Abstract:
A tabletop useful for accurate positioning of a patient for imaging and diagnosis, so that patient positioning in subsequent medical treatments, such as radiation therapy, accurately and precisely correlates with the imaging data. The tabletop of the present invention is a solid flat tabletop adapted to fit over or as an insert in a conventional CT imaging or scan table and provides a flexible support section in which the flexible support material is tensioned to provide a vertical deflection corresponding to the vertical deflection of a flexible patient support of a treatment simulator or linear accelerator. In a preferred embodiment, the flexible support section may be removed and inserted into the treatment table to provide an exact correlation in vertical deflection during treatment.

Description:
[0001]    The present application claims the benefit of provisional application U.S. Serial No. 60/305,591 filed Jul. 13, 2001 and provisional application U.S. Serial No. 60/325,323 filed Sep. 27, 2001. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to diagnostic imaging, and particularly, computed tomography (CT) scanning. In particular, the invention relates to a tabletop useful for accurate positioning of a patient for diagnostic imaging, so that patient positioning in subsequent medical treatments, such as radiation therapy, accurately and precisely correlates with the imaging data.  
         BACKGROUND OF THE INVENTION  
         [0003]    Patient positioning systems are used for accurate and reproducible positioning of a patient for radiation therapy, surgery, and other medical procedures. During these procedures, it is common to immobilize a part or parts of the patient&#39;s body. Accurate positioning of the body part is also important in initial and subsequent treatments, so that the precisely the same location of the body is exposed to the radiation each time. Therefore, different types of devices have been made to immobilize body parts and to index the body to the treatment table to assure proper and repeatable alignment for radiation therapy.  
           [0004]    As radiation therapy becomes more precise with procedures such as 3D conformal Intensity Modulated Radiation Therapy (IMRT), it is critical that all facets of treatment planning are handled with maximum accuracy. Presently, when advanced, highly technical radiation therapy is performed, an imaging scan, such as computed tomography (CT), is obtained with the patient “in treatment position.” From this scan, not only are the fields and blocking designed, but the treatment plan is calculated.  
           [0005]    The standard CT scan table has a hard, convex upper patient support surface, as generally indicated in FIG. 1 below. In practice, this table is provided with a flexible mat which conforms to the upper convex surface of the table, the primary purpose of which is to improve patient comfort during extended scanning. While this configuration contributes to patient comfort, the sidewalls are not radiolucent, making it difficult to exactly index the scanning data obtained with the conditions that will subsequently be encountered during radiation treatment. CT scans have also been performed on a standard CT scan “flat tabletop insert” to enable better positioning of the patient for advanced treatments. The flat tabletop inserts raise the patient above the level of the of the sidewalls of the CT table as shown in FIG. 1C, facilitating scanning of the entire body. This table insert is flat, very hard, allows for negligible deflection (defined as the downward movement of the tabletop) under weight of the patient, and tends to flatten the body parts to be imaged. However, in subsequent radiation oncology procedures, a mesh section of the typical radiation oncology table is usually in place in the simulator/linear accelerator during treatments. When positioning a patient for treatment, a deflection of the mesh occurs under weight of the patient, which can be as much as two to three centimeters at the maximum point.  
           [0006]    Lack of accurate position representation at the time of the CT scan will not allow advanced radiation therapy to be as accurate as possible. Higher accuracy can be obtained if the scan is performed directly in accordance with the shape and position of the patient when positioned on the linear accelerator table, especially as the accuracy in IMRT and the like equipment improves and provides greater accuracy and adjustability in treatment and treatment planning.  
           [0007]    Current problems with accurate and precise patient positioning for radiation therapy include deflection in treatment/simulator table that is different from deflection in a table used for imaging, variations in patient location on the linear accelerator table varying from day to day, lack of alignment (leveling) of table inserts used in imaging, and the fact that many facilities have already purchased and scan using table inserts that do not possess deflection capabilities. Every CT, simulator, and linear accelerator deflection should match if the patient is to be treated accurately and reproducibly.  
         SUMMARY OF THE INVENTION  
         [0008]    In accordance with the present invention, there is provided a tabletop for positioning a patient for 3-dimensional imaging of a body part comprising (a) a flat patient support having an upper patient support surface and a lower surface, a width less than the width of an aperture in an imaging device through which the tabletop must travel for imaging of body parts, and a length sufficient to support a patient thereon; and (b) a section of said support which comprises a flexible support panel for the body part to be imaged. This flexible support panel comprises a radiolucent flexible fabric or mesh material tensioned to provide a predetermined vertical deflection when a patient is positioned thereon, wherein the vertical deflection corresponds to the vertical deflection of a flexible patient support of a treatment simulator or linear accelerator. A tabletop of the present invention may also include a measuring or indexing means along the perimeter of said flexible support panel for establishing the exact positioning of a patient relative to the length of said support panel.  
