Abstract:
A lift table provides stability and portability for a radiation measurement scanning system. The lift table may be fixed for radiation measurement or configured for storage. Further, the lift table may be easily disassembled and assembled to allow efficient transporting. The lift table supports a multiple axes scanning system for measuring radiation from a radiation source, such as a linear accelerator (LINAC) and includes a leveling platform, all of which are provided by a desirable weight and portability.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/565,334, filed on Nov. 30, 2011, the contents of which are herein incorporated by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention generally relates to radiation therapy and in particular to systems and methods for measuring a dose in a phantom for commissioning treatment planning systems in radiation therapy beam delivery. 
     BACKGROUND OF THE INVENTION 
     Commissioning a linear accelerator (LINAC) for clinical use typically requires a water tank dosimetry scanner. By way of example, for commissioning a treatment planning system (TPS) for clinical use, medical physicists are faced with a need for precision during set up of measuring equipment and testing. Since commissioning beam data is treated as a reference and ultimately used by the TPS, it is vitally important that collected (i.e., scanned) data be of the highest quality to avoid dosimetric and patient treatment errors that may subsequently lead to a poor treatment outcome. It is therefore important that the scanner being used, regardless of style, must be stable under typical use conditions. In particular, and by way of example, a table used to support the scanner should be able to support the weight of a tank filled with water while maintaining stability. There needs to be stability while personnel work around the table supporting the scanner, especially when there are portions of the floor that are typically unstable, such as the bearing floor portion used to rotate the couch. The table should be able to maintain its stability during weight load changes as water is added and removed from the tank during, by way of example, tissue phantom ratio (TPR) measurements. 
     In addition to stability during measurement procedures, there remains a need for stability and portability during transport of the tank at a facility and storage at that or related facility. Also, there remains a need for stability and portability such that the scanner will not be damaged or unacceptably misaligned during transport between facilities. 
     As described in U.S. Pat. No. 8,321,179 for Multiple Axes Scanning System and Method for Measuring Radiation from a Radiation Source, the contents of which are hereby incorporated by reference in their entirety, there is a need for an accurate scan measurement of relative dose in a water phantom. 
     The measurement session of the LINAC beam scanning can take many days. During these long scanning times, there are no assurances from the radiation measurement scanning system to indicate that the scanning system or the LINAC has not changed during scans in a way that would affect the measurement data. It is incumbent upon the operator to perform periodic quality assurance (QA) tests that would reveal such changes in the scanner system. The measurement session of the LINAC beam scanning will typically include many setups. During these many setups, it is important to know that the measuring equipment has been properly and reproducibly installed. The stability or lack thereof provided by the table is clearly important. 
     The use of a LINAC for external beam irradiation and radiotherapy is well known. As presented in U.S. Pat. No. 5,160,337 to Cosman (the contents of which are also herein incorporated by reference in their entirety), a LINAC delivers a beam of photons or electrons through a collimated slit system and has multiple degrees of freedom, wherein a gantry rotates about a horizontal axis that is defined by a gantry bearing anchored to a housing which is anchored to the floor. The gantry can swing in an arc. The photon beam emerges from a collimator and aims at a target. A couch is connected to a rotating floor bearing, and both the floor bearing and the couch rotate about a vertical axis. In use, a patient lies on top of the movable couch, which can move in multiple directions to locate an anatomical target at the intersection of two axes, referred to as the isocenter of the LINAC. The couch sweeps around the vertical axis along an arc in a horizontal plane. 
     The couch is attached via the floor bearing and rotates about the vertical axis. In the event that the floor or couch bearing is unstable, stability can be achieved by an independent, collision-free or curved-shaped floor stand by anchoring a bearing mount to the floor. The fact that the bearing is independent of the couch bearing can result in aberrations in the stability of the floor bearing relative to the vertical axis. 
     There is a need for a support for radiation measuring systems that can accommodate various LINAC setups and be sufficiently portable to allow a user to efficiently and effectively move radiation measuring equipment into place with an assurance of accuracy and repeatability. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of the present invention to provide an improved support apparatus for a radiotherapy measurement system. According to an embodiment of the present invention, the support apparatus includes a table base assembly and a frame assembly. The table base assembly has an upper base end and a lower base end, the upper base end being adapted to support a leveling assembly for the radiotherapy measurement system. The lower base end is mounted to the frame assembly, which has a plurality of frame assembly legs movable to increase and decrease an effective footprint of the frame assembly. 
