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Schematic illustrations of (a) the complete block (CB) mode and (b) the directional block (DB) mode. The CB mode does not use beamlets A and B, which passed through the virtual contour, in the dose optimization process. The DB mode includes beamlet B, which reached the virtual contour after passing through the planning target volume (PTV), in the dose optimization, but it does not include beamlet A, which reached the virtual contour before passing through the PTV.
