Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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¦! TUBE FOR IRRADIATION EQUIP~IENT
BACKGROUND OF TIIE INVENTION
¦ The present invention relates to a tube for irradiation equipment for
limiting an emergent beam.
The term irradiation equipment is in particular applied, in the text
which follows, to particle accelerators, electron accelera-tors, gan~na irra- ¦
diation equipment and X-ray equipment. For therapeutic and diagnostic use
it is essential to limit the cross-section of the beam emerging from the
I i.rradiation equipment to the requisite minilllum and to screen off the irradia-
I tion effectively, at the sides, between the outlet aperture of the irradia-
tion equipment and the surface of the article to be irradiated. At the sall~etime, when using an electron accelerator the proportion of the secondary X-
¦¦ rays and scattered electrons produced by the high speed electrons in the
I diaphragm system, and manifesting itself outside the actual field of irradia-
¦ tion, should be kept as low as possible in order to reduce the side-effect
of the irradiation.
As a further condition, it shollld be possible to choose as many varia-
tions of field dimensions as possible withill the range of ~ield sizes imposed
¦ by the irradiation equipment. For this reason a variety of devices have also
I already been disclosed and are used with which the cross-section of the
¦ irradiation can be limited and the beam can be screened off laterall ~.
A first known device consists of a set o-f diaphragms, of which each is
firmly fixed to a tube. The diaphragm and tube can be fixed detachably to
I the casing of the electron accelerator. For example~ the diaphragllls are in
¦ the form of thick lead sheets which have a central aperture which limits the
cross-section of the emergent electron beam. The tube serves to limit
the electron beam and screen it oFf laterally. This relatively si Dlp le device~
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suffers from several disadvantages. It is only possible to adjust the beam
to fixedly predetermined cross-sections, and the exchangeable diaphragms with
attached tube require a great deal of storage space, are expensive, are diffi-
cult to handle because of their weight, and must, whenever a change in beam
I cross-section is necessary, be exchanged, thereby consuming a relatively large
¦l amount of time.
Another known device comprises a baseplate on which several diaphragms
I are located in succession in the direction of the beam. Each of these dia- ¦
¦ phragms has several diaphragm blocks continuously displaceable at right angles¦
¦ to the direction of the beam. This device permits continuous variation of ¦
the diaphragm cross-section and hence of the effective electron beam and does ¦
I not require an additional tube. A disadvarltage of this device is tllat because
II of the diaphragms being arranged in sUCcession, a part of the fast electrons
¦¦ is screened off near the object to be irradiated, as a result of which a rela-
~ ¦ tively high proportion of gan~lla radiation and secondary electrons is liberated,WhiCtl must be avoided particll1arly in the case of radiatioll therapy, and that
if the diaphragm aperture is smal.l the diaphragill blocks project beyond the
¦ cross-section of the useful electron beam, which makes it difficult, or even
¦¦ impossible, to introduce the device into recesses and, for example, to irra-
¦I diate the armpits or the throat.Il . Further, a device is already known Which possesses a variable diaphragm
¦¦ built into the accelerator casing, and corresponding tubes of different cross-¦
Ij section which can be attached to the accelerator housing. In this device,
¦I the advantages of the variable diaphraglll can only be utilized partially be-
il caus.e the diaphragln must necessarily be set to the dimensions of the available¦I tubes. Furthermore, this device suffers from all disadvantages already men-
¦ tioned above for exchangeable tubes.
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SU~l~lARY OF THE INVEN~ION
Accordingly, it is the object of the present invention to provlde a tube
for irradiation equipment, which tube is of infinitely variable cross-section,¦
¦ and in which the external dimensions of the free end are only slightly greater
¦ than the dimensions of the free aperture at the end of the tube, in order to
permit, as far as possible, unhindered approach to the object to be irradiated
ll According to the invention, this object is achieved by means of a tube
li of the initially described type, whicll is characterized in that on each car-
¦¦ rier plate there are provided a side wall and at least one equally high lamel-
¦! la, which side wall projects, at the side of the limiting edge which abuts thejsliding edge, at right angles from the carrier plate and which lamella or ¦
lamellae is or are pivotably fastened in the region of the limiting edge and
can be laid down on the carrier plate or be erected, as an extension of the
side wall, in order to form a side wall of a tube of variable cross-section.
