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Claims  |
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We claim as our invention:
1. A contour collimator for use in shaping a radiation beam comprising:
a plurality of radiation-impermeable diaphragm plates, each plate having an
engagement means;
means for mounting said diaphragm plates side-by-side in the path of said
radiation beam with each diaphragm plate being individually displaceable
so as to permit passage of radiation through said collimator;
means for selecting at least one of said diaphragm plates and for
displacing said at least one diaphragm plate relative to the remaining
diaphragm plates, said means for selecting and displacing being engageable
with the engagement means of said at least one diaphragm plate;
interlock means for maintaining said remainder of said diaphragm plates in
their respectively existing positions during displacement of said at least
one diaphragm plate, said interlock means being engageable with the
engagement means of each of said remaining diaphragm plates; and
means for changing the position of said means for selecting and displacing
such that said means for selecting and displacing engages the engagement
means of at least one different diaphragm plate from the at least one
diaphragm plate previously displaced, said means for selecting and
displacing then displacing said at least one different diaphragm plate
while said interlock means maintains the remainder of said diaphragm
plates in their respectively existing positions.
2. A contour collimator as claimed in claim 1, further comprising:
a further plurality of radiation-impermeable diaphragm plates, each plate
in said further plurality having an engagement means;
means for mounting said further plurality of diaphragm plates with the
diaphragm plates of said further plurality side-by-side in the path of
said radiation beam, each diaphragm plate in said further plurality of
diaphragm plates being individually displaceable so as to permit passage
of radiation through said collimator, and operating in combination with
said plurality of diaphragm plates to shape said radiation beam;
further means for selecting at least one of said diaphragm plates in said
further plurality of diaphragm plates and for displacing said at least one
diaphragm plate in said further plurality of diaphragm plates relative to
the remaining diaphragm plates in said further plurality, said further
means for selecting and displacing being engageable with the engagement
means of said at least one diaphragm plate of said further plurality;
further interlock means for maintaining said remainder of diaphragm plates
in said further plurality in their respectively existing positions during
displacement of said at least one diaphragm plate in said further
plurality, said further interlock means being engageable with the
engagement means of each of said remaining diaphragm plates in said
further plurality; and
further means for changing the position of said further means for selecting
and displacing such that said further means for selecting and displacing
engages the engagement means of at least one different diaphragm plate in
said further plurality from the at least one diaphragm plate in said
further plurality previously displaced, said further means for selecting
and displacing then displacing said at least one different diaphragm plate
in said further plurality while said further interlock means maintains the
remainder of said diaphragm plates in said further plurality in their
respectively existing positions.
3. A contour collimator as claimed in claim 2, wherein said means for
changing the position of said means for selecting and displacing is
engageable with the engagement means of said diaphragm plates in said
further plurality of diaphragm plates, and functions as said further means
for changing the position of said further means for selecting and
displacing.
4. A contour collimator as claimed in claim 1, wherein said collimator has
a center line, and wherein said plurality of diaphragm plates comprises
two groups of diaphragm plates respectively symmetrically disposed on
opposite sides of said center line, and wherein said two groups of
diaphragm plates are held in said means for mounting with the respective
diaphragm plates in said groups being individually displaceable toward and
away from said center line.
5. A contour collimator as claimed in claim 1, wherein said engagement
means is disposed at an edge of each of said diaphragm plates.
6. A contour collimator as claimed in claims 1, wherein said means for
mounting further comprises means for permitting limited rotation of said
diaphragm plates around a common focus.
7. A contour collimator as claimed in claim 1, wherein each of said
diaphragm plates has a guide channel therein, and wherein said means for
mounting includes an element engaging said guide channel.
8. A contour collimator as claimed in claim 7, wherein said guide channel
is curved.
9. A contour collimator as claimed in claim 7, wherein said means engaging
said guide channel comprises two guide bolts in said guide means parallel
to each other and extending through said guide channels.
10. A contour collimator as claimed in claim 1, wherein said engagement
means of said diaphragm plates is a plurality of teeth in each of said
plates, and wherein said means for selecting and displacing includes a
drive gear wheel which engages said teeth and which has a thickness
substantially equal to the thickness of a diaphragm plate.
11. A contour collimator as claimed in claim 10, wherein said means for
selecting and displacing further comprises a shaft connected to said drive
gear wheel and to a motor for driving said drive gear wheel.
12. A contour collimator as claimed in claim 11, wherein said shaft has a
free end, and wherein said drive gear wheel is secured to said shaft at
said free end.
13. A contour collimator as claimed in claim 1, wherein said engagement
means of said diaphragm plates is a plurality of teeth on each of said
plates, and wherein said interlock means includes at least one toothed
shaft engaging the teeth of at least some of said diaphragm plates.
