[en] The determination of internal doses is an essential component of individual monitoring programmes for workers. Assessment of internal doses can be divided into two phases: 1. determination of the amount of radioactive material in the human body by direct measurements and/or by indirect methods and 2. the interpretation of monitoring data in terms of intake and/or internal dose taking into account many influencing factors and assumptions, such as the physical and chemical characteristics of the radioactive substances, the mode of intake, the biokinetic and energy absorption processes, the individual parameters, etc. This second phase is particularly important because of the number of variables and uncertainties involved. Although the International Commission on Radiological Protection (ICRP) and International Atomic Energy Agency (IAEA) have published extensive tables of dose per unit intake (dose coefficients), these are default values based on assumptions about the intake parameters that may not be valid in specific situations