Abstract:
A patient support system to be used in conjunction with a standard linear accelerator, and other sources, is described that allows access of the treatment beam to the breast from up to 360 degrees. This support system places the patient in a prone position with the breast going through an aperture. The prone position increases the separation of the breast from the chest wall and other critical organs and reduces motion of the target tissue due to breathing. This invention offers up to 360 degree radiation beam access to the breast. This helps in skin sparing, better dose conformity, and allows one to use modern treatment techniques such as IMRT and IGRT. It also includes a provision for an imaging system. This invention can also be used with CT and MR imaging modalities.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Ser. No. 60/970,288, filed Sep. 6, 2007, the contents of which are incorporated herein by reference, in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     In order to treat cancer with radiation, it is highly desirable to maximize the dose delivered to the target volume containing the tumor which is visible with various imaging modalities and some predetermined margin while sparing normal tissue. 
     Many mechanical configurations of radiation therapy machines and the associated radiation sources have been developed since Roentgen discovered X-Rays. Modern radiation therapy systems use relatively high energy beams of radiation from radioactive isotopes, particle beam accelerators, or electron beam X-Ray generators. The X-Ray generators can employ either high voltage direct current or RF driven linear accelerators (LINACs). The conventional radiation therapy system uses a LINAC to generate an electron beam with between 4 and 22 MeV of energy at low current. The electron beam strikes a high-Z target, typically tungsten, and generates penetrating x-rays. The beam is shaped and delivered to the target volume from one or more directions. The overlapping dose at the target volume is usually higher than the dose at the surface from any one delivery angle. The skin is sensitive to radiation, so it is desirable to limit the skin dose to minimize complications. If more delivery angles are used, the surface dose can be spread out and minimized with respect to the dose delivered to the target volume. A significant fraction of all radiation therapy treatments are employed to treat breast cancer with very good success. A typical general purpose radiation therapy system is designed to treat virtually all anatomical sites with some trade-offs being made in the design in order to make a universally applicable machine. A linear accelerator rotates about a horizontal axis, around a virtual point called the isocenter that intersects with the beam axis. A typical source to axis distance, or source to isocenter distance, SAD is 100 centimeters. The treatment couch rotates about a vertical axis intersecting with the same isocenter and including three additional Cartesian motions for patient alignment. The external dimensions and geometry of different linear accelerators vary, resulting in different available treatment angles, which can be limiting to couch position and gantry rotation. 
     Currently most of the breast cancer patient population is treated in the supine (lying on the back) position, which does not allow access from more than a few angles. The supine position is also inferior due to gravitational forces compressing the breast against the chest. In addition, breast motion resulting from breathing creates inaccuracies in locating the beam with respect to the target volume. 
     Alternatively, a prone position radiation therapy is used for access to the breast. This method is implemented with a table top attachment that works with a standard linear accelerator. This embodiment helps to reduce target motion associated with breathing and create a better separation of the target tissue with respect to the chest wall and other critical structure. However, this embodiment still only allows access to a few angles, typically two. 
     SUMMARY OF THE INVENTION 
     This invention relates to a patient support system to be used with conventional radiation sources to position the patient in a more favorable geometry by allowing up to 360 degree access to the breast with the patient in the prone position. 
     This invention solves one of the remaining issues in breast cancer treatment, which is access to the breast from multiple angles, up to 360 degrees. The patient support system of the present invention can be made out of suitable materials making it CT and MR compatible for use with imaging modalities. 
     The present invention is directed to a prone position patient support system to be used in conjunction with a radiation source. The patient support system includes an anatomically contoured patient interface surface and an aperture to permit passage of the anatomy to be treated through the patient interface surface. The patient supports system further includes a support system for the patient interface surface that provides space below the patient interface surface to allow beam access from a radiation source for at least 180 degrees of rotation in a substantially horizontal plane. 
     In one embodiment, the radiation source is a LINAC. In another embodiment, the radiation source is a supervoltage x-ray generator. In another embodiment, the radiation source is a particle beam accelerator. 
     In one embodiment, the support system is CT compatible. In another embodiment, the patient support system is MR compatible. 
     In one embodiment, the support system further includes a rotational mechanism that allows rotation about the longitudinal axis of the patient support system. 
     In one embodiment, the support system includes one or more imaging components and associated software algorithms for patient registration. 
     In one embodiment, the support system for the patient interface surface further comprises a longitudinal translation stage and a rotary stage. 
     In one embodiment, the support system for the patient interface surface further comprises cross shaped radiolucent spacers for separating the patient interface surface and a bottom structure. 
     In accordance with another aspect of the invention, the invention is directed to a prone position patient support system to be used in conjunction with a radiation source. The patient support system includes an anatomically contoured patient interface surface and an aperture to permit passage of the anatomy to be treated through the patient interface surface. The patient support system further includes a support system for the patient interface surface that provides space below the patient interface surface to allow beam access from a radiation source for at least 270 degrees of rotation in a substantially horizontal plane. 
     In one embodiment, the radiation source is a LINAC. In another embodiment, the radiation source is a supervoltage x-ray generator. In another embodiment, the radiation source is a particle beam accelerator. 
     In one embodiment, the support system is CT compatible. In another embodiment, the support system is MR compatible. 
     In one embodiment, the support system includes one or more imaging components and associated software algorithms for patient registration. 
     In one embodiment, the support system for the patient interface surface is designed from radio-lucent material. 
     In one embodiment, the support system for the patient interface surface is geometrically designed such that the radiation beam is unobstructed. 
     In one embodiment, the support system includes a rotational mechanism that allows rotation about the longitudinal axis of the patient support system. 
     In one embodiment, the support system for the patient interface surface is geometrically designed to have limited interference with the radiation beam. 
     In one embodiment, the support system for the patient interface surface further comprises a longitudinal translation stage and a rotary stage. 
     In one embodiment, the support system for the patient interface surface further comprises cross shaped radiolucent spacers for separating the patient interface surface and a bottom structure. 
     In accordance with another aspect of the invention, the invention is directed to a prone position patient support system to be used in conjunction with a radiation source. The patient support system includes an anatomically contoured patient interface surface and an aperture to permit passage of the anatomy to be treated through the patient interface surface. The patient support system further includes a support system for the patient interface surface that provides space below the patient interface surface to allow beam access from a radiation source for 360 degrees of rotation in a substantially horizontal plane. 
     In one embodiment, the radiation source is a LINAC. In another embodiment, the radiation source is a supervoltage x-ray generator. In another embodiment, the radiation source is a particle beam accelerator. 
     In one embodiment, the support system is CT compatible. In another embodiment, the support system is MR compatible. 
     In one embodiment, the support system includes one or more imaging components and associated software algorithms for patient registration. 
     In one embodiment, the support system for the patient interface surface is designed from radio-lucent material. 
     In one embodiment, the support system for the patient interface surface is geometrically designed such that the radiation beam is unobstructed. 
     In one embodiment, the support system includes a rotational mechanism that allows rotation about the longitudinal axis of the patient support system. 
     In one embodiment, the support system for the patient interface surface further comprises a longitudinal translation stage and a rotary stage. 
     In one embodiment, the support system for the patient interface surface further comprises cross shaped radiolucent spacers for separating the patient interface surface and a bottom structure. 
     In accordance with another aspect of the invention, the invention is directed to a prone position patient support system to be used in conjunction with a radiation source. The patient support system includes a contoured patient support surface including an aperture to permit passage of the anatomy to be treated through the patient support surface and a lower support structure. The patient support system further includes a support member between the patient support surface and the lower support structure which provides space between the patient support surface and the lower support structure. The patient support system further includes a treatment couch on which the lower structure is coupled and the treatment couch has a rotary base. A rotational mechanism is coupled to the lower structure and the treatment couch which allows beam access from a radiation source for 360 degrees in a substantially horizontal plane. 
     In one embodiment, the radiation source is a LINAC. In another embodiment, the radiation source is a supervoltage x-ray generator. In another embodiment, the radiation source is a particle beam accelerator. 
     In one embodiment, the patient support system is CT compatible. In another embodiment, the patient support system is MR compatible. 
     In one embodiment, the rotational mechanism allows rotation about the longitudinal axis of the patient support system. 
     In one embodiment, the support system includes one or more imaging components and associated software algorithms for patient registration. 
     In one embodiment, the rotational mechanism comprises a longitudinal translation stage and a rotary stage. 
     In one embodiment, the support member comprises cross shaped radiolucent spacers for separating the patient interface surface and a bottom structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
         FIG. 1A  is a top view of the patient support system that allows radiation beam access of less than 360 degrees as the support structure for the table top obscures beam access from a limited range of angles according to an embodiment of the present invention. 
         FIG. 1B  is a side view of the patient support system shown in  FIG. 1A  that would be mounted on a conventional linear accelerator treatment couch. 
         FIG. 1C  is an isometric view of the patient support system shown in  FIG. 1A . 
