Dosimetric evaluation of a variable field electron beam applicator.

A commercially available variable electron beam applicator designed for the Phillips SL-75/20 linear accelerator was tested for possible clinical use. The basic design of this collimator consists of four movable L-shaped stainless steel blades forming the corners. In addition, four smaller fixed blades of the same material and thickness fill in the sides. Film placed in polystyrene phantoms were exposed in all experiments. Field size, field flatness, beam homogeneity and penumbra measurements, all indicated that the applicator is acceptable for clinical use. However, for use with large field sizes and/or high energy electron beams some minor modifications are suggested.