`Barnea
`
`USOO5233 990A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,233,990
`Aug. 10, 1993
`
`[54] METHOD AND APPARATUS FOR
`DIAGNOSTIC IMAGING IN RADIATION
`THERAPY
`[76] Inventor: Gideon Barnea, 7887 E. Uhl St., No.
`410, Tucson, Ariz. 85710
`[21] Appl. No.: 819,957
`[22] Filed:
`Jan. 13, 1992
`
`[51] Int. Cl.5 .............................................. .. A61B 5/05
`[52] US. Cl. .............. ..
`.... .. 128/6531; 378/65
`[58] Field of Search ...................... .. 128/6531; 378/65
`[56]
`References Cited
`U.S. PATENT DOCUMENTS
`
`3,783,251 1/1974 Pavkovich .......................... .. 378/65
`4,123,660 lO/1978 Horwitz ..... ..
`4,930,509 6/1990 Brisson ........................... .. 128/6531
`OTHER PUBLICATIONS
`Droege, R. T. et al., “In?uence of Metal Screens on
`Contrast in Megavoltage X-Ray Imaging,” Med. Phys.
`6, 487-492, 1979.
`Lutz, W. R. et al., “A Test Object for Evaluation of
`Portal Film” Int. J. Radiat. Oncol. Biol. Phys. 11,
`631-634, 1985.
`Munro, P. et al., “Therapy Imaging: A Signal-to-Noise
`Analysis of Metal Plate/Film Detectors,” Med. Phys.
`14, 975-984, 1987.
`Mark, J. E. et al., “The Value of Frequent Treatment
`Veri?cation Films in Reducing Localization Error in
`the Irradiation of Complex Fields," Cancer, 37,
`2755-2761, 1976.
`Huizenga et a1. “Accuracy in Radiation Field Align
`ment in Head and Neck Cancer: A Prospective Study,"
`Rad. Oncol. 11, 181-187, 1988.
`Pearcy et al., “The Impact of Treatment Errors on
`Post-Operative Radiotherapy for Testicular Tumors,”
`Br. J. Radiol. 58, 1003-1005, 1985.
`Rabinowitz et a1. “Accuracy of Radiation Field Align
`ment in Clinical Practice,” Int. J. Radiat. Oncol. Biol.
`Phys. 11, 1857-1867, 1985.
`
`4
`
`Lam et a1. “On-Line Measurement of Field Placement
`Errors in External Beam Radiotherapy,” Br. J. Radiol.
`60, 361-367, 1987.
`Baily et al. “Fluoroscopic Visualization of Megavoltage
`Therapeutic X-Ray Beams,” Int. J. Radiat. Oncol. Biol.
`Phys. 6, 935-939, 1980.
`Herk et al., “A Digital Imaging System for Portal Veri
`?cation,” in The Use of Computers in Radiation Ther
`apy, I. Brunvis Ed., North Holland, 371-373, 1987.
`(List continued on next page.)
`
`Primary Examiner-Lee S. Cohen
`Assistant Examiner-Samuel Gilbert
`Attorney, Agent, or Finn-Antonio R. Durando; Harry
`M. Weiss
`ABSTRACT
`[57]
`An apparatus for diagnostic and veri?cation imaging in
`radiation therapy that consists of attachments for stan
`dard radiotherapy equipment comprising an x-ray tube
`and an x-ray detector placed on opposite sides of a
`patient along the main axis of the beam produced by the
`treatment unit. The detector is placed on a plane or
`thogonal to the axis of the treatment beam and between
`the beam source and the patient, while the x-ray tube is
`placed on the other side of the patient, coaxially with
`the treatment beam and facing the detector. As a result
`of this con?guration, the radiographic view of the x-ray
`beam, as seen on the detector, is equivalent to the view
`produced on the same detector by the therapeutic beam,
`varied only by parallax deviations that can be corrected
`by geometrical calculations. Accordingly, x-ray expo
`sures and real-time verification of the position of a pa
`tient can be obtained with the same unit used for treat
`ment and without requiring movement of either patient
`or equipment. In addition, the apparatus enables a user
`to produce diagnostic images that can be used directly
`to manufacture shielding blocks in conventional shield
`ing-block cutters.
