Patent Publication Number: US-2004042582-A1

Title: Method and apparatus for locating a medical target

Description:
FIELD OF THE INVENTION  
       [0001] The present invention relates generally to methods and apparatus for accurately determining the location of a target in a medical procedure, such as for carrying out precision radiation therapy treatment or surgery of an organ in a body.  
       BACKGROUND OF THE INVENTION  
       [0002] The accurate placement and positioning of patients is crucial when performing many types of medical treatments. One category of medical treatments in which the proper placement and verification of the position of an organ is of particular importance is in the field of radiation therapy.  
       [0003] Radiation therapy involves medical procedures that selectively expose certain areas of a body, such as cancerous tumors, to high doses of radiation. The intent of the radiation therapy is to irradiate the targeted biological tissue such that the harmful tissue is destroyed. To minimize damage to surrounding body tissues, the radiation dosage is generally delivered in a planned series of treatment sessions that each delivers only a portion of the total planned dosage. Healthy body tissues typically have greater capacity to recover from the damage caused by exposed radiation. Spreading the delivered radiation over many treatment sessions allows the healthy tissue an opportunity to recover from radiation damage, thus reducing the amount of permanent damage to healthy tissues while maintaining enough radiation exposure to destroy tumoral tissue.  
       [0004] The efficacy of the radiation treatment depends in large part upon the ability to irradiate the exact same position on the body at the various radiation sessions. The goal is to place the patient in the same position relative to the radiation source at each and every treatment session. Inaccuracies in positioning the patient may result in errors in radiation dosage and/or treatment locations, leading to unpredictable disease relapse or damage to healthy tissues. In conventional medical treatment systems, the accurate placement and verification of a repeating treatment location on the human body remains a significant problem in implementing dose fractionating treatment plans.  
       [0005] There are several methods that attempt to achieve an accurate and repeatable treatment location on the human body. One method places marks or tattoos, or attaches radio-opaque balls, at specific locations on the patient&#39;s skin. Several laser or light sources from predetermined locations project beams of light at the patient&#39;s body. To control the patient positioning, a therapist shifts the position of the patient until the marks are aligned with the lines of light from the lasers or light sources. For example, a camera may cooperate with a LINAC (linear accelerator) and a computer to enable treatment of a patient with a beam that is positioned and maintained on a specific target in a patient&#39;s body. The camera may be located in a known position with respect to the LINAC and the markers at specific locations on a patient&#39;s body. Anatomical targets may be identified and positioned with respect to the treatment beam from the LINAC as identified by the camera data.  
       [0006] Another method employs an immobilization device to maneuver the patient into a particular position. A stereotactic head frame used in radiotherapy or radiosurgery procedures is an example of such a device. The immobilization device physically attaches to the human body to keep the patient from moving once proper positioning is achieved.  
       [0007] However, these and other known methods suffer from serious drawbacks. These methods are ineffective for certain internal organs that may move relative to stationary outer parts of the patient&#39;s body. For example, accurate determination of the position of the prostate in radiotherapy is problematic. The prostate may move with respect to previously recorded markers. Another complication is that the prostate is located very close to radiation sensitive tissues, such as the bladder and rectum.  
       [0008] In general, in the prior art, radiotherapy of the prostate may comprise a computerized tomography (CT) scan, or any other imaging technique, such as but not limited to, magnetic resonance imaging (MRI), of the pelvis to determine the approximate size, shape and location of the prostate gland (the intended target of the radiation). The patient may then undergo a treatment simulation in which planar, diagnostic X-ray films are taken in the plane of each of the proposed radiation fields. These X-ray films define the spatial position of the prostate (or target volume) and radiation sensitive structures, such as the rectum and bladder. The shape and position of the prostate, however, may change with time and may be different from when the CT images were taken. Consequently a margin of dimensional safety is generally drawn around the prostate volume to account for the variation of patient setup, target motion, and the spatial approximations inherent in localizing the prostate from the CT images to the simulator images. This margin is intended to insure that the prostate gland is receiving the intended dose. However, because of the uncertainties, the radiation doses to the prostate may not be optimal at all, and portions of the nearby rectum and bladder may also receive high doses.  
       SUMMARY OF THE INVENTION  
       [0009] The present invention seeks to provide methods and apparatus for locating a medical target. In the present invention, an imaging probe may be mounted directly on an irradiation device, wherein the imaging axis of the probe is aligned with the beam axis of the irradiation device. Images produced by the imaging probe may be conveniently compared with previously obtained images of the target area, and the patient may be moved with respect to the beam axis in accordance with the results of the comparison. Once the images match, the patient is now correctly aligned with the beam axis of the irradiation device, since the imaging probe has already been aligned with the beam axis. The invention may thus provide accurate location and alignment of the target, without having to take into account or correct for the gantry arm position, for example.  
       [0010] There is thus provided in accordance with an embodiment of the invention apparatus for locating a target, comprising an irradiation device comprising a radiation source adapted to emit a radiation beam along a beam axis, and an imaging probe mounted on the irradiation device along the beam axis. The imaging probe may have an imaging axis collinear with the beam axis.  
