Abstract:
The instant invention is a modular radiation beam analyzer for measuring the distribution and intensity of radiation produced by a radiation source. More specifically, the instant invention is a modular radiation scanning device that includes up to three modules. By selecting and assembling a predetermined number of modules a radiation detector may be manipulated through up to three axes for radiation beam scans as well as direct Tissue Maximum Ratio (TMR) and/or Tissue Phantom Ratio (TPR) scans.

Description:
FIELD OF THE INVENTION 
   This invention relates to a method and device for measuring the radiation dose of a linear accelerator or other radiation producing device at the target, and particularly relates to the use of a movable radiation detector, usually an ion chamber. 
   BACKGROUND OF THE INVENTION 
   Various well-known medical techniques for the treatment of malignancies involve the use of radiation. Radiation sources, for example medical linear accelerators, are typically used to generate radiation to a specific target area of a patient&#39;s body. Use of appropriate dosimetry insures the application of proper doses of radiation to the malignant areas and is of utmost importance. When applied, the radiation produces an ionizing effect on the malignant tissue, thereby destroying the malignant cells. So long as the dosimetry of applied radiation is properly monitored, the malignancy may be treated without detriment to the surrounding healthy tissue. Accelerators may be utilized, each of which have varying characteristics and output levels. The most common type of accelerator produces pulse radiation, wherein the output has the shape of a rectangular beam with a cross-sectional area which is typically between 16 and 1600 square centimeters. Rectangular or square shapes are often changed to any desired shape using molded or cast lead or cerrobend materials. More advanced accelerators use multi-leaf collimators. Other accelerators are continuous or non-pulsed such as cobalt radiation machines; and accelerators that utilize a swept electron beam, which sweep a very narrow electron beam across the treatment field by means of varying electromagnetic fields. 
   To ensure proper dosimetry, linear accelerators used for the treatment of malignancies must be calibrated. Both the electron and photon radiation must be appropriately measured and correlated to the particular device. The skilled practitioner must insure that both the intensity and duration of the radiation treatment is carefully calculated and administered so as to produce the therapeutic result desired while maintaining the safety of the patient. Parameters such as flatness, symmetry, radiation and light field alignment are typically determined. The use of too much radiation may, in fact, cause side effects and allow destructive effects to occur to the surrounding tissue. Use of an insufficient amount of radiation will not deliver a dose that is effective to eradicate the malignancy. Thus, it is important to be able to determine the exact amount of radiation that will be produced by a particular machine and the manner in which that radiation will be distributed within the patient&#39;s body. 
   In order to produce an accurate assessment of the radiation received by the patient, at the target area, some type of pattern or map of the radiation at varying positions within the patient&#39;s body must be produced. These profiles correlate 1) the variation of dose with depth in water generating percent depth dose profiles and 2) the variation of dose across a plane perpendicular to the radiation source generating the cross beam profiles. These particular measurements of cross beam profiles are of particular concern in the present invention. Although useful for other analyses, the variation of the beam uniformity within the three dimensional radiation field is the main purpose of this device. 
   There are companies that provide the calibration service to hospitals and treatment centers. These technicians must visit the facility and conduct the calibration of the radiation source with their own equipment. This requires lightweight, easily portable, less cumbersome radiation measuring devices that can be quickly assembled and disassembled on site. The actual scanning should also be expeditious with the results available within a short time frame. Such equipment allows a technician to be more efficient and calibrate more radiation devices in a shorter period of time. 
   One existing system for measuring the radiation that is produced by medical linear accelerators utilizes a large tank on the order of 50×50×50 cm filled with water. A group of computer controlled motors move the radiation detector through a series of pre-programmed steps along a single axis beneath the water&#39;s surface. Since the density of the human body closely approximates that of water, the water-filled tank provides an appropriate medium for creating a simulation of both the distribution and the intensity of radiation which would likely occur within the patient&#39;s body. The aforementioned tank is commonly referred to as a water phantom. The radiation produced by the linear accelerator will be directed into the water in the phantom tank, at which point the intensity of the radiation at varying depths and positions within the water can be measured with the radiation detector. As the radiation penetrates the water, the direct or primary beam is scattered by the water, in much the same way as a radiation beam impinging upon the human patient. Both the scattered radiation as well as the primary radiation are detected by the ion-chamber, which is part of the radiation detector. 