14. A contour collimator as claimed in claim 1, wherein said means for
selecting and displacing includes a driven element engageable with said
engagement means of said diaphragm plates and a shaft connected to said
driven element and to a motor for driving said driven element, wherein
said interlock means includes a shaft also engageable with said engagement
means of said diaphragm plates, and wherein said shaft of said interlock
means has a longitudinal core therein in which said shaft connected to
said driven element in said means for selecting and displacing is at least
partially received.
15. A contour collimator as claimed in claim 2, further comprising:
a driven element in said means for selecting and displacing, said driven
element engageable with said engagement means of said diaphragm plates in
said plurality of diaphragm plates, and a first shaft connected to said
first driven element and to a motor for driving said first driven element;
a second driven element in said further means for selecting and displacing,
said second driven element being engageable with the engagement means of
said diaphragm plates in said further plurality of diaphragm plates, and a
second shaft connected to said second driven element and to a motor for
driving said second driven element;
a first interlock shaft in said interlock means, a second interlock shaft
in said further interlock means, and a central interlock shaft shared by
said interlock means and said further interlock means, each of said first
interlock shaft in said interlock means and said second interlock shaft in
said further interlock means and said central interlock shaft having means
for engaging said engagement means of said diaphragm plates in one of said
plurality of diaphragm plates or said further plurality of diaphragm
plates and each said first interlock shaft, said second interlock shaft,
and said central interlock shaft, being axially aligned and each of said
first interlock, second interlock, and central interlock shafts having a
bore, said bores being axially aligned, said first interlock shaft in said
interlock means receiving said first shaft in said bore of said first
interlock shaft and said second interlock shaft in said further interlock
means receiving said second shaft in said bore of said second interlock
shaft and said central interlock shaft at least partially receiving both
said first and second shafts of said second interlock shaft; and
said first and second driven elements and said first and said second
interlock shafts in said interlock means and said further interlock means
and said central interlock shaft all having the same outside diameter.
16. A contour collimator as claimed in claim 15, wherein said engagement
means of said diaphragm plates in each of said plurality of diaphragm
plates and said further plurality of diaphragm plates is a plurality of
teeth in each diaphragm plate, wherein said first and second driven
elements, said first and said second interlock shafts in said interlock
means and said further interlock means, and said central interlock shaft
all have teeth thereon engageable with said plurality of teeth in said
diaphragm plates in each of said plurality of diaphragm plates and said
further plurality of diaphragm plates and wherein said first and second
driven elements and said first, said second, and said central interlock
shafts all have the same number of teeth and the same tooth division.
17. A contour collimator as claimed in claim 1, wherein said means for
mounting includes two outside wall plates between which said diaphragm
plates are arranged substantially parallel to each other with said
engagement means disposed at one edge of each of said diaphragm plates.
18. A contour collimator as claimed in claim 17, further comprising means
for coupling said means for selecting and displacing to said interlock
means.
19. A contour collimator as claimed in claim 1, wherein said means for
selecting and displacing includes a frame and means for connection to a
motor for displacement of said frame in a direction transverse to the
direction of displacement of said diaphragm plates.
20. A contour collimator as claimed in claim 19, wherein said frame
includes two spaced lateral arms, and wherein said interlock means
includes an interlock shaft engageable with said engagement means of said
diaphragm plates, said interlock shaft being disposed between and received
in said lateral arms.
21. A contour collimator as claimed in claim 19, wherein said means for
displacing said frame includes a threaded spindle connected to a motor and
said frame further includes a retaining block connected to said frame
having a threaded bore therein receiving said spindle such that said frame
is transversely displaced as said spindle is rotated.
22. A contour collimator as claimed in claim 20, further comprising means
for applying pressure to said interlock shaft for urging said interlock
shaft into engagement with said engagement means of said diaphragm plates.
23. A contour collimator as claimed in claim 22, wherein said means for
selecting and displacing includes at least one driven element engageable
with said engagement means of said diaphragm plates, wherein said
interlock shaft includes at least two axially aligned portions with said
driven element therebetween, said portions of said interlock shaft being
connected by a connecting element, and wherein said means for applying
pressure is a contact pressure piece in sliding engagement with an
exterior of said connecting element so as to maintain pressure thereon as
said frame is transversely displaced.
24. A contour collimator as claimed in claim 22, wherein said means for
mounting includes two spaced wall plates between which said diaphragm
plates are disposed and wherein said means for applying pressure is a
contact pressure spring attached to each of said wall plates.