       [0011] In accordance with an embodiment of the invention the imaging probe is rotatably mounted on the irradiation device along the beam axis.  
       [0012] Further in accordance with an embodiment of the invention the imaging probe is mounted on a rotating base attached to the irradiation device, the rotating base comprising a stopping device for arresting the imaging probe at two or more predetermined angular positions. The rotating base may be adjustable such that the imaging axis is alignable with the beam axis. The imaging probe may comprise a computerized tomography (CT) probe, a magnetic resonance imaging (MRI) probe, an ultrasound imaging probe, a positron emission tomography (PET) probe or a single photon emission computed tomography (SPECT) probe.  
       [0013] There is also provided in accordance with an embodiment of the invention apparatus for locating a target, comprising an imaging probe mounted on a rotating base attachable to an irradiation device along a beam axis thereof.  
       [0014] There is also provided in accordance with an embodiment of the invention a method for locating a target comprising providing an irradiation device comprising a radiation source adapted to emit a radiation beam along a beam axis, and mounting an imaging probe on the irradiation device along the beam axis.  
       [0015] In accordance with an embodiment of the invention, the method further comprises obtaining a first image of a target area of a body to be irradiated in a first spatial plane, positioning the target area of the body to lie within an isocenter of the irradiation device, forming a second image of the target area with the imaging probe corresponding to the first spatial plane, and comparing the first and second images corresponding to the first spatial plane, wherein if the first and second images corresponding to the first spatial plane do not match within a tolerance, moving the body and again forming a second image of the target area with the imaging probe corresponding to the first spatial plane until the first and second images corresponding to the first spatial plane match within a tolerance.  
       [0016] The method may further comprising obtaining another first image of the target area in a second spatial plane, the first and second spatial planes being rotated with respect to one another, rotating the image probe about the beam axis (e.g., by at least 90°) to a position corresponding to the second spatial plane, forming a second image of the target area with the imaging probe corresponding to the second spatial plane, and comparing the first and second images corresponding to the second spatial plane, wherein if the first and second images corresponding to the second spatial plane do not match within a tolerance, moving the body and again forming a second image of the target area with the imaging probe corresponding to the second spatial plane until the first and second images corresponding to the second spatial plane match within a tolerance.  
       [0017] The first and second images of the target area may be obtained with CT, MRI, ultrasound imaging, PET and/or SPECT.  
       [0018] In accordance with an embodiment of the invention the first image of the target area is registered with respect to a reference marker.  
       [0019] Further in accordance with an embodiment of the invention the reference marker may comprise seeds introduced to the target area, the seeds being opaque to the first and second images and being internal to an organ in which lies the target area.  
       [0020] The imaging probe may contact the body in the vicinity of the target area and may be moved along the beam axis. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0021] The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:  
     [0022]FIG. 1 is a simplified side-view illustration of apparatus for locating a target, constructed and operative in accordance with an embodiment of the invention, comprising an imaging probe attached to a gantry arm;  
     [0023]FIG. 2 is a simplified side-view illustration of the apparatus of FIG. 1 showing the imaging probe being brought into contact with a patient, in accordance with an embodiment of the invention;  
     [0024]FIG. 3 is a simplified illustration of alignment of an image obtained from the imaging probe with an image previously obtained by other imaging equipment;  
     [0025]FIG. 4 is a simplified side-view illustration of the apparatus of FIG. 1 showing a patient table being adjusted to align the imaging probe with a target in the patient, in accordance with an embodiment of the invention; and  
     [0026]FIG. 5 is a simplified illustration of the image obtained from the imaging probe aligned with the image previously obtained by other imaging equipment, as a result of the adjustment made in FIG. 4. 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT  
     [0027] Reference is now made to FIG. 1, which illustrates apparatus  10  for locating a target, constructed and operative in accordance with an embodiment of the invention.  
     [0028] Apparatus  10  may include a radiation source  12  housed in an irradiation device  14 , such as but not limited to, a linear accelerator (LINAC). The radiation source  12  may emit a radiation beam  16  along a beam axis  18 . An imaging probe  20  may be mounted on irradiation device  14  along beam axis  18 . Imaging probe  20  may comprise any type of probe used in imaging systems, such as but not limited to, a computerized tomography (CT) probe, a magnetic resonance imaging (MRI) probe, an ultrasound imaging probe, a positron emission tomography (PET) probe or a single photon emission computed tomography (SPECT) probe. A beam collimator  19  may collimate radiation beam  16 .  