   The ion-chamber is essentially an open air capacitor which produces an electrical current that corresponds to the number of ions produced within its volume. The detector is lowered to a measurement point within the phantom tank and measurements are taken over a particular time period. The detector can then be moved to another measurement point where measurements are taken as the detector is held in the second position. At each measuring point a statistically significant number of samples are taken while the detector is held stationary. 
   DESCRIPTION OF THE PRIOR ART 
   Several prior art devices are known to teach systems for ascertaining the suitable dosimetry of a particular accelerator along with methods for their use. 
   U.S. Pat. Nos. 5,621,214 and 5,627,367, to Sofield, are directed to a radiation beam scanner system which employs a peak detection methodology. The device includes a single axis mounted within a water phantom. In use, the water phantom must be leveled and a reference detector remains stationary at some point within the beam while the signal detector is moved up and down along the single axis by the use of electrical stepper motors. 
   While these devices employ a water phantom, they are limited to moving the signal detector along the single axis and can only provide a planar scan of the beam. 
   U.S. Patent Application Publication 2006/0033044 A1, to Gentry et al., is directed to a treatment planning tool for multi-energy electron beam radiotherapy. The system consists of a stand-alone calculator that enables multi-energy electron beam treatments with standard single electron beam radio-therapy equipment thereby providing improved dose profiles. By employing user defined depth-dose profiles, the calculator may work with a wide variety of existing standard electron beam radiotherapy systems. 
   U.S. Pat. No. 6,225,622, issued May 1, 2001 to Navarro, the inventor here, describes a dynamic radiation measuring device that moves the ion chamber through a stationary radiation beam to gather readings of radiation intensity at various points within the area of the beam. The disclosure of this patent is incorporated herein, by reference. 
   U.S. Pat. No. 4,988,866, issued Jan. 29, 1991, to Westerlund, is directed toward a measuring device for checking radiation fields from treatment machines used for radiotherapy. This device comprises a measuring block that contains radiation detectors arranged beneath a cover plate, and is provided with field marking lines and an energy filter. The detectors are connected to a read-out unit for signal processing and presentation of measurement values. The dose monitoring calibration detectors are fixed in a particular geometric pattern to determine homogeneity of the radiation field. In use, the measuring device is able to simultaneously check the totality of radiation emitted by a single source of radiation at stationary positions within the measuring block. 
   U.S. Patent Application Publication 2005/0173648 A1, to Schmidt et al., is directed to a wire free, dual mode calibration instrument for high energy therapeutic radiation. The apparatus includes a housing with opposed first and second faces holding a set of detectors between the first and second faces. A first calibrating material for electrons is positioned to intercept electrons passing through the first face to the detectors, and a second calibrating material for photons is positioned to intercept photons passing through the second face to those detectors. 
   These devices do not use a water phantom and are additionally limited in that all of the ionization detectors are in one plane. This does not yield an appropriate three-dimensional assessment of the combination of scattering and direct radiation which would normally impinge the human body undergoing radiation treatment. Thus, accurate dosimetry in a real-life scenario could not be readily ascertained by the use of these devices. 
   U.S. Pat. No. 5,006,714, issued Apr. 9, 1991, to Attix utilizes a particular type of scintillator dosimetry probe which does not measure radiation directly but instead measures the proportional light output of a radiation source. The probe is set into a polymer material that approximates water or muscle tissue in atomic number and electron density. Attix indicates that the use of such a detector minimizes perturbations in a phantom water tank. 