The ne~ tube can be fed to any quadranglllar cross-sectioll Witil dimensions
between a minilllum square, the side length of which corresponds to the length
of one side wall, and a maximum square, the side length of which corresponds
¦ to the length of one side wall and of the corresponding lamellae. Because
Il the lamellae not required to form the tube side walls are laid down on the
1I carrier plates, the external cross-section of the tube is only slightly great-l
¦ er than the internal cross-section, thereby permit-ting unhindered introduction¦
¦l of the tube into recesses. I
! For simpler manual adaptation of the tube walls to the selected cross-
Il section, a plurality of magnets can be fixed to each carrier plate, which
I magnets hold the lamellae laid down on the carrier plate, while a spring can
engage agains~ the base of each lamella, which spring pivots the lamellae, re-
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leased by the holding magnets, into the erect position.
In a preferred embodiment, further measures are provided whicll, on adjust-
1 ing the tube cross-section, automatically raise the lamellae or lay them down¦l on the carrier plate. For this purpose there is fixed to each carrier plate¦ along the extension of the lin]iting edge, a tongue, which carries on its end
¦¦ projecting onto the adjacent carrier plate a stop of which one side face rests
¦ against the adjacent erect lamella and prevents its pivoting into the laid-
¦ down position, while its other side face has a wedge-shaped challlfer and is I ; -
¦ pushed under the adjacent laid-down lamella and, on displacing the carrier
¦ plate in order to increase the transmission aperture, lifts this next lamellaoff the holding magnet. Furthermore, an electromagnetic switch device is fix-
ed on each side wall, which possesses a lever which, after the carrier plate
has been displaced in order to reduce the transmission aperture, pivots the
¦l lamella adjoining the side wall, on the adjoining carrier plate, into the
¦11 laid-down pOSitiOIl.
BRIEF DESCRIPTION OF THE DRAlllNGS
1¦ A more complete appreciation of the invention and many of the attendant~¦ advantages thereof will be readily obtained as the same becomes better under- ¦
Il stood by reference to the following detailed description when considered in
¦ connection with the accompanying drawings, wherein: ¦
¦ FIGURE 1 shows the schematic representation of an accelerator window with¦
I diaphragms and a tube of the hitherto conventional type,
¦ FIGURE 2 shows the plan view of an embodiment of the new tube,
FIGURE 3 shows the section along line III-III through the tube according
, to Figure 2,
¦ FIGURE 4 shows the side view, partially in sec-tion, of the tube according
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¦I to FIGURE 2, viewed in the direction of the arrow IV, appearing with Figs. 1 ar d
5, and
FIGURE 5 shows the schematic representation of a contact switch in the
I tube baseplate, appearing with Figs. 1 and 4.
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5 1I DESCRIPTION OF THE PREFERRED EMBODIME~TS
! Referring now to the drawings, whereill like referellce numerals designate ¦
¦ identical or corresponding parts throughout the several views, FIGURE 1 shows
Il schematically the aperture of an electron accelerator with diaphragms for the I
!~ electron beam, and a tube. Accelerator 10 possesses a window 11 which is in- ¦
lo I tended to transmit a narrow electron beam. At a distance froM the window, in
1I the direction of the emergent electron beam, are located a first scatterer 12 ¦
¦¦ and a main scatterer 13 "~hich broaden the narrow elec-tron beam. In order tolimit the maxinluln diameter of the electron beam issuing from the accelerator
,I casing 14, a first diaphragm 16 is fixed within the casing. Furthermore, a
15 ¦¦ screen 17 is provided, which screens off an anterior diaphragm 18, located in r
¦¦ the region oF the aperture of the casing, and possesses a central aperture 19¦¦ through which the electron beam emerges from the accelerator casing. This
¦I central aperture is framed by a holder device 21, into which an exchangeable
Il tube 22 is inserted.
20 I¦ In order to adapt the cross-section of the electron ~eam emerging from
` ¦I the tube to the intended use, it is possible to use, in this arrangement,
anterior diaphragms 18 of different free internal cross-sections or a fixedly
¦l built-in anterior diaphraglll with a variable free internal cross-section, as
I well as to use exchangeable tubes matching these cross-sections.