     According to an aspect of the present invention, the frame assembly has a central frame portion, a plurality of frame assembly legs and plurality of casters. The lower base end is mounted to the center frame portion, which includes a pair of generally opposed first sides connected by a pair of generally opposed second sides. The legs are arranged in first and second pairs of frame assembly legs. Each of the frame assembly legs includes a proximal end and distal end, and each proximal end is pivotably connected to a respective end of one of the first sides such that the first and second pairs of frame assembly legs are pivotable from a closed position, in which their respective distal ends are adjacent to their respective first side and to each other, to a measurement position, in which their respective distal ends are spaced outwardly from their respective first side and apart from each other. The casters each extend downwardly from one of the distal ends. 
     According to a further aspect, the first and second pairs of frame assembly legs are further pivotable to a travel position, in which an overall length of the frame assembly is increased and an overall width of the frame assembly is decreased relative to the measurement position. 
     These and other objects, aspects and advantages of the present invention will be better appreciated in view of the drawings and following detailed description of preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a support apparatus for a radiotherapy measurement system, including a table base assembly and a frame assembly, according to an embodiment of the present invention; 
         FIG. 2  is a partially exploded perspective view of the support apparatus of  FIG. 1 ; 
         FIG. 3  is a detail top view of the table base assembly of  FIG. 1  at its interface with the frame assembly; 
         FIG. 4  is a partially exploded perspective view of a representative leg of the frame assembly of  FIG. 1 ; 
         FIG. 5  is a side view of the support apparatus of  FIG. 1 , in a closed configuration; 
         FIG. 6  is a top view of the support apparatus of  FIG. 1 , in the closed configuration; 
         FIG. 7  is a top view of the support apparatus of  FIG. 1 , in a travel configuration; and 
         FIG. 8  is a top view of the support apparatus of  FIG. 1 , in a measurement configuration. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to  FIGS. 1 and 2 , according to an embodiment of the present invention, a support apparatus  10  for a radiotherapy measurement system  12  includes a table base assembly  14  and a frame assembly  16 . The table base assembly  14  has an upper base end  20  and a lower base end  22 . The upper base end  20  is adapted to support the radiotherapy measurement system  12  via a leveling assembly  24  and the lower base end  22  connects to the frame assembly  16 . The frame assembly  16  has a plurality of frame assembly legs  26 , which are movable to increase and decrease an effective footprint of the frame assembly  16 . 
     The table base assembly  14  incorporates a vertical actuator, with the top end  20  forming a piston received by the bottom end  22  that can raise and lower relative thereto. Power and command signals are transmitted to the table base assembly  14  for operation of the vertical actuator via a cable  30  from the leveling assembly  24 . 
     The table base assembly  14  is removably connected to the frame assembly  16  by a plurality of locking knobs  32 . Preferably, the locking knobs  32  thread into the frame assembly  16 , although other connection mechanisms could be employed. To facilitate installation and removal of the table assembly  14 , one or more base handles  34  are arranged on sides of the bottom end  22 . 
     Referring to  FIG. 3 , to ensure proper alignment of the table base assembly  14  on the frame assembly  16 , complementary keyed portions  36 ,  40  are formed on each. Similarly, to ensure proper alignment of the leveling assembly  24 , a top plate  42  with keyed portions  44  is arranged on the upper end  20 . Additionally, adjustments can be made to the bottom end  22  to adjust the level of the table base assembly  14  relative to the frame assembly  16 . 
     Referring again to  FIGS. 1 and 2 , the frame assembly  16  advantageously includes a center frame portion  46  to which the plurality of frame assembly legs  26  are attached. Preferably, the center frame portion has opposed pairs of first and second sides  50 ,  52 , with the arms  26  being pivotably connected in pairs at the intersections therebetween, such that the pivoting of the arms  26  relative to the center frame portion  46  effects the expansion and contraction of the effective footprint of the frame assembly  16 . 
