle of the fiber  16  with respect to the bottom surface  15  of the beacon  12  is about 15 degrees in order to provide better visualization of the light emitted from the second end  20  by the eyes of a user or an external detector. In the embodiment having three fiber optic beacons  12  (e.g., as illustrated in  FIG. 2 ), three fiber optics  16 - 18  coupled to fiber optic beacons  11 - 13  respectively. As illustrated in  FIG. 4 , each fiber optic cable (e.g., fiber optic cable  16 ) of a cable bundle  21  is joined by a quick connector  19  near the first end (e.g., first end  10 ), so that quick connector can be used to connect all the fiber optic cables with the breakout box at once without the need for individually connecting each fiber optic cable.  
      In one embodiment, the breakout box houses light emitting diodes (LEDs), which are associated with the first end  18  of the fiber optic cable  16 . The LEDs emit light, for example in the red spectrum, and transmits the light to the first end  18  of fiber optic cable  16 . The light is then propagated through fiber optic cable  16  and emitted out of the second end  20  of fiber optic beacon  12 .  
      In one embodiment, the respiration monitoring system includes a vest  30  which is customized to fit a particular patient tightly.  FIG. 5A  shows a front view of the vest  30  and  FIG. 5B  shows a back view of the vest  30 . The vest  30  is made from a tight fitting material, for example, spandex, lycra, and the like, that conforms to the shape of the patient&#39;s body without pleat or spacing between the patient&#39;s body and the vest. The vest includes a mechanism for securing the reference object, e.g., the fiber optic beacon  12 , thereon. In the exemplary embodiment shown in  FIGS. 5A and 5B , vest  30  is provided with strips of fabric of small hooks or loops, for example, VELCRO® strips  32 , at both the front side and the back side of the vest  30  for both prone and supine treatments. The bottom surface of the fiber optic beacon  12  is also provided with a piece of fabric of small hooks or loops to engage with the strips  32  on the vest  30 . In use, the fiber optic beacon  12  can be easily attached to the vest  30 , and after use, can be easily removed. Devices other than fabric of small hooks and loops also can be used for securing the beacons  12  to the vest  30 . The vest  30  has a waist drawstring  36  passing through a channel formed at the bottom boundary of the vest  30 . A traditional drawstring with a stop member that can slide along the drawstring and can stop at any point on the drawstring to fasten the drawstring can be used. The drawstring  36  is used to fasten the bottom boundary of the vest  30  to prevent the vest  30  from rolling up to the patient&#39;s upper body.  
      The vest  30  also includes a closure assembly, which may be an elongated zipper  38 , attached on the back of the vest  30  and extending from the neck of the vest  30  to the bottom of the vest  30 . The elongated zipper  38  allows easy applications of the vest  30  to the patients with limited mobility. In a particular embodiment, a ribbon tab  40  with small fabric hooks or loops is attached to the sliding head of the zipper  38 . The ribbon tab  40  can be attached to a piece of fabric of small hooks or loops  42  at the bottom boundary of the vest  30 , so that after the zipper head is slid down to dose the zipper  38 , the ribbon tab  40  can be secured at the bottom of the vest  30 , thus preventing the zipper head from moving upward to unintentionally open the zipper  38 .  
      The vest  30  may include more ribbon tabs as denoted by number  44  with small hooks or loops at the bottom surface of the ribbon tabs. In use, the ribbon tabs  44  are placed over the fiber optics  16  to facilitate to secure the fiber optics  16  and the beacons  12  on the vest  30 . The vest  30  may further include brand tags at the collar and/or at the side seam of the vest  30 , as shown in  FIGS. 5A and 5B . The vest  30  may further include one or more pocket for containing the patient&#39;s ID tag, picture, and/or other documents.  
      Tracking the motion of a pathological anatomy caused by respiration as described with respect to  FIGS. 2-5  may be integrated with a therapeutic radiation treatment system. The therapeutic radiation treatment system is generally associated with an imaging system, for example, an x-ray imaging system for internal imaging of the treatment area. The fiber optic cable  16 , fiber optic beacon  12 , and the vest  30  are made from plastic, eliminating metal from the treatment field, so that the x-ray imaging system is able to see any implanted fiducials during treatment while no artifacts are created during a CT scan. In one embodiment, the fiber optic cable  16 , fiber optic beacon  12 , and the vest  30  are made from a radiolucent material to allow for artifact free x-ray images during treatment.  
