Abstract:
A radiation treatment system and method of commissioning the system, the system including a gantry, a radiation source operable to produce a beam of radiation, and a measurement device. The measurement device is physically connected to the gantry, and includes a multi-dimensional scanning arm, and a detector. The method includes generating radiation from the radiation source, passing the radiation through an attenuation block, and receiving radiation with the measurement device. The measurement device is positioned such that it is not in contact with water. Data is generated from the radiation received and the system is commissioned using the generated data to match system characteristics to a previously defined standard.

Description:
RELATED APPLICATIONS  
       [0001]     This application claims priority to provisional patent application No. 60/820,690, filed Jul. 28, 2006, the entire contents of which are incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates to a radiation therapy imaging and treatment system. More specifically, the invention relates to structure within the system that is utilized to calibrate the system, and to a method of commissioning or tuning the system.  
       BACKGROUND  
       [0003]     Medical equipment for radiation therapy treats tumors tissue with high energy radiation. The dose and the placement of the dose must be accurately controlled to insure both that the tumor receives sufficient radiation to be destroyed, and that damage to the surrounding and adjacent non-tumorous tissue is minimized. Intensity modulated radiation therapy (IMRT) treats a patient with multiple rays of radiation each of which may be independently controlled in intensity and/or energy. The rays are directed from different angles about the patient and combine to provide a desired dose pattern. In external source radiation therapy, a radiation source external to the patient treats internal tumors. The external source is normally collimated to direct a beam only to the tumorous site. Typically, the radiation source consists of either high-energy X-rays, electrons from certain linear accelerators, or gamma rays from highly focused radioisotopes, though other types of radiation sources are possible.  
         [0004]     Because the dose amount and dose placement need to be sufficiently controlled so as to ensure accurate patient treatment, the system itself needs to be commissioned properly at the outset and needs to be continuously monitored to ensure that the system is operating within the appropriate, and expected, parameters. When a system or machine is commissioned, the system characteristics are measured and compared against predetermined standards to configure the system and to ensure that the system is working within expected parameters. Commissioning includes consideration of total machine calibration, tuning the geometry of the beam delivered, and ensuring that the output and energy everywhere in the beam is equal, among other things. In some cases, individual systems are not calibrated with respect to each other, such that, in a way, each individual system stands alone in that variations in beam shape, strength, etc. can vary between machines. Each system is tuned to be within a manufacturing window, and a unique planning station model is generated. In effect, with each commissioning, you change the model to fit the machine.  
       SUMMARY  
       [0005]     When commissioning is done in this manner, it is difficult to move a patient between individual systems once treatment has begun because of the necessary changes to dose and other treatment parameters that will need to be done to ensure that the patient is still receiving the appropriate treatment. Since the dose received by the patient depends not only on the beam shape and output but also varies with the energies within the beam itself, individual commissioning makes it difficult to move patients between machines once treatment has started. This type of individual commissioning also makes servicing and quality assurance (QA) analysis of the machines more difficult as there is no easy comparisons to make with known standards. Thus, it is desired to provide a treatment system that can be measured to a known set of standards for the purposes of commissioning, servicing, and QA analyses.  
         [0006]     The present invention provides a radiation therapy treatment system that allows for easy calibration of the system with respect to a known set of standards, a.k.a. a “gold standard.” The gold standard values can be determined in various ways, but are conventionally done using a water tank to produce the known attenuation results used to set the gold standard. By providing a radiation therapy treatment system capable of being tuned to the gold standard, the time and effort required to commission an individual system is reduced, and the system is easier to service and maintain from a QA standpoint. In effect, all systems are dosimetrically equivalent when tuned to the gold standard. Tuning machines to be dosimetrically equivalent is sometimes referred to as “twinning,” and the resulting machines that are tuned to the gold standard are considered “twins.” Because the tolerances of the systems stay the same from system to system, it is also possible to easily transfer patients from treatment on any individual system to another system without interfering with the patient&#39;s treatment plan. Tuning and commissioning becomes substantially automatic, and the machine can be changed to fit the model.  