     Referring to  FIG. 4 , an exemplary one of the frame assembly legs  26  is shown. The other frame assembly legs  26  substantially resemble the frame assembly leg of  FIG. 4 , with the orientation of connections to the center frame portion  46  being altered depending on the position of the legs  26 . Each leg  26  has a proximal end  54  and a distal end  56 . The proximal end  54  pivotably attaches at the corresponding intersection of the first and second sides  50 ,  52 , preferably using a pivot pin  60  inserted through a corresponding bore  62 . 
     The distal end  56  of each frame assembly leg  26  has a caster  64  extending downwardly therefrom. Preferably, each caster  64  is selectively lockable, both with respect to its rolling and rotating motion, to help fix the position of the support assembly  10  once in position, and also to facilitate transport in a straight line by not allowing all of the casters  64  to rotate at the same time. 
     Advantageously, there is also a locking mechanism  66  associated with each of the frame assembly legs  26  to releasably lock them in one of a plurality of predetermined positions. The locking mechanism  26  includes a flange  70  with a plurality of holes  72  that align with a locking hole  74  in the arm  26  when the arm  26  is in one of the predetermined positions. A locking pin  76  is inserted through the corresponding one of the holes  72  into the locking hole  74  to releasable fix the position. The locking pin  76  can thread into the locking hole  74  for more secure retention. Additionally, other locking mechanisms for some or all of the predetermined positions could be employed. A limiting peg  78  is provided to limit the pivoting motion of the leg  26 . 
     In  FIGS. 1 and 2 , the legs  26  are depicted locked into a measurement position, which corresponds to an expanded effective footprint in which the overall length and width of the frame assembly  16  are both increased. In  FIG. 5 , opposite pairs of the legs  26  are pivoted against the first sides  50 , such that the overall width and length of the frame assembly  10  are at a minimum. In this closed position, the distal ends  56  of each pair of legs  26  are adjacent to each other and to their respective first side  50 . 
     In the closed position, the casters  64  are very close to one another, making it easier for the support assembly  10  to tip towards the second sides  52 . To compensate during any tipping, casters  80  extend downwardly from midpoints of the second sides  52 . Casters  80  preferably do not extend downwardly as far as casters  64 , such that they can only contact the floor under the support assembly  10  when in the closed position. The casters  80  and tipping tendency of the support assembly  10  can advantageously assist when trying to move the support assembly  10  over an uneven threshold. 
     Referring again to  FIGS. 1 and 2 , to facilitate movement of the support assembly  82 , a handle  82  attaches to the frame assembly  16 . Preferably, the handle  82  is releasably attached in angled mounting tubes  84  so as to extend upwardly and rearwardly from the frame center portion  46 . Referring to  FIG. 5 , for more compact storage, the handle  82  can be removed from the tubes  84  and releasably connected under the center frame portion  46  in a horizontal orientation using storage tubes  86 . 
     Exemplary operations of the support assembly  10  will be described with reference to  FIGS. 5-8 . In  FIG. 5 , the support assembly  10  is in its most compact configuration, with the legs  46  locked in the closed position and the handle  82  secured below the center frame portion  46 . In  FIG. 6 , the handle  82  is secured in its generally upright position in the angled mounting tubes  84 . If desired, the support assembly  10  could be transported short distances in this configuration, although with the leveling assembly  24  and radiotherapy measurement system  12  mounted thereon, this could prove unwieldy. 
     Preferably, as depicted in  FIG. 7 , both pairs of legs  26  are moved and locked into a travel position. In the travel position, the overall width of the frame assembly  16  is reduced relative to the measurement position (see  FIG. 8 ), but the overall length is increased. Thus the support assembly  10  can be more readily pushed in straight lines and navigated through doors. 
     Referring to  FIG. 8 , when the support assembly  10  is in the vicinity of the LINAC or other treatment device, the legs  26  are moved into the measurement position for maximum stability. The casters  64  are locked in position and further position adjustments can be made using the vertical actuator of the table base assembly  14  and leveling assembly  24 . Advantageously, the table base assembly  14  can be located over a bearing floor portion  90  or other local instability without any of the weight of the support assembly  10  being support thereon. 
     In general, the foregoing description is provided for exemplary and illustrative purposes; the present invention is not necessarily limited thereto. Rather, those skilled in the art will appreciate that additional modifications, as well as adaptations for particular circumstances, will fall within the scope of the invention as herein shown and described and of the claims appended hereto.