Depth absorbed dose distributions for electrons

The author is replying to criticisms (Brahme, A., and Svensson, H., 1976, Phys. Med. Biol., Vol. 21, 304) of central axis depth absorbed dose distributions for linear accelerator electron beams (Atherton, L., and Coleman, F.G., 1976, Phys. Med. Biol., Vol. 20, 658). Comparison of data relating to SL75-20 and microtron beams under comparable conditions showed that the fall-off characteristics as judged by the 85, 50 and 35% values are virtually identical for the two beams, and the small differences in the build-up region are not clinically significant. There is therefore no justification in their claim that the narrow energy spectrum, clean geometry and small amount of scattering in the microtron produced beams which are significantly different from those obtained from linear accelerators. (U.K.)