Patent Abstract:
A method and system configured to substantially synchronize two opposite ends of a table assembly of a radiation therapy treatment system. The system includes a lateral motion control system coupled to the table assembly and configured to detect positions of the two opposite ends of the table assembly and to substantially synchronize the positions as the table assembly is laterally moved with respect to a gantry of the radiation therapy treatment system.

Full Description:
RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 60/969,904, filed Sep. 4, 2007, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a radiation therapy imaging and treatment system. More specifically, the invention relates to a patient support device for use with such a system having improved motion control. 
     BACKGROUND 
     Medical equipment for radiation therapy treats tumorous tissue with high energy radiation. The dose and the placement of the dose must be accurately controlled to ensure both that the tumor receives sufficient radiation to be destroyed, and that damage to the surrounding and adjacent non-tumorous tissue is minimized. Intensity modulated radiation therapy (IMRT) treats a patient with multiple rays of radiation each of which may be independently controlled in intensity and/or energy. The rays are directed from different angles about the patient and combine to provide a desired dose pattern. In external source radiation therapy, a radiation source external to the patient treats internal tumors. The external source is normally collimated to direct a beam only to the tumorous site. Typically, the radiation source consists of either high-energy X-rays, electrons from certain linear accelerators, or gamma rays from highly focused radioisotopes, though other types of radiation sources are possible. 
     One way to control the position of the radiation delivery to the patient is through the use of a patient support device, such as a couch, that is adjustable in one or more directions. The use of a patient support device is well known in the medical field, with similar patient support devices being used in CT scanning devices and Magnetic Resonances Imagers (MRIs). The patient support device allows the patient to be moved into and out of the field of the radiation to be delivered and in some cases, allow for adjustments of patient position during a radiation treatment. 
     SUMMARY 
     When a patient support device such as a couch is used in this manner, there are many variables that need to be accounted for. For example construction materials and configuration of suitable electronics necessary to operate the couch must be carefully selected to ensure smooth operation of the couch, and precise measurement of couch position (when the couch has multiple movable parts). When these features are thoughtfully considered in the environment of radiation delivery, the patient support device can be a key tool in improving patient outcomes. 
     In one embodiment, the present invention provides a patient support device including a base, a table assembly, a controller, and a lateral motion control system. The table assembly is configured to support a patient and includes a lower support, and an upper support movable with respect to the lower support, the upper support including a first end and a second end. The controller is electrically coupled to the table assembly and is configured to instruct the table assembly to move in a first direction along an axis, in a lateral direction with respect to the axis, and in a vertical direction with respect to the axis. The lateral motion control system is electrically coupled to the table assembly and includes a first motor including a shaft coupled to the first end of the upper support, a first encoder coupled to the shaft and configured to detect a first position of the shaft of the first motor, a second motor including a shaft coupled to the second end of the upper support, and a second encoder coupled to the shaft and configured to detect a second position of the shaft of the second motor, the controller configured to receive and compare the first position and the second position, the controller configured to communicate instructions to the first motor and the second motor to substantially synchronize the first position and the second position. 
     In another embodiment, the invention provides a radiation therapy treatment system comprising a gantry, a table assembly configured to support a patient, a controller, and a lateral motion control system. The table assembly includes a lower support, and an upper support movable with respect to the lower support, the upper support including a first end and a second end. The controller is electrically coupled to the table assembly and is configured to instruct the table assembly to move in a first direction into the gantry, in a lateral direction with respect to the first direction, and in a vertical direction with respect to the first direction. The lateral motion control system is electrically coupled to the table assembly and is configured to detect a position of the first end of the upper support and a position of the second end of the upper support and output the positions of the first end and the second end. 
     In another aspect of the invention, the present invention provides a method including the acts of detecting a position of a first end of a table assembly for a radiation therapy treatment system, detecting a position of a second end of the table assembly, comparing the position of the first end with the position of the second end, and substantially synchronizing the position of the first end with the position of the second end. 
     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a radiation therapy treatment system. 
         FIG. 2  is a perspective view of a multi-leaf collimator that can be used in the radiation therapy treatment system illustrated in  FIG. 1 . 
         FIG. 3  is a perspective view of a patient support device for use with the system of  FIG. 1 . 
         FIG. 4  is an exploded view of a table assembly of the patient support device of  FIG. 3 . 