25. A contour collimator as claimed in claim 19, further comprising a frame
shaft on which said frame is slidably disposed for said transverse
displacement thereof.
26. A contour collimator as claimed in claim 1, wherein each of said
diaphragm plates has an edge facing said radiation beam and an opposite
edge, and wherein said edge facing said radiation beam has a smaller
thickness than said opposite edge.
27. A contour collimator as claimed in claim 1, wherein said engagement
means of said diaphragm plates is a plurality of teeth, and wherein said
teeth are triangularly shaped.
28. A contour collimator as claimed in claim 27, wherein said teeth on each
diaphragm plate are disposed at a spacing of about 1.5 mm.
29. A contour collimator as claimed in claim 1, wherein said diaphragm
plates consist of a material containing tungsten.
30. A contour collimator as claimed in claim 4, wherein each of said
diaphragm plates in said two groups of diaphragm plates are individually
displaceable beyond said center line.
31. A contour collimator as claimed in claim 1, further comprising means
for identifying the displaced position of each of said diaphragm plates.
32. A contour collimator as claimed in claim 31, wherein said engagement
means of said diaphragm plates is a plurality of teeth on each diaphragm
plate, and wherein said means for identifying the displaced position of a
diaphragm plate comprises means for counting the number of teeth which
pass a point when said diaphragm plate moves to said displaced position.
33. A contour collimator as claimed in claim 1, wherein said diaphragm
plates consist of a tungsten-nickel alloy.
34. A contour collimator as claimed in claim 1, wherein said radiation beam
has a center line, and wherein said means for mounting includes a pair of
wall plates with said diaphragm plates disposed therebetween, said wall
plates having respective symmetrical interior surfaces tapering toward
said center line to a shortest dimension between said interior surfaces,
and wherein each of said diaphragm plates has an edge facing said center
line and an opposite edge, said edge facing said center line of each
diaphragm plate having a smaller thickness than said opposite edge of the
same plate.
35. A contour collimator as claimed in claim 34, wherein each of said
diaphragm plates has an edge facing said radiation beam and a further
opposite edge, and wherein said edge of each plate facing said radiation
beam has a smaller thickness than the further opposite edge of the same
plate.
36. A contour collimator as claimed in claim 1, wherein each of said
diaphragm plates has a wedge-shaped cross section in two perpendicular
directions.
37. A contour collimator as claimed in claim 36, wherein said means for
mounting includes two spaced wall plates between which said diaphragm
plates are disposed, and wherein said radiation beam has a center line
with said wall plates having respective interior surfaces with a greatest
distance therebetween at a location farthest from said center line.
38. A contour collimator as claimed in claim 37, wherein each of said
diaphragm plates has an upper edge closest to said radiation beam, wherein
said radiation beam emanates from a radiation source having a focus
disposed at a distance of about 46 cm from said upper edges of said
diaphragm plates, and wherein said wall plates taper outwardly from said
center line to said greatest distance at about 0.54 mm for each 10 cm of
wall plate length.
39. A contour collimator for use in shaping a radiation beam, said
collimator having a plane of symmetry and comprising on each side of said
plane of symmetry:
a plurality of radiation-impermeable diaphragm plates, each plate having a
plurality of teeth thereon;
means for mounting said diaphragm plates side-by-side in the path of said
radiation beam with each diaphragm plate being individually displaceable
so as to permit passage of radiation through said collimator;
at least one drive gear wheel having teeth engageable with said teeth of
said diaphragm plates and carried on a shaft connected to a motor which
rotates said shaft and said drive gear wheel to displace one of said
diaphragm plates;
at least one interlock shaft having exterior teeth for engaging said teeth
of said diaphragm plates, said interlock shaft having a bore therein in
which said shaft carrying said drive gear wheel is rotatably received,
said interlock shaft retaining a remainder of said diaphragm plates in
their respectively existing positions during displacement of said one
diaphragm plate;
a frame on which said interlock shaft and said shaft carrying said drive
gear wheel are mounted; and
means for selectively displacing said frame transversely to the direction
of displacement of said diaphragm plates for positioning said drive gear
wheel in engagement with a selected one of said diaphragm plates to be
displaced.
40. A contour collimator as claimed in claim 39, wherein said shaft
carrying said drive gear wheel extends into said bore in said interlock
shaft from one side thereof, and further comprising:
a second shaft carrying a second drive gear wheel thereon, said second
drive gear wheel having teeth engageable with another of said diaphragm
plates to be displaced simultaneously with the diaphragm plate engaging
said drive gear wheel, said further shaft extending into an opposite side
of said bore in said interlock shaft and said further shaft is connected
to a motor which rotates said further shaft and said further drive gear
wheel independently of said shaft and said drive gear wheel. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is directed to a contour collimator for radiation therapy
having a prescribed plurality of diaphragm plates displaceably arranged
relative to one another. It is particularly directed to a multi-leaf
collimator that is utilized for limiting the radiation field of an
ionizing radiation, preferably for limiting the radiation field of gamma
radiation in a linear accelerator.
