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The aim of this investigation, to construct a range of fixed wedge filters and to simulate these with a motorized wedge, led to the derivation of 5 equations. These equations can be used to construct and test a consistent set of fixed wedge filters, eliminating elaborate trial and error experiments. The fixed wedge filters already in existence for the Philips SL75-10 and SL75-20 linear accelerators fitted these equations rather well. After adapting the motorized wedge of the SL75-14 according to these equations, it simulated the fixed wedges accurately.

Using a microprocessor a method for plotting isodensity lines in film dosimetry is described. The procedure moves the measuring spot directly along an isodensity line, using information obtained in preceding steps to determine the next step. For registration of the curves no X-Y pen recorder is needed. The essentials of the procedure together with a flowchart are given.