         FIG. 2A  is a top view of the patient support system of the present invention that allows radiation beam access up to 360 degrees by using non-shadowing supports according to an embodiment of the present invention. 
         FIG. 2B  is a side view of the patient support system shown in  FIG. 2A . 
         FIG. 2C  is an isometric view of the patient support system shown in  FIG. 2A . 
         FIG. 3A  is a top view of another embodiment of the patient support system that allows radiation beam access up to 360 degrees by using non-shadowing supports with an additional rotation stage and translation stage according to an embodiment of the present invention. 
         FIG. 3B  is a side view of the patient support system shown in  FIG. 3A . 
         FIG. 3C  is an isometric view of the patient support system shown in  FIG. 3A . 
         FIG. 3D  is a bottom view of the patient support system shown in  FIGS. 3A ,  3 B and  3 C. 
         FIGS. 4A-C ,  5 A-C,  6 A-C,  7 A-C,  8 A-C,  9 A-C,  10 A-C and  11 A-C show top, side, and isometric views, respectively, of the variable patient support system technique that allows 360 degree access to the breast using the additional rotation and translation capability shown in  FIGS. 3A-D . 
         FIGS. 12A-D  illustrate the patient support system of  FIGS. 3A-D  mounted on a jointed support in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     This invention combines a unique support system with novel geometric motions to allow access to treat the breast in the prone position from up to 360 degrees. Presently this range of access and motion is not possible with conventional LINAC couches or existing attachments. An anatomically designed patient support surface  10  with contour  12  provides a surface for the patient to lie on during positioning and treatment. The contour  12  of the support surface  10  combined with the shape and size of the aperture  11  allows the patient to lie comfortably in position during set-up and treatment while allowing the anatomical volume of interest to protrude through the aperture  11 . A series of inserts of different size, shape, and symmetry (not shown) can be provided to allow small breasts to be treated comfortably in one extreme, while a large, asymmetrically shaped aperture can allow the chest wall and other related anatomy such as the axilla to be accessed for treatment. The support system can be made in mirror-image versions with left and right versions of the apertures for treating the left and right breast to maximize patient comfort and anatomy accessibility. Cushions can be provided for the support surface  10  and contour  12  to increase comfort during the procedure, which is typically 15 minutes with a beam-on time of 1 minute. The support surface  10  can be gently heated to increase patient comfort as well. A set of cushions that tilt the patient around the longitudinal axis can be provided to maximize access and comfort. The patient support system is shown in two basic configurations in  FIGS. 1A-C  and  2 A-C as attachments.  FIGS. 1A-C  have a triangular shaped support member  13  between the upper support surface  10  and bottom structure  14 . This provides unobstructed access to the breast over a wide range of angles, but not 360 degrees. This is a simple configuration that can be placed on an existing commercial LINAC treatment couch and provides much of the benefit of treating from a wide range of angles. As shown in  FIG. 7A , because a treatment couch  21  and the patient support surface  10  interfere with the LINAC gantry  20 , a full range of angles is not physically accessible. The triangular support member  13  does not limit access by the radiation beam to the breast over the range of physically possible angles for a given combination of LINAC and couch. The upper support surface  10  is made of a stiff, radiolucent material such as carbon fiber over a foam or honeycomb core, which has sufficient torsional and longitudinal stiffness to support the patient in a cantilevered configuration without significant deflection. In this configuration, the invention consists of a simple, light add-on attachment to an existing treatment system, but provides much of the advantage of the more integrated, complex implementations also described here and included in the overall invention. 
     A second level of performance and complexity is shown in  FIGS. 2A-C . A similar set of top patient support surface  10  and bottom structure  14  are separated by radiolucent spacers  15  with locations and orientations designed to minimize absorption of radiation. Radiolucent spacers  15  that are cross shaped are shown, and the orientation of the supports is such that radiation will not traverse the long axis of the material on its way to the breast at isocenter. The cross shaped radiolucent spacers  15  project about 2.8 times the thickness of the material into the path of the beam. If the beam traverses two adjacent sections of the support at 45 degrees, the total thickness seen by the beam is 2.8 times the thickness of the material. A square tube has similar characteristics, but a round tube creates shadows where the beam traverses the edges of the round tube tangentially. The support system or a similar one of the same geometry is used in a CT machine prior to treatment to obtain a set of images used for treatment planning. These images can be used to create a set of digitally reconstructed radiographs (DRRs) that can be used with an imaging system that is optionally part of this support system. These DRRs are used to compare the patient&#39;s position during set-up to insure correct positioning of the anatomy to be treated. The imaging system can consist of optical cameras mounted in one or more locations such as on the bottom of the bottom support structure  14 , out of the path of the treatment beam, on the LINAC gantry  20 , and on the walls of the room, mounted next to or coaxially with the alignment lasers typically installed in treatment rooms. The capability to acquire images, process the images and compare them to the treatment planning images is an optional part of this invention. 
