US0058 1 8902A
`
`United States Patent
`
`[.9]
`
`[11] Patent Number:
`
`5,818,902
`
`Yu
`
`[54]
`
`lN'l‘l*‘.NSlTY M()l)Ul.A'l‘l~3l) ARC 'l‘HF.RAPY
`WITH DYNAMIC MULTI-LEAF
`COLLIMATION
`
`[75]
`
`Inventor: Cedric X. Yu, Bloomfield Ilills, Mich.
`
`[73] Assignce: Elekta AB, Stockholm, Sweden
`
`[21] Appl. No.: 609,457
`
`[22]
`
`Filed:
`
`Mar. 1, 1996
`
`Int. Cl." ..................................................... .. A6lN 5/10
`[51]
`[52] US. Cl.
`............................................. .. 378/65; 3781151
`[58] Field of Search
`378x65, 147, 150,
`378/151, 152; 250l492,3, 505.1
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`........................ 378/65 X
`5,160,847 11/1992 Leavitt et al.
`5,351,280
`911994 Swerdloff et al.
`.
`5,394,452
`2/’ 1995 Swerdloff et al. .
`5,418,827
`5/1995 Deasy et al, .
`5,442,675
`8/' 1995 Swerdlotf et al. .
`5,555,283
`9/1996 Shiu et al.
`............................ 378.r‘65 X
`5,596,619
`1/1997 Carol ......................................... 378.365
`
`OTHER PUBLICATIONS
`
`McGraw—llill Encyclopedia of Science & Technology, 6th
`Edition, vol. 13, pp. 110, 112, and 126-129 (1987).
`McGmw—Hill Encyclopedia of Science & Technology, 6th
`Edition, vol. 15, pp. 154 and 155 (1987).
`
`[45] Date of Patent:
`
`Oct, 6, 1998
`
`Mc(:‘raw—Hill Encyclopedia of Science & 'I'ecImolngy 6th
`Edition, vol. 2, p. 506 (1987).
`McGruw—Hill Enc__vclo}x4dia of Science & Teclmulugy, 6th
`Edition, vol. 10, pp. 568-571 (1987).
`McGraw—Hill Encyclopedia of Science & Technology, 6th
`Edition, vol. 13, pp. 413 and 414 (1987).
`McGraw—HilI Encyclopedia of Science & Technology, 6th
`Edition, vol. 15, pp. 138 and 139 (1987).
`McGmw—Hill Encyclopedia of Science & leclmology, 6th
`Edition, vol. 4, pp. 292-293 (1987).
`McGraw-Hill Encyclopedirl of Science & Teclmology, 6th
`Edition, vol. 18, pp. 28 and 29 (1987).
`
`Primary l:'xaminer—l)avid P. Pona
`Attorney, Agent, or Fir/n—Jaek D. Slobod; Dwight H.
`Renfrew
`
`[57]
`
`ABSTRACT
`
`A method and apparatus for delivering optimized treatment
`plans to deliver relatively high doses of ionizing radiation to
`target
`tissues while minimizing dose to the surrounding
`healthy tissues. The present invention utilizes continuous
`gantry motion in which field shape, which is conformed with
`a multi-leaf collimator, changes during gantry rotation.
`Using multiple superimposing ares, arbitrary two-
`dimensional beam intensity distribution at different beam
`angles can be delivered, giving arbitrary dose distribution in
`the patient to maximize the therapeutic ratio.
