The determination of internal doses is an essential component of individual monitoring programmes for workers.  It may also be needed for members of the public, who may have intakes of radionuclides in nuclear medicine and also in normal life following accidental releases of radionuclides into the environment. Assessment of internal doses can be divided into two phases, namely

 

  • determination of the amount of radioactive material in the human body, in body organs or in wounds by direct measurements and/or by indirect methods such as excretion analysis or air monitoring,

  • interpretation of the 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.

 

The 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. Determination of the intake and the resulting internal dose can, therefore, be approached in many different ways, depending on the amount and quality of the data, the skill of the dosimetrist, computational tools available, and the assumptions made. When a set of bioassay data is given to two different dosimetrists, it is likely that these data will be interpreted differently, that different methods and dosimetric models will be applied, and therefore different numerical solutions will be obtained. Thus, it is important for laboratories dealing with internal dosimetry to undergo performance testing procedures in both phases of internal dosimetry to demonstrate the correctness of methods applied and also the consistency of the results with those obtained by other laboratories.

 

 

 

This course gives an overview over the state of the art of the determination of internal dose with the main focus being put on the second phase. The first part of the course deals with the measuring techniques for individual incorporation monitoring i.e (i) direct measurement of activity in the whole body or organs, (ii) measurement of activity excreted with urine and faeces, and (iii) measurement of activity in the breathing zone or at the workplace, respectively. In the following part the biokinetic models used for the interpretation of the monitoring data are shortly described with special regard to the new models i.e. (i) the ICRP model for the human alimentary tract and (ii) the NCRP model for the biokinetics of radioactive materials in wounds. The third part of the course deals with the application of the models for the assessment of committed dose from incorporation monitoring data. This part is based mainly on the IDEAS General Guidelines, taking into account also the improvements of the guidelines provided by some follow-up projects, such as the CONRAD project.