`
`10 Claims, 2 Drawing Sheets
`
`Varian Exhibit 2007, Page 001
`
`
`
`5,233,990
`Page 2
`
`OTHER PUBLICATIONS
`Shalev et al. “Video Techniques for On-Line Portal
`Imaging,” Comp. Med. Imag. Graph. 13, 217-226, 1989.
`Munro et al. “A Digital Fluoroscopic Imaging Device
`for Radiotherapy Localization,” Int. J. Radiat. Oncol.
`Biol. Phys. 18, 641-649, 1990.
`Durham et a1. “Portal Film Quality: A Multiple Institu- .
`tional Study,” Med. Phys. 11, 555-557, 1984.
`Biggs et al. “A Diagnostic X-Ray Field Veri?cation
`Device for a 10 MV Accelerator,” Int. J. Radiat. Oncol.
`Biol. Phys. 11, 635-643, 1985.
`Marks J. E. et a1. “Localization in the Radiotherapy of
`
`Hodgkins Disease and Malignant Lymphoma with Ex
`tended Mantle Fields,” Cancer 34, 83-90, 1974.
`Marks J. E. et a1. “Dose-Response Analysis for Naso
`pharyngeal Carcinoma: An Historical Perspective,”
`Cancer 50, 1042-1050 1982.
`White J. E. et al. “The In?uence of Radiation Therapy
`Quality Control on Survival, Response and Sites of
`Relapse in Oat Cell Carcinoma of the Lung, ” Cancer
`50, 1084-l090, 1982.
`Kinzie J. J. et a1. “Patterns of Care Study: Hodgkins
`Disease Relapse Rates and Adequacy of Portals, ” Can
`cer 52, 2223-2226, 1983.
`
`Varian Exhibit 2007, Page 002
`
`
`
`US. Patent
`
`Aug. 10, 1993
`
`Sheet 1 of 2
`
`5,233,990
`
`(PRIOR ART)
`
`Varian Exhibit 2007, Page 003
`
`
`
`US. Patent
`
`Aug. 10, 1993
`
`Sheet 2 of 2
`
`5,233,990
`
`2
`
`z’ THEZAPYEADIATION
`SOURCE
`
`T__
`
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`
`SOURCE
`
`_
`
`St
`DETECTOR
`PLANE
`(
`261
`I
`
`st
`26 \
`
`I
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`
`ANATOM/CAL
`LANDMAR K
`
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`FILM Pos/r/o/v
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`
`I
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`ANATOMICAL.
`LAINDMAEK
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`
`DIAGNOSTIC
`22;
`J _ RADIATION SOURCE
`
`,'
`_
`Fj 5
`
`F 1'
`. 4
`THERAPY j
`RADIATION
`SOURCE
`HR
`:D______'___ _______ __.._ MIRROR
`VIDEO
`/ ’
`CAMERA
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`I
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`Fig. 5
`
`DIAGNOSTIC
`RADIATION souRcE
`
`Varian Exhibit 2007, Page 004
`
`
`
`1
`
`5,233,990
`
`METHOD AND APPARATUS FOR DIAGNOSTIC
`IMAGING IN RADIATION THERAPY
`
`5
`
`15
`
`20
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`This invention is related to the general ?eld of radia
`tion imaging for medical applications. In particular, the
`invention provides a new method and apparatus for
`producing a diagnostic image of the portion of the body
`affected by a tumor, so that the required dosage of
`radiation can be accurately delivered to the prescribed
`target volume.
`2. Description of the Prior Art
`The main object of radiotherapy is to deliver the
`prescribed dosage of radiation to a tumor in a patient
`while minimizing the damage to surrounding, healthy,
`tissue. Since very high energy radiation (produced at 4
`to 25 million volts, typically generated by a linear accel
`erator). is normally used to destroy tumors in radiother
`apy, the high energy is also destructive to the normal
`tissue surrounding the tumor. Therefore, it is essential
`that the delivery of radiation be limited precisely to the
`prescribed target volume (i.e., the tumor plus adequate
`margins), which is accomplished by placing appropri
`ately constructed shielding blocks in the path of the
`radiation beam. Thus, the goal is to accurately identify
`the malignancy within the body of the patient and to
`target the prescribed dosage of radiation to the desired
`region on the immobilized patient.
`To that end, the ideal procedure requires the identi?
`cation of the exact anatomical location of the tumor and
`the corresponding accurate positioning of the radiation
`?eld during treatment. This could be easily achieved if
`it were possible to locate and treat the tumor at the same
`time. In practice, though, this is not possible because the
`equipment used to identify the tumor (x-ray machine,
`computed tomography equipment, or the like) is sepa
`rate from the equipment used for the therapeutical irra
`diation of the patient, requiring the movement and repo
`sitioning of the patient from one piece of equipment to
`the other. As illustrated in schematic form in FIG. 1, a
`conventional treatment unit 10 consists of a linear accel
`erator (linac) head 2 mounted on a gantry 4 so that its
`collimated high-energy emissions HR irradiate a patient
`P lying on a gurney 6 directly below through shielding
`blocks 8 attached to the head. A bracket 12 supporting
`a detector 14 may be mounted on the opposite side of
`the head within the ?eld of radiation in order to take
`radiographs of the patient being treated. The gantry 4 is
`movable around a pivot 16 to permit the rotation of the
`head (and of the detector) around the patient to afford
`different views of the area to be treated (“multiple
`?elds” treatment). The normal procedure involves the
`use of a diagnostic simulator, which is a diagnostic x-ray
`machine with the same physical characteristics of the
`radiation therapy machine (schematically also repre
`sented by FIG. 1, where a diagnostic x-ray head re
`places the linac head 2), so that the ?eld of view of the
`low-energy x rays emitted in the simulator is the same as
`that of the high-energy radiation emitted in the radia
`tion therapy machine. Prior to treatment, the patient is
`radiographed using the simulator and an image of the
`target area is obtained with low-energy radiation (in the
`order of 100 kVP), which yields good image quality.
`The exact target volume is then delineated on the radio
`graph by a physician and matching shielding blocks are
`constructed to limit the ?eld of view of the irradiating
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`65
`
`2
`machine to the region so delineated. A mold of the
`shielding blocks is ?rst cut out of plastic material (nor
`mally polystyrene) with a shielding-block cutter, a ma
`chine that reproduces exactly the relative positions of
`the linac head, the shielding blocks and the detector as
`they stand in the treatment unit. By using mechanical
`means, the shielding blocks are cut so that the ?eld of
`irradiation from the treatment unit will corresponds
`exactly to the area delineated by the physician on the
`diagnostic radiograph. The ?nal shielding blocks are
`then made from the mold with lead alloys that attenuate
`considerably the propagation of radiation. Thus, the
`shielding blocks function as templets that limit the radi
`ation treatment to the areas left open within the contour
`of the shielding blocks. In addition, it is common prac
`tice to mark the skin of a patient with reference mark
`ings that are used in aligning the position of the patient
`with the ?eld of emission of the radiation therapy ma
`chine.
`These apparently sound procedures in fact suffer
`from serious practical shortcomings. Errors in position
`ing the shielding blocks between the radiating source
`and the patient, as well as incorrect beam alignment and
`patient movement, all have a cumulative effect reducing
`the accuracy of the procedure. Even the markings on
`the skin of the patient may be the cause of alignment
`problems because of shifting of the skin with respect to
`the patient’s internal anatomy as a result of body motion
`or, over a period of time, even of body changes. Thus,
`the area actually irradiated during the therapeutic ses
`sion often does not correspond to the area delineated in
`the radiograph generated by the simulator.
`Positioning errors during irradiation have been found
`to have very serious consequences for the successful
`prognosis of the treatment. For example, researchers
`have been able to correlate the recurrence of lymphoma
`to such positioning errors (J. E. Marks, A. G. Haus, H.
`G. Sutton and M. L. Griem, “Localization Error in the
`Radiotherapy of Hodgkin’s Disease and Malignant
`Lymphoma with Extended Mantle Fields,” Cancer 34,
`83-90, i974); and it has been found that improved tumor
`control of nasopharingeal carcinomas can be related to
`greater accuracy in the delivery of calculated dosages
`of radiation (J. E. Marks, J. M. Bedwinek, F. Lee, J. A.
