(12) United States Patent
`Reinstein
`
`US006614036B1
`(10) Patent No.:
`US 6,614,036 B1
`(45) Date of Patent:
`Sep. 2, 2003
`
`(*) Notice:
`
`OTHER PUBLICATIONS
`(54) QUALITY ASSURANCE DEVICE FOR A
`Mini–Gard", by Nuclear Associates, Carle Place, New
`MEDICAL LINEAR ACCELERATOR
`York, 2 pages (no date provided).
`(75) Inventor; Lawrence E. Reinstein, Port Jefferson,
`* cited by examiner
`NY (US)
`Primary Examiner—John R. Lee
`(73) Assignee: The Research Foundation of the State
`Assistant Examiner—James Leybourne
`University of New York, Stony Brook,
`(74) Attorney, Agent, or Firm—Dilworth & Barrese
`NY (US)
`(57)
`ABSTRACT
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35 A quality assurance device is provided for ensuring the
`U.S.C. 154(b) by 238 days.
`accuracy and reproducibility of the mechanical parameters
`of medical linear accelerators (Medical LINACs). The qual
`ity assurance devices is configured for placement within two
`parallel slots on the gantry of a Medical LINAC and includes
`off-the-shelf components for ensuring the accuracy and
`reproducibility of an optical distance indicator (ODI) dis
`tance measurement readout, collimator and gantry angles
`indicated by a display of the Medical LINAC, a radiation
`field size indicated by the Medical LINAC display, the
`centering of cross-hairs on the gantry with the intersection of
`the Medical LINAC axes, and alignment of the two lasers
`emanating from two positions toward the Medical LINAC
`with the intersection of the Medical LINAC axes.
`8 Claims, 6 Drawing Sheets
`
`(21) Appl. No.: 09/715,517
`:12, 21.
`(22) Filed:
`Nov. 17, 2000
`(51) Int. Cl.’............................. A61N 5/00; G21G 5/00
`(52) U.S. Cl. .................................................... 250/492.3
`(58) Field of Search ............................ 250,492.1, 492.3
`(56)
`References Cited
`U.S. PATENT DOCUMENTS
`4,726,046 A * 2/1988 Nunan ..................... 250,492.1
`5,142,559 A * 8/1992 Wielopolski et al. .... 250/492.3
`5,553,112 A * 9/1996 Hardy et al. ................ 378/206
`
`
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`Varian Exhibit 2003, Page 001
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`U.S. Patent
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`Sep. 2, 2003
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`Varian Exhibit 2003, Page 007
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`1
`QUALITY ASSURANCE DEVICE FOR A
`MEDICAL LINEAR ACCELERATOR
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`The present invention relates to a medical linear accel-
`erator (Medical LINAC). More particularly,
`the present
`invention relates to a quality assurance device for ensuring
`the accuracy and reproducibility of the mechanical param-
`eters of a Medical LINAC.
`
`2. Description of the Related Art
`The use of medical linear accelerators (Medical LINACs)
`for external beam irradiation of patients, principally for the
`treatment of cancerous tumors, is a well developed field.
`Medical LINACs have been used for this purpose since the
`1940’s and are common in most major hospitals around the
`world. The use of the Medical LINAC for stereotactic
`
`external beam irradiation, so-called stereotactic radiosurgery
`or stereotactic radiotherapy, has been known since around
`1984.
`
`FIG. 1 illustrates a prior art Medical LINAC in a general
`configuration for stereotactic or radiation therapy applica-
`tion designated generally by reference numeral 100. The
`Medical LINAC 100 is similar to a Medical LINAC of the
`
`Varian Clinac Linear Accelerator family manufactured by
`Varian Medical Systems, Inc., Palo Alto, Calif. The patient’s
`body 102 is on the Medical LINAC platform 104, and a
`tumor (not shown) is identified within the patient’s body 102
`and placed at the intersection of the Medical LINAC axes
`106, 108; the axis 106 being the vertical axis about which the
`platform 104 rotates and axis 108 being the horizontal axis
`about which the gantry 110 of the Medical LINAC 100
`rotates.
`
`The Medical LINAC axes 106, 108 are aligned with the
`tumor by the use of cross-hairs (not shown) on a face plate
`112 of the gantry 110 which are projected onto the patient’s
`body 102 to form a cross-hair image 114. The platform 104
`is capable of rotating on a bearing within the floor 116, as
`well as moving up and down on stand 118 and forwards and
`backwards, in order to position the tumor at the intersection
`of the cross-hair image 114. Once the center of the cross-hair
`image 114 is aligned with the tumor, the tumor is most likely
`at the intersection of the Medical LINAC axes 106, 108.
`To ensure that the tumor has been accurately positioned at
`the intersection of the Medical LINAC axes 106, 108 prior
`to commencing treatment, three stationary lasers are used.
`Two lasers (only one laser 120 of the two lasers is shown by
`FIG. 1) emanate from each side wall 124 and the third laser
`122 emanates from a top wall (or ceiling) 126 of the room
`where the Medical LINAC 100 is located within. If all three
`
`lasers are aligned with the tumor, i.e., the lasers intersect the
`tumor, then the tumor is at the intersection of the Medical
`LINAC axes 106, 108. If the lasers 120, 122 are not aligned
`with the tumor, then the tumor is not accurately positioned
`at the intersection of the Medical LINAC axes 106, 108.
`Hence,
`the patient’s body 102 is moved by moving the
`platform 104, in order to place the tumor at the intersection
`of the Medical LINAC axes 106, 108.
`Since the patient’s body 102 needs to be moved after
`aligning the cross-hair image 114 with the tumor, then it may
`be observed that the cross-hairs are not accurately aligned
`with the intersection of the Medical LINAC axes 106, 108.
`However, the case may be that the cross-hairs are accurately
`aligned with the intersection of the Medical LINAC axes
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`106, 108, but the lasers 120, 122 are not accurately aligned
`with the intersection of the Medical LINAC axes 106, 108.
`After the laser alignment procedure, the distance of the
`patient skin surface to the radiation source within the
`Medical LINAC gantry 110 (i.e., Source-to-Surface Dis-
`tance (SSD), as known in the art) is ascertained by project-
`ing a scale onto the patient from an oblique angle. The scale
`is projected using a scale projector mechanically mounted to
`the Medical LINAC gantry 110 and a scale projector lamp.
`The distance to the tumor surface is read as the intersection
`
`of the scale with the projected cross-hairs. Since the scale
`projector can loosen and fall out of calibration, it needs to be
`tested and calibrated periodically. This scale projection of
`SSD is called an optical distance indicator (ODI).
`During treatment of the patient, a beam of radiation
`emanates from the Medical LINAC 100 towards the tumor.
`
`Since the position of the tumor is most likely at the inter-
`section of the two Medical LINAC axes 106, 108,
`the
`radiation most likely passes through the tumor.
`An adjustable collimator system 130 is attached to the
`Medical LINAC 100 to collimate the radiation beam into a
`
`specific rectangular dimension having a length and width
`and defining a radiation field size. The collimator system
`130 includes mechanical jaws which are typically indepen-
`dent and moveable so as to create the specific rectangular
`dimension to define the radiation field size. The angle of the
`collimator system, i.e., the collimator angle, as well as the
`angle of the Medical LINAC gantry 110, i.e., the gantry
`angle, are displayed by a digital display 128 of the Medical
`LINAC 100. These angles are set prior to treatment by
`moving the gantry 110 and collimator system 130 to posi-
`tions where the respective angles indicated by the digital
`display 128 are within a predetermined specification. Once
`the respective angles are within the predetermined
`specification, the Medical LINAC gantry 110 and collimator
`system 130 are stopped from moving. The dimensions of the
`radiation field size are also displayed by the digital display
`128.
`
`As described above, there are many mechanical param-
`eters that are checked and/or set prior to commencing
`radiation treatment of a patient. For example, the alignment
`of the cross-hairs with the tumor to ensure that the tumor is
`at the intersection of the Medical LINAC axes 106, 108 is
`checked by the use of the two lasers 120, 122, whereas the
`gantry and collimator angles are set by moving the gantry
`110 and collimator system 130 and viewing their respective
`angles on the Medical LINAC display 128.