       FIG. 6  illustrates one embodiment of a configuration  300  for respiration tracking system during radiation treatment. The respiration tracking system coordinates an internal image of the patient  301  near a pathological anatomy region marked by fiducials (not shown) and an external motion tracking (e.g., the up-and-down movement of the chest during breathing). The respiration tracking system includes vest  303  having one or more fiber optic beacons represented by beacons  304 - 306 . Each beacon is connected by a fiber optic cable (e.g., cable  307 ), which at an opposite end is connected to a light source such as breakout box  308 . The respiration tracking system also includes a real-time image guidance system, which includes a localizer, a digitizer system, and a computer controller. The localizer includes a camera system, which includes one or more cameras  309  working in conjunction with each other, to detect a point source of light from each fiber optic beacon and determine the location of the point source of light in an ordinate system. Breakout box  308  originates the light that propagates through each fiber optic cable and emitted through a beacon. In one embodiment, the light originates from an LED. Each point source of light, which is associated with a beacon (e.g., beacon  304 ), flashes in a pre-defined sequence so that camera  309  is able to identify each beacon and its orientation. The positions of the light sources are recorded in real-time and transmitted to a treatment system, for example, a therapeutic radiation treatment system, which uses this information to determine the real-time position of the treatment target. A radiation delivery system is then able to synchronize the radiation delivery tool to the movement of the treatment target during the treatment.  
      A digitizer system is connected to the localizer to convert the image data received from the localizer to digital information, and transmits the digital information to the computer controller. The digitizer system and computer controller can be a combination of software and hardware operating on a digital processing system, such as workstation  310 . The computer controller, which is connected to the digitizer system and the localizer, controls the camera system  309 . The controller is programmed to determine the real-time positions of fiber optic beacons  304 - 306  and transmits the position information from the beacons to the treatment system.  
      The computer controller also controls the flashing rate of the light sources on the fiber optic beacons  304 - 306  responsive to whether the light sources are in the view of the camera systems  309 . For example, if the light sources are seen by the camera systems  309 , the light sources flash at the rate used for tracking the positions of the light sources, and if any of the light sources on fiber optic beacons  304 - 306  are not seen by the camera system  309 , the light sources emit continuous red light. By this arrangement, the user can visually identify if the beacon is seen by the camera system  309 . If any of the light sources on fiber optic beacons  304 - 306  are not seen by the camera system  309 , the user adjusts the position of fiber optic beacons  304 - 306  until it starts to flash red light, which indicates that it is being seen by the camera system  309 .  
      In one embodiment, as illustrated in  FIG. 6 , radiation may be delivered by an image-guided, robotic-based radiation treatment system such as the CyberKnife® system developed by Accuray Incorporated of California. The radiation source may be represented by a linear accelerator (LINAC) 4051 mounted on the end of a robotic arm having multiple (e.g., 5 or more) degrees of freedom in order to position the LINAC 4051 to irradiate a pathological anatomy (target region or volume) with beams delivered from many angles in an operating volume (e.g., a sphere) around the patient. The internal image of the treatment region may be generated by an imaging system that includes one or more x-ray sources and x-ray image detectors, such as x-ray source  4054  and detector  4057 . In one embodiment, for example, x-ray source  4054  may be nominally aligned to project imaging x-ray beams through patient  301  from an angular position and aimed through the patient  301  on treatment couch  302  toward detector  4057 . In another embodiment, a two x-ray sources may be nominally aligned to project imaging x-ray beams through patient  301  from two different angular positions (e.g., separated by 90 degrees, 45 degrees, etc.) and aimed through the patient on treatment couch  302  toward respective detectors.  
      As the pathological anatomy moves with breathing, the LINAC 4051 is able to follow the movement by correlating the signals from fiber optic beacons  303 - 305  and the internal fiducial marker.  FIG. 7  illustrates a cross-sectional view of a chest region  400  during respiration with various elements of the internal imaging and respiration monitoring system working together to track motion of a patient and the treatment region while delivery radiation. The patient is positioned lying flat on a radiation treatment couch (e.g., as illustrated by patient  301  on couch  302 ). One or more external position sensors, such as fiber optic beacon  402 , are disposed on vest  405 , which is fitted over the chest area of the patient. The pathological anatomy is designated as part of a target area first position  404  and an internal fiducial marker  403  is positioned near target area first position  404 . An x-ray based imaging system is used image target area first position  404  using internal fiducial marker  403 .  
       FIG. 7  illustrates that during respiration, the treatment region containing the pathological anatomy moves between target area first position  404 , a second position  405 , and a third position  406  relative to internal fiducial marker  403 . Beacon  402  detects the motion of the chest area during respiration as it moves between the different positions. This external monitoring is correlated with the internal imaging of target regions  404 - 406 . In this manner, the position of target regions  404 - 406  can be constantly updated and LINAC 4051 moves with respect to the movement of the target regions. For example, LINAC 4051 is in a first position  407  corresponding to target region first position  404 . When the target region moves to target region second position  405 , LINAC 4051 moves to second position  408 . Similarly, when the target region moves to third target region third position  406 , LINAC 4051 moves to third position  409 . Radiation delivery may involve beam paths with a single isocenter (point of convergence), 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).  
      In one method to integrate the monitoring of motion of patient due to respiration, a preoperative process and a treatment process are involved. In the preoperative process, the patient is provided with a vest  30  that tightly fits the patient&#39;s torso area. A picture of the patient is taken and is placed in the pouch on the vest  30  to identify the patient. The patient puts on the vest  30 , and the vest  30  is zipped up, and the drawstring  36  is adjusted at the waist for proper fit. The patient is then placed in an immobilization device, which is generated for the patient for holding the patient. The immobilization device, made from a moldable material, is customized to fit with the patient&#39;s body curve with the vest on the patient body. The immobilization device is attached to the patient positioning system, holding the patient tightly and preventing the patient from moving during treatment. The patient held in the immobilization device is scanned, typically by a CT scanner, to determine the position of the treatment target. The vest  30 , the immobilization device, and the image data are then ready for use in the treatment, which can be conducted after the preoperative process or on another day. In an alternative embodiment, the preoperative process may be performed without the immobilization device.  
      During treatment, the vest  30  is put on the patient and the patient is immobilized in a treatment position on the patient positioning device. The first end of a fiber optic cable (e.g., first end  10  of fiber optic cable  16 ) is snapped into a breakout box (e.g., breakout box  308  and connected to the LEDs). The second end of the fiber optic cable (e.g., second end  20 ) is connected to a fiber optic beacon (e.g., fiber optic beacon  12 ) and placed on the vest  30 . Once the first ends of all the fiber optic cables, which may correspond to the number of beacons placed on vest  30 , are connected to the breakout box, the user should be able to see read light emitting out of the beacons from the second ends of the fiber optic cables. The fiber optic beacons (e.g.,  12 ) are placed on the vest  30  on the area of the patient that moves the most with respiration, e.g. the area at or near the diaphragm of the patient. The small hooks or loops on the bottom surface of the beacons engage with the hook or loop fabric strips (e.g.,  32 ) on the vest  30 , and thus, allowing each fiber optic beacon to be attached to the vest  30  securely. The beacons are positioned and orientated so that the emitted light can be seen by the camera system (e.g., camera  309 ). In one embodiment, if the emitted light is a flashing red light, then it is detected by the camera system. If the emitted light is a continuous red light, then it is not detected by the camera system, and the user has to adjust the positions and orientations of the beacons or the camera to make the emitted light from the beacons flash. Once the beacons are aligned to the correct positions, the ribbon tabs (e.g., tab  44 ) are placed over the fiber optic cables to prevent unwanted movement of the fiber optic cables during the treatment.  
      During treatment, the camera system  309  and the computer controller track the movement of the beacons  12  with the respiration of the patient, and send the information to the treatment system, so that the treatment system can determine the real-time position of the treatment target and synchronize the movement of the treatment target. Thus the treatment system administers treatment to the treatment target in a dynamic and spatially accurate manner.  