`Purdy and C. A. Perez, “Dose-Response Analysis for
`Nasopharyngeal Carcinoma: An Historical Perspec
`tive,” Cancer 50, 1042-1050, 1982). Similarly, it has
`been found that shielding inaccuracies have resulted in
`signi?cantly lower primary tumor control and survival
`of patients of oat cell lung cancer (J. E. White, T. Chen,
`J. McCracken, P. Kennedy, H. G. Seydel, G. Hartman,
`J. Mira, M. Khan, F. Y. Durrance and 0. Skinner, “The
`In?uence of Radiation Therapy Quality Control on
`Survival, Response and Sites of Relapse in Oat Cell
`Carcinoma of the Lung,” Cancer 50, 1084-1090, 1982);
`and that the local recurrence of Hodgkin’s disease was
`signi?cantly higher when the radiation ?eld did not
`adequately cover the tumor (J. J. Kinzie, G. E. Hanks,
`C. J. Maclean and S. Kramer, “Pattems of Care Study:
`Hodgkin’s Disease Relapse Rates and Adequacy of
`Portals,” Cancer 52, 2223-2226, 1983).
`The only technique widely used today to check the
`accuracy of the radiation ?eld is by imaging with the
`radiotherapy beam itself at the time of treatment. Prior
`to treatment, a “portal” image is obtained by using the
`therapy beam (at high energy) and the resulting expo
`sure is visually compared with that taken with the simu
`
`Varian Exhibit 2007, Page 005
`
`
`
`5,233,990
`3
`4
`lator (at low energy). This technique is therefore known
`Leszczynski, S. Cosby and T. Chu, “Video Techniques
`as “portal imaging” or “therapy veri?cation,” and is
`for On-Line Portal Imaging,” Comp. Med. lmag.
`repeated periodically during the period of radiation
`Graph. 13, 217-226, 1989; and P. Munro, J. A. Rawlin
`treatment. Unfortunately, though, because of the high
`son and A. Fenster, “A Digital Fluoroscopic Imaging
`energy radiation emitted by the treatment beam (pro
`Device for Radiotherapy Localization,” Int. J. Radiat.
`duced at 4-25 million volts), the resulting portal images
`Oncol. Biol. Phys. 18, 641-649, 1990. A survey of 23
`have poor resolution and show very poor contrast be
`different radiotherapy departments shows that at each
`tween soft tissues and bones, often making the images
`of eight institutions (i.e., 35 percent of the 23 institutions
`totally unsuited for veri?cation by comparison with the
`sampled) more than i of the submitted portals were
`low-energy images produced by the simulator. See, for
`evaluated as poor in quality. Furthermore, it shows that
`example, R. T. Droege and B. J. Bjarngard, “In?uence
`approximately one-half of the institutions were produc
`of Metal Screens on Contrast in Megavoltage X-Ray
`ing poor-quality ?lms at a rate of at least 50 percent. See
`Imaging,” Med. Phys. 6, 487-492, 1979; L. E. Reinstein,
`Reinstein, L. E., M. Durham, M. Tefft, A. Yu, and A. S.
`M. Durham, M. Tefft, A. Yu and A. S. Glicksman,
`Glicksman, “Portal Film Quality: A Multiple Institu
`“Portal Film Quality: A Multiple Institutional Study,”
`tional Study,” Med. Phys. 11, 555-557, 1984.
`Med Phys. 11, 555-557, 1984; W. R. Lutz and B. E.
`Another, logical, approach to obtaining diagnostic
`Bjarngard, “A Test Object for Evaluation of Portal
`quality portal ?lms has been by mounting an x-ray tube
`Film,” Int. J. Radiat. Oncol. Biol. Phys. 11, 631-634,
`on the head of the treatment unit as close to the linac
`1985; and P. Munro, J. A. Rawlinson and A. Fenster,
`gantry as possible. See P. J. Biggs, M. Goitein and M.
