United States Patent [19]
`Swerdloff et al.
`
`[54] RADIATION THERAPY SYSTEM WITH
`CONSTRAINED ROTATIONAL FREEDOM
`
`[75] Inventors: Stuart Swerdloff; Thomas Rockwell
`Mackie; Timothy Holmes, all of
`Madison. Wis.
`[73] Assignee: Wisconsin Alumni Research
`Foundation, Madison, Wis.
`
`[*] Notice:
`
`The term of this patent shall not extend
`beyond the expiration date of Pat. No.
`5,317.616.
`
`[21] Appl. No.: 591,335
`[22] Filed:
`Jan. 25, 1996
`Related U.S. Application Data
`[60] Division of Ser. No. 71,742, Jun. 9, 1993, which is a
`continuation-in-part of Ser. No. 854,521, Mar 19, 1992.
`[51] Int. Cl* ~~~~~~~~~~~~~~ A61N 5/10
`[52] U.S. Cl. .............
`378/65; 378/150
`[58] Field of Search ........................................ 378/65, 150
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`4,233,519 11/1980 Coad ....................................... 250/514
`4,660,799 4/1987 Butland ........
`... 248/676
`4,754,147 6/1988 Maughan et al.
`250/505.1
`4,794,629 12/1988 Pastyr et al. .....
`... 378/152
`4,817,125 3/1989 Skiebitz .......
`... 378/152
`4,868,843 9/1989 Nunan ....................................... 378/65
`4,868,844 9/1989 Nunan ..........
`... 378/152
`4,905,268 2/1990 Mattson et al. ......................... 378/152
`4,987,309 1/1991 Klasen et al. ....
`... 250/492.1
`4,998,268 3/1991 Winter ....................................... 37.8/63
`5,012,506 4/1991 Span et al. .............................. 378/152
`FOREIGN PATENT DOCUMENTS
`0 037 008 3/1981 European Pat. Off. .
`0 113 879 12/1983 European Pat. Off. .
`0.464 645 A1 1/1991 European Pat. Off. .
`2023648 8/1970 France .
`2 346 754 10/1977 France .
`
`
`
`US005724400A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,724,400
`*Mar. 3, 1998
`
`519887 3/1977 U.S.S.R. .................................. 378/65
`553766 11/1977 U.S.S.R. .................................. 378/65
`
`OTHER PUBLICATIONS
`Optimization by simulated Annealing Of Three-Dimen
`sional Conformal Treatment Planning For Radiation Fields
`Defined by A Multileaf Collimator, S. Webb, Phys. Med.
`Biol., 1991 vol. No. 9, 1201–1226.
`On The Use Of Cimmino's Simultaneous Projections
`Method For Computing A Solution Of The Inverse Problem
`In Radiation Therapy.
`A Constrained Least—Squares Optimization Method For
`External Beam Radiation Therapy Treatment Planning. G.
`Starkschall Med. Phys. 11 (5), Sep./Oct. 1984.
`Optimization of Conformal Radiotherapy Dose Distribu
`tions by Simulated Annealing. S. Webb. Phys. Med. Biol.
`1989, vol. 43, No. 10, 1349–1370.
`Calculation and Application of Point Spread Functions For
`Treatment Planning With High Energy Photon Beams,
`Ahnesio et al., Acta Oncol. 26:49–56; 1987.
`Methods of Image Reconstruction From Projections Applied
`to Conformation Radiotherapy. Bortfeld, et al., Phys. Med.
`Biol. 35(10), 1423–1434; 1990.
`(List continued on next page.)
`Primary Examiner—Craig E. Church
`Attorney, Agent, or Firm—Ouarles & Brady
`[57]
`ABSTRACT
`A radiation therapy machine has a constrained angular
`freedom to produce a beam only within a gantry plane. A
`radiation shield may be stationary and not attached to the
`gantry or rotating to always block the primary beam. The
`constrained motion reduces the risk of patient/gantry colli
`sion and provides for extremely accurate radiation therapy
`planning. The therapy machine, so constrained, may include
`a tomographic imaging system on a single gantry. The two
`systems cooperate and employ many of the same hardware
`components to both plan and carry out therapy sessions in
`which irregularly shaped treatment volumes are accurately
`irradiated while tissue surrounding those volumes is mini
`mally irradiated.
`
`4 Claims, 11 Drawing Sheets
`
`Varian Exhibit 2005, Page 001
`
`