I The embodilnent of the tube of variable cross-section, according to the
invention, shown in Figures 2 and 3 is built up on a baseplate 30. The base-
plate is intended for fixing to the screen 17 and has a large central aperture
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¦ 3l. Four carrier plates 32, 33, 34 and 35 are located on the baseplate. Each
¦ carrier plate has at least two edges located at right angles to one another,
¦ namely a limiting edge 37, 3~, 39 or 40 and a sliding edge 42, 43, 44 or 45.
¦ The carrier plates are so located relative to one another that the parts of
I the limiting edges which adjoin the sliding edges form the frami1lg of a trans-
I mission aperture 47 and the ren~aini1lg part of each limiting edge rests againstj
! the sliding edge of an adjacent carrier plate. The carrier plates can be dis-¦placed parallel to the plane of the baseplate by means of a displacement de-
Il vice customary for adjustable anterior diaphragms, which device is known to
¦I those skilled in the art and is therefore only indicated with broken lines 50,
51. This displaceme1lt device permits each oF the two pairs of carrier platesJ
formed by mutually opposi-te carrier plates 32, 34 or 33, 35, to be displaced
¦ syn~netrically to the center of the transmission aperture 47, independently of ¦
I¦ the other pair of carrier plates, and in the direction of its sliding edge.
lS ~¦ During this displacement, the two carrier plates of the other pair of carrier
11 plates are carried with the first pair, so that the contact between adjacent
j carrier plates and the framing of the transmission aperture always remains
I1 preserved. If, for example, the carrier plates 33, 35 are pushed apart, the
¦¦ carrier plate 34 follows the displacement of the carrier plate 33 and the car-
rier plate 32 follows the carrier plate 35. In this way, the square trans 1 -~
mission aperture 47 shown in Figure 2 can be reduced and enlarged or be re- ¦
shaped into an upright or horizontal rectangle of any desired dimensions.
! As can be seen most clearly in Figure 2, a side wall 53, 54, 55 or 56
1l projects from each carrier plate. Each side wall is located along the limit-
ing edge and one of its lateral edges terminates in the corresponding sliding
¦ edge af the carrier plate. Each side wall stands at right angles to the
carrier plate and the four side walls form a closed tube if the four carrier -~
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~¦ plates are pushed together sufficiently far that in their limiting edges frame¦
¦ the smallest envisaged transmission aperture. In the lateral extension of
each side wall, and above the limiting edge, there is additionally fixed a
I thin shaft 60, 61, 62 or 63. On this shaft a plurality of lamellae are pivot-
ably mounted, of which, for clarity, only lanlellae 69 to 71 on the shaft 60 of
the carrier plate 32 are identified by reference nunlbers. All lamellae can
be pivoted between a laid-down position in which they are located virtually
l parallel to the surface of the carrier plate, and an erect position, in which
¦I they are located parallel to the side wall. In FIGURES 2 and 3, the lamellae
¦¦ 65 to 68 on the carrier plate 32 (and the corresponding lamellae of the other !
¦I carrier plates~ are drawn in the erect position, and the lanlellae G9, 70 and ¦ r
¦ 71 on the carrier plate 32 (as well as the correspolldillg lamellae of the other
carrier plates) are drawn in the laid-down position. As will be immediately
I obvious to anyone skilled in the art, it is possible, by erecting those lanle-
llae which are located along the parts of -the limiting edges which form the
framing of the transmission aperture, to form a tube the internal cross- ¦ r
section of which is virtually of the same size ancl the same shape as the
cross-section of the transmission aperture. Because the lamellae not requiredl
for broadening the tube walls relnain in their laid-down position, the externalj
cross-section of the free end of the tube ;s not much larger than its internal
cross-section, that is to say, the cross-section of the electron beam which
. ¦ emerges through the tube. This construction makes it possible to introduce
¦I the free end of the tube "Yithout hindrance by projecting side pieces, even
¦ into recesses. As has already been described above, this is particularly im-
25 ¦ portant when using irradiation equipment in medicinal diagnostics and therapy,¦
for example if the tube is to be brought into an armpit or against the neck
ol a pe ent.
