High-energy photon and electron beam.

The optimum radiation treatment plan for any given clinical situation can be achieved by combining various irradiation modalities and beam energies. The availability of equipment that provides photon and electron beams of energies from 4 MeV to 25 MeV permits optimal dose distribution throughout the treatment volume. Since no difference in the biological effectiveness of electrons compared with megavoltage photons has been demonstrated in laboratory studies, there is no hesitation in combining electrons with photons. The selection of the various energies, the combination of electrons with photons, and the ratio of the given doses of each beam depend on the location of the tumor and the maximum depth to be treated. With the use of one beam alone, a combination of 25 MeV and 4 to 6 MeV photon beams, or a combination of photons and electrons, the most effective treatment plan with the available beams can be designed for any clinical situation.