(12) United States Patent
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`Lee
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`(10) Patent No.:
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`(45) Date of Patent:
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`Us 6,546,073 B1
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`Apr. 8, 2003
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`US006546073B1
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`Primary Examiner—David V. Bruce
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`(74) Afmmeyi Agent;
`07’
`Fi7’m—Th0H1aS, Kayden,
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`Horstemeyer & Risley, LLP
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`(57)
`ABSTRACT
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`Systems and methods for providing an optimal treatment
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`plan for delivering a prescribed radiation dose to a pre-
`defined target volume Within a patient using an external
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`beam radiation delivery unit are provided. The systems have
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`an interface which is adapted to receive information related
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`to a prescribed radiation dose, a predefined target volume
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`Within a patient, and parameters associated with an external
`beam delivery unit. The systems also have a treatment plan
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`modeling processor which is adapted to receive all of the
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`input data and develop a dose calculation optimization
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`model defining a global System. The Systems also have an
`Qptimizatign prgcessgr
`is adapted [0 determine an
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`optimal treatment plan based on the dose calculation opti-
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`mization model and all the input data. The methods involve
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`(1) receiving information related to the prescribed radiation
`dose, the predefined target volume, and parameters associ-
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`ated with the external beam delivery unit, (2) developing a
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`dose calculation optimization model based on a plurality of
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`variables corresponding to the information which define a
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`global system, and (3) outputting an optimal treatment plan
`based on the dose calculation optimization model and the
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`information
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`27 Claims, 4 Drawing Sheets
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`(54) SYSTEMS AND METHODS FOR GLOBAL
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`()pT[M[ZAT[()N OF TREATMENT
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`PLANNING FOR EXTERNAL BEAM
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`RADIATION THERAPY
`Inventor: Eva K. Lee, Atlanta, GA (US)
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`(75)
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`(73) Assignee: Georgia Tech Research Corporation,
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`Atlanta, GA (Us)
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`( * ) Notice:
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`Subject. to any disclaimer, the term of this
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`Patent 15 extended or adlusted under 35
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`U-S-C 154(b) by 60 daY5-
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`(21) Appl. No.: 09/706,915
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`(22) Bled’
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`NOV’ 6’ 2000
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`Related US_ Application Data
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`Provisional application No. 60/164,029, filed on Nov. 5,
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`1999.
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`(60)
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`(51)
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`7
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`................................................ .. A61N 5/10
`Int. Cl.
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`U.S. CI.
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`(58) Field of Search ........................... .. 378/64, 65, 901
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`References Cited
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`U'S' PATENT DOCUMENTS
`7/1991 Bova et al.
`........... .. 128/653 R
`5,027,818 A
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`5,373,844 A
`12/1994 Smith et a1-
`128/6531
`---- --
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`5:458:15 A
`10/1995 Sehweikard ~~~~ ~~
`128/6534
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`9/1996 Shin eta1'
`“““ " 578/151
`5555385 A
`
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`2/1997 Llacer .................... .. 378/65
`5,602,892 A
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`5,748,700 A
`5/1998 Shepherd et al.
`378/65
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`5,815,547 A
`9/1998 Shepherd . . . . . . . . . .
`. . . .. 378/65
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`5,879,281 A
`3/1999 Ein—Gal
`....................... .. 600/1
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`(56)
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`5,945,684 A
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`6,044,126 A
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`6,260,005 B1 *
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`* Cited by examiner
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`8/1999 Lam et al.
`............. .. 250/492.3
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`3/2000 Rousseau et al.
`........... .. 378/65
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`7/2001 Yang et al.
