Abstract:
A computed tomography (CT) system ( 300 ) includes a table ( 304 ) for holding a patient ( 302 ), a first gantry ( 311 ) for holding a radiation source ( 310 ) which emits penetrating radiation, and a second gantry ( 313 ) spaced apart from the first gantry holding a penetrating radiation detector ( 312 ) for receiving the penetrating radiation after passing through the patient. The penetrating radiation from the radiation source is angled at a non-perpendicular angle with respect to a longitudinal axis ( 322 ) of the table. A third gantry ( 320 ) is spaced apart from the first and second gantry including at least one radiation therapy source ( 321 ) or other (non-CT) imaging system, wherein the third gantry is located between the first gantry and the second gantry. The CT system thus permits computed tomography to occur simultaneously or substantially simultaneously with other procedures, such as various other radiation therapy systems, imaging modality or surgical procedures.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the national stage entry of International Application No. PCT/US2006/004998, filed Feb. 13, 2006, which claims priority to U.S. Provisional Patent Application No. 60/652,058, filed Feb. 11, 2005. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to computerized tomography. More specifically, the present invention relates to computerized tomography devices that permit computerized tomography to be performed substantially simultaneously with other radiation and/or surgical procedures. 
     BACKGROUND OF THE INVENTION 
     In recent years, much interest has been evidenced in a field now widely known as computed tomography. In a typical procedure utilizing computed tomography (or CT), an X-ray source and detector are physically coupled together on opposite sides of the portion of a sample which is to be examined. The sample may be, for example, a patient or phantom or other objects. X-rays are made to transit through the sample to be examined, while the detector measures the X-rays which make it through the sample without being absorbed or deflected. Periodically, the paired source and detector are rotated to differing angular orientations about the sample, and the data collection process repeated. 
     A very high number of measurements of attenuation values may be obtained by procedures of this type. The relatively massive amounts of data thus accumulated are processed by a computer, which typically does a mathematical data reduction to obtain attenuation values for a very high number of transmission values (typically in the hundreds of thousands) within the section of the sample being scanned. This data may then be combined to enable reconstruction of a matrix (visual or otherwise) that constitutes an accurate depiction of the density function of the sample section examined. 
     By considering one or more of such sections, skilled medical diagnosticians may diagnose various body elements such as tumors, blood clots, cysts, hemorrhages and various abnormalities, which, heretofore, were detectable, if at all, only by much more cumbersome and, in many instances, more hazardous techniques to the patient. 
     While systems of the aforementioned type have represented powerful diagnostic tools, and were deemed great advances in the radiography art, first generation systems suffered from many shortcomings. Acquisition of the raw data frequently entailed an undesirably long period, which, among other things, subjected a patient to both inconvenience and stress. The patient&#39;s inability to remain rigid for such a lengthy period, also led to blurring of the image sought to be obtained. 
     Radiation therapy is another aspect having a great deal of interest. Conventional radiation therapy techniques typically involve directing a radiation beam at a tumor in a patient to deliver a predetermined dose of therapeutic radiation to the tumor according to an established treatment plan. This is typically accomplished using a radiation therapy device. 
     Tumors have three-dimensional treatment volumes which typically include segments of normal, healthy tissue and organs. Healthy tissue and organs are often in the treatment path of the radiation beam. This complicates treatment, because the healthy tissue and organs must be taken into account when delivering a dose of radiation to the tumor. While there is a need to minimize damage to healthy tissue and organs, there is an equally important need to ensure that the tumor receives an adequately high dose of radiation. Cure rates for many tumors are a sensitive function of the dose they receive. Therefore, it is important to closely match the radiation beam&#39;s shape and effects with the shape and volume of the tumor being treated. 
     In many radiation therapy devices, the treatment beam is projected through a pre-patient collimating device (a “collimator”), which defines the treatment beam profile or the treatment volume at the treatment zone. A number of different collimator techniques have been developed to attempt to conform the dose rate and the treatment volume to the shape of the tumor while taking nearby healthy tissue and organs into account. A first technique is to use a collimator with solid jaw blocks positioned along a path of the treatment beam to create a field shape based on the shape of the tumor to be treated. Typically, two sets of blocks are provided, including two blocks making up a Y-jaw generally disposed parallel to a Y-axis (with the Z-axis being parallel to the beam path), and two blocks making up an X-jaw generally disposed parallel to an X-axis. The X-jaw is conventionally placed between the Y-jaws and the patient. 
