Patent Number: 053430484
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is directed to a contour collimator for shaping a radiation beam in radiation therapy, of the type having two sets of individually displaceable lamellae disposed opposite each other, which can be clamped in place in selected positions within a holder. 2. Description of the Prior Art Contour collimators are utilized for limiting the radiation field of ionizing radiation, such as for oncological radiation therapy, so that the distribution of the radiation dose can be matched to the shape of the target volume, which is usually irregularly shaped, particularly when treating a tumor. A contour collimator is disclosed in European Application 0 387 921 wherein the individual lamellae of two lamellae sets disposed opposite each other can be positioned with a mechanical device so that a radiation field of the desired shape is achieved. In this known apparatus, an adjustment means, for example an electric motor or a user-operable wheel, can be successively coupled to all of the individual lamellae, with the lamellae which are not momentarily coupled to the motor or wheel being locked in place. The shape of the radiation field set by displacing the lamellae can thus be achieved automatically and in a simple manner by actuation of the motor or the wheel. The overall apparatus, however, is relatively complicated and bulky. Moreover, the precision width which a desired shape can be achieved is limited by the thickness of the individual lamellae, with a finer adjustment of the contour being possible with thinner lamellae. In this known apparatus, as the lamellae become increasingly thinner, it is more difficult to couple only one lamella at a time to the displacement mechanism. This known apparatus, therefore, is primarily suitable for larger collimators. Collimators are also known which are exclusively manually operable, which also include oppositely disposed sets of individually displaceable lamellae. A form matched to the desired radiation field, such as form matched to the shape of a tumor to be treated, is first produced, and is placed into the contour collimator between the sets of lamellae, with the lamellae completely retracted from the path of the radiation beam. The lamellae are then manually pushed against the form and fixed in place. This procedure, however, is time consuming, and it must be assured that all lamellae are positively made to abut the form, in order to avoid harmful irradiation of tissue surrounding tumor. Moreover, given extremely thin lamellae, there is the risk of the operator being cut when manually displacing the lamellae. A contour collimator is disclosed in U.S. Pat. No. 4,754,147 for radiation therapy having individually displaceable rods disposed opposite each other. Adjustment of the individual rods takes place with the use of form elements at the rod ends, with the collimator being turned so that the individual rods fall against the form due to the force of gravity. The rods are then clamped in place. Adjustment of collimator elements using the force of gravity, however, creates problems because jamming can occur, particularly given lightweight collimator elements. Moreover, the necessary rotation of the collimator requires complicated mechanical devices, and manipulation of the collimator thus also becomes complicated. SUMMARY OF THE INVENTION It is an object of the present invention to provide a contour collimator of the type having two sets of individually displaceable lamellae, wherein the lamellae can be displaced to set a desired radiation field contour which has a simple structure and which permits precise placement of the lamellae against a form conforming to the desired radiation field contour. The above object is achieved in a contour collimator having a holder in which two sets of radiation-impermeable lamellae, each lamella being individually movable toward and away from its counterpart lamella in the other set. The lamellae in both sets are normally urged toward each other by a spring force applied individually to each lamella. Each lamella has a slot, and each slot has a pin engaged therein. The pins are mounted on a means operable by user for collectively displacing the sets of lamellae away from each other against the spring force. For setting a desired contour the lamellae are moved away from each other and a form conforming to the desired contour is placed between the sets of lamellae. The displacement means is then released by the user, and, under the influence of the spring force, all of the individual lamellae are urged toward the form, so as to abut the form. The sets of lamellae are disposed in the holder between two lateral holder walls, at least one of which is able to be tightened and loosened against each set of lamellae. When the lamellae have been displaced to the desired position by the spring force, the wall is clamped to fix the lamellae in place. The form can then be removed or, if it is sufficiently radiation permeable, can be left in place for conducting the therapy.