Abstract:
The present invention provides a support for a patient undergoing radiation therapy that preserves radiation build-up, such as normally spares the skin from receiving high amounts of radiation dose. The support includes at least one gas-filled bladder that displaces some tissue from the path of the radiation and/or spaces the tissue being treated from foam or the like.

Description:
RELATED APPLICATIONS 
   This application claims the benefit of U.S. provisional filing 60/701,922, filed Jul. 22, 2005 hereby incorporated by reference. 

   FIELD OF THE INVENTION 
   The present invention relates to a patient positioning device for radiation therapy, and in particular, to a patient positioning device reducing skin radiation dose. 
   The treatment of breast cancer, for example, may include radiation therapy in which high-energy beams of radiation are focused on a tumor, or the region from which a tumor has been removed. For this purpose, it is desirable to extend the breast tissue away from the chest wall so as to reduce radiation exposure to the chest. This may be done conveniently by positioning the patient in a prone position on a table having an opening through which one breast may be pendent. U.S. Pat. No. 5,564,468, incorporated by reference, describes a commercially available table for this purpose. 
   Table systems of this type can be cumbersome to operate and install. Further, while the tabletop may be relatively thin, it may nevertheless block radiation directed at a breast laterally across the untreated breast. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention provides a patient positioning device that may rest on top of a table and which provides an opening for a pendant breast treatment of a prone patient. Importantly, a portion of the support in the path of radiation is a gas-filled bladder, to prevent premature build-up of the radiation that increases skin dose, and which may occur in other support materials such as cushioning foam. The result is a lightweight support eliminating table structure or the like that can block radiation, and further providing reduced skin dosage. 
   Specifically then, the present invention provides a patient positioning device for radiation treatment of a breast of a prone patient, the positioning device including an elevating support, positionable between a table surface and a torso of the prone patient to support the patient with a first breast positioned within an opening in the elevating support. The elevating support has a thickness sized to allow the first breast to descend pendent from the patient into the opening. At least a portion of the elevating support beneath the second breast of the patient is a gas-filled bladder compressing the second breast upward toward the patient. 
   Thus, it is an object of at least one embodiment of the invention to provide a simple and light-weight patient positioner that may be easily set up and removed from a table of a radiation therapy machine. The gas-filled bladder provides supporting structure that integrates with cushioning foam surrounding the bladder, eliminating the need for rigid cantilevered table elements or the like. 
   It is another object of at least one embodiment of the invention to provide a compliant and lightweight support structure that does not increase skin dose. The gas filled bladder provides support without interposing significant mass into the radiation beam. 
   The bladder may be filled with air. 
   It is thus another object of at least one embodiment of the invention to provide a simple, safe, and readily available gas for the bladder. 
   Alternatively, the bladder may be filled with helium. 
   It is thus another object of at least one embodiment of the invention to provide an extremely low-density gas that substantially decreases radiation build-up. 
   Portions of the elevating support inferior and superior to the opening may also be gas filled bladders. 
   Thus, it is another object of at least one embodiment of the invention to provide a support surface that provides extremely wide range of access angles for radiation of a prone breast and/or that reduces the build-up of radiation that has previously passed through another material. 
   The opening may be a notch in the elevating support, open to a side of the elevating support. 
   Thus, it is an object of at least one embodiment of the invention to provide at least one access angle that is wholly free from intervening support structure. 
   The elevating support may be substantially symmetric about a horizontal plane so that the first breast may be either the right or left breast and the support surface may accommodate the patient by flipping the support about a horizontal, lateral axis. 
   Thus, it is an object of at least one embodiment of the invention to provide a support surface that may be used for treatment of either breast without complex adjustment or the like. 
   The support surface may support the patient in a substantially level attitude above the tabletop. 
   Thus, it is an object of at least one embodiment of the invention to provide a comfortable attitude for the patient that does not increase pressure on one side of the patient. 
   The foregoing objects and advantages may not apply to all embodiments of the inventions and are not intended to define the scope of the invention, for which purpose claims are provided. In the following description, reference is made to the accompanying drawings, which form a part hereof, and in which there is shown by way of illustration, a preferred embodiment of the invention. Such embodiment also does not define the scope of the invention and reference must be made therefore to the claims for this purpose. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of the support of the present invention as positioned on a treatment table and supporting a prone patient; 
       FIG. 2  is a cross-section through the support and patient of  FIG. 1  along line  2 - 2 , showing compression of a right breast upward out of the path of radiation and the pendent extension of the left breast using the present invention; 
       FIG. 3  is a fragmentary perspective detail of a first embodiment of the present invention, showing a “C” shaped gas bladder flanked by inferior and superior foam slabs; 
       FIG. 4  is a figure similar to that of  FIG. 3  showing an alternative embodiment with a single block-shaped gas bladder separating the superior and inferior foam slabs; and 
       FIG. 5  is a chart showing the relative dose of radiation for one embodiment of the present invention as compared to a standard a foam pad at various distances from each, demonstrating the reduced build up of the present invention and the ability of the present invention to correct for some premature build-up when radiation passes through foam. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to  FIG. 1 , a radiation therapy machine  10  may include a radiation source  12  for directing a radiation beam  14  toward a patient  16  supported on a patient table  18  through a range of angles from two sides of the patient  16 . 
   The present invention provides a patient positioning device  20  that may fit against the upper surface of the patient table  18  so that the patient  16  may lie prone on the upper surface of the patient positioning device  20  for radiation treatment of the breast. 
