ICRP concepts and tasks in internal dosimetry

The uptake of a radionuclide and its retention with time in an organ or tissue (source organ or tissue) following its ingestion, inhalation, or systemic administration either by injection or through wounds, is described by biokinetic models, which are sufficiently simple to facilitate estimates of organ equivalent doses for radiation protection purposes. For the assessment of annual limits for intake of radionuclides by workers (ALI) and of dose coefficients for intakes of radionuclides by members of the public and patients, the International Commission on Radiological Protection (ICRP) has developed biokinetic models for the uptake of radionuclides by the gastrointestinal tract and the respiratory system, the latter for different ages. For the systemic behaviour of radionuclides, i.e. translocation of radionuclides to and between body organs and tissues, specific biokinetic models were adopted by the ICRP. Considering urinary excretion the ICRP has developed a kidney-bladder model to be applied to all substances used for kidney function tests, and to other radionuclides if urinary excretion results in a significant absorbed dose to the bladder wall. The fraction of energy absorbed in a target organ or tissue from the transformations of a radionuclide in a source organ or tissue is mathematically described by a dosimetric model. In the Symposium 'Internal Dosimetry' the concepts of the ICRP for the assessment of doses to workers, members of the public and patients from radionuclides are described in detail by K. F. Eckerman and M. Roy considering biokinetic and dosimetric models and dosimetry of the respiratory tract, respectively. In addition application of ICRP concepts of internal dosimetry is presented by J. W. Stather for the special case of estimating the dose to the embryo and fetus following acute and chronic intakes of radionuclides by the mother. The introductory paper describes present and future activities of the ICRP on internal dose assessments. (author)