Figure 1
From: Fast IMRT by increasing the beam number and reducing the number of segments
More beams and less segments could result in better plans. Plan changes from A to A': the number of segments and gantry angles are the same for all beams except beam i. Beam i: number of segments is reduced by 1, beam n+1 - containing only one segment - is inserted at gantry angle αn+1. Segment shapes and weights of all beams are newly optimized, a better plan is found. After certain number of repetitions, only one segment per beam remains. Finally some beams can be dropped, even if this decreases the quality of the plan, as long as the plan does not become worse than the start plan.