Abstract:
A patient immobilization frame is provided that can be secured to a patient table in a radiation therapy facility. The frame includes fiducials integrated into the bottom panel of the frame. The frame is provided with a removable locking mechanism for locking the frame to the patient table. Each side walls of the frame defines a forward cut-out and a mid-side cut-out to accommodate larger girth patients. A panel insert is provided to close the mid-side cut-outs when the additional space is not required for the patient. The frame further includes an abdomen compression device supported by a cross bar that is movably mountable to the frame. The device includes a compression plate configured to contact the patient and a compression mechanism between the cross bar and the compression plate. A pressure transducer may be incorporated between the compression plate and the cross bar.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to co-pending provisional application No. 60/647,893, entitled “Method for Radiation Therapy Delivery at Varying Source to Target Distances”, filed on Jan. 28, 2005, the disclosure of which is incorporated herein by reference, and to co-pending provisional application No. 60/647,920, entitled “Relocatable Stereotactic Immobilization Apparatus”, filed on Jan. 28, 2005, the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to an apparatus used to position and immobilize a patient during a therapeutic or diagnostic treatment. The apparatus is especially useful in procedures that require stereotactic coordination of specific locations in the patient&#39;s anatomy with the therapeutic or diagnostic device. In particular, this apparatus is especially well suited to facilitate such procedures on individuals who have wide bodily girth either from large inherent size or from obesity. 
         [0003]    Patient positioning systems are used for accurate and reproducible positioning of a patient for radiation therapy, diagnostic imaging, and certain surgical procedures. Stereotactic targeting and immobilization tables support the patient and facilitate precise and accurate guidance for stereotactically directing a variety of therapeutic and diagnostic interventions toward a defined three-dimensional position within the patient&#39;s body, including the neck, chest, abdomen, pelvis and proximal thighs. 
         [0004]    In a typical radiotherapy procedure, a gantry G ( FIG. 1 ) directs a radiation beam at an iso-center I. The gantry G rotates about a horizontal axis so that the radiation beam is always directed at the iso-center. The iso-center I can be located by the intersection of laser beams generated by wall-mounted laser devices L in the treatment room ( FIG. 3 ). The patient is supported on a couch or table T, as shown in  FIG. 2 , that can be moved into a position relative to the gantry G and the iso-center I so that the area of treatment can be positioned at the iso-center. 
         [0005]    The need for effective patient immobilization for radiation therapy is well-documented. Immobilization reduces normal tissue complication rates and allows increased irradiation of the target tissue. Historically, skin marks have been used to aid in target localization and repositioning. However, skin marks may migrate as they are re-marked and the markings can shift with respect to underlying deeper target tissues. As a consequence, fiducial markings have been placed on patient immobilization frames, since these markings do not smear, fade or migrate. In some procedures, fiducial markings may be matched to skin markings to properly locate and position the target tissue relative to the iso-center. 
         [0006]    Patient comfort, the ability of the patient to maintain a position for an extended period of time, reproducibility of the patient&#39;s position and anticipated beam orientation must be considered in successful repeat radiotherapy treatments. Patient comfort is essential so that the patient is discouraged from body movement that might be caused by fatigue or pain. Patient movement can invalidate a target localization and expose healthy tissues to unwanted radiation, lead to a diagnostic misinterpretation, or result in mis-targeting of a surgical therapeutic intervention. 
         [0007]    To achieve comfortable immobilization, stereotactic body immobilization devices have been developed that support the patient on the couch or table top. In some cases the frames include a body mold that can be stored and re-used in subsequent treatments. The molds are form-fitting and are typically vacuum molded thermoplastic or polyurethane foam molds. In the typical case, the patient is positioned relative to fiducial markings to ensure repeatability over successive treatments. 
         [0008]    While current immobilization frames perform well, there are still some aspects that need improvement. For instance, most immobilization frames are designed for the particular treatment system. In other words, the frames are specific to whether the irradiation apparatus is a linear accelerator, a computed tomography apparatus or an MRI device. It is desirable to have an immobilization frame that can be used with a large number of different treatment and diagnostic devices. 
