The system of dose limitation recommended by the International Commission on Radiological Protection (ICRP) results in an upper limit of 25 Sv on the total dose that could be delivered to any organ or tissue as a consequence of 50 years of occupational exposure assuming that the organ or tissue were irradiated selectively at the limit year after year. However, in practice, consideration of stochastic effects, taking into account the simultaneous irradiation of several organs and tissues, generally limits organ and tissue doses due to intakes of radioactive materials to substantially smaller values.