`“Therapy Imaging: A Signal-to-Noise Analysis of
`20
`D. Russell, “A Diagnostic X-Ray Field Veri?cation
`Metal Plate/Film Detectors,” Med. Phys. 14, 975-984,
`Device for a 10 MV Accelerator,” Int. J. Radiat. Oncol
`1987. Indeed, positioning errors occur very frequently
`Biol. Phys. 11, 635-643, 1985. The x-ray tube is aligned
`in spite of the use of portal images. See J. E. Marks, A.
`with the linac emission ?eld so that, to the extent possi
`G. Haus, H. G. Sutton and M. L. Griem, “The Value of
`ble within the physical constraints of both devices, the
`Frequent Treatment Veri?cation Films in Reducing
`25
`x-ray emissions have the same ?eld of view of the high
`Localization Error in the Irradiation of Complex
`energy radiation. As a result, the image received on a
`Fields,” Cancer 37, 2755-2761, 1976; R. W. Byhardt, J.
`?lm placed on a detector tray on the opposite side of the
`D. Cox, A. Hornburgh and G. Lierrnann, “Weekly
`patient by exposure to either source of radiation is theo
`Localization Films and Detection of Field Placement
`retically almost exactly the same. In order to implement
`Errors,” Int. J. Radiat. Oncol. Biol. Phys. 4, 881-887,
`this approach, though, a special shielding-block holder
`1978; Huizenga, P. C. Lenendag, P. M. Z. R. De Porre
`coupled to the gantry has to be made, disabling the
`and A. G. Visser, “Accuracy in Radiation Field Align
`normal rotation of the linac’s collimator and limiting the
`ment in Head and Neck Cancer: A Prospective Study,”
`adjustment capabilities of the equipment. Thus, the
`Rad. Oncol. 11, 181-187, 1988; R. G. Pearcy and S. E.
`complexity of the procedure, the oblique view of the
`Grif?ths, “The Impact of Treatment Errors on Post
`diagnostic beam and the increased time required for
`Operative Radiotherapy for Testicular Tumors,” Br. J.
`each treatment have prevented this technique from
`Radiol. 58, 1003-1005, 1985; l. Rabinowitz, J. Broom
`gaining widespread acceptance. Furthermore, this
`berg, M. Goitein, K. McCarthy and J. Leong, “Accu
`method is unsuited for real-time portal imaging.
`racy of Radiation Field Alignment in Clinical Prac
`A similar approach has been followed by placing an
`tice,” Int. J. Radiat. Oncol. Biol. Phys. 11, 1857-1867,
`x-ray tube at a ?xed angle with respect to the axis of the
`1985; and W. C. Lam, M. Partowmah, D. J. Lee, M. D.
`therapeutic beam, so that the x-ray beam and the thera
`Wharam and K. S. Lam, “On-Line Measurement of
`peutic beam have coinciding isocenters corresponding 1
`Field Placement Errors in External Beam Radiother
`to the location of the radiation target. By rotating the
`apy,” Br. J. Radiol. 60, 361-367, 1987. Imaging devices
`gantry of the radiation unit by that angle, the target can
`other than X-ray ?lm have been used in an attempt to
`improve the quality of the image produced during ther
`be irradiated from the same point either with a treat
`ment beam or an x-ray beam, with every other variable
`apy veri?cation. These include metal and ?uorescent
`remaining unchanged. Therefore, veri?cation can be
`screens in contact with conventional ?lm, and non-?lm
`obtained simply by rotating the gantry and switching
`imaging processes and devices such as xeroradiogra
`phy, liquid ionization chambers, fluoroscopic imaging,
`from one mode of operation to the other. The main
`problem with this approach is the inevitable angular
`linear diode arrays, photostimulable phosphors, and
`others. In addition, various image processing techniques
`error introduced during the rotation of the gantry. In
`addition, because of the alternative use of either mode
`(both analog and digital) have been used to enhance the
`of operation, this equipment is also not suitable for real
`quality of the ?nal veri?cation image; but all these
`time veri?cation.