`
`25 Claims, 9 Drawing Sheets
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`Page 1 of 18
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`Elekta Exhibit 1008
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`U.S. Patent
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`Oct. 6, 1998
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`Fig—2a
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`U.S. Patent
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`Oct. 6, 1998
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`Sheet 3 of 9
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`E:
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`U.S. Patent
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`Oct. 6, 1998
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`WAIT
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`j PAUSE/TERMINATE
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`INHIBIT RADIATION
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`U.S. Patent
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`Oct. 6, 1998
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`Sheet 7 of 9
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`5,818,902
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`Fig—9a
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`Volume(%)
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`U‘! 0
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`M O
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`Page 8 of 18
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`U.S. Patent
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`Oct. 6, 1998
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`Sheet 8 of 9
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`5,818,902
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`Fig—10a
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`100
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`— 90
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`Page 9 of 18
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`Sheet 9 of 9
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`5,818,902
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`NW‘
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`Page 10 of 18
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`Page 10 of 18
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`5,818,902
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`
`
`1
`INTENSITY MODULATED ARC THERAPY
`
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`WITH DYNAMIC MULTI-LEAF
`
`
`
`COLLIMATION
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`BACKGROUND OF THE INVENTION
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`1. Technical Field
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`This invention relates to radiation therapy. Particularly,
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`the present invention relates to a method and apparatus for
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`delivering optimal radiation dose to cancer patients to
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`improve the therapeutic ratio. The apparatus of the present
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`invention relies upon a radiation generating device equipped
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`with a rotatable gantry and a computer controlled multi-leaf
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`collimator. The method of the present invention is referred
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`to as intensity modulated arc therapy. It combines irradiation
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`with gantry rotation and change of radiation field shapes.
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`Each such rotation delivers a focused radiation dose to the
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`tumor site. Arbitrary three-dimensional radiation dose dis-
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`tributions can be delivered with multiple superimposing
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`arcs.
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`2. Discussion
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`Radiation therapy is intended to irradiate a tumor to high
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`levels of radiation dose such that the growth of the tumor is
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`halted and, preferably, all tumor cells are destroyed. Where
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`it is not possible to destroy all cells of a tumor, radiation
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`therapy is employed to reduce the size of the tumor so that
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`it may be surgically removed. Radiation therapy also
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`complements surgical removal of a tumor by irradiating
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`microscopic extensions of the tumor.
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`In certain situations, chemotherapy is used instead of
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`surgical removal with radiation therapy. This combination
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`minimizes the toxicity on healthy cells normally effected by
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`high doses of chemotherapy drugs administered alone.
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`The delivery of radiation in radiation therapy is a skilled
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`art in that, in cancer therapy, the objective is to destroy a
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`tumor without causing irreparable radiation damage in nor-
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`mal body tissue which is adjacent to the target tissue. This
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`is generally made possible because of the nature of the
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`cancer cells which distinguish themselves by being quickly
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`replicating relative to normal cells. It is during the repro-
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`duction stage that cancer cells are sensitive to ionizing
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`radiation. Accordingly,
`tumor cells are more readily
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`destroyed by ionizing radiation than are normal cells
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`because of this sensitivity.
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`the cell’s chemical components. As photons or electrons
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`enter body tissue, some of the energy disrupts cellular
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`function. (Most energy is converted into heat which carries
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`no damaging biological effect.) As ionizing radiation
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`traverses the tissue, it contacts atoms, which causes them to
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`become excited. This process results in the breaking of
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`molecular bonds, followed by biological damage and cellu-
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`lar destruction.
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`While the cellular destruction caused by ionizing radia-
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`tion produces desirable lethal effects on abnormal, quickly
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`dividing cancer cells, this is not desirable for healthy cells.
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`Indeed, the greatest limitation to the broad scale use of
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`ionizing radiation in a therapy of various cancers relates to
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`the fact that in most cases the radiation beam has to traverse
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`healthy tissues in order to reach the tumor, causing damage
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`to the healthy tissues. While an increased dose of radiation
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`would be useful in curing the patient, the dose is limited by
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`the negative effects of radiation on the adjacent, normal
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`healthy tissue. Complicating radiation therapy are the two
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`types of organs, serial and parallel. In the former, radiation
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`tolerance is generally high, but the entire organ (such as
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`viscera) must be preserved to maintain minimum function.
