Dosimetric and biokinetic models of the ICRP for the assessment of internal doses from radionuclides

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. The uptake of a radionuclide and its retention with time in a source organ or tissue following its ingestion, inhalation, or systemic administration either by injection or through wounds, is described by biokinetic models. For the assessment of dose coefficients for intakes of radionuclides by workers, members of the public and patients, Committee 2 of the International Commission on Radiological Protection (ICRP) has developed biokinetic models for the uptake of radioelements 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 Committee 2 of 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 dosimetric and biokinetic models and data used for the assessment of doses per unit intake (dose coefficients) are described in detail. Present results and future activities of Committee 2 of the ICRP on secondary limits for internal exposure are briefly mentioned