     These solid jaw blocks, however, do not provide sufficient variability in the field shape. In particular, where the tumor has a shape which requires a field edge relatively parallel to the edge of the jaw blocks, the edge of the jaw block becomes more predominant in forming the field edge. As a result, undulation of the field increases as well as the effective penumbra. This can be particularly difficult where the treatment beam is an X-ray beam. It is also difficult to adjust the field shape where the treatment beam is an electron beam due to electron attenuation and scattering. 
     In a typical radiation therapy device, a frame housing the linear accelerator (X-ray tube) and collimators having a large opening into which the patient is inserted (referred to herein as a gantry) is swiveled around a horizontal axis of rotation in the course of a therapeutic treatment of the patient. The linear accelerator generates a high-energy radiation beam (referred to herein as a “photon beam” or “photons”) for use in the therapeutic treatment. 
     Historically, linear accelerators used in radiation therapy applications have been equipped to provide only a single energy photon beam. In the recent past, however, some linear accelerators have been equipped to provide two different energy beams. The limited number of energies available is a continuing problem for physicians and physicists, since it is not always possible for them to give the most efficacious treatments. Currently, certain manufacturers are attempting to provide linear accelerators with the capability of generating three different photon energies. Such machines, however, will still preclude much other intermediate energy that may be useful. 
     A therapeutic x-ray beam produced by a linear accelerator is characterized by the amount of energy that will be deposited at a treatment site by that particular x-ray beam. This characterization relates to the depth (usually measured from the surface of the skin) at which the beam&#39;s maximum energy is deposited (often referred to in the art as “dmax”). 
     Nevertheless, these radiation technologies do not permit the system to be able to perform simultaneous treatment of an area using different types of radiation treatments. Additionally, none of these systems and methods permit computerized tomography to occur during treatment, thereby leading to more accurate treatment of the patient. 
     Accordingly, it would be beneficial to provide a system that permitted multiple types of radiation therapy to be performed simultaneously. It would also be beneficial to provide a system that was capable of performing radiation therapy with computerized tomography to permit more accurate treatment. 
     SUMMARY OF THE INVENTION 
     A computed tomography (CT) system includes a table for holding a patient, a first gantry for holding a radiation source which emits penetrating radiation, and a second gantry spaced apart from the first gantry holding a penetrating radiation detector which receives the penetrating radiation after passing through and being attenuated by the patient. The penetrating radiation from the radiation source is angled at a non-perpendicular angle with respect to a longitudinal axis of the table. When used for radiation therapy, systems according to the invention thus provide independent CT because the source trajectory can be different for the therapy beam and the imaging beam. 
     The system can further comprise a third gantry spaced apart from the first and second gantry including at least one radiation therapy source or other imaging system, wherein the third gantry is located between the first and second gantry. The radiation therapy source can be a linear accelerator (X-ray tube) or a radioactive isotope (e.g. cobalt) source. The other (non-CT) imaging system can comprise an emission tomography system, such as a Single Photon-Emission Tomography system or Positron Emission Tomography system. 
     The third gantry can comprise a plurality of radiation therapy sources. In this embodiment, each of the plurality of radiation therapy sources is preferably provided a multileaf collimator. In one embodiment, the third gantry comprises an outer ring and an inner ring, wherein the inner and outer rings are independently rotatable. The outer ring can includes the plurality of radiation sources and the inner ring comprise a plurality of beam modifier slots. The outer ring can also include a plurality of electrical portal imaging devices (EPIDs). 
     A method of performing substantially real-time CT image guided treatment on a patient comprises the steps of providing a computed tomography system wherein penetrating radiation from the system is angled at a non-perpendicular angle with respect to a longitudinal axis of a table holding a patient, and performing a treatment or other imaging step on the patient while performing CT imaging using guidance from images generated by the CT system. The treatment step or other imaging step can comprise radiation therapy, emissions tomography, a surgical procedure, or a combination thereof. The treatment step can be radiation therapy delivered by a linear accelerator treatment or a radioactive isotope (e.g. cobalt) source. The other imaging step can comprise emission tomography treatment selected from Single Photon-Emission Tomography or Positron Emission Tomography. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, features and advantages of the present invention will become apparent upon reading the following detailed description, while referring to the attached drawings, in which: 
         FIG. 1  shows a prior art computerized tomography system. 
