United States Patent (19)
`Klasen et al.
`
`11
`45
`
`Patent Number:
`Date of Patent:
`
`4,987,309
`Jan. 22, 1991
`
`(54) RADIATION THERAPY UNIT
`75 Inventors: René Kasen, Rorbas; Hugo Schir,
`Flaach; Heinz Vogt,
`Oberehrendingen, all of Switzerland
`73 Assignee: Varian Associates, Inc., Palo Alto,
`Calif.
`21 Appl. No.: 440,220
`(22
`Filed:
`Nov. 22, 1989
`30
`Foreign Application Priority Data
`Nov. 29, 1988 CH Switzerland ......................... 4427/88
`51)
`int. Cl. ............................................... G21K 1/04
`52 U.S. C. .....
`. 250/492.1; 250/505.1;
`250/492.3; 378/152
`58 Field of Search ............... 250/492.1, 505.1, 492.3;
`378/152, 64, 65
`
`56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`378/152
`2,959,680 1 1/1960 Green .....
`3,060,316 10/1962 Peyser ................................. 378/152
`4,055,770 10/1977 Milcamps et al. .
`... 250/505.1
`4,359,642 i/1982 Heinz et al. ........
`... 250/505.1
`4,450,578 5/1984 Hill ...................................... 378/152
`4,463,266 7/1984 Brahme ......
`... 250/505.1
`4,672,212 6/1987 Brahme ..........
`... 250/505.1
`4,739,73 4/1988 Blosser et al...
`... 250/505.
`4,794,629 12/1988 Pastyr et al. ........................ 378/152
`4,868,843 9/1989 Nunan .............................. 250/505.1
`
`FOREIGN PATENT DOCUMENTS
`196138 10/1986 European Pat. Off. .
`259989 3/1988 European Pat. Off. .
`1037035 8/1958 Fed. Rep. of Germany .
`2753397 6/1978 Fed. Rep. of Germany .
`3621868 1/1988 Fed. Rep. of Germany .
`2524690 10/1983 France .
`Primary Examiner-Jack I. Berman
`Assistant Examiner-Kiet T. Nguyen
`Attorney, Agent, or Firm-Stanley Z. Cole; Sheri M.
`Novack
`ABSTRACT
`57
`A radiation therapy unit with a beam of rays propagat
`ing from a focal point along a beam axis comprises a
`radiator head arranged on the beam axis with a double
`focus multi-leaf collimator. The multi-leaf collimator
`exhibits a plurality of adjacently arranged diaphragm
`plates which in each case have two side faces, two front
`faces and an inside and an outside face. Each side face of
`each diaphragm plate forms a part of a surface area of a
`cone, all such cones having both a common cone axis
`which extends perpendicularly to the beam axis through
`the focal point, and a common cone point which coin
`cides with the focal point. Means are provided for guid
`ing the diaphragm plates so that each diaphragm plate
`performs a pure rotation about the cone axis during its
`displacement.
`
`11 Claims, 6 Drawing Sheets
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`U.S. Patent Jan. 22, 1991
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`U.S. Patent
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`Jan. 22, 1991
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`U.S. Patent Jan. 22, 1991
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`Jan. 22, 1991
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`U.S. Patent
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`Jan. 22, 1991
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`U.S. Patent Jan. 22, 1991
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`Sheet 6 of 6
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`1.
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`RADATION THERAPY UNIT
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`4,987,309
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`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The invention relates to a radiation therapy unit with
`a beam of rays propagating from a focal point along a
`beam axis and a radiator head arranged on the bean
`axis, having the following features:
`(a) the radiator head comprises a double-focus multi
`leaf collimator;
`(b) the multi-leaf collimator exhibits a plurality of
`adjacently arranged diaphragm plates which in
`each case have two side faces, two front faces and
`an inside and an outside face;
`(c) means are provided for displacing each individual
`diaphragm plate.
`2. Discussion of Background
`Radiation therapy units are used in medicine for ther
`20
`apeutically treating tumors by means of high-energy
`photons or electrons. In this connection, it is of impor
`tance that the beam of rays generated by the unit has
`accurately defined characteristics with respect to field
`25
`limiting. In this respect, radiation therapy units having
`multi-leaf collimators of the type initially mentioned are
`particularly suitable.