       FIGS. 3A-D  illustrate the support system with an additional longitudinal translation stage  16  and  17 , as well as an additional rotary stage  18 . The rotary stage  18  is fastened to the LINAC couch  21  of  FIGS. 4A-C ,  5 A-C,  6 A-C,  7 A-C and  8 A-C and these two additional degrees of freedom allow the support system to orient the breast for access to the treatment beam through a full range of 360 degrees. The translation stage  16  and  17  and the additional rotary stage  18  allow the support system to move in a longitudinal axis of patient support system. In the positions shown in  FIGS. 7A-C , the support surface  10  would interfere with the LINAC gantry  20  if the support surface was not moved away from the LINAC treatment head using the translational stage  16  and  17  and rotary stage  18  shown in  FIGS. 3B and 3D . In the position shown in  FIGS. 8A-C , the distance from the patient&#39;s breast to the patient&#39;s feet is greater than the typical distance from the LINAC isocenter to the treatment head. It is necessary to use an increased SAD for large treatment angles. The range of positions and angles are shown in  FIGS. 4A-C ,  5 A-C,  6 A-C,  7 A-C and  8 A-C collectively. Treatment with increased SAD can be easily planned for once the geometrical limitations of the system are characterized.  FIGS. 4A-C  show the patient support system in position to provide treatment on a LINAC at an angle which is defined as 90 degrees. The patient support system is at an angle of zero degrees when the long axis of the treatment couch  21  is parallel to the rotational axis of LINAC gantry  20 . The gantry  20  is rotated into a substantially horizontal position such that the upper surface of the radiation beam  24  is almost horizontal for this phase of treatment. All anatomy that projects through the aperture  11  can be treated in this configuration. Additional treatments can be delivered to related sites such as the axilla, in which there are lymph nodes that may contain cancer cells that have migrated from the primary tumor. These are located under the arm near the armpit and are treated with radiation if they are found to be positive for cancer cells upon biopsy. 
       FIGS. 4A ,  5 A,  6 A,  7 A and  8 A illustrate plan views of different rotations of the support surface  10 .  FIGS. 4B ,  5 B,  6 B,  7 B and  8 B illustrate side views of the corresponding conditions.  FIGS. 4C ,  5 C,  6 C,  7 C and  8 C illustrate isometric views of these configurations.  FIGS. 4A-C ,  5 A-C,  6 A-C,  7 A-C and  8 A-C illustrate the different rotational angles of the support surface  10 .  FIGS. 9A-C ,  10 A-C and  11 A-C are mirror images of  FIGS. 5A-C ,  6 A-C and  7 A-C, respectively, which together in conjunction with rotating the LINAC gantry  20  describe 45 degree steps in a full 360 degree rotation to treat the breast from all angles. Any given treatment may include treatment from one or more angles, and the most advanced version of treatment where the beam is on continuously during patient rotation is also possible.  FIGS. 4A-C ,  5 A-C,  6 A-C and  7 A-C further illustrate a LINAC cabinet  19 , a treatment couch Z axis motion  22 , a couch rotary base  23  and the radiation beam  24 . 
     The support system can be made as an integral part of a custom couch instead of as an attachment. Increased flexibility is obtained by integrating the structures instead of making an add-on attachment. Better access to oblique angles departing from the substantially horizontal position is possible by eliminating duplicate structures and providing cut-outs in strategically located areas. A patient support system as described may additionally be mounted on a “frog-leg” jointed support or robotic arm  25  which increases performance and flexibility, as shown in  FIGS. 12A-D . An additional rotational motion can be incorporated into the add-on or integrated versions to allow tilting the patient support surface along the longitudinal axis, thus allowing greater comfort for the patient and creating better positioning for the left and right breasts. Either version of this invention can be used with any radiation source including radioisotopes, LINACs, ortho- or super-voltage x-ray generators or particle beam accelerators. 
     The embodiments of the present invention can be used in conjunction with an already existing table, e.g., a treatment couch, or incorporated into the design of an entirely new treatment couch. 
     The patient support system of the present invention can be made out of materials making it CT and MR compatible for use with imaging modalities. The patient support system further includes one or more imaging components and associated software algorithms for patient registration. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.