`................. .. 703/11
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`EXTERNAL BEAM
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`RADIATION
`DELIVERY UNIT
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`TARGET
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`VOLUME
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`20
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`VISUAL EVALUATION
`FUNCTIONALITY
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`14
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`TREATMENT PLAN
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`MODELING MODULE
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`GLOBAL OPTIMIZATION
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`MODULE
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`16
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`INPUT DATA
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`3-D IMAGING
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`SYSTEM
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`Page 1 of 16
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`Elekta Exhibit 1006
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`Page 1 of 16
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`Elekta Exhibit 1006
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`U.S. Patent
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`Apr. 8, 2003
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`Sheet 1 of4
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`US 6,546,073 B1
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`N.‘
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`U.S. Patent
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`Apr. 8, 2003
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`Sheet 2 of4
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`US 6,546,073 B1
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`U.S. Patent
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`Apr. 8, 2003
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`Sheet 4 of 4
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`US 6,546,073 B1
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`Determine optimal solution to
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`global mathematical expression
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`using branch-and—bound
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`algorithm
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`48
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`Determine dose calculation
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`optimization model incorporating
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`variables, constraints, and
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`clinical objective into global
`mathematical expression
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`Determine type for each variable
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`to include in treatment plan
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`optimization model (non~
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`negative continuous variable or
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`0/1 integer variable
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`Receive information related to
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`the prescribed radiation dose
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`proximal critical structures)
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`Receive information related to
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`the target volume (e.g. spatial
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`orientation of target volume,
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`surrounding normal tissue,
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`50
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`34
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`36
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`Receive information related to
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`parameters associated with
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`external beam delivery unit
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`38
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`44
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`Determine variables to include in
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`treatment plan optimization
`model
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`Receive information related to
`the constraints to be
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`incorporated into treatment plan
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`optimization model (eg
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`dosimetric constraints, beam
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`geometry and parameter
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`constraints)
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`40
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`42
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`Receive predefined clinical
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`objective for treatment plan
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`optimization model
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`FIG. 4
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`US 6,546,073 B1
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`1
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`SYSTEMS AND METHODS FOR GLOBAL
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`OPTIMIZATION OF TREATMENT
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`PLANNING FOR EXTERNAL BEAM
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`RADIATION THERAPY
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`CROSS REFERENCE TO RELATED
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`APPLICATION
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`This application claims the benefit of U.S. Provisional
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`Application No. 60/164,029, filed Nov. 5, 1999, which is
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`also incorporated herein by reference.
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`FIELD OF THE INVENTION
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`The present invention relates generally to treatment plan-
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`ning for external beam radiation therapy, and more
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`particularly, to systems and methods for global optimization
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`of treatment planning for external beam radiation therapy.
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`BACKGROUND OF THE INVENTION
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`External beam radiation therapy is a well-known treat-
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`ment option available to the radiation oncology and neuro-
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`surgery communities for treating and controlling certain
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`central nervous systems lesions, such as arteriovenous
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`malformations, metastatic lesions, acoustic neuromas, pitu-
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`itary tumors, malignant gliomas, and other intracranial
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`tumors. As the name implies, the procedure involves the use
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`of external beams of radiation directed into the patient at the
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`lesion using either a gamma unit (referred to as a Gamma
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`Knife), a linear accelerator, or similar beam delivery appa-
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`ratus. Although treating the lesions with the radiation pro-
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`vides the potential for curing the related disorder, the prox-
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`imity of critical normal structures and surrounding normal
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`tissue to the lesions makes external beam radiation therapy
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`an inherently high risk procedure that can cause severe
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`complications. Hence,
`the primary objective of external
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`beam radiation therapy is the precise delivery of the desired
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`radiation dose to the target area defining the lesion, while
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`minimizing the radiation dose to surrounding normal tissue
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`and critical structures.
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`The process of treating a patient using external beam
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`radiation therapy consists of three main stages. First, a
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`precise three-dimensional map of the anatomical structures
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`in the location of interest (target volume) is constructed
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`using any conventional
`three-dimensional
`imaging
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`technology, such as computed tomography (CT) or magnetic
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`resonance imaging (MRI). Second, a treatment plan is
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`developed for delivering a predefined dose distribution to
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`the target volume that is acceptable to the clinician. Finally,
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`the treatment plan is executed using an accepted beam
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`delivery apparatus.