     [0029] Imaging probe  20  may be rotatably mounted on a turret  22  of a gantry arm  24  of irradiation device  14 . Imaging probe  20  may be arranged so that its imaging axis  26  is collinear with the beam axis  18 . In one embodiment of the invention, imaging probe  20  may be mounted on a rotating base  28  attached to turret  22 . A holder  29  may be used to attach imaging probe  20  to rotating base  28 , wherein holder  29  may comprise a spring arm or other biasing device  27  to enable applying constant pressure on a patient  25  with imaging probe  20 . Rotating base  28  may comprise a stopping device  30 , such as but not limited to, detents or pawls, for example, for arresting imaging probe  20  at two or more predetermined angular positions. For example, stopping device  30  may arrest imaging probe  20  at 0° and 90° with respect to a rotational axis  32  of gantry arm  24 . Axis  32  preferably coincides with a longitudinal axis of a patient table  34 . The imaging planes corresponding to the angular positions 0° and 90° with respect to rotational axis  32  correspond respectively to axial and sagittal images of patient  25  lying on table  34 . Rotating base  28  may be adjustable such that the imaging axis  26  is alignable with the beam axis  18 . The x-y-z position of table  34  may be adjusted and moved by means of a positioner  36 . The x-axis movement, for example, refers to movement along axis  32 ; the y-axis movement refers to movement along an axis perpendicular to axis  32  (in and out of the page of FIG. 1); and the z-axis movement refers to movement along axis  18  (or  26 ).  
     [0030] Beam axis  18  preferably intersects gantry rotational axis  32  at an isocenter  38 . Imaging probe  20  is preferably aligned on beam axis  18  above the isocenter  38  and pointing thereat. The isocenter  38  should be in the target area of radiation of the patient  25 .  
     [0031] An imaging processing unit  40  may be provided in communication with imaging probe  20 , for processing images and displaying them on a display  42 .  
     [0032] Reference is now made to FIGS.  2 - 5 , which illustrate a method for locating a target using apparatus  10 , in accordance with an embodiment of the invention. The invention seeks to find a match between prior images, such as but not limited to, CT sections, and current images obtained with imaging probe  20 .  
     [0033] Before commencing the procedure, registered and contoured images of the target area in a particular spatial plane may be imported to imaging processing unit  40 , such as but not limited to, axial and sagittal sections of the target area. These images may have been obtained previously with imaging equipment not necessarily connected with imaging probe  20 , such as with some CT, MRI, PET, SPECT or ultrasound system (not shown). An image  50  (e.g., axial image section) containing the contoured target area that corresponds to the isocenter may be displayed on display  42 , as shown in FIG. 3. This image of the target area may be registered with respect to a reference marker  37 , such as some mark in or on the patient  25 .  
     [0034] In accordance with an embodiment of the invention, reference marker  37  comprises metallic or non-metallic seeds introduced to the target area (e.g., the prostate), such as by insertion with a needle-like instrument. The seeds are preferably opaque to the particular kind of imaging system being used, such as ultrasonic or CT, for example. Reference markers  37  are internal to the organ of interest, and therefore may not significantly move with respect to the target area, thereby serving their purpose as a position reference.  
     [0035] As seen in FIG. 2, the patient  25  may be positioned so that the target area is supposedly or approximately in the isocenter  38 . This may be accomplished by means of body tattoos, room lasers and/or LINAC ruler, for example. Imaging probe  20  may be adjusted or moved so that its imaging axis  26  is substantially collinear with the beam axis  18  of the radiation source  12 .  
     [0036] In FIG. 2, the patient  25  may be raised (e.g., by moving the table  34 ) so that imaging probe  20  presses against patient  25  in the vicinity of the target area. Alternatively, imaging probe  20  may be moved until it presses against patient  25 . An image  52  of the target area may be produced with imaging probe  20 , corresponding to the spatial plane of the previously obtained image, e.g., the axial plane. The image  52  as obtained by imaging probe  20  may then be compared with the previously obtained image  50  corresponding to the particular spatial plane. If the images  50  and  52  do not match within a tolerance, as seen in FIG. 3, the patient&#39;s body may be moved in the horizontal plane (e.g., in the x axis, as indicated by arrow  33 ) to reduce the offset between the two images. Table  34  may be moved in increments, e.g., of about 1 mm, with imaging probe  10  pressing upon the patient  25 . The force of imaging probe is preferably small (e.g., about 2 kg), and does not interfere with the motion of table  34 . Table  34  may be moved manually or automatically with feedback control.  
     [0037] Afterwards, as shown in FIG. 4, imaging probe  20  may be used to form another image  52  of the target area corresponding to the particular spatial plane, the images  50  and  52  may be compared and the patient  25  accordingly moved again, until the two images  50  and  52  match within a tolerance.  
     [0038] Once a match has been obtained, as shown in FIG. 5, rotating base  28  may be rotated about beam axis  18  by 90°, as indicated by an arrow  43  in FIG. 4 (e.g., by means of an easy click mechanism or similar mechanism), and another set of images may be taken of the next spatial plane. These images may be compared with the corresponding previously obtained images of that particular spatial plane (e.g., the sagittal plane), and the patient moved, if necessary, as described before.  
     [0039] Once a match has been obtained in both spatial planes, then the patient  25  may be considered properly aligned. If necessary, patient  25  may then be moved generally along beam axis  18  (e.g., by lowering or raising table  34 ) to the proper z-position.  
     [0040] It will be appreciated by person skilled in the art, that the present invention is not limited by what has been particularly shown and described herein above. Rather the scope of the present invention is defined only by the claims that follow: