CHARACTERIZING OUTPUT FOR DYNAMIC WEDGES

The output factor for the dynamic wedge, unlike that for the physical wedge, is a complex function of the field dimension along the moving j aw and wedge angle. The large change in output (varying as much as 40% for 45 degrees and 60 degrees wedge angles) can be attributed clearly to the segmented treatment tables (STTs), which specify cumulative mo nitor unit weighting as a function of jaw position, y. We found that t he output factor (in air or water) on the central axis for the dynamic wedge can be characterized by multiplying the output factor (in air o r water) for an open field by a normalization factor, which is determi ned from the STTs, thus indicating that collimator scatter is similar for both the dynamic wedge field and the open field. The introduction of the normalization factor decreases the commissioning: time for dyna mic wedges significantly and is useful for quality assurance. (C) 1996 American Association of Physicists in Medicine.