`methods and devices have resulted only in a limited
`success in yielding a good quality, and therefore useful,
`Therefore, it would be very desirable to have a sim
`diagnostic image. Real-time portal imaging using video
`pler and more accurate veri?cation imaging system for
`radiation therapy veri?cation, especially for real time
`techniques has also been proposed, so that patient
`movement can be monitored during treatment. Because
`applications. This invention relates to the use of a con
`ventional x-ray tube and conventional imaging devices
`they all use the high-energy therapy beam as the source
`of radiation, though, the quality of the image remains
`in a novel geometric con?guration to produce such an
`improved veri?cation imaging system.
`poor. See N. A. Baily, R. A. Horn and T. D. Kampp,
`“Fluoroscopic Visualization of Megavoltage Therapeu
`BRIEF SUMMARY OF THE INVENTION
`tic X-Ray Beams,” Int. J. Radiat. Oncol. Biol. Phys.6,
`935-939, 1980; M. V. Herk and H. Meertens, “A Digital
`One objective of this invention is the development of
`Imaging System for Portal Veri?cation,” in “The Use
`therapy veri?cation apparatus that produces veri?ca
`of Computers in Radiation Therapy," 1. Brunvis Ed.,
`tion images of the same quality obtained with diagnostic
`North Holland, 371-373, 1987; S. Shalev, T. Lee, K.
`apparatus.
`
`50
`
`35
`
`40
`
`45
`
`55
`
`60
`
`Varian Exhibit 2007, Page 006
`
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`25
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`5,233,990
`5
`Another objective of the invention is an imaging
`apparatus that can be implemented as an accessory to
`existing radiation-therapy treatment units.
`A further goal of the invention is an imaging appara
`tus and technique that are suitable for on-line, real time,
`applications in conjunction with radiation treatments.
`Still another objective of the invention is an apparatus
`that, as a result of the position of the x-ray emission
`source, produces an image corresponding to the same
`?eld of view of the linac beam used in conjunction with
`it.
`A ?nal objective of this invention is the realization of
`the above mentioned goals in an economical and com
`mercially viable manner. This is done by utilizing com
`pone'nts and methods of manufacture that are either
`already available in the open market or can be devel
`oped at competitive prices.
`According to these and other objectives, the present
`invention consists of attachments for standard radio
`therapy equipment comprising an x-ray tube and an
`x-ray detector placed on opposite sides of a patient
`along the main axis of the beam produced by the treat
`ment unit. The detector is placed on a plane orthogonal
`to the axis of the treatment beam and between the beam
`source and the patient, while the x-ray tube is placed on
`the other side of the patient, coaxially with the treat
`ment beam and facing the detector. As a result of this
`con?guration, the radiographic view of the x-ray beam,
`as seen on the detector, is equivalent to the view pro
`duced on the same detector by the therapeutic beam,
`varied only by parallax deviations that can be corrected
`by geometrical calculations. Accordingly, x-ray expo
`sures and real-time veri?cation of the position of a pa
`tient can be obtained with the same unit used for treat
`ment and without requiring movement of either patient
`or equipment.
`Various other purposes and advantages of the inven
`tion will become clear from its description in the speci?
`cation that follows and from the novel features particu
`larly pointed out in the appended claims. Therefore, to
`the accomplishment of the objectives described above,
`this invention consists of the features hereinafter illus
`trated in the drawings, fully described in the detailed
`description of the preferred embodiment and particu
`larly pointed out in the claims. However, such drawings
`and description disclose but one of the various ways in
`which the invention may be practiced.
`
`6
`DETAILED DESCRIPTION OF THE
`INVENTION
`The heart of this invention lies in the recognition that
`veri?cation of the correct position of a patient during
`treatment can be achieved by placing a detector be
`tween the treatment beam source and the patient, and
`placing an x-ray tube along the axis of the treatment
`beam on the opposite side of the patient. Given the
`position of the various components, a ?xed geometrical
`relationship exists that permits the direct construction
`of veri?cation images for immediate use during treat
`ment.
`Referring to the drawings, wherein like parts are
`identi?ed with like symbols and numerals throughout
`this‘ speci?cation, FIG. 2 illustrates in schematic eleva
`tional representation the veri?cation apparatus 20 of
`this invention, shown as an attachment to a standard
`radiation treatment unit (as illustrated in FIG. 1). An
`x-ray tube 22 is mounted on a support bracket 24 on the
`bottom side of the gantry 4, possibly replacing the de
`tector 14 shown in FIG. 1. The x-ray tube is positioned
`facing up along the axis A of the beam radiated by the
`linac head 2, so that the axis of the x-ray beam is coaxial
`with that of the treatment beam. At the same time, a
`bracket 25 supporting a detector 26 is mounted on the
`gantry (or otherwise placed in the same position) be
`tween the patient P and the linac head, as close to the
`patient as practicable. Thus, the detector 26 may be
`exposed either to the high-energy beam HR produced
`by the linear accelerator head 2 or to the low-energy
`beam LR (x rays) produced by the x-ray tube 22, or to
`both beams at the same time.
`FIG. 3 is a diagrammatic representation of the geo
`metrical relationship of the various points of interest in
`the apparatus of FIG. 2. Point 2' represents the location
`of the source of high-energy radiation HR emitted by
`the linac head 2 and contained by the boundary 8' of the
`shielding blocks 8; similarly, point 22' corresponds to
`the location of the coaxial source of low-energy radia
`tion LR emitted by the x-ray tube 22; and the line A’
`corresponds to the axis common to the two beams. Line
`26' represents the location of the detector 26 and point
`P’ represents a point at the boundary of the target vol
`ume. S, and 8,1 are the distances of the high-energy
`radiation source (therapeutic) and the low-energy radia
`tion source (diagnostic), respectively, from the detec
`tor. Obviously, the view of point P’ on the detector 26’,
`as projected by the x-ray beam, is different from the
`view seen on the same plane by the treatment beam.
`Point P’ is projected a distance X4 from the axis by the
`diagnostic beam (LR), but it is seen (back-projected) at
`a distance X; from the axis by the treatment beam (HR).
`The relationship between Xdand X, is a function of the
`distance cl between the detector 26' and the point P’, the
`two being obviously the same for d=0. Simple trigo
`nometry permits the determination of the following
`general relationship between these variables:
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`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is an elevational schematic representation of a
`typical radiation therapy unit.
`FIG. 2 is an elevational schematic representation of
`the apparatus of the present invention, illustrated as an
`attachment to the typical radiation therapy unit shown
`in FIG. 1.
`FIG. 3 is a diagrammatic representation of the geo
`metrical relationship of the various points of interest in
`the apparatus of FIG. 2.
`7
`FIG. 4 shows, with reference to the geometry of the
`therapeutic unit represented in FIG. 3, the distance at
`which a diagnostic image must be positioned from the
`simulated radiation source’s position in a shielding
`block cutter in order to have perfect correspondence
`with a picture produced with a simulator.
`FIG. 5 illustrates in schematic form the us of a fluo
`rescent screen detector in conjunction with a mirror
`and a video camera to produce real-time veri?cation
`images with the apparatus of the invention.
`
`Xd=X,(l+d/S,)/(l-d/Sd),
`
`(l)
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`65
`
`where S, and S4 are the distances of the high-energy
`radiation source and the low-energy radiation source,
`respectively, from the'detector.
`Therefore, for a given physical con?guration of the
`equipment (i.e., for given values of 5,1, S, and d), the
`relationship between any point in the image created by
`the x-ray tube and the location of the same point in the
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`Varian Exhibit 2007, Page 007
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`5,233,990
`7
`corresponding image seen on the detector by the thera
`peutic beam is linear and ?xed. That is, one can be
`obtained from the other by a simple parallax correction
`according to the equation given above. Therefore, the
`?eld of view of the therapeutic beam on the detector
`can be correlated to the image projected on the plane by
`the diagnostic beam by a simple computation, and the
`two ?elds of view can be compared for veri?cation
`purposes.
`In practice, shielding blocks will have been manufac
`tured as outlined above and the veri?cation task before
`treatment is directed at ensuring that the treatment
`beam, as attenuated by the blocks, is irradiating the
`target area delineated in the original diagnostic picture.
`If that picture was taken using a conventional simulator
`(i.e., an x-ray machine with the exact same geometry of
`the treatment unit), the shielding blocks are developed
`by conventional techniques so that the outline of the
`permitted ?eld of view of the treatment beam coincides
`with the area delineated by the physician on the diag
`nostic image. If, for example, point P’ corresponds to a
`point in the diagnostic image outlined by the physician
`as a boundary for radiation, the shielding blocks are
`shaped to permit the treatment beam to irradiate the
`area between the axis A’ and point P’ only, and the
`object of veri?cation is to see whether that point is
`indeed at the boundary of the therapeutic beam during
`treatment. As mentioned above, current practice in
`volves taking a picture with the high-energy treatment
`beam and a detector below the patient, so that the new
`image can in theory be compared with the diagnostic
`image. Unfortunately, though, the poor quality of the
`image obtained with the high-energy treatment beam
`renders it, in many cases, nearly useless in practice.
`The present invention addresses this problem by pro
`ducing a coaxial image taken with an x-ray machine. By
`creating an x-ray image on the detector 26 through
`exposure to a low-energy beam from the tube 22, a good
`quality image of a patient’s anatomy is obtained that can
`be corrected by the parallax relationship given above to
`produce an exact replica of the corresponding image
`seen by the therapeutic beam. Therefore, the resulting
`corrected picture is in the same scale of, and can be
`directly compared with, the original diagnostic image
`outlined for targeting the treatment area. As this can be
`done just before treatment, when the patient is posi
`tioned for therapeutic irradiation, it can be an extremely
`useful tool for therapy veri?cation. In addition, the
`veri?cation image can be superimposed on an image
`obtained by exposing the detector on the plane 26’ to
`the shielded therapeutic beam, which in practice will
`only show the contour of the shield (i.e., the boundary
`of the radiation ?eld) because of the high-energy radia
`tion. These two pictures combined correspond exactly
`to the ?eld of radiation currently targeted by the treat
`ment beam. Therefore, they provide the radiotherapist
`with a current veri?cation of the area targeted for treat
`ment.
`According to another method of use of the apparatus
`of this invention, it is possible to use the x-ray tube 22
`also for the initial diagnostic image (normally taken on
`?lm); that is, it may be used as a substitute for the con
`ventional simulator. In that case, the position of the
`diagnostic ?lm in the shielding-block cutter can be ad
`justed to permit its use to cut the shielding blocks as if
`the diagnostic image had been produced by a simulator.
`As would be obvious to one skilled in the art, FIG. 4
`shows that for a given geometry of the therapeutic unit,
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`taken for example as illustrated in FIG. 3, there exists a
`distance Y at which the ?lm must be positioned from
`the simulated high-energy radiation source’s position in
`the shielding-block cutter in order to have perfect cor
`respondence with a picture produced with a simulator.
`Again, simple trigonometry shows that distance is given
`by the following equation:
`
`Y=S,(l +d/S;)/(l —d/S,1).
`
`(2)
`
`Thus, this procedure eliminates the need for a simulator
`as a separate piece of equipment. Moreover, since both
`diagnostic and veri?cation images are taken with the
`same equipment, the x-ray source 22, no correction of
`the veri?cation images is required for comparison with
`the target area in the diagnostic image. The two sets of
`pictures are automatically available in the same scale,
`taken from the same point and perspective, and of the
`same acceptable quality. The only requirement is the
`parallax correction of the radiation ?eld boundary pro
`duced by the treatment beam HR as a superimposed
`image on the detector, so that it is converted to the same
`scale of the veri?cation image. Equation 1 above is used
`for this correction.
`Finally, because this invention does not require
`movement of the patient or of the treatment unit, it is
`suitable for on-line, real-time, application, which ren
`ders it particularly valuable for radiation therapy. Many
`detectors exist that produce a real-time image, either
`directly or through computerized image enhancement
`processes. For example, FIG. 5 illustrates in schematic
`form the use of a ?uorescent screen detector in conjunc
`tion with a mirror and a video camera to produce real
`time veri?cation images with the apparatus of the in
`vention. By appropriately positioning the mirror (such
`as, for example, at a 45 degree angle with the detector),
`the video camera can be placed outside the therapeutic
`?eld of radiation (at a 90 degree angle with the detec
`tor), so that the image created on the ?uorescent screen