A system includes determination (S401) of a plurality of radiation beams for a radiation treatment fraction, each of the plurality of beams associated with a respective intensity, beam aperture and beam energy, and at least two of the plurality of beams respectively associated with two different beam energies, and determination of a forward dose associated with the plurality of input beams.If it is determined (S405) that the forward dose does not conform to a dose prescription, a beam weight is determined for each of the plurality of input beams based on the forward dose and the dose prescription using Gaussian elimination, and a second forward dose associated with the plurality of input beams and their respective beam weights is determined.