         FIG. 2  shows a side view of a beveled computerized tomography system according to one embodiment of the present invention. 
         FIG. 3  shows a top view of a beveled computerized tomography system according to another embodiment of the present invention. 
         FIG. 4  shows a side view of a radiation therapy system according to the embodiment set forth in  FIG. 3 . 
         FIG. 5  shows a transversal view of a radiation therapy gantry according to one aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is more particularly described in the following description and examples that are intended to be illustrative only since numerous modifications and variations therein will be apparent to those skilled in the art. As used in the specification and in the claims, the singular form “a,” “an,” and “the” may include plural referents unless the context clearly dictates otherwise. Also, as used in the specification and in the claims, the term “comprising” may include the embodiments “consisting of” and “consisting essentially of.” 
     In general, a CT scan is an x-ray procedure enhanced by a computer. This results in a three-dimensional view (referred to as a “slice”) of a particular part of a patient&#39;s body. During a routine x-ray, dense tissues can block other areas. Aided by a computer, a CT scan is able to put together the different “slices” and create a three-dimensional view, clearly showing both bone and soft tissue. Prior art systems performed this system using x-ray imaging that was perpendicular to the patient being examined. Accordingly, during a CT scan, the area being examined cannot be accessed. 
     The present invention provides a system and method of computerized tomography wherein CT scanning may occur substantially simultaneously as an additional radiation treatment or an additional medical treatment that, heretofore, would have needed to be done separately. The present invention is capable of performing the substantially simultaneous CT scanning using a computerized tomography system referred to herein as a beveled tomography system. As used herein, a beveled computerized tomography system refers to CT comprising system that includes separate gantries for the penetrating radiation (e.g. X-ray) source and for the penetrating radiation detector (e.g. X-ray detector) which angles the penetrating radiation from the radiation source at a non-perpendicular angle with respect to a longitudinal axis of the table holding the patient. As a result, systems according to the invention permit CT to be performed while leaving the area of interest of the patient open, either for radiation therapy and/or for access by medical staff. As such, the present invention sets forth a system and related method that provide one or more advantages compared to known CT systems. 
     As may be seen in  FIG. 1 , a standard CT that is currently available provides a system wherein the center of radiation is incident perpendicularly to the axis of gantry. In this system  100 , a patient  102  rests on a table  104 . The patient  102  includes a region of interest  106  that is to be subjected to computerized tomography. The CT portion of the system  100  includes a CT gantry  108  having an x-ray source  110  and a detector  112 . The x-ray source  110  and detector  112  are located in the CT gantry  108  in a direction perpendicular  114  to the patient  102  on the table  104 . As such, there is no room to access to the region of patient  106  that is of interest to medical staffs. 
     Conversely, as shown in  FIG. 2 , the present invention, in one embodiment, provides a CT system  200  having dual gantries  208  and  209  for imaging patient  202  disposed on a table  203  used to support the patient  202  during the procedure. Table  203  comprises a computer controlled turntable. Gantry  208  controls the position of x-ray source  210  and thus the x-ray beam, while gantry  209  controls the position of detector  212 . Accordingly, the rotation plane of detector  212  can be different from that of x-ray source  210 . Moreover, emissions from the x-ray source  210  are angled relative to the detector  212 . Therefore, imaging x-ray beams are passing through patient  202  with an angle with respect to the longitudinal axis of table  204 . Detector  212  includes an image intensifier (not shown). 
     The analog intensified video signal provided by detector  212  is communicated to PC or other computing structure having image capture hardware  222 . The output of PC  222  is communicably connected to turntable interface unit  223  which controls the position of table  203  via computer controlled turntable. PC  222  provides image reconstruction to generate conventional image views by taking the system geometry into account. The resulting design of system  200  permits the medical staff to access to the region of interest  206  of the patient  202 . Depending on the design, gantries  208 ,  209  may be mounted on rails  214  and the width of access area  216  may be adjusted. In these embodiments, angles of x-ray source  210  and detector  212  are designed to be adjustable. 