`Thus,
`the basic strategy of external beam radiation
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`therapy is to utilize multiple beams of radiation from mul-
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`tiple directions to “cross-fire” at the target volume. In that
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`way, radiation exposure to normal tissue is kept at relatively
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`low levels, while the dose to the tumor cells is escalated.
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`Thus, the main objective of the treatment planning process
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`involves designing a beam profile, for example, a collection
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`of beams, that delivers a necrotic dose of radiation to the
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`tumor volume, while the aggregate dose to nearby critical
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`structures and surrounding normal
`tissue is kept below
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`established tolerance levels.
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`One existing method for treatment planning in external
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`beam radiation therapy is standard manual planning. This
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`method is referred to as forward planning because the
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`physician solves the direct problem of determining the
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`appropriate dose distribution given a known set of beam
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`10
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`15
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`20
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`25
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`55
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`60
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`65
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`2
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`In other
`characteristics and beam delivery parameters.
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`words, standard manual planning involves a trial-and-error
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`approach performed by an experienced physician. The phy-
`sician attempts to create a plan that is neither complex nor
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`difficult
`to implement in the treatment delivery process,
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`while approximating the desired dose distribution to the
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`greatest extent possible. For instance,
`the physician may
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`choose how many isocenters to use, as well as the location
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`in three dimensions, the collimator size, and the weighting
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`to be used for each isocenter. Atreatment planning computer
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`may calculate the dose distribution resulting from this
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`preliminary plan. Prospective plans are evaluated by view-
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`ing isodose contours superimposed on anatomical images
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`and/or with the use of quantitative tools such as cumulative
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`dose-volume histograms (DVH’s).
`Standard manual planning has many disadvantages. This
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`iterative technique of plan creation and evaluation is very
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`cumbersome, time-consuming, and far from optimal. Thus,
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`manual planning results in much higher costs for patients
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`and insurers. The physician or other experienced planner can
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`evaluate only a handful of plans before settling on one. Thus,
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`standard planning has very limited success in improving
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`local tumor control or reducing complications to normal
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`tissue and critical structures, and as a result, greatly limits
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`the quality-of-life for patients. In standard manual planning,
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`there is no mechanism for allowing the advance imposition
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`of clinical properties, such as, for example, an upper bound
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`on dose received by normal tissue or the specific shape of
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`dose-response curves to the tumor and to critical structures,
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`on the resulting plans. Furthermore, manual planning is
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`subjective, inconsistent, far from optimal, and only enables
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`a small amount of treatment plans to be examined by the
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`physician.
`Another method for treatment planning in external beam
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`radiation therapy employs computer systems to optimize the
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`dose distributions specified by physicians based on a set of
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`preselected variables. This approach is known as inverse
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`planning in the medical community because the computer
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`system is used to calculate beam delivery parameters that
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`best approximate the predetermined dose, given a set of
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`required doses, anatomical data on the patient’s body and the
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`target volume, and a set of preselected or fixed beam
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`orientation parameters and beam characteristics. In order to
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`solve the complex problem of arriving at an optimal treat-
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`ment plan for the domain of possible variables, all existing
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`methods of inverse treatment planning fix at least a subset of
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`the set of variables. For example, a particular modality of
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`external beam radiation therapy may include the following
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`domain of possible variables: (1) number of beams, (2)
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`configuration of beams, (3) beam intensity, (4) initial gantry
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`angle, (5) end gantry angle, (6) initial couch angle, (7) end
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`couch angles, (8) prescription dose, (9) target volume, and
`(10) set of target points. State of the art inverse treatment
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`planning approaches preselect a subset of these variables
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`and fix them during the optimization calculation.
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`Despite its obvious advantages over the standard manual
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`approach, existing inverse treatment planning approaches
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`have several disadvantages and inadequacies. As described
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`above,
`these approaches do not
`incorporate each of the
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`domain of possible variables into the optimization calcula-
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`tion. Instead, these approaches fix at least a subset of these
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`variables to arrive at an “optimal” treatment plan. This type
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`of “local optimization” is inherently problematic because it
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`does not allow the full flexibility of choosing different, beam
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`geometries, beam orientation parameters, and beam
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`parameters, imposing dose limits, and placing constraints on
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`physical planning parameters.
`In other words,
`these
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`4
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`treatment plan optimization model. Employing a true global
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`optimization approach,
`the treatment plan optimization
`model incorporates all of the physical and clinical variables
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`related to the external beam delivery unit and the target
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`volume that define the global system. The systems also have
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`a global optimization module which is adapted to determine
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`an optimal
`treatment plan based on the treatment plan
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`optimization model and all the input data. The systems may
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`also include a visual evaluation functionality which is
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`adapted to display information related to the optimal treat-
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`ment plan to a physician.
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`The present invention can also be viewed as providing
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`methods for providing an optimal treatment plan for deliv-
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`ering a prescribed radiation dose to a predefined target
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`volume within a patient using an external beam radiation
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`delivery unit. Briefly, one such method involves (1) receiv-
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`ing information related to the prescribed radiation dose, the
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`predefined target volume, and parameters associated with
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`the external beam delivery unit, (2) developing a treatment
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`plan optimization model based on a plurality of variables
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`corresponding to the information, and (3) outputting an
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`optimal treatment plan based on the treatment plan optimi-
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`zation model and the information.
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`Other systems, methods, features, and advantages of the
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`present invention will be or become apparent to one with
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`skill in the art upon examination of the following drawings
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`and detailed description. It is intended that all such addi-
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`tional systems, methods, features, and advantages be
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`included within this description, be within the scope of the
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`present invention, and be protected by the accompanying
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`claims.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
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`3
`approaches do not enable “global optimization” of treatment
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`planning for external beam radiation therapy. Therefore,
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`these approaches are limited by “less than optimal” treat-
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`ment plans and, consequently, are unable to adequately
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`control tumor growth or reduce normal tissue complications.
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`Furthermore, there are an infinite number of possible treat-
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`ment plans in inverse treatment planning, and existing
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`methods only look at a small subset of potential plans and
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`select the “best” from the subset. Thus, the resulting treat-
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`ment plan is not a globally optimal plan.
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`Furthermore, existing inverse treatment planning are not
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`well-suited for use with newer external beam radiation
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`therapy modalities. Recent
`technological advances have
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`resulted in sophisticated new devices and procedures for
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`external beam radiation delivery, such as, for example,
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`high-resolution multi-leaf collimators, intensity-modulated
`radiation therapy (IMRT), and non-coplanar arc stereotactic
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`radiosurgery (NASR). Unlike conventional radiation
`therapy where radiation profiles are altered via the use of a
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`limited number of wedges, beam blocks and compensating
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`these new devices and procedures allow a large
`filters,
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`collection of beams to be shaped in any desired fashion with
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`regard to both the geometrical shape and fluence across the
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`field to create fixed or moving nonuniform beams of photons
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`or charged particles. While the flexibility and precise deliv-
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`ery capability resulting from these advances is clearly
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`advantageous, their full potential cannot be realized using
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`“local optimization” schemes which do not incorporate each
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`of the domain of possible variables into the optimization
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`calculation, but instead fix at least a subset of these variables
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`to arrive at an “optimal” treatment plan.
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`Thus, an unaddressed need exists in the industry to
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`address the aforementioned deficiencies and inadequacies.
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`SUMMARY OF THE INVENTION
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`invention solves the problems described
`The present
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`above by providing systems and methods for providing a
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`globally optimal treatment plan for delivering a prescribed
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`radiation dose to a target tumor volume within a patient
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`using an external beam radiation source. The present inven-
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`tion enables a physician performing external beam radiation
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`therapy to develop a globally optimal treatment plan, which
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`results in improved patient care and improved efficiency. For
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`example, in the field of external beam radiation therapy, the
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`invention reduces normal
`tissue complications,
`present
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`improves tumor control, enables physicians to evaluate a set
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`of globally optimal solutions, reduces the time and cost
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`associated with producing a treatment plan, eliminates trial
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`and error visual optimization, enables physicians to perform
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`radiation therapy in complex situations, such as where
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`critical structures are near the tumor, improves the percent-
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`age of tumor volume covered by a prescription isodose line,
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`reduces the ratio of the maximum dose to the prescribed
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`dose, improves the ratio of the volume of the prescribed
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`isodose surface to the target volume, and improves the ratio
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`of the maximum dose received by normal tissue to the
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`prescribed dose.