         [0007]     In one embodiment, the invention provides a radiation therapy treatment system. The system includes a radiation source operable to produce a beam of radiation, a gantry, and a measurement device coupled to the gantry. The measurement device includes a multi-dimensional scanning arm and a detector operable to receive radiation from the radiation source. In some embodiments, the system also includes an attenuation block coupled to a portion of the system, the attenuation block movable into and out of the path of the radiation beam produced by the radiation source. In one embodiment, the attenuation block comprises a plurality of aluminum plates coupled together to form a wedge that is substantially step-shaped. Radiation passed through the attenuation block is used to calibrate components of the system.  
         [0008]     In another embodiment, the invention provides a method of commissioning a radiation therapy system to a previously defined standard. The radiation therapy system includes a measurement device coupled to a gantry, and a radiation source operable of producing radiation. The method includes the acts of generating radiation with the radiation source, passing the radiation through an attenuation block, receiving the radiation with the measurement device, generating data from the radiation received, and commissioning the system using the generated data to match system characteristics to the previously defined standard. The method also includes positioning the measurement device such that it is not in contact with water.  
         [0009]     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a perspective view of a radiation therapy treatment system.  
         [0011]      FIG. 2  is a perspective view of a multi-leaf collimator that can be used in the radiation therapy treatment system illustrated in  FIG. 1 .  
         [0012]      FIG. 3  is perspective view of a twinning arm for use in the radiation therapy system of  FIG. 1 .  
         [0013]      FIG. 4  is a perspective view of the twinning arm of  FIG. 3  coupled to a gantry of the system of  FIG. 1 .  
         [0014]      FIG. 5  is a perspective view of an attenuation block coupled to the system of  FIG. 1 .  
         [0015]      FIG. 6  is a screen shot of a representative user interface generated by software according to the invention.  
         [0016]      FIG. 7  is a screen shot of a portion of the user interface of  FIG. 6 , illustrating the component input features.  
         [0017]      FIG. 8  is a graphical representation of data generated by the software of the invention illustrating the longitudinal profile data.  
         [0018]      FIG. 9  is a graphical representation of data generated by the software of the invention illustrating the transverse profile data.  
         [0019]      FIG. 10  is a graphical representation of data generated by the software of the invention illustrating the stepwise attenuation block data.  
         [0020]      FIG. 11  is a perspective view of a linac mounting bracket according to the invention. 
     
    
     DETAILED DESCRIPTION  
       [0021]     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings.  
         [0022]     Although directional references, such as upper, lower, downward, upward, rearward, bottom, front, rear, etc., may be made herein in describing the drawings, these references are made relative to the drawings (as normally viewed) for convenience. These directions are not intended to be taken literally or limit the present invention in any form. In addition, terms such as “first,” “second,” and “third” are used herein for purposes of description and are not intended to indicate or imply relative importance or significance.  
         [0023]     In addition, it should be understood that embodiments of the invention include hardware, software, and electronic components or modules that, for purposes of discussion, may be illustrated and described as if the majority of the components were implemented solely in hardware. However, one of ordinary skill in the art, and based on a reading of this detailed description, would recognize that, in at least one embodiment, the electronic based aspects of the invention may be implemented in software. As such, it should be noted that a plurality of hardware and software based devices, as well as a plurality of different structural components may be utilized to implement the invention. Furthermore, and as described in subsequent paragraphs, the specific mechanical configurations illustrated in the drawings are intended to exemplify embodiments of the invention and that other alternative mechanical configurations are possible.  