2. Description of the Prior Art
Radiation apparatus employed in oncological radiation therapy are equipped
with radiation field collimators which only allow the adjustment of
rectangularly limited radiation fields. It is currently known, however,
that better therapy results could be achieved in many oncological
investigations if the radiation dose distribution could be adapted to the
usually irregular shape of the target volumes (tumors are usually not
spherical).
To this end, irregularly shaped auxiliary collimators are individually
fabricated for use in radiation therapy. The equipment required for the
manufacture of such collimators is commercially available. Such equipment
enables irregular radiation field shapes to be cut out of rigid plates of
expanded plastic on the basis of X-ray picture models and to cast the part
with metal alloys having a low melting point. This manufacturing procedure
can only be carried out given individual irradiation angles and is rather
involved.
The use of arbitrarily adjustable collimators based on the multi-leaf
principle (what are referred to as "multi-leaf collimators") was proposed
by Takahashi as early as 1965 ("Confirmation Radio Therapy", Acta
Radiologica, Suppl. 242 (1965), 1-142). Such manually adjustable
collimators were then likewise utilized world-wide in various radio
therapy centers in the further course of radiation therapy. The advantage
over collimators manufactured in accord with the casting principle,
however, is slight. Cutting out and casting is replaced by the likewise
time-consuming manual adjustment of the individual "collimator leafs" or
"diaphragm plates".
The development of motor-adjustable multi-leaf collimators is currently
being pursued at many radio therapy centers in view of the availability of
inexpensive microelectronic control components. These collimators are
provided for employment at neutron irradiation systems, at photon
radiation sources and, in particular, at linear accelerators. These unit
share the principle of the single-leaf drive. Every leaf (diaphragm plate)
of the multi-leaf collimator is driven by its own stepping motor. The
number of required stepping motors is identical to the number of
individual leaves. The outlay for complicated electronics which is
susceptible to malfunction and the space requirement for the integration
of such a collimator into an iradiation installation is extremely high
since a total of at least forty leaves and, as a result thereof, forty
stepping motors, is required.
German patent No. 192 300 discloses a contour collimator wherein two
oppositely arranged groups of mutually displaceable, small rods
impermeable to X-rays are provided for admitting only a prescribed profile
from the radiation field of an X-ray source. This collimator is not
suitable for radiation therapy wherein, in particular, high-energy photons
(gamma radiation) are employed, since no actual "diaphragm plates" are
employed. Moreover, only a manual adjustment of the small rods is
provided. Such a manual adjustment, however, is usually too slow for
radiation therapy, wherein a plurality of radiation fields having
different profiles are successively applied.
German AS No. 1 010 659 discloses a collimator for shaping a useful
radiation beam from the radiation of a high-energy radiator, for example a
cobalt-60-preparation, comprising diaphragm plates which are adjustable
perpendicularly relative to the central ray of the beam to be shaped. In
this collimator, a separate adjustment element is provided for every
individual diaphragm plate. A drive element, for example, a drive shaft
shared by all adjustment elements is connected to each of the adjustment
elements only via friction clutches. The limitation of the desired
radiation field is prescribed by a perforated plate into which pins are
plugged. Given such a collimator, it is difficult to set a new radiation
field within a short time. Moreover, the collimator is not suitable for
oscillations in a vertical plane. In a certain position, the sliding
clutch responds under the influence of the weight of the collimator
plates; diaphragm plates would thus fall out, and a change in the contour
results. Further, a sliding clutch does not guarantee the patient safety
in what is referred to as a one-time irradiation in which the total dose
required is applied in fractions as the radiation source and collimator
are moved around the patient.
German patent No. 30 30 332 discloses a primary radiation diaphragm for an
X-ray examination installation wherein a plurality of gating elements
limiting the radiation cone from various sides are employed, these being
composed of thin metal strips pressing against one another. The elements
are mutually displaceable in the longitudinal direction and are combined
in packets. For remotely controllable adjustment, every metal strip
carries a nose extending transversely relative to the displacement
direction and perpendicularly relative to the gating plane. The nose is
disposed at the side of the element facing away from the symmetry axis of
the primary radiation diaphragm. Every metal strip packet has an
adjustment element allocated to it, this adjustment element being
adjustable by an x, y-drive and being engageable with the individual metal
strips. This contour collimator is only suitable for low energies since
relatively short diaphragm plates are employed. Given a 360.degree.
rotation of the collimator around a patient, the individual diaphragm
plates would fall out because no interlock is provided. An adjustment
element for the individual diaphragm plate is provided, but this can only
move low diaphragm plate weights. As a result of its design, moreover,
this is limited only to the adjustment of softly shaped contours or
profiles, i.e. contours or profiles without steps.