`Such a unit is known, for example, from U.S. Pat. No.
`4,672,212. Instead of a conventional pair of collimator
`blocks, a multi-leaf collimator is used there. In order to
`avoid unwanted half shadows at the edge of the radia
`tion field, the multi-leaf collimator is focussed twice.
`For this purpose, the individual diaphragm plates are
`segments of a circular ring and have a cross section of
`35
`the shape of an equal-sided trapezoid. The multi-leaf
`collimator composed of the diaphragm plate is thus
`circularly bent in two directions which are perpendicu
`lar to one another and thus imitates a part of a spherical
`shell (only approximately, however).
`Each diaphragm plate is provided at its rear end with
`a rod pointing upwards. The diaphragm plate is ad
`vanced and retracted on this rod by means of a motor.
`The problem of this multi-leaf collimator lies in the
`fact that an unwanted leakage radiation occurs between
`45
`the individual diaphragm plates. A further disadvantage
`lies in the complicated drive arrangement. This is be
`cause the diaphragm plates move on curved paths
`which change from plate to plate. The type of coupling
`50
`proposed between motor and diaphragm plate leads to a
`non-linear relationship between plate advance and
`motor speed.
`The published European patent application EP
`0,259,989 A1 describes quite a different multi-leaf colli
`55
`mator. This is used in a conventional radiation therapy
`unit in addition to the two pairs of collimator blocks, for
`shielding sensitive organs of the patient. The multi-leaf
`collimator consists of a plurality of laterally adjoining
`diaphragm plates. The essentially rectangular plates are
`slightly rounded on their front and have straight-line
`guide slots at the side faces. They run along straight
`tracks and are driven by associated motors by means of
`flexible cables.
`Although this multi-leaf collimator has a linear drive
`65
`arrangement, it can only be used in conjunction with
`the conventional collimator blocks due to the lack of
`double focussing.
`
`60
`
`2
`SUMMARY OF THE INVENTION
`Accordingly, it is an object of this invention to create
`a radiation therapy unit of the type initially mentioned,
`which allows great freedom in shaping the radiation
`field. At the same time, the radiation field should be free
`of half shadows and leakage radiation. Finally, the radi
`ator head should have as low a constructional height as
`possible.
`According to the invention, the solution consists in
`the fact that, in a radiation therapy unit of the type
`initially mentioned,
`each side face of each diaphragm plate forms a part of
`a surface area of a cone, all such cones having both
`a common cone axis which extends perpendicu
`larly to the beam axis through the focal point and a
`common cone point which coincides with the focal
`point, and
`means are provided for guiding the diaphragm plates
`so that each diaphragm plate performs a pure rota
`tion about the cone axis during its displacement.
`The core of the invention lies in the fact that the
`diaphragm plates are shaped in such a manner that their
`side faces adjoin one another in a form-closing manner
`and that, at the same time, the double focussing is re
`tained during the displacement of the diaphragm plates.
`In contrast to the known double-focus multi-leaf colli
`mator, each diaphragm plate has its individual shape
`which is given by its relative position in the entire pack
`age.
`In a particularly advantageous embodiment, the out
`side faces of all diaphragm plates arranged laterally
`adjacently have, overall, as an enveloping surface a part
`of a surface area of an outer cylinder the axis of which
`is the cone axis. The means for displacing the dia
`phragm plates engage the outside faces. This makes the
`drive arrangement particularly simple.
`The means for displacing preferably comprise for
`each diaphragm plate a toothed rail which is mounted
`on the outside face of the diaphragm plate, a worm-rack
`gear engaging this toothed rail and a stepping motor
`which actuates the gear. This ensures a linear relation
`between the speed of the stepping motor and the plate
`advance.
`It is particularly advantageous if the radiator head
`exhibits two multi-leaf collimators which are arranged
`above one another and are aligned perpendicularly to
`one another and if a matrix ionization chamber, by
`means of which the multi-leaf collimators are moni
`tored, is arranged on the beam axis opposite to the radi
`ator head.
`Further advantageous embodiments are obtained
`from the dependent claims.
`BRIEF DESCRIPTION OF THE DRAWINGS
`A more complete appreciation of the invention and
`many of the attendant advantages thereof will be
`readily obtained as the same becomes better understood
`by reference to the following detailed description when
`considered in connection with the accompanying draw
`ings, wherein:
`FIG. 1 shows a radiation therapy unit;
`FIG. 2 shows a radiator head with two multi-leaf
`collimators according to the invention;
`FIG. 3a, b shows a diaphragm plate seen from the
`front and from the side, respectively;
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`3
`intersection of the beam axis S with the axis of rotation
`FIG. 4 shows one collimator half with 20 diaphragm
`plates, the side faces of which are constructed to be
`A.
`step-shaped;
`The beam of rays which thus propagates along the
`FIG. 5 shows a spatial representation of the paths of
`beam axis S is transformed by a flattening filter 13 (for
`movement of the diaphragm plates;
`example into a beam of rays which is as homogeneous as
`FIG. 6 shows a three-dimensional representation of a
`possible over the maximum radiation field) and mea
`diaphragm plate;
`sured in an ionization chamber 14. Before the beam of
`FIG. 7 shows a representation of a radiation field
`rays leaves the radiator head 3, it is laterally limited by
`such as can be generated by means of a radiator head
`two pairs of collimators 17a, 17b which are aligned
`having two contour collimators which are aligned per
`perpendicularly with respect to one another.
`pendicularly to one another; and
`If necessary, a wedge filter 15 can be pushed into the
`FIG. 8 shows a representation of a radiation field
`beam of rays underneath the ionization chamber 14. A
`such as can be generated by means of reduced-height
`mirror 16 and a light source 21 allow the lateral extent
`multi-leaf collimators.
`of the beam of rays to be made visible on the patient as
`simulation.
`DESCRIPTION OF THE PREFERRED
`According to a preferred embodiment, a matrix ioni
`EMBODIMENTS
`zation chamber 19 is arranged on the beam axis S oppo
`Referring now to the drawings, wherein like refer
`site to the radiator head 3 and below the isocenter. It is
`ence numerals designate identical or corresponding
`mounted at the rotary stand 1 by means of a fixed or
`parts, FIG. 1 shows a radiation therapy unit according
`20
`retractable holder 18.
`to a preferred embodiment of the invention. It com
`FIG. 2 shows the radiator head 3. The target 12 de
`prises a rotary stand 1, a radiator arm 2 mounted
`fines the focal point Q on the beam axis S. Z designates
`thereon and a radiator head 3. The patient to be treated
`a cone axis which extends perpendicular to the beam
`lies on a treatment table 4 underneath the radiator head
`axis S through the focal point Q.
`3.
`25
`A beam diaphragm 20 limits the radiation field to a
`The treatment table 4 is not a part of the application.
`circular area. The flattening filter 13 equalizes the radia
`It can be adjusted in height, rotated about a vertical axis
`tion field (for example energy or dose peaks in the cen
`and pushed forward and back in longitudinal and trans
`ter). Instead of one single filter, several flattening filters
`verse direction, as is normal practice in the prior art.
`can also be provided which are mounted on a slider. In
`The rotary stand 1 is mounted rotatably about an axis
`30
`the same manner, the target 12 can also be interchange
`A and is moved via a drive system 5. The components
`able.
`needed for generating high-energy electrons are accom
`In the text which follows, the multi-leaf collimators
`modated in the rotary stand 1 and in the radiator arm 2.
`according to the invention are explained. In this con
`An RF source 7 controlled by a pulse transformer 6
`nection, the geometric reference points and axes defined
`generates microwaves of the power needed. The micro
`35
`above are of central significance. So that the description
`waves are fed via an RF feed 8 to an acceleration tube
`is not unnecessarily complicated, terms like "top' and
`9 which is accommodated in the radiator arm 2. An
`“bottom' and "above' and "below' are used. They
`electron gun 10 injects electrons into the acceleration
`must be understood within the context that the focal
`tube 9. The electrons are accelerated to, for example,
`point Q is "at the top' and the isocenter I is "at the
`8MeV by the microwaves, filtered with respect to en
`bottom'. Thus, the beam of rays propagates from top to
`ergy in a subsequent deflection magnet 11 and deflected
`bottom. Correspondingly, the formulation "object X is
`in the direction of a beam axis S.