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If the transmission aperture is set -to a dimension which does not corres-
~pond to the grid predetermined by the lateral length of the lamellae, the lastl -
erect lamella of each side wall projects partially beyond the corner of the
tube. This apparent disadvantage is virtually of no importance if the lateral
5` length of the lamellae is not great. I
As can be seen best in Figure 4, each lamella consists of a steel strip
75, at one lengthwise end of which is located a lamella base 76, while in the ,region of its other lengthwise end there are located several absorption pieces
¦1 77, 78 and 79. The lamella base preferably consists of bearing metal and has
¦! a bore 81, by rneans of which the lamella is pushed onto the shaft 60. The
absorption pieces are in particular intended to absorb secondary X-rays ancl
Il stray electrons. In a combina-tion whicil is particularly suitable for this
iI purpose, the absorption pieces 77, 7~ and 79 consist of light metal, steel or~ Antikorrodal.
1 In the embodiment of the new tube shown in the figures, a plurality of
! small permanent magnets is located on eacll carr-ier pla-te, among which, for
l! clarity, only magnets 83 to 89 on carrier plate 32 are identified by refer-
il ence numbers. These permanent magnets are provided in orde,- to hold the
i~ lamellae which have been laid down on the carrier plate.
As may be seen from Figure 2, the lamellae overlap in cross-section. The
result of this is that the tube wall cori~posed of adjacently located lamellae
I! is "tight" and that none of the erect lamellae can be laid down as long as
¦, the last erect lamella is locked in its position. For this purpose, a thin
¦ tongue 92 is fixed to each carrier plate (Figure 4) which tongue projects, in
¦ the extension of the limiting edge 38, beyond the adjacent carrier plate 32, 1 ;
¦ and carries a stop 90. This stop rests, with one of its sides, against ;the
particul r last lamella 66 of a tube wall, and thereby prevents this lamelld
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¦ from being pivoted ~rom the erect p~sition into the laid-down position. pre- I -
¦¦ ferably, this stop is wedge-shaped in the direction of the sliding edge. Thismakes it posssible, when displacing a pair of carrier plates in order to
i enlarge the cross-section of the framed transmission aperture 47, to slide
1I the stops, fixed to the two displaced carrier pla-tes, with their wedge-
¦¦ shaped surfaces under the lamellae 69 of the adjacent carrier plates 32 and
to lift these lamellae off the permanent magnets 87.
To each lamella there is allotted a spring 91 which engages in the region
¦ of the base of the lamella (Figure 4) and pivots it into the erect position
¦ as soon as it has been released from the holding magllet.
In the shown embodilllen-t o-f the tube there is furtherlllore located, on the ¦¦ outside of each side wall 54, an electromagnetic switch device 93 which com-
prises a lever 94 which has a virtually vertical rest position and can be
I pivoted through about 90 into the working position sho~qn with broken lines
~ in Figure 4. After displacing one pair of carrier plates ;n order to reduce
¦I the cross-section of the transmissioll aperture, the switch devices on the side
walls of the displaced carrier plates are actuated, whereupon in each cas~
¦ the last lamella of the adjacent tube wall is pivoted into its laid-down
j'l position and is held by the corresponding permanent magnet. Because of the
¦¦ mutual overlap of the lamellae, which has already been mentioned above, laying
¦I down one lamella results in all further lamellae automatically being laid down
1 in the direction facing away from the corresponding side wall. This ensures
jl that on reducing the cross-section of the transmission aperture all lamellae
lii no longer required to form the tube have been laid down on the corresponding ¦ ¦
ijl carrier plate.
I ¦1 As has already been described above, it is necessary, when using irradia- I
1¦ tion equipment for diagnostics and therapy, to briny the free end of the tube t
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as close as possible to the object or to the patient. Because of the large
weight of the entire installation, special drive motors are used for the re-
quired displacement motions or rotary motiolls of individual parts of the equip
ment. In order to ensure that these drive motors are switched off as soon as
the tube has been brought to a minimum distance from the patient, special
¦ proximity switches are used. In a first embodiment of such a safety device, ¦
I an insulated electrode 100 is fixed to the free end of each side wall. The
il electrodes, numbering four in total, are preferably wired electrically in
¦¦ parallel, and form a capacitor with the tube. This capacitor is connected,
¦I in a known manner, to an HF measuring bridge which is put out of balance as
¦I the tube approaches a patient and switches off the feed voltage for the drive¦ motors! via a comparator/trigger circuit, when a presettable unbalance has
been reached.
Il In another embodilnent of this safety device, the baseplate of the tube
11 is fixed in an insulated manner to the accelerator casing, and the entire tube
¦l is used as a capacitor electrode.
In yet another embodinlent, the safe-ty device is actuated not on approach-¦
ing, but only on touching, the object to be irradiated. As is shown schematic
Il ally in Figure 5, this embodinlent uses a tube insert 102 which is located ¦
¦I parallel to the baseplate 30 and can be inserted into the holding device 21.¦ A stud bolt 103, which passes through a corresponding bore in the baseplate
I¦ 30, is fixed to each of the four corners of this tube insert. In addition,
¦1 an electrical switch is provided, of which one contact 104 is fixed by meansI of an insulating disc 105 to the baseplate, while its other contact 106 is
¦ fixed by means of an insulating disc 107 to the free end of the stud bolt.
Around each stud bolt is inserted, between the tube insert 102 and the base-
¦ plate 30, a spring lOû which presses the baseplate away frolll the tube insert
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¦l and presses the contac-t 104 onto the contact 106. The Four switches are
preferably ~ired electrically in series. I~hen, on moYing or turnin.g the in-
stallation or the patient, the tube is touched and compressed or tipped against
the force of one or more springs, the contacts of the corresponding switches
I are separated from one another and a safety circuit is broken and switches offi the feed voltage for the drive motors. .
In an embodiment of the new tube used in practice the side length of each
¦ side wall is 4 cm, which makes it possible to telescope the carrier plate suf-II ficiently that the minimum transmission aperture 47 corresponds to a square
¦I with sides 4 cm long. Furthermore, with this embodilllent 16 lamellae are loca-¦
¦¦ ted on each carrier plate, the side length of each lalllella being 1 cm. Accord
ingly, the max;lllunl transmission aperture can be set to correspond to a square¦I with sides 20 cm long. As has already been described in detail above, any
¦I quadrangular transmission aperture with dimensions lying between the two stat-
! ed extreme values can be set up with the new tube. In ti~is embodinlent, the r
il height of the side walls and lamellae is 17 cm.
ii It has already been mentioned that the preliminary diaphragm 18 must be
li set to the cross-section of the tube. Since the object to be irradiated de- ¦termines the cross-section of the tube, this tube cross-section is first set
20 up. This setting can be effected manually or by means of servo-motors. Pref-
.. : ¦ erably, an adjust~ble anteribr diaphragm is used, and the cross-section of the
¦¦ tube as well as the apertul-e of the preliminary diaphraglll are picked up by
li actual value indicators, For example potentiometers. The ac-tual values are~ ¦I then compared in comparators and the resulting error signal is used to con- ¦
~. 25 il trol the diaphragm servo-motors until the actual values for the diaphragm
ll aperture corresponds to the actual values of the tube cross-section. It will ¦
be understood that in this way it is also possible to set up a non-linear re-
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lation of tube cross-section to diaphragm aperture.
In a further embodilllent of the new tube, an anterior diaphragm 1~, ¦
¦I forming part of the accelerator, is not required. In this embodinlent, the
I¦ distance between the baseplate and the carrier plates is increased, and dia-¦ phragm blocks are nlounted on the surfaces, facing the baseplate, oF each car-
rier plate, or the carrier plates are constructed as diaphragm blocks. It
will be appreciated that with this embodinlent each adjustment of the tube
¦ cross-section simultaneously also results in an adjustment of the effective
I¦ diaphragm aperture.
¦¦ Finally, it is also possible to adjust the tube cross-section and the
diaphragm aperture by means of remote control from an operating panel or from
¦l a data store. Appropriate circuits are known to all those skilled in the
¦ art and will therefore not be described in detail.
l Though the new tube has been described in relation to an illustrated
i embodilllent which possesses four displaceable baseplates and defines a quadran-
¦¦ gular transmission aperture, it will be obvious to all those skilled in the
! art that it is also possible to construct a corresponding tube with three or
, five or more baseplates which are displaceable symmetrically to one another.
ll Obviously, numerous modifications and variations of the present invention¦
¦l are possible in light of the above teachings. It is therefore to be under-
stood that within the scope of the appended claims, the invention may be
i practiced othei^wise than as specifically described herein.
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