SUMMARY OF THE INVENTION
An object of the present invention is to fashion a contour collimator of
the type initially cited such that a simple, finely stepped adjustability
of the diaphragm plates is guaranteed with low outlay, whereby an adequate
security against the maladjustment of a selected radiation contour is
simultaneously established.
This object is achieved in accordance with the principles of the present
invention in a collimator having:
(a) teeth at every diaphragm plate,
(b) an adjustment element shared by the prescribed plurality of diaphragm
plates for the adjustment of a first diaphragm plate relative to the
remaining diaphragm plates, this adjustment element being in engagement
with the teeth of the first diaphragm plate,
(c) an interlock mechanism in engagement with the teeth of the remaining
diaphragm plates, and
(d) a mechanism for displacing the adjustment element from the teeth of the
first diaphragm plate to the teeth of a neighboring, second diaphragm
plate, the first diaphragm plate being locked during this displacement and
the second diaphragm plate being unlocked.
The second diaphragm plate need not be the plate placed immediately next to
the first diaphragm plate; it can also be a further diaphragm plate.
What is guaranteed in such a contour collimator is that the contour set for
a prescribed irradiation direction does not automatically change. As a
result thereof, the collimator is especially suited for application in
combination with radiation sources which move during the irradiation. In
particular, this collimator can be utilized when circling around a tumor
to be irradiated. Tumors are normally irregularly shaped. In radiation
therapy, they are usually approached from various irradiation directions.
The through aperture or contour of the contour collimator in continuous or
stepped revolution around the tumor can thus be quickly adapted to its
respectively current contour, i.e. the contour seen from the irradiation
direction. This enables short irradiation times, being particularly
significant for high-energy gamma radiation which is generated by a linear
accelerator. Given a known profile of the tumor which, for example, can be
identified by a computer tomograph exposure and by three-dimensional
calculation and irradiation planning following thereupon, the contour can
be motor-adjusted when circling around without having to fear that
individual diaphragm plates will change their established position or will
even fall out. What is thereby achieved is that the tumor is irradiated
tightly bounded and healthy tissue is optimally preserved.
In one embodiment of the invention a further prescribed plurality of
diaphragm plates is arranged next to the first-cited diaphragm plate, and
an identically constructed interlock and displacement mechanism is
allocated to these further diaphagm plates. In this way, a displacement of
diaphragm plates for the purpose of adjustment of a new contour can be
carried out from two sides, which shortens the access time and thus the
irradiation duration.
A further embodiment has a symmetrical structure with respect to a center
line. Packets of diaphragm plates which are respectively displaceable
relative to one another are thus arranged at both sides of this center
line. The diaphragm plates of the two packets are thereby arranged so as
to be moveable toward one another. The arrangement is preferably
undertaken such that the diaphragm plates can be respectively swiveled
beyond the center line into the region of the other packet of diaphragm
plates. Asymmetrical radiation fields can be set in this way.
Given a suitable selection of the tooth spacings in the teeth of every
diaphragm plate, the individual diaphragm plates can be displaced to a
greater or lesser degree in the direction toward the center line in fine
steps. The desired irradiation profile can be set with great precision in
this way.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a linear accelerator wherein a contour collimator of the
invention is utilized.
FIG. 2 is a side view of the contour collimator of the invention.
FIG. 3 is a side view of a diaphragm plate which is inserted in the right
diaphragm plate packet of FIG. 2.
FIG. 4 is an end view of the straight edge of the diaphragm plate of FIG. 3
which defines the radiation beam.
FIG. 5 is a view as seen from direction A in FIG. 2 of the contour
collimator of FIG. 2, partially broken away.
FIG. 6 is a view as seen from direction B in FIG. 2 of the left part of the
contour collimator of FIG. 2 without diaphragm plates.
FIG. 7 is a sectional view taken along line C--C through the right part of
the contour collimator of FIG. 2.
FIG. 8 is a view from above of a portion of another embodiment of contour
collimator in accord with the invention.
FIG. 9 is a side view of a diaphragm plate that is utilized in the right
front diaphragm plate packet group of FIG. 8.
FIG. 10 is a section through the left part of the diaphragm plate of FIG. 9
along the line X--X.
