Patent Number: 058898344
Section: description

FIG. 1 shows a left set of blades 1 and a right set of blades 2. To simplify the illustration, each set of blades is shown with only 16 blades, whereas the collimators according to the invention that are normally produced can have very many more blades. The configuration of blades depicted in the drawing is variable as regards their displacement. However, there is a symmetrical number of blades relative to two perpendicular axes. The blades in each set can be grouped in sets 3, 4 and 5 of uniform width; due to their symmetrical arrangement, they are labelled with references only in one comer of the drawing. Each set of blades 1, 2 consists of four outer wide blades, six medium-width blades adjoining them, and six inner narrow blades, which in this manner comprise the outer blade sets, the middle blade sets 4 and the inner blade sets 5. The blades are depicted in section on the right and left sides of the drawing. Adjustment devices (not shown), which engage the left and right terminal faces of the individual blades (also not shown), are driven by activating mechanisms such as electric motors. In this drawing, the blades are shifted toward the middle of the collimator from left and right for irradiation of tumor contour K. Contour K is drawn in and hatched for purposes of illustration. The blades are shifted for radiation shielding to match the contour of the tumor, so that the inner open area is irradiated, while the region shielded by the blades remains unexposed. Although the blades are moved separately, they can be grouped in blade sets 3, 4 and 5 as described above. It is evident that the narrow blades contained in set 5 run up against the central part of the tumor, which has a very irregular contour. This permits a very good match of the radiation shielding to this irregular contour; only very small "stair-shaped" radiation steps remain, which means the vital tissue can be protected very well. For the somewhat less irregular contour in the outer middle range, the medium-width blades of set 4 provide an adequate fit, while the wider blades of blade set 3 provide a very good match to the regular contours of the outer part of the tumor. Rotation of the blade field brings it into the best possible position for the tumor to be treated. It is clear that a variation in the width of the blades facilitates excellent adjustment to a contour with the narrow blades, whereas the deployment of medium-width and wide blades permit shielding of contours of relatively large dimensions. The use of traditional blade collimators with blades of uniform width would present great difficulties in the case presented here, because if these blades were very narrow, the collimator would have to be kept small due to the limited selection of blades, meaning that the entire area could not be irradiated. Although in this case the use of traditional wide blades of uniform width could cover the entire area of exposure, large radiation leaks would occur in areas with irregular contours, thus exposing vital tissue to damaging radiation. The collimator according to the invention solves these problems with its blades of varying width, and combines the advantages of both classes mentioned above, as becomes clear in the illustrated embodiment. FIG. 2 shows a view of a set of blades belonging to a collimator according to the invention in the direction of travel of the blades with connecting strips that engage a position measurement device and are mounted on the upper side of the blades. In the blade collimator depicted here, oblong connecting cords (21) are mounted on the upper edges, toward the rear, of the individual blades; the other ends of these connecting cords engage the rods of a secondary position measurement device, which is not shown, via a mechanism such as a ball connector (27). Seen from the direction of travel of the blades, the connecting cords (21) spread out upwards in roughly a fan shape to meet contact points on the rods, which are more widely separated than the blades. The connecting cords (21) consist of flat metal strips that bend in their course from the edges of the blades to the contact points on the rods of the position measurement device (the bend runs perpendicular to the plane of the drawing and is therefore not visible); the end segments of these strips are straight. One method of connecting the lower ends of the metal strips to the blades is by soldering. FIG. 2 also shows that the blades, as seen from the direction of travel, exhibit from top to bottom a cross-sectional shape with widened sections (23) on both sides of the bisecting line of the individual blades, as well as matching narrowed sections (22). In each case, the adjacent, identically shaped blades have their widened sections (25) and narrowed sections (26) at corresponding, longitudinally displaced sites such that the side faces of the blades nestle against each other in essentially flat contact. Tapped holes (24) as counterparts to a drive-threaded rod are found in the widened cross-sectional areas of each blade. They can be relatively wide in diameter and therefore accommodate stable threaded rods. FIG. 3 is a schematic diagram of a staggered motor configuration of the invention. In a blade collimator in which the blades are driven by electric motors (31, 34) and the electric motors each have a drive-shaft (32, 35) and a drive-connecting rod (33, 36), the motors (31, 34) are arranged in a staggered pattern one behind the other in the direction of travel of the blades. Depending on the number of motors, the stagger can be two-step or, as illustrated here, three-step. The stagger can of course have still more steps in the longitudinal direction. The motors are also usually height-staggered--that is, staggered in the direction perpendicular to the plane of the drawing. It is clear from the schematic diagram of FIG. 3 that with a configuration such as this, the shaft (32) or the threaded rod (33) can pass between the two motors lying in front of it with ease, thus permitting a linear drive for the blades.