Patent Number: 
Section: description

Reference is now made to FIGS. 1-5 which illustrate a collimator system 10 constructed and operative in accordance with a preferred embodiment of tie present invention. Collimator system 10 preferably includes a plurality of revolvable plates 12A-12H stacked one above another. It is appreciated that this is just one example of the collimator system and that any other number of plates can be employed to carry out the present invention. Plates 12A-12H are preferably formed of a material substantially impervious to passage therethrough of radiation in a predetermined range of wavelengths, such as tungsten which is generally impervious to radiation used in most types of radiotherapy. As seen best in FIG. 2, one or more collimator apertures are preferably formed in each of the plates. (For the sake of simplicity, FIG. 2 is an exploded illustration of plates 12A, 12B and 12C only.) For example, plate 12A is formed with collimator apertures 14A-14G, plate 12B is formed with collimator apertures 16A-16G, and plate 12C is formed with collimator apertures 18A-18H. The plates 12A-12H are arranged relative to each other such that the collimator apertures formed in neighboring plates are alignable with each other to form a collimation path adapted for a radiation beam to pass therethrough. Preferably plates 12A-12H are arranged to revolve about a common axis 20. Alternatively the plates can revolve about different axes. It is noted that there is not necessarily the same amount of collimator apertures on each plate. In the example illustrated in FIG. 2, plates 12A and 12B have 7 collimator apertures each while plate 12C has 8 collimator apertures. It is appreciated that any number of collimator apertures may be formed in the plates. It is also noted that the collimator apertures of one plate may be differently sized than the collimator apertures on another of the plates. For example, collimator aperture 14G of plate 12A is smaller in diameter than collimator aperture 16A of plate 12B. Moreover, the same plate may have differently sized collimator apertures. For example, collimator aperture 18H of plate 12C is greater in diameter than collimator aperture 18A. Alternatively, one of the plates can have generally equally sized collimator apertures, such as apertures 14A-14G of plate 12A. The collimator apertures of the plates may span any diameter range, such as, but not necessarily, 5-35 mm. As seen in FIG. 2, the plates may have different thicknesses. For example, plate 12A is thicker than plates 12B and 12C. The illustration in FIG. 2 is an exploded view of the plates. As seen in FIGS. 3 and 5, in reality the plates are closely spaced to each other. Preferably a gap between neighboring plates is sufficiently small such that a radiation beam of a desired wavelength is substantially prevented from passing through the gap. In accordance with a preferred embodiment of the present invention, a controller 22 is connected to plates 12A-12H which selectively revolves the plates, as is now described with particular reference to FIGS. 3-5. It is noted that the following description is only one example of mounting and revolving the plates, and it is appreciated by persons skilled in the art that other arrangements are possible within the scope of the invention. Plates 12A, 12C, 12E and 12G are preferably securely mounted to a central axle 24 such as by means of keys 26 (FIG. 5). Plates 12B, 12D, 12F and 12H are preferably mounted on bearings 28 about the common axle 24 and are each fastened to a drum 30, such as by means of pins 32. Drum 30 is mounted to a support base 34 by means of another bearing 36. In this manner, plates 12B, 12D, 12F and 12H can rotate together with drum 30 about a longitudinal axis 38 of axle 24. Support base 34 remains stationary and can be fastened to a gantry arm 40 (FIG. 3) of a radiotherapy system. Axle 24 is preferably mounted to base 34 by means of yet another bearing 42. In this manner, plates 12A, 12C, 12E and 12G can rotate together with axle 24 about longitudinal axis 38. Plates 12A, 12C, 12E and 12G thus rotate about axis 33 independently of plates 12B, 12D, 12F and 12H. Controller 22 preferably includes a servomotor 44 linked by means of wearing, timing belt or any other suitable linkage, to plate 12A and another servomotor 46 linked similarly to drum 30 or one of plates 12B, 12D, 12F and 12H. Servomotor 44 controls rotation of plates 12A, 12C, 12E and 12G, and servomotor 46 controls rotation of plates 12B, 12D, 12F and 12H. (In FIG. 5 the servomotors are not shown for the sake of clarity.) The plates can be rotated so as to align any selected plurality of collimator apertures with a source of radiation 48 (FIG. 3). A radiation beam 50 (FIG. 3) thus passes through and is collimated by the aligned collimator apertures. Reference is now additionally made to FIG. 6 which illustrates a stop mechanism 52 which selectively arrests rotational movement of the plates. A ring 54 is preferably attached to plate 12A by means of fasteners 56. Ring 54 has a plurality of pegs 58 radially protruding therefrom. A pawl 60 is pivotally mounted to a bracket 62 and is actuated by a motor or actuator 64. Pawl 60 selectively catches one of the pegs 58 and thereby arrests rotational movement of ring 54, as well as plates 12A, 12C, 12E and 12G which are mechanically linked with ring 54. In a similar fashion, pegs 58 may be mounted on one of plates 12B, 12D, 12F and 12K, such as plate 12D, and another pawl may be used to arrest rotational movement thereof. (In FIG. 5 the stop mechanisms are not shown for the sake of clarity.) It is appreciated that although the best mode of carrying out the present invention employs revolvable plates, nevertheless the plates can alternatively be movable linearly with respect to each other. It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and subcombinations of the features described hereinabove as well as modifications and variations thereof which would occur to a person of skill in the art upon reading the foregoing description and which are not in the prior art.