Accessory beam flattening filter for the varian clinac-4 linear accelerator.

An accessory beam flattening filter (brass disk with critical angles) attaches to the shadow tray of the clinac-4 linear accelerator, intercepts the x-ray beam, and eliminates higher dose areas at the edges of large fields near the skin surface. This improves the x-ray beam dose distribution within the patient and results in a reduction of dose to normal tissues near the surface.