         [0009]    Another problem faced by current frame designs is that they cannot be used by patients of large girth. This physical characteristic poses two problems. The first is that most current immobilization frames place the fiducial markings on the side walls of the frame. When a patient of large girth is positioned within the frame, the side walls can bow slightly outward. This displacement of the fiducials disturbs the repeatability of the stereotactic positioning of the patient. 
         [0010]    A second problem is that the patient just cannot fit within some of the current frame designs. Many immobilization frames are designed to fit within a limited width dictated by the aperture of the smallest imaging platform, namely MRI, to avoid collision with the imaging unit. In a typical MRI, the aperture is 43 cm. (about 16 in.) so the immobilization frame is necessarily smaller than that dimension (about 40 cm. wide). Many patients seen in diagnostic or therapy clinics, particularly in North America where patients are generally larger, cannot fit into existing frames. 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0011]      FIG. 1  is a perspective view of a radiation treatment apparatus. 
           [0012]      FIG. 2  is a perspective view of a patient couch or table for use with the treatment apparatus of  FIG. 1   
           [0013]      FIG. 3  includes a view of a laser device for use in establishing an iso-center and a view of that iso-center. 
           [0014]      FIG. 4  is a perspective view of a patient immobilization frame in accordance with one embodiment of the present invention. 
           [0015]      FIG. 5  is a rear perspective view of the immobilization frame of  FIG. 4 . 
           [0016]      FIG. 6  is a side elevational view of the immobilization frame of  FIGS. 4-5 . 
           [0017]      FIG. 7  is a top elevational view of the immobilization frame of  FIGS. 4-5 . 
           [0018]      FIG. 8  is a bottom elevational view of the immobilization frame of  FIGS. 4-5 . 
           [0019]      FIG. 9  is an end elevational view of the immobilization frame of  FIGS. 4-5 . 
           [0020]      FIG. 10  is a perspective view of a panel insert for use with the immobilization frame shown in  FIGS. 4-9 . 
           [0021]      FIG. 11  is a perspective view of an immobilization frame according to the present invention with the panel inserts of  FIG. 10  in position. 
           [0022]      FIGS. 12   a - d  are perspective and side views of a locking bar assembly for use with the immobilization frame of  FIGS. 4-9  in accordance with one aspect of the invention. 
           [0023]      FIG. 13  is a top perspective view of a mounting insert forming part of the locking bar assembly shown in  FIG. 12 . 
           [0024]      FIG. 14  is a top elevational view of a locking cam forming part of the locking bar assembly shown in  FIG. 12 . 
           [0025]      FIG. 15  is an enlarged side perspective view of a portion of the immobilization frame of  FIGS. 4-9  with the locking bar of  FIG. 12  mounted thereto, shown with the frame supported on a patient table. 
           [0026]      FIG. 16  is an enlarged side perspective view of the frame and locking bar shown in  FIG. 15 , with the locking cam inserted into the locking bar. 
           [0027]      FIG. 17  is an enlarged view of the locking cam shown in  FIG. 16 . 
           [0028]      FIG. 18  is a side perspective view of the immobilization frame of the present invention with a normally sized patient supported therein. 
           [0029]      FIG. 19  is an end perspective view of the patient within the frame of the present invention supported on a patient table and oriented at the iso-center for a treatment apparatus. 
           [0030]      FIG. 20  is an end partial cross-sectional view of the immobilization frame of  FIGS. 4-9  with an abdominal compression device mounted thereto in accordance with one embodiment of the invention, particularly depicting the relationship of the device to the immobilizing frame and the patient. 
           [0031]      FIG. 21  is the side elevational view of the abdominal compression device shown in  FIG. 20 . 
           [0032]      FIG. 22  is a side perspective view of the side of an immobilization frame of an alternative embodiment of the present invention. 
           [0033]      FIG. 23  is a top perspective view of the immobilization frame shown in  FIG. 22  with an alternative abdominal compression device and a measuring frame mounted on the immobilization frame. 
           [0034]      FIG. 24  is an enlarged side view of a hinge component of the abdominal compression device shown in  FIG. 23 . 
           [0035]      FIG. 25  is an enlarged top perspective view of the abdominal compression device shown in  FIG. 23 . 
           [0036]      FIG. 26  is an enlarged side view of a vertical arm of the measuring frame shown in  FIG. 23 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0037]    For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the invention is thereby intended. It is further understood that the present invention includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the invention as would normally occur to one skilled in the art to which this invention pertains. 
         [0038]    The present invention provides an immobilization frame that can be used with a number of different diagnostic imaging and therapeutic apparatus. A typical system includes a gantry G that rotates around an iso-center I, as shown in  FIG. 1 , and a patient couch or table T, as shown in  FIG. 2 . The iso-center can be located by lasers L ( FIG. 2-3 ). The table T establishes a three-dimensional coordinate system (x,y,z) that is used to make measured patient movements or to locate the target tissue. The present invention contemplates an immobilization frame  10  that defines its own three-dimensional coordinate system that can be mapped onto the table coordinate system. 
         [0039]    The details of one embodiment of the frame  10  are depicted in  FIGS. 5-9 . The frame includes a bottom panel  12  that provides the surface on which the patient rests during the irradiation procedure. A pair of opposite side panels  14  project upward from the bottom panel so that the frame defines an open channel. In particular, in the illustrated embodiment, the frame  10  is open at its opposite ends  16 . 
         [0040]    In one feature of the invention, the bottom panel  12  is provided with an array of fiducial markings  18 . Since the fiducials are not on the side panels they cannot be displaced by outward bowing of the panels. Instead, the fiducials are on the bottom panel which will not deform because the bottom panel is supported by the patient table T ( FIG. 2 ). In accordance with the preferred embodiment, the fiducial markings  18  are linear so that the markings can be readily associated with the three-dimensional coordinate system of the frame  10  itself In addition to the fiducial markings  18 , the frame can be provided with coordinate markers for use with the room lasers L ( FIG. 3 ) to orient the frame relative to the iso-center I. When the fiducial marks are placed on the bottom panel, the frame can be made as wide as allowed by the MRI, CT or linear accelerator without considering the visibility or accuracy of the side panel on the 3D image. 
         [0041]    The frame  10  may be provided with angled supports  20  that interface between the bottom panel  12  and the opposite side panels  14 . The supports  20  also help establish and maintain the position of the patient within the frame, especially when a positioning mold  71  ( FIG. 18 ) is used. 
         [0042]    The side panels  14  include forward cut-outs  22  at the head end of the frame. The forward cut-outs provide clearance around the patient&#39;s head and are particularly useful when the patient must position his/her arms in the overhead position shown in  FIG. 18 . 
         [0043]    In one aspect of the invention, the side panels  14  also define mid-side cut-outs  24 . Preferably, the mid-side cut-outs  24  extend over about half the length of the frame  10 . In addition, the mid-side cut-outs are oriented so that the patient&#39;s hips and upper thighs can be aligned with the mid-side cut-outs when the patient is lying in the frame  10 , as shown in  FIG. 18 . Thus, the larger portions of the patients anatomy can extend through the mid-side cut-outs  24  while the patient is positioned with the frame. This aspect of the design directly facilitates the treatment or diagnostic intervention of patients with large girth. 
         [0044]    For a normally sized patient, the mid-side cut-outs  24  can be closed with panel inserts  30 , shown in  FIG. 10 . In one embodiment of the invention, the panel inserts includes a center panel  32  that corresponds to the configuration and dimensions of the mid-side cut-outs  24 . An outer panel  34  is affixed to the outer face of the center panel  32  and a pair of inner panels  36  are affixed to the inside face and at the ends of the center panel, as show in  FIG. 10 . The inner and outer panels  34 ,  36 , respectively, cooperate to define an engagement slot  38 . As shown in  FIG. 11 , the panel insert  30  extends into the mid-side cut-outs with portions of the side panel  14  disposed within the engagement slots  38  at the ends of the panel insert. 
         [0045]    In one embodiment, the panel insert  30  can be integrally formed as a unitary piece. Gripping handles can be formed into the panel inserts to facilitate placement and removal of the insert from the mid-side cut-outs. While the illustrated embodiment shows the single outer panel  34  disposed on the outside of the frame, a similar construction can be implemented on the inner face of the center panel  32  in lieu of the two inner panels  36 . Alternatively, the orientation of the panel insert can be reversed, with the single piece panel  34  extending along the inside of the frame  10 . The panel inserts  30  can be configured to support ancillary components of the patient immobilization system, such as straps or body mold portions. 
