1. A method for delivering to a subject a selected radiation treatment described by a treatment radiation dosage distribution objective, the delivering including application of at least one intensity-modulated beam whose radiation output is described by a plurality of beamlet parameters, the method comprising: (a) dividing the beamlet parameters into a plurality of groups, each group including one or more beamlet parameters; (b) assigning a group weighting for each group based at least on a fraction of the beamlet parameters included in the group; (c) selecting a first group; (d) computing a first intermediate radiation dosage distribution objective based on the treatment radiation dosage distribution objective and the first group weighting; (e) optimizing the first group of beamlet parameters respective to the first intermediate radiation dosage distribution objective; (f) selecting a next group; (g) determining a second intermediate radiation dosage distribution objective based on the treatment radiation dosage distribution objective and the next group weighting; (h) optimizing the next group of beamlet parameters respective to the second intermediate radiation dosage distribution objective; (i) repeating the steps (f)-(h) to optimize all the beamlet intensity parameters; (j) converting the optimized beamlet intensity parameters to a deliverable sequence of radiation fields; and (k) applying the at least one intensity-modulated beam to effectuate the deliverable sequence.