Constancy of wedge factors in a Siemens Mevatron 74 linear accelerator

The variation of the wedge factor (WF) with field size is an important piece of data which determines the radiation output in treatments using wedge filters. WF is closely related with the accelerator head layout, and the choice of the wedge tray mounted above or below the jaws plays a predominant role. In this work we have studied the WF variations in our linac and found that, in apparent contradiction with the literature, the WF remains constant with field size. Nevertheless, these results cannot be used directly in other linacs, and individual dosimetry must be carried out.