         [0046]    In accordance with one feature of the invention, the underneath surface of the bottom panel  12  is provided with a sliding or friction-resistant coating, such as TEFLON®. This coating allows the frame  10  to slide easily on the patient table T when the patient is positioned within the frame. With this feature, the patient can enter the frame  10  at one end of the patient table T, and then the frame can be manually slid to a pre-determined position on the table to match the frame coordinate system with the table coordinate system. This friction-resistant coating enables the treatment of patients with large girth. Thus, one important feature of the invention is that the frame  10  can be easily slid along the table even when supporting a patient of large overall weight without excessive strain or injury to hospital personnel. Alternatively, the frame  10  may be formed of a material that slides easily on the table surface, such as a carbon-fiber composite. 
         [0047]    In one important feature of the invention, the frame  10  is also provided with means to rigidly fix the position of the frame relative to the table. In accordance with the invention, a locking bar assembly  40  is provided, as shown in  FIGS. 11-17 . As shown in  FIG. 12(a) , the assembly  40  includes a mounting plate  42  that includes enlarged ends  44 . Openings  46  are defined in the ends  44  to receive a corresponding mounting insert  50  or locking cam insert  60 . 
         [0048]    The mounting plate  42  is provided with a plurality of screw holes to fasten the locking bar assembly  40  to the bottom panel  12  of the frame  10 . In particular, the bottom panel defines a pair of slots  26  at opposite ends of the frame, as shown in  FIGS. 6 and 8 . The slots are separated by a pre-determined distance that corresponds to the position of securement recesses on the patient table, such as the recesses S shown in  FIG. 15 . Thus, as illustrated in  FIGS. 15-16 , the openings  46  of the locking bar assembly  40  can be positioned over corresponding securement recesses S in opposite sides of the patient table. 
         [0049]    Returning to  FIG. 8 , the bottom panel further defines a plurality of mounting holes  27  in the bottom slots  26 . Two mounting plates  42  are attached to the bottom panel  12  within the slots  26  by screws passing through the screw holes  48  into the mounting holes  27 . Thus, it can be appreciated that two locking bar assemblies  40  may be rigidly attached to the frame  10 , so that when the bar assemblies are rigidly attached to the table T, as described below, the position of the frame  10  is fixed relative to the table T. At this point, then, the coordinates of any point on the frame  10 , such as a point on one of the fiducial markings  18 , can be translated to the coordinates of the table T, the room coordinates, and ultimately to a position location relative to the iso-center I. 
         [0050]    The engagement between the locking bar assemblies  40  and the patient table T is accomplished through the mounting insert  50  and locking cam insert  60 . As shown in  FIG. 13 , the mounting insert  50  includes a bottom disc  52  that is configured to reside at the base of the securement recess S. An engagement groove  53  is provided above the disc to receive a complementary feature within the securement recess S. This engagement between the groove  53  and the complementary recess feature fixes the mounting insert  50  against vertical movement out of the recess. 
         [0051]    The mounting insert  50  further includes a post portion  55  that is sized to fit snugly through the opening  46  at one end  44  of the locking bar assembly  40 . An enlarged head  56  traps the locking bar assembly beneath the head to prevent removal of the frame from the table once the mounting insert  50  is in its operative position. In the embodiment depicted in  FIG. 13 , the mounting insert  50  has a cylindrical shape; however, other configurations are contemplated, provided comparable changes are made in the opening  46  at the one end of the locking- bar assembly. Since the mounting insert  50  is intended simply to orient one end of the locking bar, the insert may be semi-circular and engage only half of a circular securement recess S. 