       FIGS. 8-10  illustrate another embodiment of a respiration motion tracking system, in which a magnetic-based monitor is correlated with an internal imaging system during radiation treatment. In magnetic tracking, a transmitter broadcasts an electromagnetic field and sensors placed within the magnetic field can capture translation (x, y, z) coordinates and yaw, pitch, roll (y, p, r) rotation coordinates of objects to which the sensors are attached.  FIG. 8  illustrates one configuration of a magnetic motion tracking system established for patient  501  viewed from a top position as if patient  501  were lying on a treatment couch. A vest  504 , placed on patient  501 , includes three magnetic sensors or transducers  505 ,  506 , and  507 . Magnetic sensors  505 ,  506 , and  507  are connected to an interface device  510  via wires  511 . Interface device  510  is also connected to a digital processing system such as computer  509 . A transmitter  503  is also connected to computer  509 .  
      Transmitter  503  creates electromagnetic field  502  within the vicinity of patient  501 , and in particular, magnetic sensors  505 ,  506 , and  507  disposed on vest  504 . In one embodiment, transmitter  503  includes one or more coils on an orthogonal axes and current (either alternating or direct) is passed through the coils to generate electromagnetic field  502 . Magnetic sensors  505 ,  506 , and  507  also include similar coils, but are passive coils that only detect current. The movement of magnetic sensors  505 ,  506 , and  507  during respiration sends a combination of signal strengths to interface  510  which is then interpreted by computer  509  to determine the exact position and orientation of the chest region of patient  501 . Interface  510  also serves to filter the signals from magnetic sensors  505 ,  506 , and  507  to reduce jitter. Magnetic transmitter and sensors are known in the art; accordingly, a detailed description is not provided herein.  
       FIG. 9  illustrates another top view of patient  501  and showing the position of pathological anatomy  512  that is targeted for radiation treatment. The region containing and around pathological anatomy  512  is also the internal image zone  513  that is captured in real time during radiation treatment. In one embodiment, internal image zone  513  may include internal fiducial markers (not shown) utilized by an x-ray imaging system.  FIG. 10  illustrates a side view of the magnetic motion tracking configuration for patient  501  lying treatment couch  514 . In one embodiment, transmitter  503  may be coupled to treatment couch  514  to generate the electromagnetic field  502  that surrounds magnetic sensors  505 ,  506 , and  507  disposed on vest  504 . Transmitter  503  does not need to be attached to treatment couch  514 , and in alternative embodiments, transmitter  503  is positioned close enough to patient  501  to generate magnetic field  502 .  
      Interface device  510  receives signals from magnetic sensors  505 ,  506 , and  507  corresponding to motion during respiration. The signals are translated and filtered to reduce jitter before being transmitted to computer  509 . The motion tracking data provided by interface device  510  is correlated with imaging data of the pathological anatomy  512  (e.g., x-ray imaging of zone  513  with fiducial markers) to provide real-time tracking. For clarity,  FIG. 10  is shown without an imaging system and a radiation treatment system such as x-ray source  4054 , detector  4057 , and LINAC 4051 as described above and shown in  FIG. 6 . In one embodiment, the magnetic sensor-based tracking system may be integrated with an imaging system and radiation treatment system.  
       FIG. 11  illustrates an alternative embodiment of a respiration monitoring system  600  that allows for the use of LEDs as reference objects for motion tracking. External LED markers  602  are disposed on vest  601  that are connected to a power source (not shown) by wires  603 . One feature in the configuration illustrated in  FIG. 11  is that wires  603  are significantly thin enough so that the use of substantially metallic wire to propagate the electrical current to the LEDs, even if they may appear on an internal image of the treatment area, is easily discernable from the internal markers  604  (e.g., fiducials). In one embodiment, a thickness or diameter of each individual wire of wires  603  is less than a width of each internal marker  604 . For example, each individual wire of wires  603  may be a single or a bundle of multiple wires woven together to form a greater than 12 gauge wire (i.e., diameter of the wire is less than the diameter of a 12 gauge wire). In one embodiment each individual wire of wires  603  may be greater than a 29 gauge wire. As shown, wires  603  can be disposed directly over an image zone that includes internal markers  604 .  
      In another embodiment of a respiration monitoring system  700  illustrated in  FIG. 12 , wires  703  connecting a power source and external LED markers  702  are positioned on vest  701  so that no part of any wire is directly over any of the internal markers  704 . The non-overlapping position of wires with respect to internal markers  704  makes the wires easily discernable from the internal markers  704 .  