FIG. 11 is a section through the right part of the diaphragm plate of FIG.
9 along the line XI-XL.
FIG. 12 is a plan view of the diaphragm plate of FIG. 9.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a part of a known embodiment of a linear accelerator 2 wherein
a contour collimator 4 having serial drive of the individual diaphragm
elements in accordance with the principles of the present invention is
utilized. The linear accelerator 2 has a gantry 6 which is rotated around
a horizontal rotational axis 8 in the course of a theraputic treatment.
The principle ray of the radiation beam emerging from the linear
accelerator 2 is referenced 10. During the treatment, the ray 10 is
directed onto the zone 12 of a patient 13 to be treated which lies in the
isocenter. The rotational axis 8 of the gantry 6, the rotational axis 14
of a treatment table 16 and the radiation axis 10 intersect in the
isocenter.
FIG. 2 shows a lateral view of details of the contour collimator 4. This is
composed of two parts or sides I, II which are fashioned symmetrically
relative to one another with respect to a vertical plane which proceeds
through the one symmetry line 20. Given optimum adjustment, the symmetry
line 20 coincides with the direction of maximum radiation of the radiation
beam of high-energy radiation emanating from a focus F. In particular,
this radiation can be x-radiation. As proceeds from FIG. 5 (viewed in
direction A in FIG. 2), a center line 22 lies between the sides I and II,
this center line 22 defining the vertical symmetry plane together with the
symmetry line 20. The center line 22 coincides with the y-axis of an
xyz-coordinate system. The z-axis thereof is formed by the symmetry line
20. The beam contour (profile) lying in the region of the symmetry line 20
and achieved by beam blocking out is referenced 24.
As shown in FIGS. 2 and 5, first and second vertically placed, lateral
outside plates 26 and 28 are arranged parallel to one another at some
distance from one another. Beginning at a certain distance from the
symmetry plane defined by lines 20 and 22, the upper edges of these
outside plates 26 and 28 are provided with teeth 30 and 30' and 32, 32' in
recesses shaped as circular arcs.
The sides I and II are symmetrically constructed with respect to the
symmetry plane so that it suffices to describe only the left side I in
detail. The corresponding component parts placed at the right side II are
respectively provided with a prime at the allocated reference numeral.
They have the same structure and the same function. They shall also be
occasionally discussed below.
A packet of two groups of diaphragm plates 36 and 38 displaceable relative
to one another is arranged between the two lateral outside plates 26 and
28. All diaphragm plates 36 and 38 in the front or back group are
constructed in the same fashion and are arranged side-by-side. They are
nonetheless provided with different reference characters because--as shall
be set forth in greater detail below--they are actuated by different
devices. For example, the overall packet can comprise 28 diaphragm plates
36 and 38. The same is true of the diaphragm plates 36' and 38' of the
diaphragm plate packet arranged at the right.
One arbitrary diaphragm plate of the identical diaphragm plates 36' and 38'
of the right side II is shown in greater detail in FIGS. 3 and 4 and is
referenced 37'. It is essentially quadratically shaped. The straight end
39' at the left serves for limiting the radiation beam or cone. The upper
edge 41' is provided with a circular arc-shaped recess in which a tooth
arrangement 43' is disposed at the right. This tooth arrangement 43'
preferably comprises triangular teeth 45' which are arranged at respective
spacings of about 1.5 mm. As a result of this fine tooth arrangement 43',
the diaphragm plates 36' and 38' can be individually pivoted and can be
pivoted in fine steps parallel to the x-z plane, namely in respective
steps of 1.5 mm. The tooth arrangement 43' coincides with the toothings
30' and 32' of the retained outside plates 26 and 28.
An arcuate guide channel 47' is cut into the diaphragm plate 37' below the
center thereof. This curved guide channel 47' serves for the guidance of
the diaphragm plate 37' such that the straight edge 39' always proceeds
parallel to the outer ray of the limited radiation cone. In other words,
the straight edge 37' is always directed onto the focus F of the radiation
source while being guided along the guide channel 47'. The radius R of
curvature for this guide channel 47' can, for example, amount to 53 cm.
The radius R of curvature is entered at the swiveling arc 46' in FIG. 2.
In particular, the diaphragm plate 37' can be composed of tungsten or of a
material containing tungsten such as a tungsten-nickel alloy. In accord
with FIG. 4, it has a wedge-shaped cross section. In other words, the edge
41' facing the radiation source, and thus the focus F, has a thickness d1
that is smaller than the thickness d2 at that edge 42' facing away from
the radiation source.
