Patent Number: 
Section: abstract

The invention relates to a collimator (1) for limiting a bundle of high-energy rays (2), which is emitted by a substantially point-like radiation source (3) and directed towards a treatment object (20) and used in particular for the stereotactic conformation radiotherapy of tumors. According to the invention the collimator (1) comprises a plurality of diaphragm leaves (4, 4xe2x80x2) which are arranged opposite each other and which are made of a radiation-absorbing material and which, by means of drive mechanisms, can be moved into the optical path in such a way that the contours and/or exposure period of said optical path can be freely defined, the front edges (5, 5xe2x80x2) of the diaphragm leaves (4, 4xe2x80x2) being parallel to the optical path at all times. Avoiding penumbral shadows with this kind of collimator (1) is made considerably easier if the diaphragm leaves (4, 4xe2x80x2) consists of a rear partial element (6, 6xe2x80x2) which can be linearly displaced and a front partial element (7, 7xe2x80x2) which is hinged to same. Drive means adjust the front partial element (7, 7xe2x80x2) in accordance with the prevailing position of the rear partial element (6, 6xe2x80x2) in such a way that the front edges (5, 5xe2x80x2) are parallel to the optical path at all times.