   Referring now to  FIG. 2 , the patient positioning device  20  provides an opening  22  allowing one breast  24  of the patient  16  to extend pendent into the opening  22 , drawn by the force of gravity downward toward the table  18 . A thickness  19  of the patient positioning device  20  is such as to allow breast  24  to extend downwardly without interference with the table  18 . 
   The remaining breast  24 ′ is compressed upward towards the patient  16  by a portion of the patient positioning device  20 , adjacent to the opening  22 . In this way, only breast  24  extends into a generally horizontal treatment window  26 , along which radiation beams  14  may pass, while breast  24 ′ is compressed away from the treatment window  26 . 
   Referring now to  FIG. 3 , the patient positioning device  20  preferably provides a cushion, extending generally along a longitudinal axis  27 , aligned with the superior/inferior axis of the patient  16  when the patient  16  is positioned prone on the patient positioning device  20 . A first elastomeric foam block  28 , for example, being a closed-cell polyurethane foam, covered with a washable surface, may provide support for the patient&#39;s head and neck. Attached to an inferior side of foam block  28  is a “C” shaped gas bladder  30 , defining the opening  22  with a parallelepiped upper leg  32  attached to the foam block  28 , spaced from a parallelepiped lower leg  34  in parallel orientation as separated by spacer portion  36 , extending approximately halfway across the width of the patient positioning device  20  along a lateral axis  38 . The opening  22  is thus generally rectangular such as simplifies construction and surrounded on three sides by the parallelepiped upper leg  32  (on a superior side of the opening  22 ), the parallelepiped lower leg  34  (on an inferior side of the opening  22 ) and the spacer portion  36  (on a medial side of the opening  22 ). The lateral side of the opening  22  is unobstructed to provide free passage by the radiation beams  14 . 
   Generally the width of the parallelepiped upper leg  32  and parallelepiped lower leg  34  along the longitudinal axis  27  will be at least three centimeters, to provide some decrease in lost build-up when radiation passes through the foam blocks  28  and  40  as will be described below 
   An inferior side of leg  34  attaches to a second foam block  40 , which provides support for the lower chest, pelvis, and upper legs of the patient  16 . Foam blocks  28  and  40  and the “C” shaped gas bladder  30  all have the same thickness  19  near the “C” shaped gas bladder  30 , but may taper away from the “C” shaped gas bladder  30 . 
   When high-energy radiation beams  14  strike the skin, the dose of radiation deposited in the tissue gradually builds-up with depth so that the skin dose is relatively low and a higher dose is yielded beneath the skin, thus preventing painful and undesired radiation bums to the skin. The delay between the entry of the radiation into tissue and its point of maximum dose is called the build-up region and is desirably preserved for treatment of tumors beneath the skin. The present inventors have determined that a foam-filled nylon cushions can measurably exhaust the build-up distance, increasing the skin dose by as much as 300 percent when the breast is placed directly against the foam in comparison to the breast being placed directly against a gas-filled bladder. Accordingly, use of a bladder presents undesired loss of this build-up region and better control of the desired dose. 
   The “C” shaped gas bladder  30  is preferably constructed of a thin elastic material that provides a cushioning comparable to the cushioning provided by the foam blocks  28  and  40  to support the patient in generally horizontal attitude above the table  18 . The “C” shaped gas bladder  30 , for example, may be heat-sealed Mylar, vinyl, or other suitable material that can retain a gas under small amounts of pressure necessary to provide suitable cushioning. The bladder may be filled with air, or in a preferred embodiment, with helium, the latter having extremely low density and thus preserving radiation build-up length after the radiation strikes the breast  24 . Internal gussets or battens (not shown) can be used to control the shape of the bladder  30   
   Referring momentarily to  FIG. 5 , on average, the skin will receive three to four times more dose when radiation passes through a foam pad touching the skin than when radiation passes through gas-filled bladder  30 . As also shown in  FIG. 5 , the exhaustion of the build-up distance when radiation passes through foam is strongly dependent upon the distance between the foam and the breast and thus some passage through foam may be tolerated so long as the breast is spaced away from the foam, for example, by a gas filled bladder. Thus, the embodiment of  FIG. 3  allows not only radiation directed along the lateral axis  38  (from either left or right sides of the patient  16 ), but along angled axis  42  (or  42 ′) that pass through the upper leg  32  (from either left or right sides of the patient  16 ) or a similar axis  42 ″ passing though only lower legs  34  from both sides of the patient  16 , the left and right (only the patient right shown), but also through an angled axes  44   44 ′ and  44 ″ passing to some extent through portions of the foam block  28 , where the loss of build-up is remedied by the spacing of the foam block  28  from the breast by the gas filled upper leg  32 . 
   Referring now to  FIG. 4 , a simpler version of the present invention employs the foam blocks  28  and  40 , separated from each other (to provide for the opening  22 ) by a generally parallelepiped gas bladder  30 ′, that eliminates the complexity of the legs  32  and  34 . 
   The bladders  30 ′, and  30  described above, provides a spacing without eliminating the support of the patient which holds other tissue, including the opposed breast  24 ′, away from the treatment window  26 . 
   Referring to  FIGS. 3 and 4 , the patient support device  20  is generally symmetric about a horizontal axis (as used) and so may be flipped about the lateral axis  38  for use with either the left or right breast. 
   It will be understood that the invention need not be limited to radiation treatment of the breast, but may be used in any situation where radiation must pass through a cushioned support material into the patient and it is desired to reduce skin dosage. Further, the gas filled bladders may conform to the breast or other tissue to provide for stabilization. 
   It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but that modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments also be included as come within the scope of the following claims.