           [0009]    The tabletop of the present invention may also include means to provide for accurate leveling of the table, adaptations to mount and slide the table top over an existing imaging table, and for removal and/or replacement of the flexible section of the tabletop.  
           [0010]    While the present invention is primarily described with reference to CT scans, it is equally applicable to other imaging technologies and methods, for example, magnetic resonance imaging (MRI), nuclear medicine (molecular imaging), positron emission tomography (PET), and ultrasound. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is an illustration of a typical prior art CT scan table and table insert.  
         [0012]    [0012]FIG. 2 is an illustration of a tabletop of the invention in which the tabletop contains a flexible, indexed support panel or section.  
         [0013]    [0013]FIG. 3 is an illustration of a tabletop insert of the invention in which the tabletop contains a flexible, indexed support panel or section and means for leveling the tabletop in a horizontal position.  
         [0014]    [0014]FIG. 4 is an illustration of a tabletop of the invention in which patient position markers are shown. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]    In the description which follows the present invention is described with particular reference to the typical CT scan table illustrated generally in FIGS. 1A and 1B. The table  10  has a concave top surface  11  upon which a patient rests. A soft cushion and/or a sanitary covering (not shown) can be placed on the concave top surface  11  of the table. The concavity of the upper surface  11  prevents effective imaging of body parts resting on concave surface  11  below the top of sidewalls  12 , since sidewalls  12  are not radiolucent.  
         [0016]    [0016]FIG. 1C illustrates a typical CT scan table  10 , upon which a flat-top insert  20  has been placed, for the purpose of raising the position of a patient for more accurate imaging. As shown in FIG. 1C, the tabletop insert has a hard, inflexible flat upper patient support surface  21  and a convex lower surface  22  substantially conforming to the concavity of the CT scan table  10 . It is positioned on and above the concave surface on support pads  23  which are mounted on lower surface  22 . As shown in the drawing, upper surface  21  is elevated above and overlaps sidewalls  12  of the CT tabletop.  
         [0017]    A tabletop of the present invention, which is particularly useful for accurate and precise repeated patient positioning for diagnostic procedures, is illustrated in FIGS. 2, 3 and  4 . FIG. 2A illustrates a tabletop  30  having a flat (planar) upper patient support surface  31 , a width less than the width of an aperture in an imaging device through which the tabletop must travel for imaging of body parts and a length sufficient to support a patient thereon. Tabletop  30  of the present invention also has a defined bottom surface which is suitably but not necessarily parallel to the top surface  31 .  
         [0018]    A section of tabletop  30  has a flexible support panel  32  for the body part to be imaged. The flexible support component  33  of the panel is necessarily made of a radiolucent flexible component, which can be material, fabric, or mesh. Suitable radiolucent materials include, but are not limited to carbon fiber, plastic, rubber, nylon, or other materials well-known in the art.  
         [0019]    The flexible support component  33  is tensioned to provide a predetermined vertical deflection when a patient is positioned thereon. The vertical deflection is predetermined to match the vertical deflection of a flexible patient support portion of a treatment simulator or linear accelerator and is generally in the range of up to 0.5 to 2 cm at the maximum point of deflection when the weight of a patient is positioned thereon. To further insure accuracy in deflection of flexible support  33 , a stop may be positioned below the bottom surface of the tabletop to limit deflection of flexible support  33 .  
         [0020]    The flexible support panel  32  of the invention is preferably a removable piece, which can be removed from the tabletop  30  and replaced with a solid insert, or with another flexible support panel of compatible size and shape, if so desired.  
         [0021]    The removable flexible support panel may, for example, be sized such that it may be placed on an appropriately configured irradiation treatment table for radiation treatments. Thus, the removable support panel may be configured so that the same support, or similarly configured supports can be used for both imaging and radiation treatment procedures. The ability for interchanging the flexible support panel between the imaging and treatment tables provides additional consistency in the patient positioning for precise treatment application.  
         [0022]    Typically, however, the flexible support panel consists of a flexible component  33 , as described above and shown in FIG. 2C, connected to a frame  34 , as illustrated in FIG. 2D. The flexible component  33  can be adjustably tensioned on the frame  34  to adjust the amount of deflection upon load bearing. For example, a suitable string or yarn may be strung through holes in the frame  34  of panel  32  similar to the stringing of a tennis racket, as shown in FIG. 2D. In another embodiment, a fabric used as the flexible component  32  may be held in place on the frame  34  with a groove and spline, similar to the way a screen window is fixed to a frame. Other methods for affixing the mesh to the frame will be apparent to those skilled in the art. A tabletop  30  of the invention may also be designed such that the flexible support panel  33  is an integral, non-removable part of tabletop  30 . In such an embodiment, flexible support  33  is directly attached to tabletop  30 . In this embodiment, flexible support  33  may be tensioned to provide a predetermined deflection and may be made of materials as described above.  