         [0024]      FIG. 1  illustrates a radiation therapy treatment system  10  that can provide radiation therapy to a patient  14 . The radiation therapy treatment can include photon-based radiation therapy, brachytherapy, electron beam therapy, proton, neutron, or particle therapy, or other types of treatment therapy. The radiation therapy treatment system  10  includes a gantry  18 . The gantry  18  can support a radiation module  22 , which can include a radiation source  24  and a linear accelerator  26  (a.k.a. “a linac”) operable to generate a beam  30  of radiation. Though the gantry  18  shown in the drawings is a ring gantry, i.e., it extends through a full 360° arc to create a complete ring or circle, other types of mounting arrangements may also be employed. For example, a C-type, partial ring gantry, or robotic arm could be used. Any other framework capable of positioning the radiation module  22  at various rotational and/or axial positions relative to the patient  14  may also be employed. In addition, the radiation source  24  may travel in path that does not follow the shape of the gantry  18 . For example, the radiation source  24  may travel in a non-circular path even though the illustrated gantry  18  is generally circular-shaped. The gantry  18  of the illustrated embodiment defines a gantry aperture  32  into which the patient  14  moves during treatment.  
         [0025]     The radiation module  22  can also include a modulation device  34  operable to modify or modulate the radiation beam  30 . The modulation device  34  provides the modulation of the radiation beam  30  and directs the radiation beam  30  toward the patient  14 . Specifically, the radiation beam  30  is directed toward a portion  38  of the patient. Broadly speaking, the portion may include the entire body, but is generally smaller than the entire body and can be defined by a two-dimensional area and/or a three-dimensional volume. A portion or area desired to receive the radiation, which may be referred to as a target or target region, is an example of a region of interest. Another type of region of interest is a region at risk. If a portion includes a region at risk, the radiation beam is preferably diverted from the region at risk. Such modulation is sometimes referred to as intensity modulated radiation therapy (“IMRT”).  
         [0026]     The modulation device  34  can include a collimation device  42  as illustrated in  FIG. 2 . The collimation device  42  includes a set of jaws  46  that define and adjust the size of an aperture  50  through which the radiation beam  30  may pass. The jaws  46  include an upper jaw  54  and a lower jaw  58 . The upper jaw  54  and the lower jaw  58  are moveable to adjust the size of the aperture  50 . The position of the jaws  46  regulates the shape of the beam  30  that is delivered to the patient  14 .  
         [0027]     In one embodiment, and illustrated in  FIG. 2 , the modulation device  34  can comprise a multi-leaf collimator  62  (a.k.a. “MLC”), which includes a plurality of interlaced leaves  66  operable to move from position to position, to provide intensity modulation. It is also noted that the leaves  66  can be moved to a position anywhere between a minimally and maximally-open position. The plurality of interlaced leaves  66  modulate the strength, size, and shape of the radiation beam  30  before the radiation beam  30  reaches the portion  38  on the patient  14 . Each of the leaves  66  is independently controlled by an actuator  70 , such as a motor or an air valve so that the leaf  66  can open and close quickly to permit or block the passage of radiation. The actuators  70  can be controlled by a computer  74  and/or controller.  
         [0028]     The radiation therapy treatment system  10  can also include a detector  78 , e.g., a kilovoltage or a megavoltage detector, operable to receive the radiation beam  30 , as illustrated in  FIG. 1 . The linear accelerator  26  and the detector  78  can also operate as a computed tomography (CT) system to generate CT images of the patient  14 . The linear accelerator  26  emits the radiation beam  30  toward the portion  38  in the patient  14 . The portion  38  absorbs some of the radiation. The detector  78  detects or measures the amount of radiation absorbed by the portion  38 . The detector  78  collects the absorption data from different angles as the linear accelerator  26  rotates around and emits radiation toward the patient  14 . The collected absorption data is transmitted to the computer  74  to process the absorption data and to generate images of the patient&#39;s body tissues and organs. The images can also illustrate bone, soft tissues, and blood vessels. The system  10  can also include a patient support, shown as a couch  82 , operable to support at least a portion of the patient  14  during treatment. While the illustrated couch  82  is designed to support the entire body of the patient  14 , in other embodiments of the invention the patient support need not support the entire body, but rather can be designed to support only a portion of the patient  14  during treatment.  