The diaphragm plates 36 and 38 of the left side I are fashioned identical
to the diaphragm plates 36' and 38'. They are merely arranged
side-inverted between the outside plates 26 and 28. In general, they are
respectively referenced as diaphragm plate 37.
In FIG. 2, diaphragm plates 37 and 37' from the respective packets at the
left and right sides I and II are shown in broken lines. Both diaphragm
plates 37 and 37' are shown in a position pushed out from the middle line
22. They are shifted relative to the outside plates 26 and 28. It may also
be seen in FIG. 2 that the two diaphragm plates 37, 37' are pivoted around
the focus F in this position. Guide pins 48 and 49 (or 48' and 49') which
connect the lateral outside plates 26 and 28 to one another serve for
guidance along the guide channels 47 and 47' during swiveling (drive via
the teeth arrangements 43 and 43'). When the contour collimator 4 is in a
symmetrical position and entirely closed, then the straight edges 39 and
39' which are directed toward the focus F are in the symmetry plane
defined by lines 20 and 22. In order, however, for the diaphragm plate 37
to be also be able to travel into the region of the right side II (and,
correspondingly, the diaphragam plate 37' into the region of the left side
I), the guide channels 47 and 47' are executed somewhat longer than
actually required for the symmetrical closed position. This is indicated
by the spacing a and a' in FIG. 2. It has been shown that given a spacing
a=a'=10 mm a diaphragm plate 37 and 37' having a base width of 10 cm can
be moved adequately far into the neighboring side II or I.
A common adjustment element is provided for the prescribed plurality of
diaphragm plates 30 of the front group. This serves for the serial
displacement of a respectively first diaphragm plate selected from these
diaphragm plates 36 relative to the remaining diaphragm plates 36. As set
forth further below, this adjustment element is in engagement with the
teeth of the selected diaphragm plate 36. Further, an interlock mechanism
engaged with the teeth of the remaining diaphragm plates 36 of the front
group is provided. There is also a mechanism for displacing the adjustment
element from the teeth of the selected diaphragm plate to the tetth of a
neighboring, second diaphragm plate. When the adjustment element is
displaced from the first to the second diaphragm 36, the first diaphragm
plate 36 is interlocked and the neighboring, second diaphragm plate 36 is
unlocked. The second diaphragm plate 36 can then also be shifted relative
to all diaphragm pluralized 36 that are now interlocked. Instead of this,
one can also proceed to a third, fourth, etc. diaphragm plate 36 and these
can be pivoted.
A corresponding adjustment element and corresponding mechanisms are also
provided for the back group of diaphragm plates 38. The two mechanisms for
displacing the adjustment elements are largely identical, i.e are formed
by the same component parts.
The adjustment element and the interlock mechanism for the front group of
diaphragm plates 36 shall be considered first; the back group shall then
be considered.
According to FIGS. 5 and 6, this adjustment element comprises a driving
gear wheel 50 of roughly the thickness d1 of the allocated diaphragm
plates 36 measured at the teeth arrangement 43 and which is in engagement
with the selected diaphragm plate. This gear wheel 50 is connected to an
electric motor 52, preferably to a stepping motor via an adjustment shaft
51. The adjustment shaft 51 extends roughly up to the center of the
system, cf. FIG. 6. As proceeds from FIG. 7, a coupling 53 can also be
arranged between the front end of the adjustment shaft 51 and the motor
52. The back end region of the adjustment shaft 51 is toothed and the
drive gear wheel 50 is slipped onto this end region. When the motor 52
turns, the drive gear wheel 50 also rotates in the desired direction,
whereby the selected diaphragm plate 36 is entrained via its teeth until
it has assumed the desired final position.
An interlock mechanism is also provided for the adjustment element for the
selected diaphragm plate 36. This interlock mechanism encompasses first
and second toothed shafts 54 and 56. These two shafts 54 and 56 are broad
gear wheels comprising longitudinal bores which are axially aligned with
one another. The teeth coincide with the teeth 30 and 32 of the lateral
plates 26 and 28 and the teeth 37 of the diaphragm plates 36 and 38. The
drive gear wheel 50 lies axially between the two shafts 54 and 56. Its
outside diameter as well as its teeth are respectively identical to the
outside diameter and the teeth of the shafts 54 and 56. The adjustment
shaft 51 is thereby conducted through the longitudinal bore of the shaft
54 and is introduced into the longitudinal bore of the shaft 56. The two
shafts 54 and 56 are connected to one another by a sleeve-shaped
connecting part 57 comprising a lower recess 58 (cf. FIG. 7) for enabling
an engagement into the tetth arrangement 43. The fastening screws employed
for this purpose and arranged at the top are referenced 59 in FIG. 5.