   Additionally, there is an apparatus called a Wellhofer bottle-ship which utilizes a smaller volume of water than the conventional water phantom. The Wellhofer device utilizes a timing belt and motor combination to move the detector through the water, thus requiring a long initial set-up time. 
   Thus, there exists a need for a modular radiation beam analyzer device. The device should be portable and capable of being quickly assembled for use and disassembled for transport. The device should also be capable of repeated, accurate detection of both scattering and direct radiation components from radiation devices along at least two, and more preferably three, axes for three dimensional scans of radiation beams. 
   SUMMARY OF THE INVENTION 
   The instant invention is a modular radiation beam analyzer for measuring the distribution and intensity of radiation produced by a radiation source. More specifically, the instant invention is a modular radiation scanning device that is capable of moving a radiation detector through up to three axes for precision three dimensional radiation beam scans. 
   The present invention is based upon the general principle of scanning a simulated target area of radiation by the use of a radiation detector attached to a moving modular platform to develop a one, two or three dimensional plot of the dosage delivered. 
   The modular apparatus of this invention may be used in a water phantom or with solid water slabs or wafers simulating that portion of the target area which affects the radiation beam. Therefore, the water phantom may be mobile or immobile with the dynamic detector moving through the phantom or moving through the radiation beam carrying the phantom. 
   In one embodiment, the modular platform translates the detector in a water phantom. The use of the water phantom results in the scattering of the directly applied radiation in the water tank in a manner similar to that which occurs when this direct radiation impinges upon the human body being treated. 
   One characteristic of the invention is the over-all speed of the process of producing a plot of radiation dosage; eg., this modular apparatus may be assembled and disassembled in less than 5 minutes. Each axis is constructed and arranged for attachment to an orthogonal axis with thumb screws for ease and speed of assembly. All three axes may be leveled manually using only two leveling screws. Alternatively, the device may be leveled electronically, whereby the computer will move the radiation detector parallel to the surface of the water within the phantom tank. 
   The controller utilized with the instant invention permits incremental and/or continuous movement of the radiation detector. In addition, the controller permits up to about 42000 samples to be taken for every “step” of movement. The size of the step can be changed electronically from 0.01 millimeter to 1 millimeter depending upon the accuracy desired. The device may be operated manually, via a hand control, or alternatively the controller may include a computer whereby the field of scan may be pre-programmed. Thereafter, the scan will be completed automatically. 
   Accordingly, it is a primary objective of the instant invention to provide a portable and easily assembled modular apparatus for radiation detection and measurement which utilizes rapid and accurate setup and significantly reduces the measurement time required by traditionally used scanning systems. 
   It is another objective of the instant invention to provide a modular radiation measuring device including up to three axes, each including electrically powered motors and lead screws. 
   It is yet another objective of the instant invention to provide a platform having two leveling points to level the axes of the apparatus with respect to the water surface within the water phantom tank. 
   It is a further objective of the instant invention to provide a system and method for electronically leveling the movements of the device. 
   It is yet a further objective of the instant invention to provide a system and method for traversing a dynamic phantom through a radiation beam for radiation measurement. 
   It is still yet a further objective of the instant invention to provide a water phantom of unique shape for direct measurement of radiation. 