         [0029]     The first step in the twinning process introduced above is to set the gold standard against which all systems  10  will be measured. The gold standard is a standard of all the fundamental characteristics of the system that can be measured during commissioning, servicing, or the QA process (including calibration). The fundamental characteristics can include alignment, output, energy, beam shape, and the multi-leaf collimator  62 . More specifically, transforming to the gold standard includes consideration of beam symmetry (linac alignment); intensity of source or number of photons released per second (output fluence rate); wavelength, color of light, or penetration depth of the radiation (energy); x and y-direction profiles, field width, and jaw position (beam shape); and leaf open/closed times and leaf response (MLC).  
         [0030]     To accomplish the twinning process, additional hardware and/or software is coupled to the system  10 . As illustrated in  FIGS. 3 and 4 , the system  10  includes a twinning arm  90 . The arm  90  is coupled to the gantry  18  via a mounting pad  94  that is pre-mounted to the gantry  18 . As shown in the illustrated embodiment, multiple mounting pads  94  are located about the gantry  18  to provide for multiple mounting locations. The mounting pads  94  are tightly toleranced so that the arm  90  can be mounted to the gantry  18  without the need for further tolerancing or adjustment. As shown, the arm  90  is bolted to the mounting pads  94  using a bracket  96 . By coupling the arm  90  to the gantry  18 , the control of the gantry and the arm  90  can be unified.  
         [0031]     The arm  90  includes a two-dimensional (2D) scanner  98  that can take measurements in the x and y-directions. It is understood that in other embodiments, the arm  90  may include scanners capable of measuring in three dimensions, or in other numbers of dimensions. The twinning arm also includes an ion chamber  102  that receives signals from the linac  26 . The ion chamber  102  includes a build-up cap  106  coupled thereto. In the illustrated embodiment, the build-up cap  106  is composed of virtual water and functions to increase the signal received in the ion chamber  102 . Movement of the scanner  98  and the ion chamber  102  is accomplished using conventional controllers  110 ,  114 . The height of the ion chamber  102  within the gantry aperture  32  is determined by the location of the mounting pads  94  and is adjusted using the isocenter of the gantry  18 . In the illustrated embodiment, the height of the ion chamber  102  is not centered on the isocenter of the gantry  18 , but rather the isocenter is used as a reference point to set the height of the ion chamber  102 . In the illustrated embodiment, the ion chamber  102  is centered just above the isocenter of the gantry  18 .  
         [0032]     It should be understood that while a single ion chamber  102  is utilized in the illustrated embodiment, in other embodiments of the invention one or more ion chambers can be mounted in an array, grid, or volume. Utilizing multiple ion chambers would allow for more efficient calibration of a multi-dimensional radiation beam. It is further understood that while the illustrated embodiment utilizes an ion chamber as a detector, that other types of detectors, including but not limited to diode detectors, diamond detectors, etc., could be used in place of the ion chamber and still accomplish the desired results.  
         [0033]     The system  10  also includes an attenuating block  118  that further assists with the twinning process. Conventional commissioning processes utilize a water tank to attenuate the signal from the linac to the ion chamber to make absolute measurements of dose, with the measurement device being submerged in the water tank. The depth of the water in the tank results in a known attenuation that can be used to adjust the components of the system. However, the use of the water tank in commissioning an individual system is unwieldy and difficult to adjust, as the water tank is often very large and difficult to move accurately into the path of the radiation beam. Further, with certain, more narrow beam geometries, it is difficult to get accurate measurements using the water tank. Additionally, any presence of water that could come in contact with the sensitive components of the system  10  adds additional uncertainty and risk. Thus, the system  10  utilizes the attenuating block  118 , with the arm  90  coupled to the gantry  18  (i.e., without being submerged in water) to achieve the same results.  
