Fig. 1From: A fast optimization approach for treatment planning of volumetric modulated arc therapyThe illustration of progressive sampling scheme. a The first beam set with 5 control points (beam spacing 72°). b The second beam set with additional 5 control points (beam spacing 36°). c The third beam set with additional 10 control points (beam spacing 18°). d The fourth beam set with additional 20 control points (beam spacing 9°). e The fifth beam set with additional 20 control points (beam spacing 6°)Back to article page