`Since the mechanical parameters depend on the accurate
`alignment and placement of various mechanical devices of
`the Medical LINAC 100, the mechanical parameters tend to
`shift from their nominal preset values. For example, the
`alignment accuracy of the cross-hair image 114 depends on
`the cross-hairs and light source position being accurately
`aligned with the Medical LINAC axes 106, 108; the radia-
`tion field size readout depends on the accurate linkage
`between a position sensor (e.g., a potentiometer) of the
`mechanical jaws and the digital display 128; and the ODI
`distance measurement readout depends on an accurate posi-
`tioning of the scale projector lamp on the Medical LINAC
`gantry 110.
`Accordingly, like any medical instrument, the Medical
`LINAC 100 needs to be checked to ensure that a radiation
`
`oncology facility can accurately and reproducibly deliver the
`exact prescribed radiation dose by a medical professional to
`the tumor. For example, a medical professional needs to
`check whether the collimator and gantry angles are accu-
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`Varian Exhibit 2003, Page 008
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`rately set at 90.0° and 170.0°, respectively, before setting the
`collimator and gantry angles to the angles earlier determined
`for the particular patient. Also, quality control tests need to
`be performed on the Medical LINAC 100 to ensure the
`accuracy of the mechanical parameters within predeter-
`mined quality control specifications. For example, one needs
`to ensure that the gantry and collimator angles as indicated
`by the Medical LINAC display 128 are within :0.1° and that
`the centering of the cross-hairs and the alignment of the
`lasers 120, 122 are within 10.5 mm.
`To achieve these goals,
`the geometric accuracy of the
`radiotherapy unit must be tested and verified. It is important
`to at least test and verify that the following mechanical
`parameters are within the predetermined specifications: the
`ODI distance measurement readout, the gantry and collima-
`tor angles indicated by the Medical LINAC display 128, the
`centering of the cross-hairs with the intersection of the
`Medical LINAC axes 106, 108,
`the radiation field size
`indicated by the Medical LINAC display 128, and the
`alignment of the two lasers 120, 122 with the intersection of
`the Medical LINAC axes 106, 108.
`Accordingly, there exists a need for a quality assurance
`device for testing and verifying that several mechanical
`parameters of a Medical LINAC are within predetermined
`specifications to ensure accuracy and reproducibility of the
`mechanical parameters.
`
`SUMMARY OF THE INVENTION
`
`The present invention provides a quality assurance device
`for ensuring the accuracy and reproducibility of several
`mechanical parameters of a Medical Linear Accelerator
`(Medical LINAC). The quality assurance device is config-
`ured for placement within two parallel slots on the gantry of
`the medical LINAC and includes off-the-shelf components
`for ensuring the accuracy and reproducibility of an optical
`distance indicator (ODI) distance measurement readout,
`collimator and gantry angles indicated by a display of the
`Medical LINAC, a radiation field size indicated by the
`Medical LINAC display, the centering of cross-hairs on the
`gantry with the intersection of the Medical LINAC axes, and
`alignment of the two lasers emanating from two positions
`toward the Medical LINAC with the intersection of the
`Medical LINAC axes.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`Preferred embodiments of the invention are described
`
`below with reference to the drawings, which are described
`as follows:
`
`FIG. 1 illustrates a prior art medical linear accelerator
`(Medical LINAC) used for stereotactic radiosurgery;
`FIG. 2 is a top view of a quality assurance device for
`ensuring the accuracy and reproducibility of the mechanical
`parameters of the Medical LINAC according to the present
`invention;
`FIG. 3 is a perspective view of the quality assurance
`device of FIG. 2;
`FIG. 4 is a perspective view of the quality assurance
`device of FIG. 2 placed within a slot of a gantry of the
`Medical LINAC of FIG. 1;
`FIG. 5 is a perspective view showing the quality assur-
`ance device of FIG. 2 being used to measure a distance from
`the device to a platform of the Medical LINAC;
`FIG. 6 is a perspective view showing the quality assur-
`ance device of FIG. 2 being used to measure collimator and
`gantry angles;
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`FIG. 7 is a top view of a Medical LINAC platform
`illustrating the measurement of the dimensions of a radiation
`field according to the present invention;
`FIG. 8 is a top view of a plexiglass which is mounted onto
`a base of the quality assurance device of FIG. 2;
`FIG. 9 is a top view of the Medical LINAC platform
`illustrating verification of the centering of cross-hairs pro-
`jected from the gantry of the Medical LINAC according to
`the present invention;
`FIG. 10A is a perspective view of the Medical LINAC
`gantry illustrating alignment verification of a laser emanat-
`ing toward the Medical LINAC from a side position accord-
`ing to the present invention; and
`FIG. 10B is a perspective view of the Medical LINAC
`gantry illustrating alignment verification of a laser emanat-
`ing toward the Medical LINAC from a top position accord-
`ing to the present invention.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`The present invention provides a quality assurance device
`which tests and verifies that the mechanical parameters of a
`medical linear accelerator (Medical LINAC), as shown by
`FIG. 1, are within predetermined specifications to ensure
`accuracy and reproducibility of the mechanical parameters.
`The quality assurance device can also be used to test and
`verify the Medical LINAC mechanical parameters for a
`particular patient prior to commencing treatment to ensure
`accuracy and reproducibility of the mechanical parameters.
`The mechanical parameters need to be tested and verified in
`order that a radiation oncology facility accurately and repro-
`ducibly delivers the exact prescribed radiation dose to a
`tumor within a patient, during radiation therapy.
`The quality assurance device of the present invention is
`configured for placement within two parallel slots on the
`gantry 110 of the Medical LINAC 100 and includes off-the-
`shelf components for ensuring the accuracy and reproduc-
`ibility of an optical distance indicator (ODI) distance mea-
`surement readout, collimator and gantry angles indicated by
`the display 128 of the Medical LINAC 100, a radiation field
`size indicated by the Medical LINAC display 128,
`the
`centering of cross-hairs on the gantry 110 with the intersec-
`tion of the Medical LINAC axes 106, 108, and alignment of
`the two lasers 120, 122 emanating from two walls 124, 126
`toward the Medical LINAC 100 with the intersection of the
`Medical LINAC axes 106, 108.
`With reference to FIGS. 2 and 3, there are shown top and
`perspective views of the quality assurance device of the
`present invention which is capable of ensuring the accuracy
`and reproducibility of the mechanical parameters of the
`Medical LINAC 100. The quality assurance device is des-
`ignated generally by reference numeral 200 and includes a
`base 202, a plexiglass 204, four spring-loaded screws 206
`which align with tapped holes 208 on the base 202 for
`mounting the plexiglass 204 to the base 202, and two thumb
`screws 210 which align with tapped holes 212 on the base
`202 for locking the plexiglass 204 in position.
`The quality assurance device 200 further includes a swing
`arm mechanism 214 having a swing arm stop 216 attached
`to a digital tape measure 218 for allowing the digital tape
`measure 218 to swing to a 45-degree angle with respect to
`an edge 219 of the base 202 (see FIGS. 3 and 5), a swing arm
`locking mechanism 220,
`two digital angulometers 222a,
`222b, two mounting plates 224 and two pairs of screws 226
`which align with mounting holes 228 on the base 202 for
`orthogonally mounting the digital angulometers 222a, 222b
`with respect to each other to the base 202.
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`The thickness of the base 202 is approximately 0.64 cm
`and the width and length of the base 202 are approximately
`30.00 cm. These dimensions permit the base 202 to be fitted
`and locked within two parallel slots 228 on the face of the
`Medical LINAC gantry 110 as shown by FIG. 4.
`The swing arm mechanism 214 having the swing arm stop
`216 and the swing arm locking mechanism 220 are known
`in the art and are not described in detail herein. The digital
`tape measure 218 can be any known digital tape measure
`known in the art. The digital angulometers 222a, 222b are
`preferably the SMARTTOOLTM digital angulometers avail-
`able from Macklanburg-Duncan, Oklahoma City, Okla.
`With continued reference to FIGS. 2 and 3, one of the
`digital angulometers 222a is mounted with the digital read-
`out facing up, while the other digital angulometer 222b is
`mounted to the base 202 with the digital readout facing away
`from the device 200. The digital angulometer 222a is used
`to measure the collimator angle and the other digital angu-
`lometer 222b is used to measure the gantry angle as further
`described below with reference to FIG. 6. The plexiglass 204
`includes various markings 205 which are further described
`below with reference to FIGS. 7-10.
`
`A description will now be given with respect to testing
`and verifying the mechanical parameters of the Medical
`LINAC 100 using the quality assurance device 200 of the
`present invention. The device 200 is used for testing and
`verifying the following six mechanical parameters of the
`Medical LINAC 100: the distance from a face plate 112 of
`the Medical LINAC gantry 110 to a platform 104 of the
`Medical LINAC 100 (i.e., verifies the ODI distance mea-
`surement readout), collimator and gantry angles indicated by
`a display 128 of the Medical LINAC 100, a radiation field
`size indicated by the Medical LINAC display 128,
`the
`centering of cross-hairs 238 on the gantry 110 with the
`intersection of the Medical LINAC axes 106, 108, and
`alignment of the two lasers 120, 122 emanating from two
`walls (not shown) toward the Medical LINAC 100 with the
`intersection of the Medical LINAC axes 106, 108.
`
`A. Verifying the ODI Distance Measurement
`With reference to FIG. 5, there is shown a perspective
`view showing the quality assurance device of FIG. 2 being
`used to measure the distance from the gantry face plate 112
`(i.e., the location of the quality assurance device 200) to the
`Medical LINAC platform 104. The digital tape measure 218
`having a digital readout 244 and a tape measure 246 is
`moved to a 45-degree angle with respect to the edge 219 of
`the base 202 using the swing arm mechanism 214.
`As mentioned above,
`the swing arm mechanism 214
`includes a swing arm stop 216 configured for stopping the
`digital tape measure 218 when the digital tape measure 218
`is at 45-degrees with respect
`to the edge 219. At
`this
`position, the digital tape measure 218 is situated along the
`central axis of a radiation beam path, i.e., the path of the
`radiation beam capable of being emanated by the Medical
`LINAC 100. It is important that the swing arm mechanism
`214 stops and aligns the tape measure 246 of the digital tape
`measure 218 exactly along the central axis of the radiation
`beam path to measure the SSD accurately and test the ODI.
`While the digital tape measure 218 is at 45-degrees with
`respect to the edge 219, the operator guides the tape measure
`246 towards the Medical LINAC platform 104 and reads the
`distance from the device 200 to the platform 104 from the
`digital readout 244. It is preferred that the distance mea-
`surement is read from the digital readout 244 rather than the
`tape measure 246, since the digital readout 244 provides a
`more accurate reading than the tape measure 246.
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`The distance measurement read from the digital readout
`244 is then compared with a distance measurement dis-
`played by the ODI (not shown) on the Medical LINAC
`display 128. If the ODI distance measurement is signifi-
`cantly different from the distance measurement provided by
`the digital readout 244 and an offset distance added thereto
`which takes into account the distance from the base 202 to
`
`the radiation source within the Medical LINAC gantry 110,
`then the Medical LINAC 100 must be calibrated appropri-
`ately until the ODI distance measurement is identical to the
`measurement provided by the digital readout 244 or until the
`ODI distance measurement
`is within the predetermined
`specifications, e.g., within 11.0 mm.
`When the distance measurement process has been com-
`pleted the digital tape measure 218 is swung back towards
`the edge 219 of the base 202 and locked into position by the
`swing arm locking mechanism 220.
`
`B. Verifying the Gantry and Collimator Angles
`
`With reference to FIG. 6, the gantry and collimator angles
`are tested and verified against angle reading provided by the
`Medical LINAC display 128 by using the two angulometers
`222a, 222b as indicated above. The digital angulometer
`222a is used to measure the collimator angle and the other
`digital angulometer 222b is used to measure the gantry
`angle.
`The gantry angle is measured by rotating the Medical
`LINAC gantry 110 to an angle of 90° or 270° and reading
`the angle measurement provided by the digital readout 223
`of the digital angulometer 222b as shown by FIG. 6. The
`angle measurement is then compared with a gantry angle
`measurement provided by the Medical LINAC display 128.
`It is contemplated for the digital angulometer 222b to
`include audible means for providing an audible sound when
`the Medical LINAC gantry 110 is rotated by multiples of
`90°. For example, an operator can rotate the Medical LINAC
`gantry 110 to a position where the audible sound is heard and
`check the digital readout 223 to determine how many
`degrees the Medical LINAC gantry 110 was rotated, i.e., 0°,
`90°, 180°, etc. The operator can then check the Medical
`LINAC display 128 to determine if it provides a readout
`identical to the readout provided by the digital readout 223
`of the digital angulometer 222b. That is, if the Medical
`LINAC gantry 110 was rotated to an angle of 90°, does the
`digital display 128 display a reading of 90°.
`If the gantry angle measurement provided by the Medical
`LINAC display 128 is significantly different from the gantry
`angle measurement provided by the digital readout 223, then
`the Medical LINAC 100 must be calibrated appropriately
`until the gantry angle measurement provided by the Medical
`LINAC display 128 is identical to the gantry angle mea-
`surement provided by the digital readout 223 or until the
`gantry angle measurement provided by the Medical LINAC
`display 128 is within the predetermined specifications, e.g.,
`within 10.1. The digital angulometer 222b can then be
`turned off by pushing the on/off button 250.
`After the gantry angle is measured and with the Medical
`LINAC gantry 110 pointing horizontally, i.e.,
`the gantry
`angle is at 90° or 270°, the collimator angle can be measured
`by reading the angle measurement provided by the digital
`readout 223 of the digital angulometer 222a as shown by
`FIG. 6. The angle measurement is then compared with a
`collimator angle measurement provided by the Medical
`LINAC display 128.
`It is contemplated for the digital angulometer 222a to
`include audible means for providing an audible sound when
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`Varian Exhibit 2003, Page 010
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`US 6,614,036 B1
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`7
`the collimator system 130 is at an angle that is a multiple of
`90°. Upon hearing the audible sound, the operator can then
`check the Medical LINAC display 128 to determine if it
`provides a readout identical to the readout provided by the
`digital readout 223 of the digital angulometer 222a. That is,
`if the collimator system 130 is at an angle that is a multiple
`of 90°, does the digital display 128 display a similar or
`identical reading.
`If the collimator angle measurement provided by the
`Medical LINAC display 128 is significantly different from
`the collimator angle measurement provided by the digital
`readout 223, then the Medical LINAC 100 must be cali-
`brated appropriately until the collimator angle measurement
`provided by the Medical LINAC display 128 is identical to
`the collimator angle measurement provided by the digital
`readout 223 or until
`the collimator angle measurement
`provided by the Medical LINAC display 128 is within the
`predetermined specifications, e.g., within 10.1. The digital
`angulometer 222a can then be turned off by pushing an
`on/off button 250.
`
`C. Verifying the Dimensions of the Radiation Field
`
`With reference to FIGS. 7 and 8, a description will now
`be provided for measuring and verifying the dimensions of
`a radiation field against the dimensions displayed by the
`Medical LINAC display 128 using the quality assurance
`device 200. The radiation field produced by the Medical
`LINAC 100 is generally rectangular-shaped and is con-
`trolled by the collimator system 130 which is attached to the
`Medical LINAC gantry 110 to collimate the radiation beam.
`The collimator system 130 typically includes four rectan-
`gular jaw structures which are movable to change the
`radiation field size of the rectangular-shaped radiation field.
`In order to determine the radiation field size, the four
`rectangular jaw structures or other components of the col-
`limator system 130 are moved and the dimensions of the
`radiation field size are viewed on the Medical LINAC
`
`display 128 as known in the art. The shape of the radiation
`field can be ascertained by projecting a light localizer field
`onto the Medical LINAC platform 104 to form a light field
`image 251 as shown by FIG. 7. The light field image 251 is
`projected onto the platform 104 by turning on a light source
`within the Medical LINAC gantry 110 behind the rectan-
`gular jaw structures of the collimator system 130. When the
`quality assurance device 200 is inserted within the two
`parallel slots 228 of the gantry 110, the light source also
`projects the markings 205 on the plexiglass 204 to form a
`projected markings image 253 on the Medical LINAC
`platform 104.
`With reference to FIG. 8, the markings 205 include a
`series of concentric squares 252 and two intersecting lines
`254 forming cross-hairs 256 at the intersection. The two
`intersecting lines 254 have calibration lines 258. When the
`markings 205 are projected onto the Medical LINAC plat-
`form 104 to form the projected markings image 253, each
`calibration line 258 is preferably 1.0 mm from an adjacent
`calibration line 258 when the plexiglass 204 is preferably at
`a precise distance of 100.0 cm SSD. Also, when the plexi-
`glass 204 is preferably at a precise distance of 100.0 cm
`SSD, the series of concentric squares 252 and the calibration
`lines 258 specify various radiation field sizes in centimeters.