`
`5,724,400
`Page 2
`
`OTHER PUBLICATIONS
`
`Feasibility solutions in Radiation Therapy Treatment Plan
`ning. Altschuler et al., IEEE Comp. Soc. 1984: 220–224.
`Optimization of Stationary and Moving Beam Radiation
`Therapy Techniques. Brahme, Radiotherapy and Oncol.
`12:129–140; 1988.
`A Unified Approach to the Optimization of Brachytherapy
`and External Beam Dosimetry, Holmes et al., Int. J. Rad.
`Oncol. Biol. Phys., vol. 20, 859–873, 1991.
`
`A Primer on Theory and Operation of Linear Accelerators in
`Radiation Therapy, Medical Physics Pub. Corp., (1981) C.J.
`Karzmark, et al.
`Tomotherapy: A New Concept for the Delivery of Confor
`mal Radiotherapy Using Dynamic Compensation, Jul. 1992,
`Swerdloff, et al.
`Progress in Medical Radiation Physics vol. 2, 1985, added
`by Colin Orton, Plenum Press, W.A. Jennings pp. 1–111.
`The Accuray Neutron 1000, A Medical Systems for Frame
`less Stereotoxic Radiosurgery. Accuray, Inc., J.R. Adler, et
`al., May 1992.
`
`Varian Exhibit 2005, Page 002
`
`

`
`U.S. Patent
`
`Mar. 3, 1998
`
`5,724,400
`
`
`
`CAJ
`C0
`
`O pr)
`
`//
`
`Varian Exhibit 2005, Page 003
`
`

`
`U.S. Patent
`
`Mar. 3, 1998
`
`Sheet 2 of 11
`
`5,724,400
`
`2A —
`2 TN
`
`
`
`Varian Exhibit 2005, Page 004
`
`

`
`U.S. Patent
`
`Mar. 3, 1998
`
`Sheet 3 of 11
`
`5,724,400
`
`
`
`Varian Exhibit 2005, Page 005
`
`

`
`U.S. Patent
`
`Mar. 3, 1998
`
`Sheet 4 of 11
`6O
`
`RAD/ATION
`CONTROL
`
`62
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`COMPENSATOR
`CONTROL
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`Varian Exhibit 2005, Page 006
`
`

`
`U.S. Patent
`
`Mar. 3, 1998
`
`Sheet 5 of 11
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`5,724,400
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`
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`Varian Exhibit 2005, Page 007
`
`

`
`U.S. Patent
`
`Mar. 3, 1998
`
`Sheet 6 of 11
`
`5,724,400
`
`FIG. IO
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`Varian Exhibit 2005, Page 008
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`

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`U.S. Patent
`
`Mar. 3, 1998
`
`Sheet 7 of 11
`
`5,724,400
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`Varian Exhibit 2005, Page 009
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`

`
`U.S. Patent
`
`Mar. 3, 1998
`
`Sheet 8 of 11
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`5,724,400
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`Varian Exhibit 2005, Page 010
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`

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`Varian Exhibit 2005, Page 011
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`

`
`U.S. Patent
`
`Mar. 3, 1998
`
`Sheet 10 of 11
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`5,724,400
`
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`Varian Exhibit 2005, Page 012
`
`

`
`U.S. Patent
`
`Mar. 3, 1998
`
`Sheet 11 of 11
`
`5,724,400
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`Varian Exhibit 2005, Page 013
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`Varian Exhibit 2005, Page 013
`
`

`
`1
`RADIATION THERAPY SYSTEM WITH
`CONSTRAINED ROTATIONAL FREEDOM
`
`FIELD OF THE INVENTION
`This application is a divisional application of U.S. Ser.
`No. 08/071,742 which was a continuation in part of a patent
`application Ser. No. 07/854,521 filed Mar. 19, 1992, entitled
`“Method and Apparatus for Radiation Therapy”.
`This invention was made with United States Government
`support awarded by the National Institute of Health (NIH).
`Grant Nos. NCI R29 CA48902 and NIH Training Grant
`NRSA CA09206. The United States Government has certain
`rights in this invention.
`This invention relates generally to radiation therapy
`equipment for the treatment of tumors, or the like, and
`specifically to a radiation therapy machine having reduced
`freedom of angular rotation.
`DESCRIPTION OF THE ART
`Medical equipment for radiation therapy treats tumorous
`tissue with high energy radiation. The dose and the place
`ment of the dose must be accurately controlled to ensure
`both that the tumor receives sufficient radiation to be
`destroyed, and that damage to the surrounding and adjacent
`non-tumorous tissue is minimized.
`External-source radiation therapy uses a radiation source
`that is external to the patient, typically either a radioisotope,
`such as *Co, or a high energy x-ray source, such as a linear
`accelerator. The external source produces a collimated radia
`tion beam directed along an axis of radiation toward a tumor
`site. Although external-source radiation therapy avoids the
`disadvantages of surgically invasive procedures, it undesir
`ably but necessarily irradiates a significant volume of non
`tumorous healthy tissue within the path of the radiation
`beam as the beam passes through the patient to the tumor
`site.
`The adverse effect of irradiating healthy tissue may be
`reduced, while maintaining a given dose of radiation in the
`tumorous tissue, by projecting the radiation beam into the
`patient along a variety of radiation axes with the beams
`converging on the tumor site. As a radiation beam is directed
`along a plurality of radiation axes the particular volume
`elements of healthy tissue along the path of the radiation
`beam change, reducing the total dose to each such element
`of healthy tissue during the entire treatment.
`Beams may be directed toward a tumor along a variety of
`radiation axes in three dimensions. By directing the radia
`tion beam toward the tumor site at different angles in three
`dimensions, the tumor site is “crossfired” from the largest
`possible number of directions and the individual voxels of
`healthy tissue traversed by the radiation beam receive a low
`dose of radiation.
`The irradiation of healthy tissue is also reduced by tightly
`collimating the radiation beam to the general cross section of
`the tumor taken perpendicular to the axis of radiation.
`Numerous systems exist for producing such a circumferen
`tial collimation, some of which use multiple sliding shutters
`which, piecewise, may generate a radio-opaque mask of
`arbitrary outline.
`The treatment of tumors that are convex in a single plane
`may be performed in a simple manner by restricting the
`different radiation axis of the beam to angles within that
`plane. For such tumors, a single rotation of the radiation
`source about a suitable rotation axis can adequately irradiate
`the tumor. However, a conventional system constraining the
`
`2
`radiation axis to a single plane is inadequate to irradiate
`tumors that are concave within a rotation plane (which is
`usually the case).
`Thus, multiply articulated radiation sources are generally
`5 preferred because of their unconstrained ability to irradiate
`tumors from virtually any angle thereby minimizing irradia
`tion of individual voxels of healthy tissue and allowing
`tumors that are convex in a single plane to be targeted in that
`plane regardless of the plane's spatial orientation.
`It is important to limit scattered, uncontrolled radiation in
`a therapy area. Uncontrolled radiation can scatter off therapy
`equipment and back into a patient or operator. Radiation
`scatter from a multiply articulated source requires a protec
`tive barrier which is at all times opposed to the radiation
`source, the patient being disposed between the source and
`barrier. Ideally, the primary protective barrier absorbs the
`unattenuated x-rays passing through the patient. With a
`multiply articulate source, the primary barrier must be
`moveable to assume any angle directly opposed to the
`radiation source.
`SUMMARY OF THE INVENTION
`The present invention provides an improved architecture
`for radiation therapy equipment in which the motion of the
`radiation source is constrained to a single plane. This single
`plane configuration provides a number of benefits over the
`multiply articulated systems.
`Specifically, the present invention employs a gantry rotat
`ing within a gantry plane about a table near its axis of
`rotation. A radiation source is attached to the gantry for
`directing a radiation beam, including a plurality of rays,
`toward the patient during its rotation. A compensator posi
`tioned between the radiation source and the patient inter
`cepts the beam and independently controls the intensity of
`each ray according to a control signal based on the gantry
`angle and the position of the translation table.
`It is a first object of the invention to provide a radiation
`therapy system that is readily adapted to high accuracy
`radiation planning techniques. By treating the patient on a
`slice-by-slice basis with radiation directed at angles within
`a single plane, and by controlling the intensity of each ray
`of the radiation as a function of angle, tumors of arbitrary
`shape can be accurately irradiated.
`The gantry and radiation source may be enclosed within
`a torroidal housing embracing the swept volume of the
`gantry. This configuration helps ensure that the table or
`patient or operators remain out of the path of the rotating
`radiation source. A primary barrier may be positioned for
`rotation within the gantry diametrically opposed to the
`radiation source. The primary barrier intercepts and
`occludes radiation as the radiation exits the patient. The
`torroidal housing of the gantry may also be constructed with
`materials providing scatter shielding to be used as a station
`ary secondary barrier to limit scatter radiation within a
`therapy area. Because the secondary barrier need not rotate
`with the radiation source, the secondary barrier may be
`heavier and more effective,
`In one embodiment, the gantry rotates continuously as the
`tumor is translated along the axis of rotation so that a volume
`of arbitrary length may be treated. The compensator is
`controlled as a function of both gantry angle and table
`position.
`It is thus another object of the invention to employ the
`simplified architecture of the present invention in a manner
`that provides for smooth irradiation of volumes extending
`along the axis of rotation and wider than the radiation beam.
`
`5,724.400
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`3
`As will be described in detail below, the resultant helical
`path of the changing radiation axis produced by the con
`tinuous rotation of the gantry and simultaneous table motion
`smooths the irradiated field reducing “gaps” or “hot spots”
`in the irradiated field.
`In addition, helical scanning improves the speed of treat
`ment by eliminating the need to accelerate and decelerate the
`patient for repositioning between 360° rotations of the
`gantry such as might be required if the patient were treated
`along a series of distinct slices perpendicular to the axis of
`rotation and separated along the axis of translation.
`In another embodiment, the gantry may support not only
`a radiation source for radiation therapy, but also a low
`energy x-ray source and an opposed detector array for
`acquiring data for computerized tomographic reconstruc
`tions as the gantry rotates.
`It is yet another object of the invention to decrease the
`time and improve the accuracy of both therapy planning and
`therapy sessions so that both planning and therapy may be
`conducted in short succession. By reducing the freedom of
`movement of the radiotherapy system to a single plane there
`is improved correlation between the data generated by the
`tomographic imaging system and the data necessary to
`control the radiation therapy system. The similar geometries
`of the two systems permit their effective combination.
`The tomographic images developed by the CT machine
`may provide the necessary data to produce signals to control
`the compensator. In one embodiment, the therapist identifies
`the tumor directly with reference to the tomographic image.
`By having the tomographic imaging system and radiation
`therapy system on a common gantry, a new tomographic
`image can be produced each time a patient is to receive
`treatment. The radiologist can view and use the image to
`adjust therapy protocol while a patient remains on the
`translation table.
`Yet another object of the invention is to provide a method
`of tracking the position of the tumor during therapy and
`stopping a therapy session if the tumor is in an unanticipated
`position. The CT machine provides images of the patient
`that can be related to the image generated during treatment
`planning. If the patient moves, the mechanism can automati
`cally turn off the radiation source or alert a therapist of the
`movement.
`The foregoing and other objects and advantages of the
`invention will appear from the following description. In the
`45
`description, reference is made to the accompanying draw
`ings which form a part hereof and in which there is shown
`by way of illustration several preferred embodiments of the
`invention. Such embodiments do not necessarily represent
`the full scope of the invention, however, and reference must
`be made therefore to the claims herein for interpreting the
`scope of the invention.
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a view in partial section of the radiation therapy
`machine of the present invention;
`FIG. 2 is a cross sectional view of the therapy machine of
`FIG. 1 taken along line 2–2 of FIG. 1 showing the lateral
`orientation of the treatment and imaging sources;
`FIG. 2(a) is a cross sectional view of the therapy machine
`of FIG. 1 taken along line 2A—2A of FIG. 2 showing the
`radial orientation of the treatment and imaging sources as
`well as the detector array;
`FIG. 3 is a perspective view of the compensator assembly
`used in the present invention. showing the compensator
`leaves and their associated motive sources (e.g. pneumatic
`cylinders);
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`FIG. 4 is a cross-section of the compensator assembly of
`FIG. 3 along line 4–4 showing the trapezoidal aspect of
`each compensator leaf, for a fan beam of radiation, and the
`guide rails for supporting the compensator leaves when they
`move;
`FIG.5 is a cutaway perspective view of a set of guide rails
`and one leaf of FIG. 4 showing a collar for supporting the
`leaf in its fully closed position;
`FIG. 6 is a block diagram showing the elements of a
`radiation therapy apparatus incorporating a conventional CT
`scanner and the compensator of the present invention and
`including a computer suitable for controlling that compen
`sator per the present invention;
`FIGS. 7(a)-(d) are dose distributions of a hypothetical
`tumorous region showing dose intensity by lines of equal
`dose, with FIG. 7(a) showing a desired dose distribution and
`FIGS. 7(b), (c), and (d) showing progressive actual dose
`distributions after two, three and ten iterations per present
`invention;
`FIG. 8 is a diagrammatic representation of a patient
`receiving radiation therapy, showing the scatter kernel and
`the coordinate system used to describe the present invention;
`FIG. 9 is a perspective representation of a monodirec
`tional scatter kernel associated with a radiation beam at one
`gantry angle;
`FIG. 10 is a perspective representation of a composite
`multidirectional scatter kernel associated with a plurality of
`radiation beams at multiple gantry angles;
`FIG. 11 is a block diagram depicting the fluence profile
`calculator which takes a desired dose map and calculates a
`fluence profile;
`FIG. 12 is a block diagram depicting the overall iterative
`method of controlling the compensator of the present
`invention, employing the fluence profile calculation method
`of FIG. 11;
`FIGS. 13(a)–(c) are perspective views of plots showing
`the error between the desired dose distribution and the actual
`dose distribution obtained with the present invention for
`one, two and four steps of iteration respectively.
`FIGS. 14(a)–(c) are a perspective view of a simplified
`tumor and graphs showing gaps or hot spots that may result
`from two junctioned radiotherapy beams;
`FIG. 15(a) is an elevational view of the simplified tumor
`of FIG. 14(a) and FIGS. 15(b)–(e) are graphs showing the
`radiation beam position relative to the tumor in FIG. 15(a)
`from various gantry angles during a helical therapy session;
`FIGS. 16(a)–(e) are an elevational view of the simplified
`tumor of FIG. 14(a) and graphs showing the cumulative
`radiation dose delivered to the tumor in FIG. 16(a) at
`different times during a helical therapy session, each graph
`in FIGS. 16(b)–(e) corresponding to an adjacent graph in
`FIGS. 15(b)–(e); and
`FIG. 17 is a block diagram depicting the motivating
`mechanism operation of the present invention.
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`Referring to FIG. 1, a radiation therapy machine 10
`embodying the present invention includes, a stationary,
`generally block shaped radiation barrier 12 constructed of a
`dense concrete or other suitable radiation attenuating mate
`rial. A cylindrical bore 13 centered on horizontal bore axis
`15 passes through the front and rear surfaces 24 and 25 of
`the barrier 12.
`
`Varian Exhibit 2005, Page 015
`
`

`
`5
`A table 11 disposed along a translation axis 17 may slide
`along that axis 17 through the bore 13 passing first the front
`surface and then the rear surface 25. The table 11 is
`supported along guide tracks 6 and moved by a motorized
`drive, such as is well known in the art, so that its position
`may be controlled by a computer as will be described.
`Referring also to FIG. 2, the bore 13 includes internal
`recesses 16, 19 and 16', each generally cylindrical and
`co-axial with the bore axis 15. Recess 16 is disposed near the
`front surface 24 of the protective barrier 12 and receives the
`radially outer edge of an annular ball bearing 27 as will be
`described below. Recess 16' is similar to recess 16 but
`displaced along the axis of the bore 13 near the back surface
`25 of the protective barrier 12. Recess 16' holds the radial
`outer edge of annular ball bearing 27".
`Centered between recesses 16 and 16' is recess 19 having
`a radius greater than recess 16 or 16' so as to form a volume
`for the support of various equipment, to be described,
`outside of the volume of the bore 13.
`Referring to FIGS. 2 and 2a, an annular gantry 14,
`radially symmetric about the bore axis 15, fits within the
`recesses 16, 16' and 19 and has outer surfaces conforming
`generally to the recesses 16, 16 and 19. The gantry 14 is
`supported at two ends by the radially inner edges of bearings
`27 and 27" for rotation on those bearings within the barrier
`12. The gantry 14 is generally concave inwardly, having a
`U-shaped portion 20 held with recess 19 with radially
`inwardly extending walls 21. Attached to the radially
`extending wall 21 nearest to the back edge 25 is a radiation
`therapy source 32 producing a fan beam of high energy
`radiation 26 directed toward and perpendicular to bore axis
`15. The fan beam 15 lies generally within a plane 22
`perpendicular to the bore axis 15 and at all times is directed
`toward the barrier 12.
`Diametrically opposed to the therapy source 32 on the
`opposite side of the gantry 14 is a primary barrier 107. The
`primary barrier 107 subtends and occludes each ray 47
`exiting the patient and hence minimizes scatter within a
`therapy area. For verification purposes, a megavoltage
`detector array 105 may be placed on the internal surface of
`the primary barrier 107.
`An x-ray source 28 and an imaging detector array 30 are
`securely disposed along the vertically extending walls 21
`closest to the front end 24 of the barrier 9 so as to direct a
`beam of x-rays 29 along a plane parallel to, but spaced from
`plane 22 and along an axis at substantially right angles to
`that of the fan beam 26. This spacing of the plane of the
`x-rays 29 and fan beam plane 22 ensures sufficient space
`within the barrier 9 to house the therapy source 32 and x-ray
`source 28 and prevents unwanted signal interference
`between the two systems.
`The radiation source 32, primary barrier 107, the x-ray
`source 28 and x-ray detector 30 are all removed from the
`volume of the bore 13 so as not to interfere with a patient
`within the bore 13 upon rotation of the gantry 20.
`The gantry 20 may be rotated by a shaft 7 extending
`through the barrier 12 and driven by conventional means.
`Attached to the shaft is an encoder (not shown) for providing
`signals indicating the exact angle of the gantry 20 within the
`barrier 12.
`I. The Compensator and Collimator
`Referring now to FIG. 3, a radiation therapy source 32
`produces a generally conical radiation beam 34' emanating
`from a focal spot 35 and directed towards a patient (not
`shown). The conical beam 34 is collimated by a radiational
`opaque mask 36 constructed of a set of rectangular colli
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`mator blades to form a generally planer fan beam 26
`centered about a fan beam plane 38.
`A compensator 40 is centered in the fan beam 26 produced
`by the therapy source and about the fan beam plane 38, prior
`to the radiation being received by the patient, and includes
`a plurality of adjacent trapezoidal leaves 41 which together
`form an arc of constant radius about the focal spot 35. The
`leaves 41 are held in sleeves 43. The sleeves 43 are con
`structed of relatively radio translucent materials and
`attached at their inner ends 44 to a mounting plate 45 which
`is fixed relative to the focal spot 35. The mounting plate 45
`is constructed of a sturdy, radiopaque material and is posi
`tioned just outside the fan beam 26 to prevent interference
`with the fan beam 26.
`Preferably, the leaves 41 of the compensator 40 subtend
`the entire fan beam 26 to divide the fan beam 26 into a set
`of adjacent slab-like rays 47 at offset angles (p. Referring also
`to FIG. 4, each sleeve 43 is open at its outer end 48 to
`receive, by sliding, a comparably sized trapezoidal leaf 41
`constructed of a dense, radiopaque material such as lead,
`tungsten, cerium, tantalum or a related alloys.
`Each leaf 41 may slide completely within its correspond
`ing sleeve 43 to block the ray 47 associated with that sleeve
`43. When the leaf 41 blocks its corresponding ray 47, it is
`referred to as being in a “closed state”. The sleeves 43 are
`of ample length to permit each leaf 41 to slide out of the path
`of the fan beam 26, so as to leave its corresponding ray 47
`completely unobstructed, and yet to still be guided by the
`sleeve 43. In this non-blocking position, a leaf is referred to
`as being in the “open state”.
`Each leaf 41 may be moved rapidly between its open and
`closed states by means of a corresponding pneumatic cyl
`inder 51 connected to the leaf 41 by a flexible link 50. The
`pneumatic cylinders 51 have internal pistons (not shown)
`that may be moved at high velocity between the ends of the
`cylinders 51 by means of pressurized air coupled to the
`cylinders 51 through supply hoses 52. The supply hoses 52
`are fed by a compensator control to be described below. The
`pneumatic cylinders 51 are capable of applying high forces
`to the leaves 41 to move them rapidly and independently
`between the open and closed states.
`Referring now to FIGS. 4 and 5, the leaves 41 are
`supported and guided within the sleeves 43 by guide rails 54
`fitted into notches 55 cut along the edges of the leaves 41.
`The notches 55 allow the guide rails 54 to slidably retain the
`leaves 41 within the sleeves 43 during motion between the
`open and closed states.
`In the closed State, the inner end 57 of each leaf 41 is
`captured by a rigid collar 58 attached to the mounting plate
`45, which aligns the leaf 41, more accurately than may be
`done by the guide rails 54, with the mounting plate 45 and
`hence with the fan beam 26. Whereas the guide rails 54.
`which are ideally radio translucent, are relatively
`insubstantial, in contrast, the collar 58, positioned outside
`the fan beam 26 on the mounting plate 45, need not be
`radio-translucent and hence is more substantial in construc
`tion. A collar (not shown) similar to collar 58, supports each
`leaf 41 when it is fully in the open state. Because the leaves
`41 spend most of their time fully in the open or closed states.
`they are, at most times, firmly located by a supporting collar.
`II. Radiation Therapy Control Circuitry
`Referring now to FIG. 6, the radiation therapy source 32
`is controlled by a radiation control module 60 which turns
`the radiation beam 26 on or off under the control of a
`computer 61.
`A compensator control module 62 provides a source of
`compressed air and valves to gate that air through supply
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`hoses 52 to control, separately, the pneumatic cylinders 51
`to move each of the leaves 41 in and out of its corresponding
`sleeve 43 and ray 47 (see also FIG. 3). The compensator
`control module 62 also connects with the computer 61 to
`allow program control of the compensator 40 to be
`described.
`A collimator module 64 controls the spatial relationship
`between the collimator Jaws 156, 157 to effect a single
`steady state collimated beam 26. The collimator module 64
`is also connected to the computer 61 to allow program
`control of the collimator jaws 156, 157 to be described.
`A tomographic imaging system 63 employing the x-ray
`source 28 and the opposed detector array 30 are advanta
`geously mounted on the same gantry 14 as the radiation
`source 32 to produce a tomographic or slice image of the
`irradiated slice of the patient 59 prior to radiation therapy for
`planning purposes. Control modules for the tomographic
`imaging system 63 include: x-ray control module 67 for
`turning on and off the x-ray source 28, and data acquisition
`system 68 for receiving data from the detector array 30 in
`order to construct a tomographic image. An image recon
`structor 69 typically comprising a high speed array proces
`sor or the like receives the data from the data acquisition
`system 68 in order to assist in “reconstructing” a tomo
`25
`graphic image from such data according to methods well
`known in the art. The image reconstructor 69 also commu
`nicates with computer 61 to assist in high speed computa
`tions used in the present invention as will be described
`below. The tomographic image allows verification of the
`patient setup just prior to radiation therapy treatment.
`A gantry control module 66 provides the signals necessary
`to rotate the gantry 14 and hence to change the position of
`the radiation source 32 and the angle 6 of the fan beam 26
`for the radiation therapy, as well as to change the position of
`the computed tomography x-ray source 28, the x-ray detec
`tor array 30 and the primary barrier 107. Gantry control
`module 66 connects with computer 61 so that the gantry may
`be rotated under computer control and also to provide the
`computer 61 with a signal indicating the gantry angle 6 to
`assist in that control.
`A terminal 70 comprising a keyboard and display unit 71
`allows an operator to input programs and data to the com
`puter 61 and to control the radiation therapy and tomo
`graphic imaging equipment 63 and to display tomographic
`45
`images produced by the image reconstructor 69 on the
`display 71. A mass storage system 73, being either a mag
`netic disk unit or drive for magnetic tape or optical media,
`allows the storage of data collected by the tomographic
`imaging system 11 for later use.
`Computer programs for operating the radiation therapy
`system 10 will generally be stored in mass storage unit 73
`and loaded into the internal memory of the computer 61 for
`rapid processing during use of the system 10.
`III. Operation of the Therapy System
`As part of a therapy planning session, a patient is placed
`on the translation table 11 and translated through the gantry
`14. During translation the x-ray imaging source 28 is rotated
`about the patient while directing an x-ray beam 29 toward
`the detector array 30. Through detecting methods well
`known in the art, the x-ray source 28 and detector array 30
`cooperate to produce x-ray data from a plurality of gantry
`angles 6 and table positions. The computer 61 stores the raw
`x-ray data. This data is used by the reconstructor 69 to
`produce tomographic images of each slice of the patient that
`are in turn used to generate treatment sinograms for therapy
`Sessions.
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`Each sinogram contains a plurality of fluence profiles that
`will control the compensator during a later therapy session.
`The fluence profiles describe the intensity or fluence of each
`ray 47 of the radiation beam 26 from the radiation source 32
`that is desired for that gantry angle 6 at a given position of
`the patient translation table (not shown) as translated
`through the radiation beam 26. Together, the fluence profiles
`for each gantry angle make up a treatment sinogram for a
`particular position of the translation table 11.
`During operation of the radiation therapy unit 10,