X-ray or gamma ray systems or devices – Beam control – Collimator
Reexamination Certificate
1998-05-15
2001-02-13
Porta, David P. (Department: 2876)
X-ray or gamma ray systems or devices
Beam control
Collimator
C378S065000, C378S152000
Reexamination Certificate
active
06188748
ABSTRACT:
This invention relates to a contour collimator for radiotherapy, comprising a plurality of plate-shaped diaphragm elements movably arranged with respect to each other in a guiding block to form a contour diaphragm for a radiation beam emitted by a radiation source towards the collimator, and at least one drive for moving the diaphragm elements.
Such a contour collimator is known from EP 0 387 921 B1. In radiotherapy, such contour collimators serve for forming a diaphragm whose opening corresponds to the contour of the area of the human body to be irradiated, so that the high-energy rays emanating from the radiation source only impinge on this area and the surroundings of this area are shielded from the radiation.
The known contour collimator provides for each group of a given number of plate-shaped diaphragm elements a common adjusting part which serves for serially moving one select diaphragm element each relative to the remaining diaphragm elements. For this purpose, a gear of the adjusting part meshes with a rack provided at the diaphragm element and a non-rotary, toothed area of the adjusting part meshes with the rest of the diaphragm elements to fix them. In order to accelerate the adjusting step, the prior art proposes to provide two such adjusting parts on either side of the contour collimator.
For moving the individual diaphragm elements, the prior art makes necessary that the respective adjusting part is initially moved translatorily and transversely to the diaphragm elements, so that the adjusting gear comes into engagement with the rack of a select diaphragm element. Then, a rotation is applied to the gear to move the associated diaphragm element. This process has to be repeated for each diaphragm element of a group.
It is the object of the present invention to create a contour collimator of the generic kind, which can be adjusted more rapidly and altogether has a simpler and thus operationally more reliable design requiring less maintenance.
According to the characterizing part of claim
1
this object is achieved in that a drive is associated with each diaphragm element, that the drives of one group of diaphragm elements are substantially adjacent to one another and that a driving transmission is provided between each drive and the associated diaphragm element.
In spite of the distance which is laterally very narrow between the individual diaphragm elements and corresponds approximately to the thickness of a diaphragm, e.g. 1 mm, it is possible with this design to equip each diaphragm element with a drive of its own thus actuating it separately. This serves for considerably accelerating the adjusting time for a contour collimator, so that the irradiation time for each patient is reduced in one respect, which is a relief for the patient and is also simultaneously accompanied by an increase in economic efficiency.
In an advantageous embodiment, the drives are arranged substantially as a semicircle. This serves for obtaining an especially simple and clearly arranged design in which the driving transmissions have substantially equal length, so that equal components can be used for the design.
In a further advantageous embodiment, each driving transmission has a flexible towards tension-resistant and pressure-resistant power-transmitting element, one end of which is connected with the associated diaphragm element and the other end of which is connected with the associated drive and which is movably supported in translatory fashion in a moving guide. Such a power-transmitting element permits an especially flexible arrangement of the drives.
When each power-transmitting element is detachably coupled to its associated diaphragm element via a coupling linkage, this creates a simple design of the contour collimator, which also permits the rapid exchange of individual elements without any difficulties.
The same advantage occurs when each power-transmitting element is detachably coupled to its associated drive via a coupling linkage.
Each power-transmitting element advantageously comprises a spring band.
Each drive is preferably formed by a linearly acting motor. This renders possible an especially slim or narrow design of the arrangement of drives, so that the arrangement of drives can be very compact.
In this connection, the motor is preferably an electric linear motor.
As an alternative, the motor is an electric motor having a linearly acting gearing, preferably a rack-and-pinion gear or a spindle gearing.
When the guiding block has upper and lower guide plates each of which is provided with a plurality of upper guide grooves and lower guide grooves, respectively, for the diaphragm elements, an especially reliable and fail-safe adjustability of the diaphragm elements is guaranteed.
In a preferred embodiment, the upper and lower guide plates are each provided with a preferably rectangular opening, which determine the maximum diaphragm opening and have a common middle plane extending substantially rectangularly with respect to the longitudinal direction of the guide grooves.
When the moving guides are arranged substantially side by side in a moving guide block and have moving guide gaps which diverge in bent and fan-shaped fashion and each of which accommodates a power-transmitting element in translatorily movable fashion, safe guidance of the power-transmitting elements is achieved, so that an accurate translatory adjustment of the diaphragm elements is possible, since undesired bulging of the power-transmitting elements is prevented by the gap walls tightly abutting against the respective power-transmitting element.
An especially compact arrangement will be formed when two superposed planes of drive arrangements are associated with each moving guide block, two superposed drives each being applied to one power-transmitting element accommodated in contiguous moving guides. By this, the overall width of the contour collimator can be limited effectively in spite of a plurality of movable diaphragm elements.
When two opposite groups of translatorily drivable diaphragm elements are provided in the guiding block, two opposite diaphragm elements each being guided in upper and lower common guide grooves, on the one hand, the provision of the opposite groups of diaphragm elements creates the possibility of adjusting contours rotating about an angle of 360° and, on the other hand, it is made possible to achieve complete screening in the area of said guide groove by contact of two opposite diaphragm elements.
When each diaphragm element of a pair of opposite diaphragm elements is movable with its free edge facing away from the respective drive beyond the common middle plane of the openings in the lower and upper guide plates, contours can be produced which have strong constrictions on one side as is the case e.g. with kidney-shaped contours.
It is preferred to associate with each drive a displacement pickup, preferably a potentiometer, for detecting the current position of the corresponding diaphragm element.
This serves for enabling an accurate control of the diaphragm element positions, so that e.g. the contour can automatically be adjusted by a computer program.
This embodiment is especially reliable and inexpensive when the displacement pickup has a moving potentiometer which can be actuated translatorily.
If at least one of the diaphragm elements disposed within the region of the central middle ray of the radiation beam is provided with at least one thickening rib extending in the translational direction, reliable shading of the central middle ray will be achieved, since the thickening rib shades the middle ray extending parallel to the diaphragm element. As an alternative, the diaphragm elements can be inclined towards the ray. Moreover, the top of a middle diaphragm element can alternatively be thicker than its bottom.
This shading effect is even intensified when each thickening rib meshes with a corresponding groove in the adjacent diaphragm element.
REFERENCES:
patent: 4313349 (1982-02-01), Heitman
patent: 4868844 (1989-09-01), Nunan
patent: 5160847 (1992-11-01), Leavitt e
Höver Karl-Heinz
Maier-Borst Wolfgang
Pastyr Otto
Schlegel Wolfgang
Barrett William A.
Deutsches Krebsforschungszentrum Stiftung des Offentlichen Recht
Hultquist Steven J.
Porta David P.
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