`For example, the innermost or first concentric square indi-
`cates a radiation field size of 5.0 cm><5.0 cm, the second
`concentric square indicates a radiation field size of 10.0
`cm><10.0 cm, the third concentric square indicates a radia-
`tion field size of 15.0 cm><15.0 cm, and the fourth concentric
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`8
`square indicates a radiation field size of 20.0 cm><20.0 cm.
`It is contemplated that the markings 205 on the plexiglass
`204 may be sized to provide accurate radiation field sizes
`when the plexiglass 204 is at a distance in the range of 80.0
`to 150.0 cm SSD.
`
`In order to verify the dimensions of the radiation field as
`indicated by the Medical LINAC display 128, the projected
`concentric squares and calibration lines of the projected
`markings image 253 are used to measure the dimensions of
`the light field image 251, and hence the actual dimensions of
`the radiation field. This is accomplished by the operator
`noting which projected concentric square the rectangular-
`shaped light field image 251 overlaps, as shown by FIG. 7.
`The concentric square overlapped by the light field image
`251 provides the length and width of the radiation field or
`the dimensions of the radiation field. The measured dimen-
`
`sions are then compared with the dimensions provided by
`the Medical LINAC display 128.
`If the dimensions of the radiation field provided by the
`Medical LINAC display 128 are significantly different from
`the measured dimensions using the quality assurance device
`200, then the system of the Medical LINAC 100 which
`measures the radiation field must be calibrated appropriately
`until the dimensions provided by the Medical LINAC dis-
`play 128 are identical to the measured dimensions or until
`the dimensions of the radiation field provided by the Medi-
`cal LINAC display 128 are within the predetermined
`specifications, e.g., within 11.0 mm.
`
`D. Verifying Cross-hair Centering
`
`FIG. 9 is a perspective view showing the quality assur-
`ance device 200 being used to ascertain whether the center
`of a cross-hair image 260 projected from the Medical
`LINAC gantry 110 is positioned at the intersection of the
`Medical LINAC axes 106, 108. One of the axis of the
`Medical LINAC axes 106, 108 being the vertical axis about
`which the platform 104 rotates and the other axis being the
`horizontal axis about which the gantry 110 rotates.
`The cross-hair image 260 is used to position the tumor in
`the path of the radiation beam which is along the intersection
`of the Medical LINAC axes 106, 108. Specifically,
`the
`intersection of the two Medical LINAC axes 106, 108 is the
`point where all of the radiation converges for any position of
`the platform 104 or gantry 110. If the center of the cross-hair
`image 260 does not coincide with the intersection of the
`Medical LINAC axes 106, 108, then the tumor would not be
`accurately positioned in the path of the radiation beam.
`In order to verify whether the center of the cross-hair
`image 260 is at the intersection of the Medical LINAC axes
`106, 108, the light source is once again used, as described
`above with reference to FIG. 7, to project the markings 205
`on the plexiglass 204 onto the platform 104 to form the
`projected markings image 253. The center of the two inter-
`secting lines 254 is preset
`to define the center of the
`intersection of the Medical LINAC axes 106, 108.
`If the center of the cross-hair image 260 does not overlap
`with the center of the two intersecting lines of the projected
`markings image 253, then the center of the cross-hair image
`260 also does not overlap with the intersection of the
`Medical LINAC axes 106, 108. If this cross-hair image 260
`is not corrected to overlap with the intersection of the
`Medical LINAC axes 106, 108, a medical professional is apt
`to position the tumor at a position which is not in the path
`of the radiation beam.
`
`To prevent this from occurring the Medical LINAC 100
`must be calibrated in order for the cross-hair image 260 to
`
`Varian Exhibit 2003, Page 011
`
`Varian Exhibit 2003, Page 011
`
`

`
`US 6,614,036 B1
`
`9
`overlap with the center of the two intersecting lines of the
`markings image 253. Once the center of the cross-hair image
`260 overlaps with the center of the two intersecting lines of
`the markings image 253, the center of the cross-hair image
`260 also overlaps with the intersection of the Medical
`LINAC axes 106, 108, and the tumor can be accuratel