A new approach to overcome the inconveniences in electron dosimetry associated with the beam scanning technique in linacs

The therapeutic advantages of scanned electron beams from medical linear accelerators are accompanied by difficulties in electron dosimetry. Owing to short-time dose inhomogeneities in the treatment field, implicit in the system, time-consuming point-by-point measurements of dose distributions are normally required. However, by triggering the measuring time synchronously with the slow scan frequency, the time necessary to record reliable dose distributions can be shortened considerably. The instrumentation for the computer-controlled dosimetry system developed for this task is described. The results of our measurements show that reproducibility in dose within +/- 1% is achievable in less than 6.3 s per point for scanned electron beams.