         [0052]    The final fixed connection is accomplished by the locking cam insert  60 . This insert is configured similarly to the mounting insert in that it is configured to extend through an opening  46  in an opposite end  44  of the locking bar assembly, and to project into and be fixed to a securement recess S in the patient table T. Thus, the insert  60  includes a post portion  65  sized to fit snugly through an opening  46  at the bar end  44 , as well as an enlarged head  66 . The insert also defines an engagement groove  63  that is engaged by a complementary feature of the securement recess S. However, unlike the other insert  50 , the cam insert  60  includes a cam disc  62  that defines an eccentric cam edge  64 . A handle  68  is provided on the head  66  to facilitate rotation of the cam insert  60 . As the insert  60  is rotated, the eccentric cam edge  64  is disposed within the securement recess to lock the cam insert  60  within the recess. In particular, as the cam edge engages the complementary interior features of the securement recess, the locking cam insert generates a laterally outward force to shift the locking bar assembly laterally relative to the table T. This lateral shift locks the mounting insert  50  in within its table recess S, and continued rotation of the cam insert  60  locks that insert within a securement recess S on the opposite side of the table. 
         [0053]    It is contemplated that the mounting insert  50  will be positioned in the ends of the locking bars  40  on one side of the frame, such as the left side. The cam insert  60  is then positioned at the ends of the locking bars on the opposite side of the frame. Thus, when the cam inserts are rotated they uniformly pull the immobilization frame toward that opposite side and effectively lock the mounting inserts  50  within their corresponding table recesses. 
         [0054]    In order to facilitate access to and operation of the locking bar assembly, the frame  10  is provided with access cut-outs  28  in the side panels  14  and in the angled supports  20 . The access cut-outs are preferably sized so that the corresponding mounting inserts  50  and cam inserts  60  can be positioned within the openings  46  in the locking bar ends  44 . In the illustrated embodiment, the openings  46  are oriented just at the opening of the access cut-outs  28 . In an alternative embodiment, the side walls  14  of the frame  10  generally coincide with the edge of the table T, so that the access cut-outs  28  are positioned directly above the securement recesses S in edges of the table T. 
         [0055]    The locking cam insert provides a means for ready securement of the immobilization frame  10  to the table T by way of the existing securement recesses S. Once the patient is positioned within the frame  10 , the low friction surface of the bottom panel  12  allows the frame to be easily slid along the length of the table T until the openings  46  in the ends  44  of the locking bar assembly  40  are aligned with predetermined securement recesses S in the patient table. Mounting inserts can be placed within the bar end openings on one side of the frame. The cam inserts are then placed within the bar end openings on the opposite side of the frame and then rotated to fix the frame  10  to the table T. This rigid securement avoids accidental movement of the frame that might lead to mal-alignment. Moreover, as explained above, this coupling of the frame to the patient table effectively links the frame coordinate system to the table and room coordinate systems. This linking of coordinate systems allows accurate alignment of room mounted devices, such as a linear accelerator beam or a biopsy system, with target tissue in the patient&#39;s internal anatomy. Systematic coordinate transformation and error correction algorithms may be used to accomplish this link. This capability can lead to the enabling of a “virtual iso-center” where a variable source-to-target distance is accurately realized. 
         [0056]    As depicted in  FIGS. 18-19 , the patient rests within the frame  10 , ideally surrounded by a body mold  70  or support cushions or the like, that helps comfortably restrain the patient. It can be appreciated from these figures that a patient of larger girth may require a modified body mold, but at any rate would likely require that the mid-side cut-outs  24  be open. 
         [0057]    The frame  10  is preferably formed as a unitary body, with the bottom panel  12 , side panels  14  and angled supports  20  integrally formed. In certain embodiments, the frame may be molded from a high density plastic or resin material. The material of the frame must be sufficiently strong so that the side walls  14  do not bend outwardly under pressure from the patient and body mold within the frame. 
         [0058]    The mounting plate  42  of the locking bar assembly may be molded directly into the molded frame with appropriate interlocking features to rigidly secure the assembly to the frame. Alternatively, the mounting plate itself may be formed of the same material as the frame so that the plate can be molded as one piece with the bottom panel  12 . 
         [0059]    In other embodiments, the frame is a carbon fiber frame composed of multiple layer inner and outer skins separated by a honeycomb support structure. The inner and outer skins may be formed of multiple carbon fiber layers glued together by epoxy. The same epoxy may be used to glue the honeycomb structure between the inner and outer skins. One benefit of this material and construction is that the frame may be as lightweight as possible so that it can be easily manipulated in a treatment setting. Of course, any material used to form the frame  10  must not interfere with the operation of the therapeutic or diagnostic equipment. 
