Patent Number: 044505787
Section: summary

BACKGROUND OF THE INVENTION The present invention relates to the field of energy beam collimators, and more particularly to an apparatus providing an array of movable blocks to define a variable aperture to allow an energy beam to be precisely controlled and directed toward the target. In using energy beams in general, and neutron beams in particular, especially in therapeutic applications, it is necessary to be able to adjust both the size and the shape of the beam; that is to collimate the beam. At least two basic approaches to varying collimator aperture size are well known. In one technique, individual collimating devices are removed and replaced to provide variations in aperture size and shape. Generally a set of individual collimator devices having mating configurations is used. With this technique, substantial time must be spent in removing and replacing the individual collimator devices. In addition, space must be set aside for storing the individual devices when they are not in use. A second approach to collimator aperture control is seen in U.S. Pat. No. 3,688,402 to Palermo et al in which an adjustable collimator is disclosed. The collimator is used with an X ray beam and has two web assemblies, one horizontal and one vertical. Each web assembly has a pair of spaced and connected webs forming a continuous loop over a pair of rollers. The size of the aperture is adjusted by rotating the rollers to move the interconnected web to adjust the amount of space between the ends of the webs. In this arrangement, horizontal and vertical beam opaque material overlap or are stacked in certain horizontal and vertical areas, and, as a result, twice as much beam opaque material is present in areas of overlap as compared with areas which are not overlapped. The overlapping is an undersirable and inefficient use of the beam opaque material. Thus, the basic need for a new, more efficient, approach to beam collimation is identified. Neutrons from ion beam devices and cyclotrons are becoming increasingly important in the treatment of certain types of malignant tumors. Neutron beams, having no charge, cannot be directed and focussed by electrostatic or electromagnetic fields. To protect the patient, the beam must be attenuated and/or blocked in unwanted peripheral areas while being left an unimpeded path in a desired direction to form the desired effective beam. In other words, the beam must be collimated. Often it is desirable to obtain a collimated beam having either diverging or converging characteristics. In U.S. Pat. No. 3,781,564 to Lundberg a neutron beam collimator providing a divergent collimated beam is disclosed. For variations in divergence characteristics, the Lundberg device requires a plurality of fixed dimension divergent beam collimators. In contrast, it would be desirable to be able to have variably adjustable divergent beam collimation. SUMMARY OF THE INVENTION Accordingly, it is a primary object of the present invention to provide a variable aperture energy beam collimator that is easily and rapidly adjustable. It is another object to provide an adjustable beam collimator that is efficiently operable to provide either a fixed or diverging beam without individually handling beam moderating devices. Another object of the invention is to provide a variable aperture collimator efficient in the use of beam shielding material by not having overlapping or stacking of the shielding material. Another object of the invention is to provide a variable aperture collimator capable of easy set-up for defining a divergent collimated beam. Additional objects, advantages, and the novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned by the practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. To achieve the foregoing and other objects, and in accordance with the purposes of the present invention as described herein, an improved apparatus is provided for varying the aperture of an energy beam collimator. The invention includes the novel approach of employing an assembly of beam opaque blocks having adjacent edges in interfacial contact. The blocks slide with respect to each other while maintaining the sliding interfaces. When the blocks slidingly separate, an aperture forms for transmittal of the collimated energy beam. When the blocks come together in the closed position, a completely beam-opaque surface results, and no collimated beam is transmitted. Adjustment means are provided for sliding the blocks with respect to one another thereby providing the selected aperature to define the beam. By use of the invention, rapid adjustments of the collimator are possible without removing and replacing fixed-size collimator devices. In addition, with the apparatus of the invention, the array of blocks in a single block assembly are not stacked or overlapping. The adjustable blocks converge at apexes adjacent to the center of the block assembly. As to the number of blocks in the block assembly, three, four, six and eight are suitable. Four blocks, however, is the preferred number. In general, there are n blocks in number where n is greater than two. The apex angle of the blocks is equal to 360/n degrees. For four blocks, the apex angle is 90 degrees; for three blocks, 120 degrees; for six blocks, 60 degrees; and for eight blocks, 45 degrees. In accordance with the invention, the means for adjusting the blocks to provide variable aperture assembly includes a selectively movable cable attached to at least one block; the remaining blocks being followers due to the mechanical pressure transmitted at the sliding interfaces. Block guide rods engage slide brackets on the blocks to restrain the block movement along predetermined paths. Preferably, the adjusting means further comprises an elongated perforated belt section connected to the cable. The belt section is operated by a drive sprocket driven by a drive wheel assembly having a hand wheel and a worm gear and pinion. In a further aspect of the invention, in accordance with its objects and purposes, a variable aperture beam collimator is provided wherein the moving means for the guide rods allows for providing a non-equilateral variable aperture. The guide rods are moved toward and away from the center of the block assembly to control the shape of the aperture. For efficient actuation, the ends of the block guide rods are pivotally connected to T-shaped intermediate actuators mounted on rotatable shafts. When the shafts are rotated, the intermediate actuators laterally translate the guide rods causing the blocks to be offset or skewed with respect to one another. In the closed position, regardless of the offset positioning of the blocks, a completely beam-opaque surface is formed thus preventing beam transmission. In the open position, the offset blocks provide the selected, equilateral or non-equilateral collimator aperture. In still another aspect of the present invention, multiple block assemblies may be provided forming a beam channel for providing additional collimating action for an energy beam. In the preferred embodiment shown, four separate block assemblies defining separate nonequilateral apertures combine to form the beam confining channel. The center axis of the apertures are in alignment and the sides of the apertures are maintained in alignment with each other in all adjusted sizes. Alternate block assemblies are inverted front-to-back with respect to each other. As a result, the contacting edges of the blocks of the second and fourth block assemblies are not in alignment with the contacting edges of the blocks in the first and third block assemblies. This arrangement virtually eliminates the possibility of energy leakage along the edge interfaces. The only energy beam energing from the collimating apparatus is the collimated beam passing through the channel defined by the four apertures. By adjusting the block assemblies to have increasing size apertures along the channel, a collimated beam that diverges may be readily obtained. The aperture nearer the energy source is smaller with each aperture farther from the energy source being incrementally larger so that the divergent collimated beam is obtained. On the other hand, if desired, apertures nearer the energy source may be increasingly larger and then a partially convergent collimated beam may be obtained. Still other objects of the present invention will become readily apparent to those skilled in this art from the following description wherein there is shown and described a preferred embodiment of this invention, simply by way of illustration of one of the best modes contemplated for carrying out the invention. As it will be realized, the invention is capable of other different embodiments, and its several details are capable of modifications in various, obvious aspects all without departing from the invention. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive.