Variation of linear accelerator wedge factors with field size and wedge position

We refer to the letter by Dean and Davis (1991) in which the authors suggested that “no extensive wedge factor versus field size measurements need be done for linear accelerators designed with a wedge mounted below the movable collimators”. They reported measurements on a Varian 2100C linear accelerator showing very little variation of wedge factor with field size, and contrasted these measurements on a Philips SL75/14 (Palta et al, 1988) and on an ABB LA20 (Thomas, 1990), both of which exhibited large increases in wedge factor (WF) with increasing field size.