         [0060]    The present invention also contemplates an abdominal compression device for use with the immobilization frame, as depicted in  FIGS. 20-21 . The device is configured to deliver abdominal compression to restrain the abdomen of the patient for breathing control by altering the fashion in which the lungs expand. In accordance with the invention, the abdominal compression device  80  may be positioned at nearly any point along the length of the immobilization frame depending on the location of the sub-sternal area of the patient. 
         [0061]    In accordance with the preferred embodiment, the compression device  80  includes a generally rigid cross beam  82  that is positioned above the patient. Most preferably, the cross beam  82  has a width sufficient to contact the upper edges of the side walls  14  of the immobilization frame  10  to help prevent accidental over-compression by the device. The cross beam is held in a stable position by a strap arrangement or a belt  84  that spans the cross beam and extends down around the side walls  14  of the frame  10 , as shown in  FIG. 20 . The cross beam can include features along its length or particularly at its ends to contain the strap  84  and keep it positioned on top of the cross beam. 
         [0062]    The ends of the straps  85  are engaged to the frame  10  through an attachment means  87 . In one embodiment, the attachment means can be in the form of a hooked bracket that fits within slots defined in the frame side walls  14 . The attachment means  87  is most preferably easily removed from the frame  10 . In order to accommodate a wide variety of patient anatomies, the attachment means  87  may provide multiple attachment points along the length of the side walls  14  of the immobilization frame  10 . 
         [0063]    The patient&#39;s abdomen is compressed through a compression plate  92  that is connected to the cross beam  82  through a scissor mechanism  94  attached to the plate at a mounting axle  93 . The depth of compression of the device  80  can be adjusted by altering the angle of the scissor mechanism  94 . In particular, the mounting ends  95  of the scissor links  96  can be adjustably engaged to the cross beam by a pair of indexing mechanisms  97 . The indexing mechanisms  97  provide means for engaging the link ends  95  are different positions along the length of the cross beam. The compression plate is at its greatest depth when the link ends  95  are at the inboard positions  97   a  of the indexing mechanism  97 . Similarly, the plate  92  is at its most shallow position when the link ends are at the outboard positions  97   b.    
         [0064]    With the compression plate  92  in contact with the patient&#39;s abdomen, as shown in  FIG. 20 , the amount of compression may be adjusted by adjusting the tension in the strap  84 , or more specifically by shortening the length of the strap that spans the immobilization frame  10 . In accordance with one embodiment of the invention, a strap tightening mechanism  89  is mounted to the top of the cross beam  82 . The strap passes through the mechanism, such as through a slotted axle  90 . A ratcheting knob  91  is manually rotated to increase the strap tension. A manual tightening mechanism  89  is preferred to minimize the risk of over-tightening the compression device on the patient&#39;s abdomen. 
         [0065]    The actual pressure generated by the device is measured accurately by an electronic pressure sensor situated within a housing  99  between the compression plate  92  and the scissor mechanism mounting axle  93 . In this way, pressure can be consistently and reproducibly applied irrespective of the contents of the patient&#39;s stomach on a particular day. 
         [0066]    In accordance with the present invention, a stereotactic targeting and immobilization frame is provided that facilitates precise and accurate guidance for stereotactically directing a variety of therapeutic or diagnostic interventions toward a defined three-dimensional position within a patient&#39;s body. This inventive frame includes special accommodations for patients with larger body habitus. The frame also includes features for repeat re-positioning, stereotactic coordination both via visual scales and fiducials for a variety of imaging platforms (including plain-films, computed tomography, magnetic resonance imaging, positron emission tomography, and nuclear medicine scans). The frame also incorporates features for accounting for respiratory motion of the patient. 
         [0067]    In one feature of the invention, the frame  10  secures rigidly to a linear accelerator or computed tomography couch or patient table by means of locking assemblies. This rigid securement allows the frame coordinate system to be registered to the couch system of coordinates, thereby facilitating automated directed targeting of both therapeutic and diagnostic interventions. 
         [0068]    In a further feature, the frame is configured to accept patients having large girth. The frame includes removable panel inserts that leave mid-side cut-outs to allow portions of the patient&#39;s body to bulge outside the frame. These removable panels make the frame of the present invention readily usable by larger patients undergoing CT, MRI, PET and other nuclear medicine scans. 
