Radiation parameters of 6 to 20 MeV scanning electron beams from the Saturne linear accelerator.

Depth doses of the scanning electron beams from the Saturne Therac–20 linear accelerator at nominal energies of 6,9,13,17, and 20 MeV were measured in polystyrene using a thin window parallel plate ionization chamber. Central axis depth dose curves are derived and are analyzed according to the method of Brahme and Svensson.2 For each of the five electron energies, values are obtained for the most probable energy at the absorber surface E p,0 , the practical range R p , the 50% range R 50, the therapeutic range R 85, the electron dose gradients, total collision energy losses, and other radiation parameters, and these are compared to corresponding values for electron beams from a 22 MeV medical microtron and a 20 MeV betatron.