         [0034]     The attenuating block  118 , as illustrated in  FIG. 5 , is substantially wedge-shaped and is formed of a stack of aluminum plates  120  of consistent thickness, resulting in a stepwise attenuation pattern (see  FIG. 10  for a graphical representation of the stepwise attenuation pattern). The attenuating block  118  of the illustrated embodiment is coupled to the couch  82  and is moved into and out of the path of the radiation beam with movement of the couch  82  (i.e., the attenuating block  118  is moved into and out of the path of the x-ray source, which is the linac  26  in the illustrated embodiment). In other embodiments, the attenuating block  118  can be coupled to a separate device used to move the block  118  into and out of the path of the radiation beam generated by the linac  26 . In further other embodiments, the attenuating block  118  may be stationary. The attenuation block  118  can be used for measurement with a beam having any given energy, though the thicknesses of the aluminum plates  120  (or the overall thickness of the attenuating block  118 ) may need to be adjusted to compensate for the beam strength.  
         [0035]     The attenuating block  118  achieves similar attenuation results as the conventional use of the water tank. The results obtained by using the block  118  can be compared to the expected results from using the water tank attenuation. The use of aluminum as the material to form the attenuating block  118  has certain benefits. First, aluminum is denser than water such that less material is required to simulate a given depth of water. This reduces both the weight of the attenuator and the thickness of the required aluminum plates. Further, at the energy levels that are tested during the commissioning, service, and QA processes, the aluminum exhibits relatively similar properties to the water, making it easier to compare the attenuation results of the block  118  and the expected water results. However, any number of materials can be used to create the block so long as the signature of the material is known. For example, plastics or other metals can be used to create the block  118 , though in many cases thicker plates of the other materials would be required to generate the same results as the aluminum plates. In addition, although the aluminum plates of the illustrated embodiment are all of equal thicknesses, in other embodiments the plates themselves can be of varied thicknesses, depending on the desired results.  
         [0036]      FIG. 6  illustrates a screen shot  122  generated on a graphical user interface of the system  10  by the software that controls the twinning process. As illustrated in  FIGS. 6 and 7 , the user can input information regarding the control of various portions of the system  10 , including the beam (at  126 ), the couch  82  (at  130 ), the MLC  62  (at  134 ), the gantry  18  (at  138 ), and the jaws  46  (at  142 ). The software collects data from the system  10  and generates outputs, such as the graphical representations illustrated in  FIGS. 8-10 . The software provides for efficient system tuning by integrating the control and measurement functions, and is essentially fully automated. The software includes fixed scripts that determine how to appropriately collect the data generated by the system  10 . Thus, if any of the measurements gathered by the software are found to be outside of the predetermined range, the software itself can determine how to appropriately change the inputs to generate the desired results. The software can have a feedback mechanism to take the data, remediate the data where necessary, and then re-measure the data without requiring further input from the user.  
         [0037]      FIG. 8  is an exemplary graphical output created by the software. The graph  146  represents the longitudinal profile (i.e., the IEC y-direction data) of the beam. The shape of the graph  146  is determined by the position of the jaws  46 . The graph  146  includes a first data line  150  (shown in purple) generated from data received by the ion chamber  102  overlaid onto the gold standard data line  154  (shown in gray) for a twinned system  10 . As illustrated, the first data line  150  is virtually identical to the gold standard data line  154 , confirming that the system  10  is twinned to the gold standard in the y-direction. Similarly,  FIG. 9  is a graph  158  representing the transverse profile data (i.e., the x-direction data) of the beam. Here again, a first data line  162  (in purple) is overlaid onto the gold standard data line  166  (in gray) to confirm the twinning in the x-direction. Both the longitudinal and transverse profile data are a function of the shape of the beam  30 .  FIG. 10  is a graphical output  170  representing the attenuation data of the step-wedge attenuation block  118 .  
