Some Aspects of Dosimetry with a 4 MV Linear Accelerator

A performance study of the Varian Clinac 4 linear accelerator is presented. Previously published data for dosimetry with 4 MV x-ray units differ by 2% or more from those obtained with the softer radiation of the Clinac 4. Small differences were found between the data provided by the manufacturer and the data obtained experimentally, probably due either to experimental differences or to characteristics of the unit tested. Good agreement was found between per cent depth doses for circular and equivalent square fields, thereby allowing data originally developed for square fields to be applied to circular fields.