Optimizing beam weights and wedge filters with the concept of the super-omni wedge

This study introduces a new concept, the super-omni wedge, and proposes an algorithm for optimizing beam weights, wedge angles, and wedge orientations on the basis of this new concept. The super-omni wedge is a generalization of the omni wedge. Instead of combining one open beam and two orthogonal w edged beams, it uses two orthogonal pairs of nominal wedged beams to genera te a wedged dose distribution with an arbitrary wedge angle and an arbitrar y wedge orientation. The orientations of a pair of nominal wedges are oppos ite each other. In this way, the effective wedge orientation can vary from 0 degrees to 360 degrees rather than being restricted to one quadrant. When the concept of the super-omni wedge is used, the optimization of beam weig hts, wedge angles, and wedge orientations for J beams is transformed into t he optimization of beam weights for 4J beams. A quadratic dose-based object ive function is defined, and the method of sequential quadratic programming is used to find the 4J beam weights that minimize it. After the weights of the nominal wedged beams have been determined, the beams can be delivered in one of four methods: Directly, by using the omni wedge technique, by usi ng the universal wedge technique, and by using the virtual wedge technique. When tested with two clinical cases, the algorithm achieved homogeneous do se distributions in target volumes while meeting the constraints to the org ans at risk. A prominent feature of the algorithm is that there is no need to manually preselect the orientations of nominal wedges. (C) 2000 American Association of Physicists in Medicine. [S0094-2405(00)00812-9].