   Other objects and advantages of this invention will become apparent from the following description taken in conjunction with any accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. Any drawings contained herein constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
       FIG. 1  is a top perspective view of one embodiment of the instant invention; 
       FIG. 2  is a front view of one embodiment of the X-axis guideway of the instant invention; 
       FIG. 3  is a back view of one embodiment of the X-axis guideway of the instant invention; 
       FIG. 4  is a bottom view of one embodiment of the X-axis guideway of the instant invention; 
       FIG. 5  is a front view of one embodiment of the Z-axis guideway of the instant invention; 
       FIG. 6  is a rear view of one embodiment of the Z-axis guideway of the instant invention; 
       FIG. 7  is a left side view of one embodiment of the Z-axis guideway of the instant invention; 
       FIG. 8  is a partial perspective view of one embodiment of the Z-axis guideway of the instant invention, illustrating the carriage, the third lead screw and the line-shaft of the instant invention; 
       FIG. 9  is a top view of one embodiment of the Y-axis guideway of the instant invention; 
       FIG. 10  is right side view of the Y-axis guideway shown in  FIG. 9 ; 
       FIG. 11  is an end view of the Y-axis guideway shown in  FIG. 9 ; 
       FIG. 12  is a partial perspective view of the Y-axis guideway shown in  FIG. 9  illustrating the Y-axis carriage; 
       FIG. 13  is a graph illustrating a method of electronically leveling the radiation detection device of the instant invention; 
       FIG. 14  is a perspective view illustrating the X, Y and Z axes guideways packed into a storage case for ease of transport; 
       FIG. 15  is a perspective view illustrating the X-axis guideway of the instant invention in combination with a trapezoidal shaped tank for direct measurement of Tissue Maximum Ratio and/or Tissue Phantom Ratio; 
       FIG. 16  is a perspective view illustrating operation of the embodiment shown in  FIG. 15 ; 
       FIG. 17  is a perspective view illustrating the X-axis and the Z-axis being used in combination with a dynamic phantom. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIGS. 1 and 14 , the modular radiation beam analyzer  10  for measuring the distribution and intensity of radiation produced by a radiation source is illustrated. The radiation beam analyzer  10  generally includes a phantom tank  11  constructed and arranged to contain a material having a density approximating that of a human body. In general, the phantom tank is sized to accommodate an X-axis module  20 , a Y-axis module  60  and a Z-axis module  32  of the radiation beam analyzer. The base and walls of the tank may be constructed of acrylic or other suitable material. When filled with water, the tank  11  serves as a water phantom simulating the body of a patient undergoing radiation treatment. The independent X-axis, Y-axis and Z-axis modules are constructed and arranged to fit neatly within a carrying case  102  for ease of transport. Each axis is also constructed and arranged for independent operation with respect to the other axes. In this manner, the desired number of axes may be quickly assembled together at a desired location and radiation measurements may be quickly taken with the predetermined assembly. 
   Referring to  FIGS. 1–4 , the X-axis module  20  includes an X-axis guideway  21  ( FIGS. 2–4 ) extending substantially across an upper portion of the phantom tank  11 . The X-axis guideway includes an X-axis carriage  22 A and  22 B slidably secured to the X-axis guideway  21  for controlled movement along the length thereof. In the preferred embodiment, the X-axis guideway  21  includes a first lead screw  24  rotatably mounted thereon. The first lead screw  24  is operably connected to the X-axis carriage  22 A to provide linear motion thereto during rotation of the first lead screw. A first stepper motor  26  is operably connected to the first lead screw for controlled bi-directional rotation thereof. In one embodiment the stepper motor is connected to the first lead screw via a geared timing belt (not shown). Alternatively, the stepper motor could be connected to the first lead screw with gears, chains, cables or suitable combinations thereof without departing from the scope of the invention. The first stepper motor  26  is in electrical communication with the controller  12  to provide electrical commands thereto, and if needed to receive feedback from the first stepper motor. Also secured to the X-axis guideway are two leveling screws  28  and  30 . Leveling screw  28  cooperates with an upper surface of the tank to provide leveling of all three axes in one plane, while leveling screw  30  cooperates with an inner surface of the tank to provide leveling of all three axes in a second plane. In this manner all three axes may be leveled with only two leveling screws. 
