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Electrons from radioactive substances or beta rays have been used for many years in radiation therapy. Because of their relatively low energy, the effects are confined to a depth of a few millimeters, and because of the distribution of energy the depth dose characteristics are similar to those of x-rays. With the development of the betatron by Kerst, the acceleration of electrons to very high energies became possible. Experiments to liberate a beam of electrons from the betatron, with the ultimate goal of using them for therapy, were successful at the University of Illinois in 1946. The advantage of using electrons for therapy is expected to lie principally in the depth distribution of dose. Quastler observed no qualitative difference between the biological effects of 20-Mev and 200-Kev x-rays. Quantitatively there is a dosage factor which is probably partially real and partially due to an energy variation in the response of the measuring instruments. The only physical difference between the secondary ele... |
