[en] Organ and tissue doses outside of focus volume were calculated for their occurrence under radio therapy conditions. Organ-specific hazard co-efficients can be deduced from data of the incidence of secondary tumours obtaining in the irradiation of Bechterew's disease and from the data of calculated organ doses, and can be compared with the corresponding results of other epidemiological studies. Based on the hazard co-efficients obtained, it is possible to assess the risk of stochastic delayed damage occurring after radio therapy. Irradiation of a low abdominal tumour was selected for matters of exemplification. (orig./DG)