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`Briefly described, the systems according to the present
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`invention for providing an optimal treatment plan have three
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`main components. The systems have an interface which is
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`adapted to receive information related to a prescribed radia-
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`tion dose, information related to a predefined target volume
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`within a patient, and information related to parameters
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`associated with an external beam delivery unit. The systems
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`also have a treatment plan modeling module which is
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`adapted to receive all of the input data and develop a
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`10
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`15
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`20
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`25
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`30
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`35
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`Page 7 of 16
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`The systems and methods according to the present inven-
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`tion can be better understood with reference to the following
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`drawings.
`FIG. 1 is a functional block diagram of one embodiment
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`of a system according to the present invention.
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`FIG. 2 is a functional block diagram of another embodi-
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`ment of a system according to the present invention.
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`FIG. 3 is a block diagram of a preferred implementation
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`of the system illustrated in FIG. 2.
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`FIG. 4 is a flowchart illustrating the functionality and
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`operation of the system illustrated in FIGS. 2 and 3.
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`DETAILED DESCRIPTION OF THE
`
`
`INVENTION
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`Having summarized the invention above, reference is now
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`made in detail to the description of the invention as illus-
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`trated in the drawings. While the invention will be described
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`in connection with these drawings, there is no intent to limit
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`to the embodiment or embodiments disclosed. On the
`it
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`contrary, the intent is to cover all alternatives, modifications
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`and equivalents included within the spirit and scope of the
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`invention as defined by the appended claims.
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`System Overview
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`FIG. 1 illustrates a functional block diagram of a preferred
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`embodiment of a system 10 according to the present inven-
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`tion for enabling global optimization of treatment planning
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`for external beam radiation therapy. System 10 is connected
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`to an external beam delivery unit 12, visual evaluation
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`functionality 14, and three-dimensional imaging system 16.
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`External beam delivery unit 12 may be any conventional
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`equipment used in external beam radiation therapy for
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`delivering doses of radiation to a target volume 20 within a
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`Page 7 of 16
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`US 6,546,073 B1
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`5
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`5
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`patient, such as, for example, a linear accelerator (LINAC),
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`a Gamma Knife, or any other external device capable of
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`providing a radiation source. External beam delivery unit 12
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`may comprise a plurality of external beams having variable
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`intensity, a plurality of collimators for adjusting the size of
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`the beams, and a mechanism for moving the unit with
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`respect to a patient positioned within a stereotactic frame in
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`order to adjust the angle and entry point of each radiation
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`beam.
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`System 10 also contemplates using various radiation
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`modalities with external beam delivery unit 12. For
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`example, system 10 may be used with static conformal
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`radiation therapy (SCRT), non-coplanar arc stereotactic
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`radiosurgery (NASR), intensity modulated radiation therapy
`(IMRT), and intensity modulated arc therapy (IMAT).
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`SCRT involves the use of three-dimensional computer
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`planning systems to geometrically shape the radiation field
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`to ensure adequate coverage of the target, while sparing
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`normal tissue. The tools for SCRT include patient-specific
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`CT data, beam’s-eye-view (BEV) treatment planning, and
`multileaf collimators (MLC). Guided by the target contours
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`identified in the CT images, beam orientations are chosen
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`and beam apertures are accurately delineated using BEV.
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`The beam aperture can be fabricated with conventional
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`blocks or defined by MLC. The dose distribution within the
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`field is determined by choice of beam intensity and simple
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`modulators such as wedges and tissue compensators.
