Evaluation of electron-beam uniformity during commissioning of a linear accelerator.

Electron-beam profiles measured during acceptance testing and commissioning of a linear accelerator were analyzed according to manufacturer's specifications and more stringent AAPM TG-25 recommendations. The difference between specifications of the AAPM report and those experienced commercially is discussed. Although all the electron beams met the manufacturer's specifications, the uniformity parameters for some of them were outside the limits suggested by the AAPM report. Profiles acquired at depths larger than dmax were extremely valuable for evaluation and adjustment of the beams. The following suggestions for practical machine commissioning are made: Profiles taken deeper than at dmax are extremely useful indicators of the beam nonuniformity; acquisition of these profiles should be a part of the routine acceptance testing procedure; and beam uniformity should be evaluated against AAPM recommendations, and this should be included in the purchase specifications.