      Because respiration monitoring system  600  operates similarly to monitoring system  700 , a description of both is provided with respected to monitoring system  600 . An internal image of the patient near a pathological anatomy region marked by internal markers  604  is correlated with movement caused by respiration as tracked by external LED markers  602 . Wires  603  connect LED markers  602  to a power source (such as a breakout box, not shown). In one embodiment, wires  603  may be made of a metallic material, such as copper. The respiration tracking system also includes a real-time image guidance system, which includes a localizer, a digitizer system, and a computer controller. The localizer includes a camera system, which includes one or more cameras (such as camera  309 ) working in conjunction with each other, to detect a point source of light from each external LED markers  602  and determine the location of the point source of light in an ordinate system. Each of external LED markers  602  flashes in a pre-defined sequence so that the camera is able to identify each marker and its orientation. The positions of the LED markers  602  are recorded in real-time and transmitted to a treatment system, for example, a therapeutic radiation treatment system, which uses this information to determine the real-time position of the treatment target. A radiation delivery system is then able to synchronize the radiation delivery tool to the movement of the treatment target during the treatment.  
       FIG. 13  is a flowchart  800  describing one method for tracking movement of a pathological anatomy caused by respiration. A combination of imaging internal fiducial markers and tracking external reference objects is used to track the movement of the pathological anatomy in real-time, allowing for a radiation delivery source to follow the movement of the pathological anatomy during radiation delivery. The method overcomes the problems of prior art tracking methods because the external reference objects are clearly distinguishable from the internal fiducial markers in the internal image generated by x-ray imaging. Alternatively, the external reference objects do not appear on an internal image generated by x-ray imaging. The external reference object tracking may involve one of fiber optic beacons, magnetic sensors, or LED beacons. The method of flowchart  800  is described with respect to the treatment of a pathological anatomy or tumor located within the chest region of a patient. The patient is first fitted with a motion tracking vest that covers the region under the chest targeted for treatment, step  801 . In a first embodiment, the vest may have one or more fiber optic beacons disposed on an outer surface, such as vest  30  and fiber optic beacons  11 - 13  described above with respect to  FIG. 2 . In a second embodiment, the vest may have one or more magnetic sensors, such as vest  504  and magnetic sensors  505 - 507  described above with  FIG. 8 . In a third embodiment, the vest may have one or more LED markers, such as vest  601  and LED markers  602  described above with respect to  FIG. 11 .  
      Next, a CT image is generated of the chest including the target region to determine the position of the pathological anatomy, step  802 . The CT image may include the location of one or more fiducial markers near the pathological anatomy. During radiation treatment, the target region is imaged with x-ray imaging and with the aid of the internal fiducial markers (e.g., fiducial  403 ), step  803 . The external reference objects do not appear on the internal image or alternatively, are easily discernable from the fiducial markers. During respiration of a patient, movement of the external reference objects may be detected by a number of different methods, depending on the type of reference object used, step  804 . For example, for a fiber optic beacon or an LED marker, an emitted light is detected by a camera system (e.g., camera  309 ). The fiber optic cables do not appear on the internal images generated by x-ray imaging, allowing the internal fiducial markers to be easily identified. For LED markers, the wires that connect a power source to the LED markers may be made of significantly thin metallic material so that they are easily discemable from the fiducial markers in the internal image (e.g., wires  603  illustrated in  FIG. 11 ). Alternatively, the wires may be positioned on the vest so that there is no overlap with the internal fiducials below the vest (e.g., as illustrated by wires  703  in  FIG. 12 ).  
      For a magnetic sensor, an electromagnetic field (e.g., electromagnetic field  502 ) is generated to encompass the patient, and movement of the magnetic sensor is detected by an interface device (e.g.,  510 ) that interprets signals from the magnetic sensor. The electromagnetic field may be generated by a transmitter positioned near the patient or the treatment couch (e.g., as illustrated in  FIG. 10 ). During radiation treatment, the position of the external reference objects is correlated with the internal markers to follow the motion of a pathological anatomy in real-time, step  805 . The new position of the target region can then be displayed with an updated internal image, step  806 . An internal image of the treatment region can be updated and displayed at regular intervals as movement is detected by the external reference objects (by repeating the process starting at step  804 ).  
       FIG. 14  illustrates one embodiment of systems that may be used to perform radiation treatment in which features of the present invention may be implemented. As described below and illustrated in  FIG. 14 , system  1000  may include a diagnostic imaging system  2000 , a treatment planning system  3000 , and a treatment delivery system  4000 .  
      Diagnostic imaging system  2000  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 (e.g., image zone  513  shown in  FIG. 9 ). For example, diagnostic imaging system  2000  may be a computed tomography (CT) system, a magnetic resonance imaging (MRI) system, a positron emission tomography (PET) system, an ultrasound system or the like. For ease of discussion, diagnostic imaging system  2000  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  2000  includes an imaging source  2010  to generate an imaging beam (e.g., x-rays, ultrasonic waves, radio frequency waves, etc.) and an imaging detector  2020  to detect and receive the beam generated by imaging source  2010 , 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  2000  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, may also be used that would be illuminated by each x-ray imaging source. For imaging of a target region containing a pathological anatomy, the x-ray source may be aimed toward fiducial markers planted (e.g., fiducial  403 ) in the patient. Alternatively, other numbers and configurations of imaging sources and imaging detectors may be used.  
      Diagnostic imaging system  2000  also includes an external motion detector  2040  to monitor the movement of the patient, for example during respiration. The external motion detector  2040  may be a vest-based system that includes fiber optic beacons, magnetic sensors, or LED marker as discussed above. The data from the external motion detector  2040  can be correlated with the imaging detector to track the motion of the pathological anatomy in real time.  
      The imaging source  2010 , the imaging detector  2020 , and the external motion detector  2040  are coupled to a digital processing system  2030  to control the imaging operation and process image data. One example of a digital processing system is computer  310  described above with respect  FIG. 6 . Diagnostic imaging system  2000  includes a bus or other means  2035  for transferring data and commands among digital processing system  2030 , imaging source  2010  and imaging detector  2020 . Digital processing system  2030  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  2030  may also include other components (not shown) such as memory, storage devices, network adapters and the like. Digital processing system  2030  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  2030  may generate other standard or non-standard digital image formats. Digital processing system  2030  may transmit diagnostic image files (e.g., the aforementioned DICOM formatted files) to treatment planning system  3000  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  3000  includes a processing device  3010  to receive and process image data. Processing device  3010  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  3010  may be configured to execute instructions for performing motion tracking operations discussed herein, for example, correlating the movement of a pathological anatomy during respiration.  
      Treatment planning system  3000  may also include system memory  3020  that may include a random access memory (RAM), or other dynamic storage devices, coupled to processing device  3010  by bus  3055 , for storing information and instructions to be executed by processing device  3010 . System memory  3020  also may be used for storing temporary variables or other intermediate information during execution of instructions by processing device  3010 . System memory  3020  may also include a read only memory (ROM) and/or other static storage device coupled to bus  3055  for storing static information and instructions for processing device  3010 .  
      Treatment planning system  3000  may also include storage device  3030 , representing one or more storage devices (e.g., a magnetic disk drive or optical disk drive) coupled to bus  3055  for storing information and instructions. Processing device  3010  may also be coupled to a display device  3040 , such as a cathode ray tube (CRT) or liquid crystal display (LCD), for displaying information (e.g., a 2-dimensional or 3-dimensional representation of the VOI) to the user. An input device  3050 , such as a keyboard, may be coupled to processing device  3010  for communicating information and/or command selections to processing device  3010 . 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  3010  and to control cursor movements on display  3040 .  
      It will be appreciated that treatment planning system  3000  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  3000  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  3000  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  3000  may share its database (e.g., data stored in storage device  3030 ) with a treatment delivery system, such as treatment delivery system  4000 , so that it may not be necessary to export from the treatment planning system prior to treatment delivery. Treatment planning system  3000  may be linked to treatment delivery system  4000  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  2000 , treatment planning system  3000  and/or treatment delivery system  4000  may be in decentralized locations such that the systems may be physically remote from each other. Alternatively, any of diagnostic imaging system  2000 , treatment planning system  3000  and/or treatment delivery system  4000  may be integrated with each other in one or more systems.  