         FIG. 5  is a perspective view of an upper support of the table assembly of  FIG. 4 . 
         FIG. 6  is a perspective view of a lower support of the table assembly of  FIG. 4 . 
         FIG. 7  is an assortment of views of a control keypad for use with the patient support device of  FIG. 1 . 
         FIG. 8  is an exploded view of the keypad of  FIG. 7 . 
         FIG. 9  is a front view of the keypad of  FIG. 7 , illustrating the control buttons in greater detail 
         FIG. 10  is a perspective view of the keypad of  FIG. 7 , illustrating operation of the buttons by the operator of the patient support device 
         FIG. 11  is a perspective view of the patient support device of  FIG. 3 , shown in the lowered position. 
         FIG. 12  illustrates a riser of the patient support device of  FIG. 3 . 
         FIG. 13  is a diagram of a lateral motion control system according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. 
     Although directional references, such as upper, lower, downward, upward, rearward, bottom, front, rear, etc., may be made herein in describing the drawings, these references are made relative to the drawings (as normally viewed) for convenience. These directions are not intended to be taken literally or limit the present invention in any form. In addition, terms such as “first,” “second,” and “third” are used herein for purposes of description and are not intended to indicate or imply relative importance or significance. 
     In addition, it should be understood that embodiments of the invention include hardware, software, and electronic components or modules that, for purposes of discussion, may be illustrated and described as if the majority of the components were implemented solely in hardware. However, one of ordinary skill in the art, and based on a reading of this detailed description, would recognize that, in at least one embodiment, the electronic based aspects of the invention may be implemented in software. As such, it should be noted that a plurality of hardware and software based devices, as well as a plurality of different structural components may be utilized to implement the invention. Furthermore, and as described in subsequent paragraphs, the specific mechanical configurations illustrated in the drawings are intended to exemplify embodiments of the invention and that other alternative mechanical configurations are possible. 
       FIG. 1  illustrates a radiation therapy treatment system  10  that can provide radiation therapy to a patient  14 . The radiation therapy treatment can include photon-based radiation therapy, brachytherapy, electron beam therapy, proton, neutron, or particle therapy, or other types of treatment therapy. The radiation therapy treatment system  10  includes a gantry  18 . The gantry  18  can support a radiation module  22 , which can include a radiation source  24  and a linear accelerator  26  (a.k.a. “a linac”) operable to generate a beam  30  of radiation. Though the gantry  18  shown in the drawings is a ring gantry, i.e., it extends through a full 360° arc to create a complete ring or circle, other types of mounting arrangements may also be employed. For example, a C-type, partial ring gantry, or robotic arm could be used. Any other framework capable of positioning the radiation module  22  at various rotational and/or axial positions relative to the patient  14  may also be employed. In addition, the radiation source  24  may travel in path that does not follow the shape of the gantry  18 . For example, the radiation source  24  may travel in a non-circular path even though the illustrated gantry  18  is generally circular-shaped. The gantry  18  of the illustrated embodiment defines a gantry aperture  32  into which the patient  14  moves during treatment. 
     The radiation module  22  can also include a modulation device  34  operable to modify or modulate the radiation beam  30 . The modulation device  34  provides the modulation of the radiation beam  30  and directs the radiation beam  30  toward the patient  14 . Specifically, the radiation beam  30  is directed toward a portion  38  of the patient. Broadly speaking, the portion may include the entire body, but is generally smaller than the entire body and can be defined by a two-dimensional area and/or a three-dimensional volume. A portion or area desired to receive the radiation, which may be referred to as a target or target region, is an example of a region of interest. Another type of region of interest is a region at risk. If a portion includes a region at risk, the radiation beam is preferably diverted from the region at risk. Such modulation is sometimes referred to as intensity modulated radiation therapy (“IMRT”). 
     The modulation device  34  can include a collimation device  42  as illustrated in  FIG. 2 . The collimation device  42  includes a set of jaws  46  that define and adjust the size of an aperture  50  through which the radiation beam  30  may pass. The jaws  46  include an upper jaw  54  and a lower jaw  58 . The upper jaw  54  and the lower jaw  58  are moveable to adjust the size of the aperture  50 . The position of the jaws  46  regulates the shape of the beam  30  that is delivered to the patient  14 . 