     As may be seen from  FIG. 2 , the x-ray source  210  is angled at an angle that is not perpendicular to the longitudinal axis of table  204 . The detection panel  212  is also angled at an angle that is not perpendicular to the longitudinal axis of the table  204 . Depending on the selected distance between the gantries  208  and  209 , the x-ray source  210  and detection panel  212  may be angled from between about 10 to about 80 degrees with respect to the longitudinal axis of the table  204 . In select embodiments, the x-ray source  210  and detection panel  212  may be angled from between about 30 to about 60 degrees with respect to the longitudinal axis of the table  204 . In yet other embodiments, the x-ray source  210  and detection panel  212  may be angled from between about 40 to about 50 degrees with respect to the longitudinal axis of the table  204 . 
     Accordingly, in one embodiment of the present invention, a beveled CT system is used in conjunction with a novel radiation therapy (RT) system that enables image guided radiation therapy (IGRT) to be performed. In one embodiment, these systems and methods permit computerized tomographic imaging to occur independently and thus simultaneously during radiation therapy beam delivery. As set forth herein, this may be referred to as “CT-based through-RT IGRT”, which refers to a system capable of performing independent CT that is capable of being carried out during treatment beam delivery. This system may also be referred to as an RT Ultimate (RTU) system for convenience. In an RTU system, a third gantry, which may be referred to as an RT gantry, is added in between CT source gantry  208  and CT detector gantry  209 . 
       FIGS. 3 and 4  show a top view and a side view, respectively, of an RTU system  300  according to one embodiment of the present invention. As may be seen in  FIG. 3 , the system  300  includes a CT source gantry  311  for housing the x-ray or other CT source  310 , a CT detector gantry  313  for housing the x-ray detector or other CT detector  312 , and an RT source gantry  320  for housing the radiation therapy source  321 . The radiation therapy source  321  may be any radiation therapy source including, but not limited to, a linear accelerator, a cobalt therapy unit, or any other radioactive isotope radiation source. As may be seen from  FIG. 3 , the patient (not shown) rests on a table  304  and the CT source gantry  311  and CT detector gantry  313  are separated by the RT source gantry  320 . 
     As may be seen better from  FIG. 4 , as the CT source gantry  311  and CT detector gantry  313  are separated, emissions from the x-ray source  310  are angled with respect to the plane of the patient  302 , and this angle is not a perpendicular angle. As a result, the CT detector panel  312  is also angled with respect to the plane  322  of the patient  302 , and this angle is also not a perpendicular angle. As with system  200  shown in  FIG. 2 , system  300  communicates the analog video signal provided by detector  312  (detector  212  in  FIG. 2 ) to PC  222 , with the output of PC  222  being communicably connected to turntable interface unit  223  which controls the position of table  203  which holds the patient via computer controlled turntable. 
     PC  222  is connected to PC or other computing and control structure  351 . PC  351  receives position data from PC  222  regarding patient and uses the position data improve control of radiation therapy source  321 . For example, if patient  302  moves during a radiation therapy procedure, one or more parameters of the radiation therapy beam output by source  321  can be modified, such as the position of the beam to redirect the beam to the target location on patient  302 . 
     System  300  permits the area of interest of the patient  302  to be accessed and treated by the radiation therapy source  321 , which may be directed at an angle substantially perpendicular to the patient, which is the standard CT scanning angle in prior art systems. As a result, image guided radiation therapy may be performed wherein CT scanning (which provides position data) is occurring substantially simultaneously with RT treatment, thereby resulting in a more accurate radiation therapy treatment system. 
     Other embodiments of an RTU system may also be used based upon the advantages present in the beveled CT system of the present invention. For example, in one embodiment (not shown), the RT gantry may contain multiple radiation treatment sources. Any of the RT sources  321  previously mentioned, such as a linear accelerator or radioactive isotope source, may be utilized as the radiation source  321 . Each source may be designed to rotate both concurrently and independently. If independent rotation is used, it will generally be limited to the adjacent source. 