         [0023]    Tabletop  30  of the invention may be designed to accept support panel  32 , in much the same way a screen window fits into a window opening in a house. There may be an opening in tabletop  30 , wherein the periphery of the opening has rabbet edges to accept a mating surface of support panel frame  34 . Alternatively, the opening in the tabletop  30  may be beveled, with the wider portion of the bevel at the top surface  31 , and a corresponding bevel on the outer edges of frame  34  to mate with the corresponding bevel in the tabletop. Other well known means for retaining the frame the tabletop opening will be apparent to those skilled in art. Regardless of the means used for retaining the frame in the tabletop. In a typical embodiment of the invention, the flexible support panel  32  will remain approximately flush with the plane of the top surface  31  of the tabletop. However, the flexible support panel  32  may rest lower or higher than the plane of the top surface  31  of a tabletop of the present invention.  
         [0024]    Tabletop  30  of the present invention also has, along the perimeter of the flexible support panel  32 , a means for indexing  37  the exact position of a patient relative to the length and optionally the width of the support panel. An indexing means or ruler  37  may be provided along at least one edge of support panel  32 , and may extend around the perimeter of the support panel. In one embodiment, an indexing means  37  may be part of or attached to the upper surface  31  of tabletop  30 . In another embodiment, indexing means  34  may be part of or attached to the frame of flexible support panel  32 . In any embodiment, indexing means  34  may be either radiolucent or radiopaque.  
         [0025]    The support panel  32  is preferably adapted to be positioned in the tabletop  30  so that the center of the support panel is in alignment with the longitudinal center of the tabletop. In another aspect of the invention, the longitudinal center of the tabletop is provided with a visible radioopaque support marking extending along the center of the tabletop and along the centerline of the support panel, as shown at  50  of FIG. 4. There may be one or more such longitudinal lines, but one of them must extend down the centerline of the table and the support panel. One or more lateral support markings extend laterally across the flexible support to perpendicularly cross and intersect the longitudinal centerline support marking  50 , as shown generally at  54  of FIG. 4, one of which is positioned at the center line of longitudinal axis of the support panel. The longitudinal and lateral support marks are preferably a visible coating on the surface of the flexible support, and are radiopaque. Radiopaque markers are preferred if it is desired to relate the patient&#39;s position relative to the support in the radioimages.  
         [0026]    Radiopaque markers would be helpful to practitioners when, for example, the patient is aligned with the visible markers  54  on the flexible support panel, and the patient alignment is recorded or noted. A patient&#39;s position may be recorded by simply applying a mark on the patient&#39;s body at the location where the patient&#39;s skin contacts the positioning markers  54  on the support panel. However, when the positioning markers are radiopaque, any adjustment in the patient&#39;s position on the tabletop may be accurately assessed relative to the location of the makers on the radioimage. In each case the peripheral markings and/or the centerline and/or lateral support markings may contain lettered or numerical designations indicating relative lateral or longitudinal position of the patient on the support panel.  
         [0027]    A tabletop of the present invention may also have a lateral guide rail composed of a fixed portion  35  extending downward from the outside edge of the bottom of the tabletop and a stiff, yet flexible slide rail  36  extending inward from the fixed portion  35 , below the bottom of the tabletop, as illustrated in FIG. 2B. Both the lateral guide rail and the slide rail may extend along the entire length of the tabletop. The fixed portions  35  of the lateral guide rail may be designed to rest over and in close proximity to the outer edge of an existing table of a diagnostic scanning instrument upon which the tabletop of this invention is to be placed. The flexible inner portions  36  of the slide rail may be designed to rest on the outer top edge of an existing table of a diagnostic scanning instrument to facilitate lengthwise movement and adjustment along the length of the table.  
         [0028]    It will be appreciated that the embodiment of the invention illustrated in FIG. 2 may be an overlay, i.e., a table insert for an existing imaging table. Likewise it may itself be a table top which is supported by a base suitable for supporting and leveling the table top and having other suitable mechanisms appropriate for imaging procedures, including operative components which interact with the table top to transport it into and out of the imaging device.  
         [0029]    [0029]FIG. 3 illustrates another embodiment of the present invention. In this embodiment, a tabletop  30  may have leveling means  40  and  41  for adjusting the horizontal plane of the entire tabletop. Leg-type leveling means  40  may be embedded in the corners of the tabletop and extend downward from the bottom of the tabletop. Leveling legs  40  may extend downward from the bottom, either perpendicular to the tabletop or at an angle less than 90° but greater than 0°. Leveling legs  40  should be designed to provide sufficient clearance for deflection of the flexible insert portion  33  panel  32 . In addition, the leveling means also includes at least one longitudinal level indicator and one lateral level indicator positioned on or in the surface of the tabletop. This embodiment is particularly suited for use as a tabletop to overlay an existing imaging table, facilitating appropriate leveling of the patient support surface independent of the leveling of the imaging table.