`above object Y' means that object X is closer to the
`The parts of the radiation therapy unit described until
`focal point than object Y.
`now are known as such. They can be replaced by other
`FIG. 2 shows an embodiment with two multi-leaf
`means which are suitable for generating a high-energy
`collimators which lie one above the other and are
`electron beam.
`aligned perpendicularly with respect to one another and
`The electrons emerging from the deflection magnet
`which in each case comprise two collinator halves 22a,
`11 can either be used themselves for the treatment or
`22b, 22c (the fourth collimator half is not drawn in favor
`converted into photons by means of a target 12. The
`of clear representation in FIG. 2). Each collimator half
`parts of the radiator head according to the invention
`50
`22a, 22b, 22c is composed of a plurality of diaphragm
`develop their effect independently of whether photons
`plates 23 arranged next to one another which are in
`or electrons or other particles are used in the therapy.
`each case individually supported and guided by two
`This is why only a beam of rays is mentioned in the text
`holding yokes 24a (the second holding yoke of the colli
`following.
`mator half of the top multi-leaf collimator is not visible
`The essential parts of the radiator head 3 are only
`in FIG. 2), 24b and 24c, 24d and 24e. The diaphragm
`indicated in FIG. 1. A target 12 (for generating the
`plates 23 can be displaced independently of one another.
`photons or an electron diffusing filter for diffusing the
`In FIG. 2, for example, the diaphragm plates of the
`electrons) is located at the output of the deflection mag
`upper multi-leaf collimator move perpendicularly to the
`net 11 and generates the beam of rays. An important
`plane of the drawing and those of the lower multi-leaf
`point of reference for the geometric-optical consider
`60
`collinator move in parallel with the plane of the draw
`ations is a point, hereinafter designated as focal point Q,
`in the three-dimensional space from which the beam of
`1ng.
`For each diaphragm plate 23, a stepping motor 25 is
`rays propagates in accordance with optical geometry.
`provided which pushes this plate forward and back by
`Another important point of reference in space is the
`means of a worm-rack gear 35 and a toothed rail 31. The
`isocenter I. This is the location at which the beam of
`65
`rays develops the required optimum effect. Usually this
`stepping motors 25 of a multi-leaf collimator or of the
`corresponding collimator halves, respectively, are ar
`is where the beam of rays encounters the tumor. Geo
`ranged to be staggered both vertically and horizontally.
`metrically considered, the isocenter I is the point of
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`at a rightangle at the focal point Q. The cone axis Z is
`Naturally, instead of the stepping motor, any other
`axis of an inner and of an outer cylinder having the
`drive (for example a direct-current motor with shaft
`radius Ri and Ra, respectively, Ribeing<Ra. A plane
`encoder) can be used.
`perpendicular to the cone axis Z through the focal point
`The holding yokes guide, on the one hand, the dia
`phragm plates, and, on the other hand, support the
`Q is defined as center plane. Thus, the beam axis S is
`worm-rack gears. In this arrangement, each diaphragm
`located in the center plane.
`plate is supported and guided at four points by the two
`The outer cylinder is now intersected with planes
`which are parallel to the center plane and equidistant
`holding yokes of one collimator half.
`The advantage of the stepping motor lies in the fact
`from one another (distance b). The curves of intersec
`that it is continuously under voltage and thus under
`tion produced in this manner are circles.
`control and that it always stops in a defined position. In
`For each circle, an area is defined which is produced
`consequence, it is possible to detect the position of the
`by the fact that the point of a vector originating from
`diaphragm plates via the stepping motors alone (with
`the focal point Q revolves on the circle. The area thus
`out potentiometers). The worm-rack gear is self-inhibit
`defined is in each case the envelope of a cone.
`Each cone envelope also intersects the inner cylinder.
`ing. This dispenses with an additional braking device
`which ensures that the diaphragm plates cannot shift
`A space which is in each case bounded by two edges
`independently.
`and cone envelopes and by the inner and the outer
`cylinder represents the path along which a diaphragm
`FIGS. 3a and 3b show a single diaphragm plate from
`plate of the multi-leaf collimator according to the inven
`the front and from the side, respectively. It has two side
`tion moves. The diaphragm plate itself is none other
`faces 26a, 26b, two front faces. 27a, 27b, an inside face 28
`20
`than a segment of this space bounded by angles.
`and an outside face 29. The projection of the side faces
`26a, 26b on a plane which is perpendicular to the cone
`On the basis of this geometric consideration, the fol
`axis (see later) has the shape of a circular ring segment.
`lowing becomes clear:
`The diaphragm plate has the shape of a trapezoid with
`1. The multi-leaf collimator according to the inven
`unequal sides in cross section, the parallel sides of the
`tion is double-focussed. This is because in each position,
`trapezoid being given by the inside and the outside face
`the diaphragm plates are aligned both with the side and
`28, 29 and the unequal sides of the trapezoid being given
`with the front faces in such a manner that a beam origi
`nating from the focal point can only be tangent to them
`by the side faces 26a, 26b. The diaphragm plate has a
`height d and a thickness b.
`but cannot intersect them.
`2. The relationship between plate advance and speed
`The inside face 28 is slightly narrower than the out
`30
`side face 29 by exactly the amount that an extension of
`of the motor is linear. This is because the outside faces
`of the diaphragm plates are all of equal length and move
`an edge between side face 26a and front face 27a and an
`along the same cylinder surface.
`extension of an edge between front face 27a and side
`The outer and inner cylinder surface, respectively, is
`face 26b (that is to say an extension of the legs of the
`to be understood as enveloping surface. That is to say
`trapezoid) intersect at the focal point Q (see FIG. 2).
`35
`the outside and inside faces of the diaphragm plates do
`To minimize any leakage radiation between the dia
`not need to be precisely a part of a cylinder surface. It
`phragm plates, the side faces 26a, 26b can be provided
`with mutually corresponding steps 30, 31. These would
`is quite within the field of the invention to specially
`develop these faces for guiding purposes.
`extend in parallel with the inside and outside face 28 and
`FIG. 6 shows a three-dimensional representation of a
`29, respectively, that is to say they would be circular
`arc-shaped.
`diaphragm plate by means of which the features of the
`invention necessary in accordance with the concept of
`FIG. 4 shows a collimator half having 20 diaphragm
`the invention are to be picked out. There are two of
`plates. Each of these has at its outside face 29a, 29b, . . .
`a toothed rail 31a, 31b, . . . which is engaged by the
`these:
`previously mentioned worm-rack gear. The toothed
`1. Each side face 26a, 26b forms a part of a surface
`rails 31a, 31b of adjacent diaphragm plates have a differ
`area of a cone K1, K2. All such cones K1, K2 have their
`point at the focal point Q. Furthermore, they have a
`ent height in each case. This makes it possible to accom
`modate the worm gears in the small space available. To
`common cone axis Z. It follows from this that the two
`cones K1, K2 belonging to one diaphragm plate have
`obtain the same ratio between motor speed and plate
`advance for all diaphragm plates, the toothed rails also
`different slopes. On the other hand, the cones of side
`faces of adjacent diaphragm plates facing one another
`have a correspondingly different pitch.
`are identical. For this reason, adjacent diaphragm plates
`The two holding yokes of one collimator half are cut
`fit against one another in a form-closing manner.
`in in the shape of a comb on the inside of one external
`2. The diaphragm plates must be guided by suitable
`yoke. The toothed rails are inserted in the cut-ins and
`the appropriate diaphragm plate rests in each case with
`means in such a manner that they execute a pure rota
`55
`its outside face on adjacent teeth of the comb.
`tion about the common cone axis Z. The result is that
`the diaphragm plates do not move apart during the
`Naturally, the diaphragm plates can also be supported
`displacement. Thus, the side faces of adjacently ar
`and guided by other means. Thus, the outside faces can
`ranged diaphragm plates also remain in form-closed
`also be constructed, for example, to be V-shaped and
`mounted on rollers. Instead of attaching racks on the
`Contact.
`outside faces, adjusting means can be provided which
`These two central points of the invention are unaf.
`directly engage the appropriately shaped outside face.
`fected by any other shape of the diaphragm plate (out
`side face, inside face, stepped side face and so forth) and
`In addition, beam axis S, focal point Q, cone axis Z.
`the type of guiding means.
`and inside radius Ri and outside radius Ra are drawn in
`FIG. 4. The meaning of these geometric reference
`FIG. 7 shows a representation of a radiation field
`quantities is explained with reference to FIG. 5.
`such as can be generated by means of a radiator head
`FIG. 5 shows a spatial representation to explain the
`having two multi-leaf collimators. A plane perpendicu
`lar to the beam axis through the isocenter is represented
`invention. The beam axis S and the cone axis Z intersect
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`4,987,309
`8
`7
`and a projection of the diaphragm plates on this plane.
`which controls the diaphragm plates in such a manner
`that each field point to be covered is always covered
`In the center of the figure, the area 36 to be irradiated is
`both by a diaphragm plate of the upper and by one of
`drawn. It has, for example, several indentations 36a,
`36b, 36c which must be taken into account during the
`the lower multi-leaf collimators. Such a control circuit
`can be implemented best by programmed microproces
`irradiation, in the sense that they should be protected 5
`against the radiation as far as possible.
`SO.
`The diaphragm plates are then advanced by such an
`The advantage of this embodiment lies in the fact that
`amount that an effective radiation area 33 approximates
`there is more space available in the radiator head or,
`the area 36 to be irradiated as closely as possible. In
`conversely, the constructional height becomes smaller
`FIG. 7, the shading indicates that
`and that the weight of the multi-leaf collimators be
`1. Certain areas (checked) are covered both by the
`comes less.
`upper and the lower multi-leaf collimator and
`A preferred embodiment of the invention comprises a
`2. Certain edge regions (obliquely shaded) are only
`matrix ionization chamber 19 for monitoring the radia
`covered by one of the two multi-leaf collimators.
`tion field.
`It has hitherto been necessary for each individual 15
`Radiation therapy units are subject to certain safety
`collimator to be at such a height that it was capable of
`regulations. This also includes, for example, the regula
`completely attenuating the beam of rays, that is to say
`tion that the collimators must be monitored by two
`down to a required harmless level. If, however, two
`separate channels. One of these channels is the stepping
`multi-leaf collimators according to the invention are
`motor which holds the diaphragm plate in an accurately
`used as in FIG. 2, the height d (see FIG. 3) of the dia- 20
`defined position. The other channel is now the matrix
`phragm plates can be reduced. The reason for this is
`ionization chamber 19 (see FIG. 1). It is arranged below
`that each point of the radiation field can be selectively
`the isocenter I on the beam axis S. Thus, it detects the
`covered both by the upper and by the lower multi-leaf
`shape of the radiation field in the way in which it acts on
`collimator.
`the patient, and that almost in real time. If a fault occurs
`FIG. 8 illustrates the drive arrangement of multi-leaf 25
`in the multi-leaf collimator, the therapy can be immedi
`collimators at reduced height. The same plane as in
`ately interrupted.
`FIG. 7 is shown.
`This arrangement also makes it possible to change the
`The radiation field has a square maximum radiation
`radiation field during the therapy. This is of advantage,
`area 32 of, for example, 40 cm x 40 cm. The effect of
`for example, when the direction of irradiation is
`radiation area 33 is understood to be the part of the 30
`changed during the treatment (rotation around the isoc
`radiation field which is not covered by diaphragm
`enter I).
`plates.
`The matrix ionization chamber as such is known. This
`In the present example, each of the four collimator
`is why it will not be discussed in greater detail at this
`halves is built up of 20 diaphragm plates. The dia
`point but express reference is made to the published
`phragm plates of the lower multi-leaf collimator move
`European patent application EP-0,196,138 A2.
`in the X direction in the representation of FIG. 7 and
`The invention can be realized in the most varied
`those of the upper multi-leaf collimator move in the Y
`manners. In the text which follows, a few further possi
`direction (see coordinate system drawn) The thickness
`bilities will be indicated briefly.
`b of the individual diaphragm plates is selected in such
`Naturally, potentiometers can also be used for moni
`a manner that their central projection from the focal 40
`toring the diaphragm plates. In particular, these can
`point to a plane perpendicular to the bean axis S is of
`handle the monitoring function of the matrix ionization
`the same size. The diaphragm plates of the upper multi
`chamber as an alternative.
`leaf collimator are thus slightly narrower than those of
`The reduction of the leakage radiation between the
`the lower one.
`diaphragm plates can also be achieved by means of
`23d designates a freely selected diaphragm plate of 45
`slot-like recesses instead of by means of the steps de
`the lower and 23e one of the upper multi-leaf collima
`scribed. In this connection, it is understood that the
`tor. These two diaphragm plates together control a field
`recesses extend in parallel with the inside and outside
`point 34. Thus, if the two diaphragm plates 23d and 23e
`face and allow an essentially form-closed contact be
`are advanced as shown in FIG. 7, it is sufficient if they
`tween adjacent diaphragm plates.
`are capable of covering the radiation field together.
`To keep the number of actuators needed for driving
`Thus, the height d can be reduced compared with a
`the multi-leaf collimators as small as possible, the step
`conventional collimator. In principle, the height can be
`ping motors are advantageously operated in multiplex
`reduced to one half.
`However, the height d is advantageously only re
`mode.
`The diaphragm plates consist of a material conven
`duced by about one third compared with the original
`55
`tionally used for collinators. Tungsten alloys should be
`value. This is because such a height already produces a
`mentioned as an example. If then a height d=70 mm of
`reduction in the intensity to a few percent. In the case of
`such a material is required for covering the radiation
`a region to be irradiated such as, for example, in FIG. 7,
`field, a height of d=35 mm is sufficient for a multi-leaf
`the indentations 36a, 36b, 36c to be protected can in
`most cases already be protected sufficiently well against
`collimator in the embodiment with reduced height. A
`preferred height would be about 50 mm.
`radiation damage even though they are only covered by
`the diaphragm plates of one multi-leaf collimator. (The
`Finally, it can be said that the invention creates a
`radiation therapy unit which can be used in many differ
`obliquely shaded regions which, of course, cannot be
`ent ways.
`covered at all by means of conventional collimator
`Obviously, numerous modifications and variations of
`blocks are thus only loaded with a few per cent of the
`the present invention are possible in light of the above
`radiation dose).
`teachings. It is therefore to be understood that within
`A radiation therapy unit having multi-leaf collimators
`the scope of the appended claims, the invention may be
`with reduced height must comprise a control circuit
`
`65
`
`10
`
`50
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`ViewRay Exhibit 1008
`Page 11 of 12
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`4,987,309
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`practised otherwise than as specifically described
`(b) a gear which engages this adjusting aid and
`(c) a drive actuating this gear.
`herein.
`5. Radiation therapy unit as claimed in claim 4,
`What is claimed as new and desired to be secured by
`Letters Patent of the United States is:
`wherein
`1. Radiation therapy unit with a beam of rays propa
`(a) the adjusting aid is a toothed rail mounted on the
`gating from a focal point along a beam axis and a radia
`outside face,
`tor head arranged on the beam axis, having the follow
`(b) the gear is a self-inhibiting worm-rack drive and
`ing features:
`(c) the drive is a stepping motor.
`(a) the radiator head comprises a double-focus multi
`6. Radiation therapy unit as claimed in claim 1,
`leaf collimator;
`wherein the radiator head (3) exhibits two multi-leaf
`10
`(b) the multi-leaf collimator exhibits a plurality of
`collimators which are arranged one above the other and
`adjacently arranged diaphragm plates which in
`are aligned perpendicularly with respect to one another.
`7. Radiation therapy unit as claimed in claim 6,
`each case have two side faces, two front faces and
`an inside and an outside face;
`wherein the multi-leaf collimators have a reduced
`(c) means are provided for displacing each individual
`height, the reduced height of a single multi-leaf collima
`diaphragm plate; wherein
`tor not being sufficient but the sum of the heights of the
`(d) each side face of each diaphragm plate forms a
`multi-leaf collimators arranged above one another being
`sufficient for attenuating the beam of rays to a required
`part of a surface area of a cone, all such cones
`having both a common cone axis which extends
`level.
`perpendicularly to the beam axis through the focal
`8. Radiation therapy unit as claimed in claim 1,
`point and a common cone point which coincides
`wherein a matrix ionization chamber, by m