Characteristic parameters of 6-22 MeV electron beams from a 25-MeV linear accelerator.

Depth-ionization measurements were performed using a thin wall parallel plate chamber in water at nominal electron energies of 6, 9, 12, 15, 18, and 22 MeV for the standard available square field sizes. The characteristic parameters of the central axis depth-dose distributions were derived and compared to corresponding values for other accelerators. Vacuum packed therapy-verification films were used in water to obtain isodose distributions in a plane containing the central axis of the beam. The uniformity index and penumbra of the beams were measured from isodose distributions obtained in planes perpendicular to the beam central axis, at depths of 1/2R85 in water.