It is provided a method for generating a plurality of treatment plans for radiation therapy, each treatment plan specifying weights for a plurality of geometrically defined fluence elements. Each weight defines an amount of radiation fluence, to thereby provide radiation dose to a target volume. The method is performed in a treatment planning system and comprises the steps of: generating a first set of treatment plans； determining a subset of the fluence elements, based on the first set of treatment plans； and generating a second set of at least two treatment plans, wherein the treatment plans only contain weights for the subset of fluence elements.
