EVALUATION OF ELECTRON-BEAM UNIFORMITY DURING COMMISSIONING OF A LINEAR-ACCELERATOR

Electron-beam profiles measured during acceptance testing and commissi oning of a linear accelerator were analyzed according to manufacturer' s specifications and more stringent AAPM TG-25 recommendations. The di fference between specifications of the AAPM report and those experienc ed commercially is discussed. Although all the electron beams met the manufacturer's specifications, the uniformity parameters for some of t hem were outside the limits suggested by the AAPM report. Profiles acq uired at depths larger than d(max) were extremely valuable for evaluat ion and adjustment of the beams. The following suggestions for practic al machine commissioning are made: Profiles taken deeper than at d(max ) are extremely useful indicators of the beam nonuniformity; acquisiti on of these profiles should be a part of the routine acceptance testin g procedure; and beam uniformity should be evaluated against AAPM reco mmendations, and this should be included in the purchase specification s.