         [0038]      FIG. 11  illustrates an adjustment bracket  174  according to an embodiment of the invention. The adjustment bracket  174  includes a plurality of fasteners, shown as bolts  178 , which allow for easy adjustment of the linac  26  on the gantry  18 . During the alignment phase of the twinning process, the linac  26  needs to be aligned, or “dialed-in”, so to speak. In previously known linac mounting configurations, the linac did not move naturally in the x-direction independently of motion in the y-direction, and vice versa. The natural motion was closer to diagonal in effect. Thus, it was difficult to accurately move the linac and any movement made had a compound effect, with an x-direction component and a y-direction component. By moving the opposing sets of bolts  178 , the bracket  174  allows for independent movement of the linac  26  in the x and y-directions so that the linac  26  can be adjusted with precision and with ease.  
         [0039]     In the embodiments described above, certain components, such as the arm  90  and the attenuating block  118 , have been described for use together in commissioning, servicing, or performing QA on the system  10 . However, it is understood that in other embodiments of the invention, certain components can be used separately, or can be used to perform other functions within the system  10 .  
         [0040]     For example, it is understood that as the gantry  18  rotates, the arm  90 , and thus the ion chamber  102 , will rotate with the gantry  18 . By rotating the arm  90 , other measurements are possible, such as measurements of the changes in beam field shape, the measurement of any gantry sag, etc. In some gantry configurations, such as with C-arm gantries, it is important to ensure that the beam is consistent at all angles. The beam geometry can be validated using the arm  90  (e.g., the scanner  98 ) without using the attenuation block  118 . If preferred, a separate movement apparatus can be utilized to move the block  118  into the path of the linac  26  at any beam angle. Other measurement functions, such as measuring energy output of the linac  26 , can also be performed without the use of the block  118 .  
         [0041]     In other embodiments, where the system includes a detector opposite the x-ray source, the arm  90  can be used to gather calibration data in both the x and y-directions. This allows for more robust calibration of the detector, as the data could be used to determine how the detector signals vary with system wobble. The calibration would thus be a function of gantry angle, rotation, and stability. The arm  90  could be replaced with a detector or detector array operable to measure in two dimensions (e.g., measure the y-profile in addition to the x-profile).  
         [0042]     When multiple ion chambers (or multiple detectors) are utilized to measure for different beam penetration depths, there would be no need for a separate attenuation block. In essence, in some embodiments, the attenuation block and ion chambers could be integrated into one unit.  
         [0043]     The data generated by the system  10  utilizing the twinning mechanisms described above can also be used in various other ways. For example, in other embodiments the arm  90  and/or block  118  can be used to get profiles for single leaves  66  of the MLC  62 . The leaves could be static or moving and characterizing the output during leaf motion. The MLC could be the MLC  62  illustrated above, or could be a two-dimensional MLC having sliding leaves. We could also calibrate for all jaw thicknesses, altering the beam shape to get different field shapes in the y-direction. In yet other embodiments, especially those where the linac is designed to be movable, the arm  90  and/or block  118  can be used to get beam characteristics as a function of the position of the linac, or vice versa. Thus, the device could be used for linac tuning. The apparatus could also be used in an MLC tongue and groove test for MLC alignment. In some cases, the arm  90  could be normalized out of the measurement, where appropriate.  
         [0044]     Overall, the use of the twinning mechanisms discussed above make the commissioning, servicing, and QA analyses of the system  10  much simpler as very little set-up is required. The time to commission an individual system drops from a few days to a few hours. Additionally, measuring any system against the gold standard, rather than individually commissioning the machine, cuts down on training and servicing time, and allows for greater patient mobility between machines to receive treatment. All beam field sizes can be easily commissioned using these processes, as the twinning process described above can create a generic calibration that will yield a commissioning for any arbitrary field size. Adjustment after service and re-tuning of the system as needed during the life of the machine are also much more efficient, and service issues are easier to diagnose on twinned systems.