Subsequent steps transform the positive values of the segmentation grid to increase with decreasing distance to the OAR projections and to increase with longer pathlengths measured along rays from their entrance point through the skin contours to their respective grid point. ![]() Outside these regions, grid values are set to zero. These projections are used to make a segmentation grid with negative values across the expanded OAR projections and positive values elsewhere inside the expanded PTV projections. ![]() During the initial steps, beam's eye view (BEV) projections of the planning target volumes (PTVs) and organs at risk (OARs) are generated. The objective of this report is to describe ABST.įor each beam direction, ABST generates segments by a multistep procedure. At Ghent University Hospital, segments are created by an anatomy-based segmentation tool (ABST). In the inverse planning approach, segments are a result of ''clipping'' intensity maps. In segmental intensity-modulated radiation therapy (IMRT), the beam fluences result from superposition of unmodulated beamlets (segments).
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