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`In parallel organs (such as the liver or the lungs), while in the
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`latter tolerance is normally low, a substantial portion of the
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`organ may be destroyed and the organ still remains mini-
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`mally operative. Accordingly, the goal of radiation therapy
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`has been to maximally irradiate the tumor while keeping the
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`dose to adjacent structures under their tolerance or preserve
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`part of the healthy structure such that enough of the organ is
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`maintained so as to guarantee a minimal functional reserve.
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`In keeping with the goal of administering maximum
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`the delivery of radiation to healthy organs surrounding the
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`tumor, various techniques and devices have been employed.
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`Two general approaches are taken today to delivering
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`radiation therapy. One is to use multiple fields, and the other
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`is to employ arc therapy.
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`In using multiple fields, each radiation beam incident is at
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`a different orientation from the next. Since these radiation
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`beams overlap at the tumor site, a higher dose can be given
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`to the tumor than to the normal structures. To minimize the
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`exposure of healthy structures around the tumor to radiation,
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`masks of lead alloy are employed to shape each field as the
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`two dimensional projection of the treatment target.
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`therapy through the use of multiple fields, both of which are
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`related to the use of only a few fields of exposure. One
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`problem is that the dose to the healthy surrounding structure
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`(which is roughly the tumor dose divided by the number of
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`fields) is still too high. The other problem is that the ability
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`to shape the high dose volume is limited. (For example, if
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`four or fewer fields are used [as is typical],
`the tumor
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`high-dose area is substantially like a box.) Another problem
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`associated with the use of multiple fields is the length of time
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`it takes to produce the alloy blocks, which is usually a matter
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`of hours or days. Storage of the bulky blocks is also a
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`problem.
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`In arc therapy, irradiation is combined with the rotation of
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`the gantry of the radiation producing apparatus. During
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`gantry rotation, the radiation field is set to a fixed rectangular
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`shape. While delivering radiation to the target tissue, the
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`relatively large field delivers the same amount of radiation
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`to surrounding healthy tissue. The apparatus leaves in its
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`path a cylindrically-shaped swath as it completes its arc
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`around the patient.
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`However, arc therapy shares the burden of dose to all
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`structure surrounding the tumor and maximal overlap of
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`beams from all orientations. Again, at least two problems
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`result. First, there is no discrimination between structures.
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`Arc therapy treats all structures around the target tissue the
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`same way, but, as noted above, not all tissue has the same
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`tolerance. Second,
`the cylindrical shape of the delivered
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`high dose is not the typical shape of the tumor.
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`The above-noted problem related to the fabrication and
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`use of blocks in multiple field therapy is generally solved
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`with a device known as a multi-leaf collimator. This device
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`consists of opposing arrays of radiation-impregnable, mov-
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`able leaves or veins placed in front of the radiation beam. By
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`driving each vein into different positions, virtually any
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`desired field shape can be achieved in radiation therapy.
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`While directed to solving the time and labor expenses
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`related to the use of blocks, the multi-leaf collimator does
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`not solve the problems associated with conventional treat-
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`ment techniques, as discussed in the preview section.
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`Thus,
`it would be desirable to provide a means for
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`accurately shaping the high dose volume to conform to the
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`Page 11 of 18
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`

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`5,818,902
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`3
`actual three-dimensional shape of the tumor while keeping
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`the dose to all surrounding structures under their tolerance or
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`keeping the unaffected volume larger than the required
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`functional reserve.
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`SUMMARY OF THE INVENTION
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`there is provided a
`Pursuant to the present invention,
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`method and system for improving local tumor control and to
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`provide an increased cure rate for cancer patients. The
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`present invention is coupled with advances in computer
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`technology and linear accelerator design. These features
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`allow for the new method of delivering three-dimensional
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`conformal radiotherapy provided for in the present inven-
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`tion.
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`The present invention delivers high doses of ionizing
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`radiation to the target tissues while minimizing dose to the
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`surrounding healthy tissues.