The two rollers or shafts 54 and 56 are part of a frame 60 and are thus not
rotatable around their longitudinal axes. 0f the entire section between
the front end of the shaft 54 and the back end of the shaft 56, only that
part which is occupied by the drive gear wheel 50 is rotatable around the
longitudinal axis. The two shafts 54 and 56 thus serve for arresting the
diaphragm plates 36 lying therebelow, whereas the drive gear wheel 50 is
provided for swiveling, i.e for displacing the selected diaphragm plate 36
in the x-direction.
It may be seen from FIGS. 5 and 6 that a third toothed shaft 62 having the
same diameter and same teeth spacing is also provided. This is axially
aligned relative to the two other shafts 54 and 56. Together with the
shaft 56, it serves as an interlock element for the non-selected diaphragm
plates 38 of the back group. Accordingly, a second drive gear wheel 64 of
the same diameter is arranged between the two shafts 56 and 62. This is
seated on one end region having teeth of a second adjustment shaft 65. The
second adjustment shaft 65 has its other end likewise connected to a motor
66. A coupling (not shown) can also be provided here again between the
second adjustment shaft 65 and the motor 66. The motor 66 is provided for
swiveling, i.e. for advancing the respectively selected, back diaphragm
plate 38 parallel to the x-direction. The motor-driven swiveling ensues
until the apertaining diaphragm plate 38 has assumed the desired final
position.
By employing two adjustment elements 52, 51, 50 as well as 66, 65, 64 the
adjustment time in which the diaphragm plates 36, 38 are set in the
displacement direciion x is cut in half.
Given small fields to be irradiated, the spacing a between the two drive
gear wheels 50 and 64 should be selected relatively small. Both drive
units can then be utilized and the afore-mentioned, halved adjustment time
then derives.
The sleeve-shaped connecting piece 57 also holds the third shaft 62 axially
aligned relative to the two other shafts 54 and 56. Screws 69 are also
provided at the top for fastening. These are arranged in a line parallel
to the y-axis together with the screws 59. As may be seen from FIG. 6, all
three shafts 54, 56 and 62 are a component part of the aforementioned
frame 60.
This frame 60 is a component part of the aforementioned means for
displacing the said adjustment element. It comprises first and second
lateral arms 71 and 72 which are aligned parallel to the x-axis and which
are rigidly connected to one another by two parallel guide rods 73 and 74,
being connected in roughly their central region. The two guide rods 73 and
74 thereby have their end sides connected to the lateral arms 71 and 72.
The frame 60 also includes the axial arrangement of the shafts 54, 56, 62.
The toothed shafts 54 and 62 thereby have their end sides firmly connected
to the respective lateral arms 71 and 72. This can ensue firmly fitting
the end teeth into a hole in the respective lateral arms 71 and 72. This
frame 60 is displacable by a further stepping motor 75, being displacable
transversely relative to the diaphragm plates 36 and 38, i.e. in
y-direction. The motor 75 for the cross-displacement is shown next to the
motor 66 in FIG. 6. It is thereby connected to an adjustment spindle 76,
i.e. to a rod comprising a thread 77. The adjustment spindle 76 is
conducted through a hole in the second lateral arm 72 and is rotatably
seated in the first lateral arm 71. It turns in a thread that is attached
in a retaining block 78 transversely relative to the longitudinal
direction. The retaining block 78 thereby has its longitudinal direction
extending parallel to the xz-plane. The parallel arrangement of the
adjustment spindel 76 between the guide rods 73 and 74 may be seen from
FIGS. 2, 5 and 6. The retaining block 78 is rounded at its ends, and also
accepts the guide rods 73 and 74, if necessary in respective linear ball
bearings (cf. FIG. 6).
The retaining block 78 receives a shaft 79 parallel to the y-direction. The
thrust shaft 79 is thereby secured to the retaining block 78 with a screw
(not shown) at both sides, and is conducted through holes in the lateral
arms 71 and 72 and can glide or slide therein (upon actuation of the
spindle 76). When, under the influence of the motor 75, the adjustment
spindle 76 rotates in one of the two directions, the entire, inherently
rigid frame 60 composed of the component parts 54, 56, 57, 62, 71, 72, 73
and 74 is shifted parallel to the y-axis with the parts 50, 51, 52 and 64,
65, 66. The retaining block 78 thereby remains stationary. The
displacement ensues in whole steps equal to the thickness d1 of the
diaphragm plates, for example in respective whole multiples of d1=3 mm.
The diaphragm plates 36 and 38 to be adjusted are selected in this way.
During displacement, moreover, both gear wheels 50 and 64 are
simultaneously displaced parallel to each o | | |
