Patent Number: 062663933
Section: description

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Reference is now made to FIG. 1 which illustrates a radiation system 10 in which a multileaf collimator 12, constructed and operative in accordance with a preferred embodiment of the present invention, is installed. Radiation system 10 is illustrated as having a conventional LINAC gantry design, but it is appreciated that the multileaf collimator of the present invention is applicable to any radiation system design, such as the system of applicant/assignee's U.S. patent application Ser. No. 08/753,822 now U.S. Pat. No. 5,879,281, the disclosure of which is incorporated herein by reference. Radiation system 10 includes a gantry 14 which can be rotated about a horizontal axis 16 in the course of a therapeutic treatment. Collimator 12 is fastened to an extension 18 of gantry 14. Extension 18 includes a source of radiation, such as a linear accelerator, for generating a radiation beam 20 which is emitted from a central axis of radiation system 10 which is coincident with a central axis of collimator 12. Any radiation may be used, such as electron radiation or photon radiation (gamma radiation). During treatment, beam 20 is trained on a target in a patient 24 to be treated and which lies in the isocenter 22 of the gantry rotation. Axis 16 of gantry 14, an azimuthal rotational axis 26 of a treatment table 28 and beam 20 all intersect at the isocenter 22. Imaging apparatus 25, such as a fluoroscope or ultrasound apparatus, for example, is preferably provided for imaging the target irradiated by radiation beam 20. Imaging apparatus 25, inter alia, may be used in conjunction with a closed loop, feedback control system (not shown) for controlling a position of gantry 14 and for controlling the functioning of collimator 12. Reference is now made to FIG. 2 which illustrates (in a top view) a first layer 30 of a plurality of radiation blocking leaves 32 of multileaf collimator 12, constructed and operative in accordance with a preferred embodiment of the present invention. Leaves 32 are arranged adjacent one another so as to form two opposed rows of adjacently positioned leaves movable in a longitudinal direction (Y) 34 which is generally traverse to the direction of beam 20, i.e., pointing perpendicularly to the plane of FIG. 1, so as to define a radiation beam shaping field 36, shown in phantom outline, between the opposed ends of the leaves 32. Actuator apparatus 38 is provided for moving leaves 32 in longitudinal direction 34 so as to controllably define radiation beam shaping field 36. Actuator apparatus 38 preferably includes an actuator 39 dedicated for each leaf 32. An example of actuator 39 is an individually driven worm gear for individually engaging a toothed track or floating nut mounted on each leaf 32, such as the prior art leaf driving means described in U.S. Pat. No. 5,160,847 to Leavitt et al., the disclosure of which is incorporated herein by reference. Radiation beam shaping field 36 is tailored to fit as closely as possible to the shape of a target 37 to be irradiated. Reference is now made to FIG. 3 which similarly illustrates (in a top view) a second layer 40 of a plurality of radiation blocking leaves 42 of multileaf collimator 12, constructed and operative in accordance with a preferred embodiment of the present invention. Leaves 42 are arranged adjacent one another so as to form two opposed rows of adjacently positioned leaves movable in a cross-over direction (X) 44 which is generally traverse to the direction of beam 20, i.e., pointing perpendicularly to the plane of FIG. 1, so as to define a radiation beam shaping field 46, shown in phantom outline, between the opposed ends of the leaves 42. Cross-over direction 44 is shown in FIG. 3 as being generally orthogonal to longitudinal direction 34, however, cross-over direction 44 may make any arbitrary angle with longitudinal direction 34 other than 90.degree.. Actuator apparatus 48 is provided for moving leaves 42 in cross-over direction 44 so as to controllably define radiation beam shaping field 46. Actuator apparatus 48 preferably includes an actuator 49 dedicated for each leaf 42, as described hereinabove for actuator apparatus 38. Radiation beam shaping field 46 is tailored to fit as closely as possible to the shape of target 37. However, it can be seen in FIG. 3 that the irregular shape of target 37 is poorly covered by leaves 42 alone, which is one of the drawbacks of the prior art systems such as that of U.S. Pat. No. 5,591,983. As will be described with reference to FIG. 5, an advantage of the present invention is that the overlapping of layers 30 and 40 helps to improve the resolution of coverage of target 37. Leaves 32 and 42 are constructed of a radiation impervious material, such as tungsten. Referring now to FIG. 4, each of the leaves is characterized by a length L and a width W traverse to the direction of beam 20, and a thickness T generally along the direction of beam 20. Adjacent leaves in each layer 30 and 40 are separated by a spacing G and layers 30 and 40 are separated by a spacing F. All of the above geometric parameters, L, W, T, G and F may be the same or different for each individual leaf or layer. Another advantage of the present invention is that the unique, crossed overlapping of layers 30 and 40 allows employing smaller values of T than prior art systems such as that of U.S. Pat. No. 5,591,983, thereby realizing cost savings in materials and manufacture. Referring again to FIG. 1, layers 30 and 40 of leaves 32 and 42, respectively, are housed in a frame 50. Reference is now made to FIG. 5 which is a simplified top view illustration of overlapping of first and second layers 30 and 40 in accordance with a preferred embodiment of the present invention, wherein layers 30 and 40 are orthogonal to each other. It may be seen that the overlapping of layers 30 and 40 helps to improve the resolution of coverage of target 37. Gaps 52 are formed generally traverse to the beam direction 20 and generally in a plane of the X and Y directions, 34 and 44. Each of gaps 52, which may be of equal or varying sizes, only allow an amount of radiation to pass therethrough below a predetermined threshold within the safety standards of the industry. Moreover, if beam 20 is not exactly orthogonal to layers 30 and 40, but rather tilted with respect thereto, even less radiation will pass through gaps 52. In accordance with a preferred embodiment of the present invention an optical control device 54 is provided that monitors travel of any of the leaves 32 or 42 and signals actuator apparatus 38 and 48, respectively, to stop moving leaves 32 and 42. Optical control device 54 may comprise any suitable optical equipment, such as a camera, CCD or equivalent. Reference is now made to FIG. 6 which is a simplified top view illustration of overlapping of first and second layers 30 and 40 in accordance with another preferred embodiment of the present invention. It is seen that the present invention may comprise a plurality of first layers 30 of radiation blocking leaves, only one leaf of an additional layer being shown for the sake of simplicity and designated as leaf 32', and a plurality of second layers 40 of radiation blocking leaves, only one leaf of an additional layer being shown for the sake of simplicity and designated as leaf 42'. As described above, the present invention is not limited to any particular angle between layers 30 and 40. 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.