     In one embodiment, and illustrated in  FIG. 2 , the modulation device  34  can comprise a multi-leaf collimator  62  (a.k.a. “MLC”), which includes a plurality of interlaced leaves  66  operable to move from position to position, to provide intensity modulation. It is also noted that the leaves  66  can be moved to a position anywhere between a minimally and maximally-open position. The plurality of interlaced leaves  66  modulate the strength, size, and shape of the radiation beam  30  before the radiation beam  30  reaches the portion  38  on the patient  14 . Each of the leaves  66  is independently controlled by an actuator  70 , such as a motor or an air valve so that the leaf  66  can open and close quickly to permit or block the passage of radiation. The actuators  70  can be controlled by a computer  74  and/or controller. 
     The radiation therapy treatment system  10  can also include a detector  78 , e.g., a kilovoltage or a megavoltage detector, operable to receive the radiation beam  30 , as illustrated in  FIG. 1 . The linear accelerator  26  and the detector  78  can also operate as a computed tomography (CT) system to generate CT images of the patient  14 . The linear accelerator  26  emits the radiation beam  30  toward the portion  38  in the patient  14 . The portion  38  absorbs some of the radiation. The detector  78  detects or measures the amount of radiation absorbed by the portion  38 . The detector  78  collects the absorption data from different angles as the linear accelerator  26  rotates around and emits radiation toward the patient  14 . The collected absorption data is transmitted to the computer  74  to process the absorption data and to generate images of the patient&#39;s body tissues and organs. The images can also illustrate bone, soft tissues, and blood vessels. The system  10  can also include a patient support device, shown as a couch  82 , operable to support at least a portion of the patient  14  during treatment. While the illustrated couch  82  is designed to support the entire body of the patient  14 , in other embodiments of the invention the patient support need not support the entire body, but rather can be designed to support only a portion of the patient  14  during treatment. The couch  82  moves into and out of the field of radiation along an axis  84  (i.e., Y axis). The couch  82  is also capable of moving along the X and Z axes as illustrated in  FIG. 1 . 
     With reference to  FIGS. 3-6 , the couch  82  includes a table assembly  92  coupled to a base  93  via a platform  95 . The table assembly  92  includes an upper support  94  movably coupled to a lower support  98 . With particular reference to  FIG. 5 , the upper support  94  is a substantially flat, rectangular support member on which the patient is supported during treatment. The upper support  94  is movable with respect to the lower support  98  to move the patient into and out of the radiation beam  30  during treatment. In the illustrated embodiment, the upper and lower supports  94 ,  98  are composed of a carbon fiber composite, though other compositions of the supports are possible. 
     The upper support  94  has an upper surface  102  and a lower surface  106  that contacts an upper surface  110  of the lower support  98 . As shown in the illustrated embodiment, the lower surface  106  includes a bearing layer  114  that is intended to reduce friction between the lower surface  106  and the upper surface  110  of the lower support  98  when the upper support  94  is moved with respect to the lower support  98 . In the illustrated embodiment, the bearing layer  114  is a polyimide laminate that is coupled to the lower surface  106  using a pressure sensitive adhesive. In the illustrated embodiment, the laminate is Kapton™, available from DuPont. When the upper support  94  moves with respect to the lower support  98 , any friction that builds up between the supports can interrupt the operation of the electronics that control the operation of the couch  82  and thus minimizing the friction is one of the goals of the invention. Further, when the supports are composed of the carbon fiber composite, the friction can cause the creation and build-up of carbon dust, which can cause problems with couch operation. Additionally, if the surfaces of the upper and lower supports  94 ,  98  were to contact each other directly, the contact would result in additional wear and possible warping of the supports themselves, which may not only reduce the precision with which the couch can operate to position a patient, but can also cause couch failure. 
     With reference to  FIG. 4 , the lower support  98  includes two channels  118  that are designed to receive and house wiring necessary for the operation of the couch  82 . In some embodiments, a retaining member  122  is placed over the wiring within the channels  118  to hold the wiring in place and force the wiring to lie straight within the channels  118  to reduce the possibility of the wiring being pinched between the upper support  94  and the lower support  98 . Furthermore, it is desirable to hold the wires in a straight and constant position for image reproducibility. Both the retaining member  122  and the outer sheathing of the wiring itself are composed of radiation resistant material to provide for the protection and proper functioning of the wiring in the high radiation environment of the couch  82 . The spacing and design of the channels  118  is selected to separate the power lines from the data lines to prevent interference problems that occur when the two lines are not sufficiently spaced. 
     The table assembly  92  is movable in the X, Y, and Z directions, as illustrated in  FIG. 1 . Positioning of the table assembly  92 , and thus the position of the patient, with respect to the gantry  18  and the radiation beam  30  must be precise to ensure that the radiation is delivered to the proper areas of the patient. The movement of the table assembly  92  is controlled by the couch operator using a control keypad  140 , illustrated in  FIGS. 7-10 . Once the user actuates the buttons  144  of the keypad  140 , the table assembly  92  will move at the direction of the user. 
     Another feature of the couch  82  according to the present invention is that lateral motion (i.e., motion in the X direction) is automatically controlled, and the lateral motion of both ends of the table assembly  92  is synchronized. In conventional patient support tables, lateral motion adjustment is accomplished using a knob or screw that is manually turned to adjust position in the lateral direction. Not only is this adjustment manual, but also the adjustment of each end of the support table must be done separately and there is no mechanism that synchronizes the position of the table ends. This can cause patient positioning errors as one end may be moved to a more extreme lateral position than the other and obtaining a true, synchronized position of both ends in the lateral direction is very difficult. 
     In addition, synchronization of the ends is also useful in assuring reliable and reproducible imaging results. In a system such as the system of the present invention where a patient on the couch  82  is subject to radiation for the purposes of taking an image of that patient, anything in the path between the radiation source and the detector that feeds data to the system to produce the image can impact the quality of the images. The wiring that runs underneath the table assembly  92  as discussed above can interfere with the quality of the images taken, and may result in an artifact on the resulting images that a therapist or physician will want to take into consideration when reviewing the resulting images. The channels  118  in the lower support  98  discussed above function to keep the wiring separated and contained. By synchronizing the motion of the ends of the table assembly  92  in addition to knowing the position of the channels  118 , the physician/therapist has predictable artifacts that can be effectively eliminated by the physician/therapist when viewing the images because those artifacts will be in predictable locations, will be correctable, and the images will be reproducible. Without the synchronization, the artifacts would be more of a distraction to the user. 
     The couch  82  includes a lateral motion control system  200  according to one embodiment of the present invention as illustrated in  FIG. 13 . The lateral motion control system  200  includes a controller  204  electrically coupled to a first motor  208  positioned near a first end  212  of the table assembly  92  and electrically coupled to a second motor  216  positioned near a second end  220  of the table assembly  92 . The first motor  208  includes a shaft  224  and an encoder  228  coupled to the shaft  224 . The second motor  216  includes a shaft  232  and an encoder  236  coupled to the shaft  232 . The encoders  228 ,  236  communicate with the controller  204  to transmit position data of the respective motor shaft. The controller  204  receives motion instructions from the keypad  140 . The controller  204  includes computer code that compares the position data from the encoders  228 ,  236  to ensure that the shafts  224 ,  232  of the respective motors  208 ,  216  at both ends of the table assembly  92  are synchronized. The controller  204  moves the table assembly  92  in both axes (X and Y) at the same time and looks for yaw at the same time as the motion. The encoders  228 ,  236  are absolute encoders that incorporate feedback, such as SSI or other appropriate types of feedback, to make the synchronicity possible. 
     The use of motors  208 ,  216  in conjunction with the linear absolute feedback of the encoders  228 ,  236  allow the system to be able to detect yawing and crab motion of the table assembly  92  and display that information for the operator. The fact that the feedback is linear allows the user to see what is happening on the load side as well. All of this feedback information is possible due to the separation of the feedback lines (data wires) from those supplying power in the channels  118  as described above. 
     Y axis motion is controlled using a stepper motor. While the table assembly  92  is moving, absolute linear feedback is used to servo the table assembly  92  to keep it within tolerance limits, thereby improving the accuracy with which couch motion can be controlled. Furthermore, the Y axis motion control has the benefit of being able to detect obstructions or impending couch collisions (such as with the gantry), causing the couch to stop prior to the collision. Collision detection occurs dynamically with continuous double-checking on couch position. Any error propagation is displayed to the end user on the PCP. 
     Additional features of the invention can be found in the following claims.

Technology Classification (CPC): 0