   Referring to  FIGS. 5–8 , the Z-axis module  32  is illustrated. The Z-axis module is secured to the X-axis carriage  22 A and  22 B via thumb screws  34  for movement therewith. A Z-axis carriage  36  is slidably secured to the Z-axis guideway  38  for controlled movement along the length thereof. The Z-axis guideway  38  includes a third lead screw rotatably mounted thereon. The third lead screw  40  is operably connected to the Z-axis carriage  36  to provide linear motion thereto during rotation of the third lead screw. A third stepper motor  42  is operably connected to the third lead screw  40  for controlled bi-directional rotation thereof. In one embodiment the stepper motor  42  is connected to the third lead screw  40  via a geared timing belt (not shown). Alternatively, the stepper motor  42  may be connected to the first lead screw with gears, chains, cables or suitable combinations thereof without departing from the scope of the invention. The third stepper motor  42  is in electrical communication with the controller  12  ( FIG. 1 ) to provide electrical commands thereto and if needed to receive feedback from the third stepper motor  42 . The Z-axis guideway also includes a line-shaft  44  rotatably secured thereon. The line-shaft is operably connected to a second stepper motor  46  for selective bi-directional rotation thereof. The second stepper motor is in electrical communication with the controller  12  ( FIG. 1 ). The line-shaft is constructed and arranged to include at least one and more preferably a plurality of splines  48  extending substantially along the length thereof. Slidably mounted on the line shaft is a first beveled gear  50 . The beveled gear  50  is secured to the Z-axis carriage  36  so that it moves therewith. The Z-axis carriage is provided with an aperture  52  positioned to allow a second bevel gear  54  ( FIG. 11 ), secured to Y-axis lead screw  56 , to engage the first bevel gear  50  when the Y-axis  60  ( FIG. 9 ) is secured to the Z-axis  32 . In this manner, the second stepper motor  46  provides rotation to the line-shaft  44  and the same or similar rotation is transferred through the bevel gears to the Y-axis lead screw throughout the motion range of the Z-axis carriage  36  to cause movement of the Y-axis carriage. 
   Referring to  FIGS. 9–12  the Y-axis module  60  is illustrated. The Y-axis module includes a Y-axis guideway  62 . The Y-axis guideway is secured to the Z-axis carriage  36 , via thumb screws  34 , for movement therewith. A Y-axis carriage  64  is slidably secured to the Y-axis guideway  62  for controlled movement along the length thereof. At least one radiation detection probe  66  ( FIG. 1 ) is secured to the Y-axis carriage, via thumb screw  68  for movement therewith. The radiation detection probe is preferably an ion chamber however, it should be noted that other suitable radiation detection probes such as, but not limited to, diodes and the like may be utilized without departing from the scope of the invention. The radiation detection probe is electrically connected to the controller  12 , as is well known in the art. The Y-axis guideway  62  includes a second lead screw  56  rotatably mounted thereon. The second lead screw is operably connected to the Y-axis carriage  64  to provide linear motion thereto during rotation of the second lead screw. 
   Referring to  FIGS. 1–12 , it should be noted that the X, Y, and Z axes modules are preferably constructed of aluminum having a hard anodized surface for oxidation control, wear properties and appearance. However, it should be noted that other materials well known in the art suitable for construction of the guideways, carriages and lead screws could be utilized without departing from the scope of the invention. Such materials may include, but should not be limited to, metals, plastics, and suitable composites. It should also be noted that while stepper motors are the preferred embodiment for rotation of the lead screws, other electrical motors such as servo motors and the like, suitable for providing smooth controlled rotation and/or feedback to the controller, may be utilized without departing from the scope of the invention. 
   Referring to  FIG. 1 , the radiation beam analyzer is illustrated. The controller includes a hand control  72  having at least one manually operable member  74 , e.g. switch, for instructing an input of a desired direction for manually controlled movement of an operator determined axis carriage. Within the preferred embodiment the controller includes a computer  76  electrically connected thereto for operational control of the axes movements, whereby the computer is constructed and arranged to accept commands from an operator to cause movement of the radiation detection probe under computer control throughout a predetermined field within a two or three-dimensional space. In response to the radiation measurements taken, the computer is constructed and arranged to produce a graphical representation  78  of the recorded density and distribution of the radiation beam associated with the scan. 
   Referring to  FIG. 13  a graphical representation of an electronic leveling method is illustrated. In this embodiment, the computer is constructed and arranged to permit electronic leveling of the axes with respect to the top surface of the water within the phantom tank. To complete the electronic leveling, a scan having a large profile, about 30 cm×30 cm, is taken at a depth close to the surface of the water represented by line  80 . The first scan is preferably taken at a depth referred to in the art as Dmax, or the depth at which the radiation is at the highest level within the phantom tank. Then a second scan of the same field size is taken at a depth close to the bottom of the phantom tank, about 30 cm, represented by line  82 . The center of the radiation field is found for each scan  80  and  82 . A theoretical line, represented by line  84 , is drawn through the field centers. Because variations in water depth result in variations in radiation intensity, line  84  will be substantially perpendicular with respect to the upper surface of the water. The computer includes an algorithm that utilizes line  84  to create a datum plane substantially parallel with respect to the upper surface of the water. Thereafter the computer can manipulate movement of the axes to maintain the probe on a parallel course with respect to the datum plane and thus the upper surface of the water. 
   Referring to  FIGS. 15 and 16 , an alternative method of utilizing the X-axis module for direct measurement of Tissue Maximum Ratio (TMR) and/or Tissue Phantom Ratio (TPR) is illustrated. In this embodiment the X-axis module  20  is secured to a base member  86  in a oriented 90 degrees from the vertical as shown in  FIG. 1 . A trapezoidal water tank  88  is secured to the carriages  22 A and  22 B of the x-axis guideway  21  for movement therewith. The trapezoidal shaped tank has a base  90  and upstanding planar walls in a trapezoidal shape with a short wall  92 , an opposite a long wall  94 , and two connecting opposite side walls  96 . The base and walls of the tank may be constructed of acrylic or other suitable material. The radiation detection probe  66  is secured in a fixed position with a suitable probe fixture  100 . When filled with water, the tank  88  serves as a water phantom simulating the body of a patient undergoing radiation treatment. The trapezoidal shape reduces the amount of water necessary for the calibration and eliminates the need to pump water to and from the tank, as required by the prior art. In operation, the depth of the water phantom is unaffected but the radiation beam may be oriented 90 degrees from the vertical, as shown in  FIG. 16 , and the short wall  92  placed next to the radiation source  98  which aligns the horizontal dimensions of the water phantom with the broadening scatter of the beam. The tank is traversed along the X-axis guideway toward the radiation source and radiation level measurements are taken. The duration of the process taking about 1 minute. 
   Referring to  FIG. 17 , an alternative method of utilizing the X-axis module and the Y-axis module in combination with a dynamic phantom is illustrated. In this embodiment the X-axis module  20  is secured to a base member  86  in a oriented 90 degrees from the vertical as shown in  FIG. 1 . The Z-axis module  32  is secured to the X-axis module  20  for two-dimensional movement of a dynamic phantom  104 . In operation, the dynamic phantom is moved throughout two axes and radiation level measurements are taken. The duration of the process taking about 1 minute. A more detailed description of dynamic phantoms and their applications can be found in U.S. Pat. No. 6,255,622, issued to the instant inventor, the contents of which are incorporated herein in their entirety. 
   All patents and publications mentioned in this specification are indicative of the levels of those skilled in the art to which the invention pertains. All patents and publications are herein incorporated by reference to the same extent as if each individual publication was specifically and individually indicated to be incorporated by reference. 
   It is to be understood that while a certain form of the invention is illustrated, it is not to be limited to the specific form or arrangement herein described and shown. It will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is shown and described in the specification and any drawings/figures included herein. 
   One skilled in the art will readily appreciate that the present invention is well adapted to carry out the objectives and obtain the ends and advantages mentioned, as well as those inherent therein. The embodiments, methods, procedures and techniques described herein are presently representative of the preferred embodiments, are intended to be exemplary and are not intended as limitations on the scope. Changes therein and other uses will occur to those skilled in the art which are encompassed within the spirit of the invention and are defined by the scope of the appended claims. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention which are obvious to those skilled in the art are intended to be within the scope of the following claims.