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`NASR is a technique used for treating brain tumors.
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`Radiosurgery is distinguished from conventional external
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`beam radiation therapy of the central nervous system by its
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`localization and treatment strategy.
`In radiosurgery,
`the
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`target volume of tissue is much smaller (tumors 10-35 mm
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`in diameter), the number of fractions (treatment sessions) is
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`much less, and the dose per fraction is much larger than in
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`conventional radiotherapy. Radiosurgery involves the use of
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`external beams of radiation guided to a desired point within
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`the brain using a precisely calibrated stereotactic frame
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`mechanically fixed to the head, a beam delivery unit, such as
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`a LINAC Gamma Knife, and three-dimensional medical
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`imaging technology. For LINAC radiosurgery, the table on
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`which the patient lies and the beam delivery unit are capable
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`of rotating about distinct axes in order to adjust the angle and
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`entry point of a radiation beam. The tissue affected by each
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`beam is determined by the patient’s position within the
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`stereotactic frame, by the relative position of the frame in
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`relation to the beam delivery unit, by collimators that adjust
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`the size of the beam, and by the patient’s anatomy.
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`Additionally, the intensity of each beam can be adjusted to
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`govern its dose contribution to each point.
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`IMRT is a recently developed treatment modality in
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`radiotherapy. In IMRT the beam intensity is varied across
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`the treatment field. Rather than being treated with a single,
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`large, uniform beam, the patient is treated instead with many
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`very small beams, each of which can have a different
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`intensity. When the tumor is not well separated from the
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`surrounding organs at risk—such as what occurs when a
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`tumor wraps itself around an organ—there may be no
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`combination of uniform intensity beams that will safely
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`separate the tumor from the healthy organ. In such instances,
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`adding intensity modulation allows more intense treatment
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`of the tumor, while limiting the radiation dose to adjacent
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`healthy tissue.
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`IMAT is a form of IMRT that involves gantry rotation and
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`dynamic multileaf collimation. Non-coplanar or coplanar
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`arc paths are chosen to treat the target volume delineated
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`from CT images. The arcs are chosen such that intersecting
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`a critical structure is avoided. The fluence profiles at every
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`rotates, the dynamic MLC modulates the intensity to deliver
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`the dose to the target volume while sparing normal tissue.
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`The large number of rotating beams may allow for a more
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`conformal dose distribution than the approach of multiple
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`intensity modulated beams.
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`Thus, the systems and methods of the present invention
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`are not limited to a particular type of external beam delivery
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`unit 12 or a particular modality, but instead may employ any
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`type of external beam delivery unit or radiation modality.
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`Visual evaluation functionality 14 may be any conven-
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`tional imaging module adapted to interface with system 10
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`and capable of visually displaying an optimal treatment plan
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`for delivering radiation to a patient using external beam
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`delivery unit 12. Visual evaluation functionality 14 may be
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`a computer monitor, a television monitor, any type of
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`printout from a computer, or any other imaging module used
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`by physicians to evaluate the effectiveness of a particular
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`treatment plan for a patient. For example, visual evaluation
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`functionality 14 may be configured to enable physicians to
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`view dose-volume histograms and isodose surfaces for a
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`treatment plan overlayed with a diagram of the target
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`volume and surrounding areas, including normal surround-
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`ing tissue and critical structures.
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`Three-dimensional imaging system 16 may be any three-
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`dimensional imaging technology used to delineate target
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`volume 20 of a tumor or similar region within a patient, such
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`as, for example, a computed tomography (CT) system, a
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`magnetic resonance imaging (MRI) system, or any similar
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`system. It should be understood by skilled persons in the art
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`that there are many ways to capture images of lesions within
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`a human body, and, therefore, this invention should not be
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`limited to any particular type of imaging system. The
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`important aspect is that imaging system 16 is capable of
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`identifying the contours of target volume 20 along with
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`surrounding normal tissues and critical structures.
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`As shown in FIG. 1, system 10 comprises two main
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`components: global optimization module 22 and treatment
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`plan