[Optimation of the dose geometry during irradiation of the para-aortic lymph nodes with 42 MeV photons (author's transl)].

Different irradiation techniques for therapy of para-aortic lymph nodes are compared using fixed or pendulous fields of photons with the energy 42 MeV from a 42 MeV betatron. The techniques are estimated considering the load to the radio-vulnerable contiguous organs, especially to the spinal cord and kidneys. The findings presented, being founded on measurements and on computations resulting therefrom, show that the most satisfying dose distributions are obtained by the Y-shaped three-field technique, by the combination of telecentric-excentric dorso-ventral pendulous irradiation with a ventral irradiation by fixed fields, or be means of a biaxial excentric pendulous irradiation. By examples evidence is given of the possibility of delivering a focal dose of 6000 rd or more to the tissue within a large-sized target volume, whilst the radiation load to the contiguous radiosensitive organs, i.e. spinal cord and kidneys, does not exceed the tolerance dose.