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`In general, the present invention relates to a method for
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`delivering optimized treatment plans to improve the thera-
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`peutic ratio. The present invention utilizes continuous gantry
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`motion as in known arc therapy. However, unlike known arc
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`therapy, the field shape, which is conformed with the multi-
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`leaf collimator, changes during gantry rotation. The three-
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`dimensional shape of the resultant high dose volume, which
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`can only be cylindrical with known arc therapy, can take
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`more complex forms.
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`The apparatus and method for delivering radiation therapy
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`according to the present invention takes consideration of the
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`differences in tolerance levels among the various normal
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`body organs surrounding the target area.
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`The present invention also compensates for differences in
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`homogenous overlapping structures. For example, if in one
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`direction there is an air space in the body, the path to the
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`tumor is less than if that space was filled with tissue. The
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`present invention compensates for such density differences.
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`In addition, by taking consideration of the differences in
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`normal structure tolerances and by compensating for the
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`differences in homogenous overlapping structures, angle
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`preferences are created.
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`Furthermore, by again taking consideration of the differ-
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`ences in normal structure tolerances and by compensating
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`for the differences in homogenous overlapping structures,
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`intensity preference within a beam angle may be created.
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`The present invention also provides a system of delivering
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`the intensity-modulated arc therapy of the present invention.
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`The intensity-modulated arc therapy of the present inven-
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`tion combines spatial and temporal intensity modulation
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`with the movement of the gantry. It can be shown that the
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`dose conformity is theoretically equivalent to that achiev-
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`able with slice-based treatment
`techniques. The present
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`invention also presents advantages over tomotherapy.
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`As with tomotherapy or other sliced delivery schemes, the
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`intensity modulated arc therapy can deliver beams with both
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`spatial and temporal intensity modulations. In comparison
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`with the sliced delivery schemes, intensity modulated arc
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`therapy has many advantages. It is implemented on existing
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`linear accelerators equipped with a multi-leaf collimator.
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`Therefore, it maintains the flexibility of a linear accelerator.
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`Electron beam therapy and traditional treatment methods
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`can coexist using the same device. Non-transaxial arc treat-
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`ments can be achieved to a certain extent and partial arc
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`rotations are easily achievable. Since a tomotherapy
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`machine is a specialized device, the conventional treatment
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`cannot be delivered.
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`With tomotherapy, a photon beam generated at the X-ray
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`target is collimated into a slit, most of the photons generated
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`Page 12 of 18
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`4
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`in the target will be blocked, resulting in inefficient beam
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`delivery and long delivery time. With intensity modulated
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`arc therapy, most of the target will be in the beam during the
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`delivery, maintaining a high efficiency in utilizing the pho-
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`tons generated in the X-ray target.
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`With tomotherapy, the patient is required to be moved in
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`his length direction to cover the entire treatment area. This
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`increases the cost and complexity of treatment. With inten-
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`sity modulated arc therapy, no additional patient transport
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`mechanisms are required to move the patient from slice to
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`slice. Eliminating the slicing also eliminates the problem of
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`beam abutment between slices, and the cold and hot spot
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`associated with the abutments. Theoretically, such an abut-
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`ment problem among slices will be much more severe if
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`patient motion between treatment slices is considered.
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`Finally, since the intensity modulation in tomotherapy
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`relies on a set of leaves to open or close the slit beam, the
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`resolution of the beam intensities is the slit width by the leaf
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`width. For practical design, such resolution is on the order
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`of 1 cm by 1 cm. The smooth three-dimensional target shape
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`has to approximated by a collection of 1 cm3 cubes.
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`Therefore, the dose conformity is limited. Such limitation is
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`most severe for smaller targets, which are more suitable for
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`conformal treatment. For intensity modulated arc therapy
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`treatments, the leaf travel is continuous in the length direc-
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`tion of the leaves. The field aperture in the leaf width
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`direction is collimated by the backup jaws and is, therefore,
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`also continuous. Therefore, intensity modulated arc therapy
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`can deliver higher dose conformity than tomotherapy.
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`The steps for employing the therapy of the present inven-
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`tion are as follows. First is the optimization of a treatment
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`plan that uses a beam every 1-5 degrees around the patient.
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`Second, besides the beam energy and prohibiting angles,
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`describe the beams at all angles (i.e., having intensity
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`distribution).
`(Appropriate methods and algorithms are
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`these first
`two steps.) Third,
`translate two-
`made for
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`dimensional intensity distributions at all beam angles into
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`arcs (i.e., field shape sequences, number of beam monitor
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`units per shape, et cet.). Fourth, write the field shape
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`sequences, the number of monitor units per shape, et cet., in
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`the format required by the multi-leaf collimator controller
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`and transfer the information to the controller. Fifth, deliver
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`the dosage.
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`One of the key steps involved in creating optimized dose
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`distributions using the present invention is directed to a
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`method to convert the intensity distributions at all beam
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`angles required by the treatment plan into multiple arcs.
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`Translation is affected by: (1) Determining the angle of
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`multi-leaf collimator veins along which the radiation fields
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`are conformed such that the field shape formed by the veins
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`best coincides with the preferred field shape for all the
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`various beam angles; (2) segmenting the two-dimensional
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`beam intensity distributions of all beam angles into multiple,
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`one-dimensional ones, each aligned with a pair of multi-leaf
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`collimator veins;
`(3) determining the openings of each
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`opposed pair of veins and the sequence of opening such that
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`no large movement
`is required between two successive
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`beam angles; (4) at every beam angle, constructing from the
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`sets of vein openings a stack of field shapes; and (5)
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`constructing arcs from the stacks of field shapes by picking
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`one shape from each beam angle.
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`The present
`invention also provides the simultaneous
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`synchronizing of radiation delivery, gantry rotation, and
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`field shape alteration. This synchronizing is accomplished
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`by slaving rotation and changes in field shape to delivered
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`radiation monitor units so that the delivery is immune to
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`machine dose rate fluctuations.
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`10
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`15
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`5,818,902
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`5
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`Since there is no need to move the patient during treat-
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`ment and radiation is not interrupted between different beam
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`angles, the treatment is also very time efficient using the
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`present invention. Total treatment time including patient
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`set-up and irradiation is comparable to or shorter than
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`conventional treatments. Beam delivery time is proportional
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`to the number of arcs required, which depends on the
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`number of intensity levels and the complexity of the inten-
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`sity distributions. The total beam time may be further
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`reduced with modifications of the linear accelerators and
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`with improved algorithms for converting the intensity dis-
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`tribution into the arc field sequences.
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`invention will
`The various advantages of the present
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`become apparent to one skilled in the art by reading the
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`following specification and by reference to the following
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`drawings, in which:
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`FIG. 1 is a perspective view illustrating a patient under-
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`going intensity-modulated arc therapy according to the
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`present invention and further illustrating the general position
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`of the apparatus for delivering the radiation and its general
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`motions;
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`FIG. 1a is a diagrammatic perspective view illustrating a
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`radiation field shaped by a multi-leaf collimator;
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`FIGS. 2a through 2d illustrate various ways to translate
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`discreet beam intensity distributions into multiple unit-
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`intensity fields with “intensity” being defined along the
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`Y-axis and “position” being defined along the X-axis;
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`FIG. 3 is a diagrammatic view of some exemplary adja-
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`cent and coplanar gantry positions achieved according to the
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`intensity-modulated arc therapy of the present invention;
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`FIG. 4 is an illustration of the data processing and system
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`control by the multi-leaf collimator controller during
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`dynamic beam delivery;
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`FIG. 5 is a treatment plan example used for the delivery
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`of intensity-modulated arc therapy according to the present
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`invention;
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`FIG. 6 represents samples of intensity distributions
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`required by the inverse treatment planning to deliver the
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`prescribed dose constraints;
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`FIG. 7 is an image illustrating a delivered dose distribu-
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`tion pattern;
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`FIGS. 8a and 8b illustrate cumulative dose volume his-
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`tograms calculated from the treatment plans;
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`FIG. 9a illustrates a treatment plan application limited to
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`five levels for a prostate treatment geometry;
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`FIG. 9b illustrates a cumulative dose volume histogram
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`produced by the treatment plan application of FIG. 9a;
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`FIG. 10a illustrates a treatment plan application limited to
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`ten levels for a prostate treatment geometry;
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`FIG. 10b illustrates a cumulative dose volume histogram
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`produced by the treatment plan application of FIG. 10a; and
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`FIG. 11 illustrates a prostate treatment plan.
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`DETAILED DESCRIPTION OF THE
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`PREFERRED EMBODIMENTS
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`Known arc therapy techniques rely upon a rotating gantry
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`that produces a fixed radiation field shape on the patient
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`which creates a cylindrical high dose region. The intensity-
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`modulated arc therapy of the present invention provides a
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`method and an apparatus for delivering an optimized dose of
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`radiation for radiation therapy to a patient by rotating the
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`radiation beam in an orbit around the patient and changing
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`Page 13 of 18
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`6
`the field shape during delivery of the therapeutic radiation.
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`Not only can the target shape be highly complex, but the
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`treatment may be optimized to assign higher weights to
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`more favored beam angles and favored areas within a beam
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`based upon both anatomical and biological constraints.
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`Therefore, for the same tumor dose, patients are exposed to
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`less radiation toxicity.
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`Referring to FIG. 1, an apparatus 10 used to provide
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`intensity-modulated arc therapy to a patient 12 according to
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`the present invention is shown. The apparatus 10 incudes a
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`movable gantry 14 and a couch 16. The gantry 14 is mounted
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`so as to allow revolution about the patient 12 as illustrated
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`by the orbit “O” shown in broken lines. The gantry 14 is also
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`movable along the long axis of the couch 16 as indicated by
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`arrows “A” and “B”.
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`The gantry 14 is supported by a frame (not shown) that
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`allows for both orbital and axial movement with respect to
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`the couch 16. The gantry 14 itself comprises a radiation
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`source 18 that includes a gas x-ray tube or a similar radiation
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`source as is known to those skilled in the art. The gantry 14
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`further comprises a multi-leaf collimator 20 which consists
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`of opposing arrays of narrow tungsten leaves or veins placed
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`in front of a radiation beam. (These are illustrated in FIG.
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`1a.) The multi-leaf collimator 20 consists of several
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`(preferably 40) pairs of opposing veins. By driving each vein
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`into different positions, virtually any desired field shape can
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`be achieved in radiation therapy.
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`FIG. laillustrates a diagrammatic perspective view illus-
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`trating a radiation field shaped by the multi-leaf collimator.
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`A sample series of veins or leafs 21 are illustrated between
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`a shaped field (shown for illustrative purposes and not
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`intended to be limiting), generally illustrated as “SF”, and a
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`radiation source, generally illustrated as “RS”. Each of the
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`veins 21 of the multi-leaf collimator 20 is free to move along
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`its length and projecting about 1 cm in width in the isocenter
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`plane at about 100 cm from the source of radiation. Two
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`pairs of back-up diaphragms (not shown) comprising solid
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`tungsten jaws are provided complementary to the pairs of
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`veins in the X and Y directions. The multi-leaf collimator 20
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`defines a maximum field size of about 40 cm><40 cm at the
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`isocenter. Avariety of geometric constraints affect collima-
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`tion. These include permissible ranges of vein and dia-
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`phragm movements and minimum vein separation.
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`A video system and an image processor (not shown) are
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`used to provide actual real time vein positions and dynamic
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`vein motion capabilities. A multi-leaf controller 22 com-
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`pares the actual vein positions with prescribed positions. A
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