         [0069]    The frame  10  provides linear fiducials that provide a straight-forward system for reading the three-dimensional coordinates of any position within the frame itself. This allows accurate registration between PET and nuclear medicine scans and prior CT or MRI imaging scans. 
         [0070]    In an alternative embodiment, an immobilization frame  100  may be configured similar to the frame  10  described above. As shown in  FIG. 22 , the frame  100  includes a bottom panel  116  and side cutouts  122  defined in the side walls  114 . In accordance with this embodiment, a mounting bar  124  is affixed to each side immediately above the locking mechanism  104  and extending along substantially the entire length of the frame  100 . The mounting bar defines an engagement edge  126  that provides a point of securement for an abdominal compression device  140  and a measuring rig  180  as illustrated in  FIG. 23 . 
         [0071]    As shown in  FIG. 22 , the bar includes a measurement scale  125  that provides for measurement along the length of the frame, corresponding to the Z axis shown in  FIG. 4 . As explained below, the scale  125  permits measurement of the longitudinal location of a measuring rig  180  used to ascertain the location of body features of the patient, or more particularly the position of the target tissue. 
         [0072]    Turning to  FIG. 23 , an alternative embodiment of an abdominal compression device  140  is illustrated. The device  140  includes a compression plate  142  that is configured to comfortably compress the patient&#39;s abdomen just below the sternum. The compression plate  142  is supported by a compression screw  150  that passes through a threaded boss  152  on a cross beam  144 . The cross beam  144  spans the opposite sides of the frame  100  and more particularly is supported on side walls  114 . The cross beam includes a center portion  143  which carries the threaded boss  152  and spanning portions  144  that are pivotably connected to the center portion at hinges  162 . The ends of the cross beam  140  are pivotably connected by a pivot  146  to side portions  145  that extend down the side of the immobilization frame  100 . 
         [0073]    The hinges  162  double as a support for support straps  160 . The straps  160  extend over the spanning portions  144  and side portions  145  and include a clip (not shown) at their lower ends for engaging the engagement edges  126  of the mounting bars  124  at the opposite sides of the frame. The hinges  162  may be rotated to tighten the straps to hold the abdomen compression device  140  in solid engagement with the frame. The pivots  146  may incorporate a groove  147  that fits over a top rail  115  on the frame side wall  114  to facilitate movement of the device  140  along the frame while the compression plate  142  is being properly oriented over the patient. 
         [0074]    Once the compression plate  142  is properly aligned, the hinges  162  are rotated to tighten the straps  160  to fix the longitudinal location of the abdominal compression device. Then the compression screw  150  is rotated to push the compression plate  142  into the patient&#39;s abdomen, as depicted in  FIG. 20 . The amount of compression may be verified visually; however, in the preferred embodiment, a pressure transducer  172  is introduced between the end  151  of the pressure screw  150  and the compression plate  142 , as illustrated in  FIG. 25 . The transducer  172  is mounted at the end of an introducer  170  that may be used to position the transducer. The transducer includes leads  174  that are fed to a monitor that can be positioned adjacent the table T for easy viewing as the abdominal compression device  140  is manipulated. 
         [0075]    The frame  100  of this embodiment further includes a measuring rig  180  that is slidably supported on the side walls  114  of the frame. The rig includes a central beam  184  supported by side beams  182 . The side beams are configured at their ends to slidingly mate with the mounting bar  124 , as shown in  FIG. 26 . The side beams  182  include an eyelet  190  that permits visualization of the scale  124  ( FIG. 22 ) to ascertain the longitudinal position of the measuring rig  180  relative to the frame. 
         [0076]    The central beam  184  is slotted to receive a position indicator  186 . The central beam preferably includes a horizontal scale that defines the lateral location (X axis) of the position indicator  186 . The indicator further includes a vertical slide  188  that is mounted to the indicator to slide vertically relative to the central beam. The measuring rig  180  thus provides means for establishing the location of a landmark on the patient in the frame coordinate system (X, Y, Z) by moving the rig until the working end  189  of the vertical slide  188  is aligned with the body feature. 
         [0077]    While the invention has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the invention are desired to be protected.