     In an alternative embodiment wherein field shaping may be beneficial, a multi-leaf collimator (MLC) may be used for each source. In most current radiation therapy systems, one of the most time consuming steps is the rotation of the gantry. Accordingly, in this embodiment, by installing multiple sources, the amount of gantry rotation may be minimized, resulting in efficient beam delivery. This system may also decrease the chance of patient intra-fraction displacement, which is very beneficial in modern high-precision radiation therapy. 
     One of the disadvantages of current radiation therapy systems that are equipped with an MLC system is that the MLC system significantly increases machine down time because of its high failure rate. When MLC malfunctions, it is not possible to continue a high-precision therapy such as IMRT (intensity modulated radiation therapy). However, in the RTU system of the present invention, the treatment can continue using any functioning MLC. As there is an increased number of MLCs, the likelihood of all MLCs malfunctioning at the same time is significantly reduced. 
     In an alternative embodiment of the invention an electrical portal imaging device (EPID) may be installed for each RT source. An EPID may be used to improve the alignment of the radiation beam with respect to a tumor during radiation treatment. EPIDs are commercially available. In this inventive embodiment, the EPIDs provide images of the patient using the RT beam. EPIDs provides planar image quality which is generally not very high, but can provide a quick check for bony anatomy. A CT is also preferably provided since the CT provides accurate volumetric image which permits a more accurate setup and real time adjustments during the actual procedure to be achieved. Each EPID may be rotated independently, such as using an independent mechanical system inside the gantry. Therefore, the EPIDs can be positioned either in or out of the treatment field as needed. 
       FIG. 5  shows a transverse view of a RT gantry  520  having multiple radiation sources according to one embodiment of the present invention. The RT gantry  520  comprises two rings, outer ring  530  and inner ring  540 . Inner ring  540  is connected to outer ring  530  to permit independent rotation, such as using rotating bearings (not shown). RT gantry  520  call be integrated into system  300  by replacing RT gantry  320  with RT gantry  520 . RT gantry  520  is shown including three (3) radiation therapy sources  521 , three (3) EPIDs  524 , three (3) MLCs  526 , and six (6) beam modifier slots  528 . However, it is to be understood that the number of radiation therapy sources, EPIDs, MLCs, and/or beam modifier slots (also referred to as “compensator blocks”) may vary as needed depending on the selected parameters of the final system. In addition, while the number of beam modifier slots may be greater than that of the number of radiation sources, this is not required and alternative embodiments may include RT systems having the same number or fewer beam modifier slots than that of the number of radiation sources. 
     As noted above, slots  528  are designed to rotate independently from the radiation sources  521 . When IMRT is delivered using modifier slots  528 , all modifier slots may be mounted at the same time. For each beam angle, different modifier slots  528  are needed. If multiple fields are used, multiple modifier slots are needed. Because there are multiple slots  528  in gantry  520 , tip to six ( 6 ) modifier slots can be preloaded. 
     In alternative embodiments, the beveled CT system and method may be used in conjunction with nuclear imaging modalities. Examples of nuclear imaging modalities that may be used in the present invention include, but are not limited to, emission tomography technologies, such as Single Photon-Emission Tomography (SPECT) and Positron Emission Tomography (PET). 
     PET measures the emission of positrons from the patient after a small amount of radioactive isotopes, or tracers, have been injected into the blood stream. This technique has proven extremely useful in research regarding functioning of organs. However, the half-lives of the isotopes used are very short. SPECT is closely related to PET, but uses isotopes with longer half-lives that can be stored on site. However, its resolution is generally lower, yielding less detailed images. As such, it would be beneficial to perform CT scanning during either SPECT or PET to provide real time patient contour and attenuation information during SPECT or PET. The present invention is capable of performing these techniques, which is an improvement over earlier systems wherein SPECT/CT and PET/CT scans must be carried out in series. 
     In yet another embodiment, the beveled CT system and method may be used in an operating room without anything located between the two gantries. As such, a real time CT scan may be performed with minimum interruption of operation procedure. As a result, real time CT image guided surgery may be performed. This embodiment may be used with any surgical procedure in which CT imaging may be beneficial during surgery. 
     It is to be understood that while the invention has been described in conjunction with the specific embodiments thereof, that the foregoing description as well as the examples which follow are intended to illustrate and not limit the scope of the invention. Other aspects, advantages and modifications within the scope of the invention will be apparent to those skilled in the art to which the invention pertains.