A beam width improving device for a 25 MV X ray beam.

We have made a device that improves the dose distributions of X ray fields from a 25 MV accelerator by increasing the width of the 95% dose relative to the 50%. This device, called a beam width improving device, is a specially designed "compensator," consisting of two lead sheets taped onto a plastic blocking tray and is tailored for each field so that it can accommodate square fields, rectangular fields and fields with corner cuts. Comparison of profiles with and without this compensator indicates an increase in the width of the 95% dose of approximately 8 mm for small fields to approximately 14 mm for large fields.