      Treatment delivery system  4000  includes a therapeutic and/or surgical radiation source  4010  to administer a prescribed radiation dose to a target volume in conformance with a treatment plan. Treatment delivery system  4000  may also include an imaging system  4020  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. Treatment delivery system  4000  may also include a digital processing system  4030  to control radiation source  4010 , imaging system  4020 , and a patient support device such as a treatment couch  4040 . Digital processing system  4030  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  4030  may also include other components (not shown) such as memory, storage devices, network adapters and the like. Digital processing system  4030  may be coupled to radiation source  4010 , imaging system  4020  and treatment couch  4040  by a bus  4045  or other type of control and communication interface.  
      In one embodiment, as illustrated in  FIG. 15 , treatment delivery system  4000  may be an image-guided, robotic-based radiation treatment system (e.g., for performing radiosurgery) such as the CyberKnife® system developed by Accuray Incorporated of California. In  FIG. 15 , radiation source  4010  may be represented by a linear accelerator (LINAC) 4051 mounted on the end of a robotic arm  4052  having multiple (e.g., 5 or more) degrees of freedom in order to position the LINAC 4051 to irradiate a pathological anatomy (target region or volume) with beams delivered from many angles in an operating volume (e.g., a sphere) around the patient. Treatment may involve beam paths with a single isocenter (point of convergence), 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). Treatment can be delivered in either a single session (mono-fraction) or in a small number of sessions (hypo-fractionation) as determined during treatment planning. With treatment delivery system  4000 , in one embodiment, radiation beams may be delivered according to the treatment plan without fixing the patient to a rigid, external frame to register the intra-operative position of the target volume with the position of the target volume during the pre-operative treatment planning phase. The treatment delivery system  4000  can be integrated with a pathological anatomy tracking system, such as The Synchrony™ system developed by Accuray Incorporated of California, which can correlates the motion of the pathological anatomy with respiration motion in real-time, enabling the LINAC to deliver highly accurate radiation beams.  
      In  FIG. 15 , imaging system  4020  may be represented by X-ray sources  4053  and  4054  and X-ray image detectors (imagers)  4056  and  4057 . In one embodiment, for example, two x-ray sources  4053  and  4054  may be nominally aligned to project imaging x-ray beams through a patient from two different angular positions (e.g., separated by 90 degrees, 45 degrees, etc.) and aimed through the patient on treatment couch  4050  toward respective detectors  4056  and  4057 . In another embodiment, a single large imager can be used that would be illuminated by each x-ray imaging source. Alternatively, other numbers and configurations of imaging sources and imagers may be used.  
      Digital processing system  4030  may implement algorithms to register images obtained from imaging system  4020  with preoperative treatment planning images in order to align the patient on the treatment couch  4050  within the treatment delivery system  4000 , and to precisely position the radiation source with respect to the target volume.  
      The treatment couch  4050  may be coupled to another robotic arm (not illustrated) 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  4050  may be a component of another mechanical mechanism, such as the Axum® treatment couch developed by Accuray Incorporated of California, or be another type of conventional treatment table known to those of ordinary skill in the art.  
      Alternatively, treatment delivery system  4000  may be another type of treatment delivery system, for example, a gantry based (isocentric) intensity modulated radiotherapy (IMRT) system. In a gantry based system, a radiation source (e.g., a LINAC) is mounted on the gantry in such a way that it rotates in a plane corresponding to an axial slice of the patient. Radiation is then delivered from several positions on the circular plane of rotation. In IMRT, the shape of the radiation beam is defined by a multi-leaf collimator that allows portions of the beam to be blocked, so that the remaining beam incident on the patient has a pre-defined shape. The resulting system generates arbitrarily shaped radiation beams that intersect each other at the isocenter to deliver a dose distribution to the target. In IMRT planning, the optimization algorithm selects subsets of the main beam and determines the amount of time that the patient should be exposed to each subset, so that the prescribed dose constraints are best met.  
      In other embodiments, yet another type of treatment delivery system  4000  may be used, for example, a stereotactic frame system such as the GammaKnife®, available from Elekta of Sweden. With such a system, the optimization algorithm (also referred to as a sphere packing algorithm) of the treatment plan determines the selection and dose weighting assigned to a group of beams forming isocenters in order to best meet provided dose constraints.  
      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).  
      In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.