[Use of electrons above 20 MeV for reduction of radiation exposure].

After many years of clinical application of a 42 MeV betatron, the following indications were found for deep therapy with electrons above 20 MeV: tumors situated in the brain, mediastinum, kidney, liver, bladder, rectum, as well as peripheral tumors situated in different body regions. For eight different cases, the total body exposure and the radiation exposure of some risk organs was calculated for an irradiation with electrons alone, a combination of electrons and photons, an irradiation with 42 MeV X-rays and with Co-60 gamma rays alone. All these calculations were based on a most favorable irradiation technique. The results showed that electrons up to 40 MeV can spare more than 30% of the total body dose; a combination of electrons and photons allows a reduction of the total dose of about 15% as against that of photons alone, which makes possible a better conservation of skin. This total dose reduction corresponds to that achieved by the substitution of ultrahard X-radiation for Co-60 gamma radiation in deep therapy. The radiation exposure of risk organs can often be reduced by the use of electrons, too. Thus electron deep therapy shows to be justified for the mentioned tumor cases. This is also confirmed by clinical experience.