Influence of collimating design on central axis depth dose of 10-40 MeV electron beams

Electron beam measurements were performed in this investigation on three different collimating arrangements in order to study their effect on central axis depth doses. The relative central axis doses for 10, 20 and 34 MeV as a function of area from 10 to 200 cm2 for rectangular, square and circular field sizes were studied at 2.6 and 4.8 gm/cm2 depths in a lucite phantom. Results are presented and are discussed in terms of electron contamination produced by the internal structure of the collimator used.