Biokinetics and internal dosimetry of radionuclides
Background:
The incorporation of radioactive materials can represent a health risk. The radiation dose from incorporated radionuclides is determined to a large extent by the biokinetic behaviour of the radionuclides in the body. Biokinetics describes the behaviour of a substance with respect to its uptake, its transfer to and retention in particular organs and tissues, and its subsequent excretion from the body. Biokinetic parameters and models are an essential part in the calculation of radiation doses from incorporated radionuclides. However, for many incorporated radionuclides there are still considerable uncertainties in the biokinetic parameters for humans and thus in the dose estimates. Therefor, our research concentrates on the improvement of our knowledge on biokinetic behaviour of radionuclides in the human body after intake by inhalation or ingestion
Our group performs human volunteer studies using stable isotopes as tracers, which provide an excellent tool for gaining new experimental data for the improvement of biokinetic models for radiologically relevant radionuclides. The intestinal absorption, systemic and excretion kinetics of radionuclides has being studied for e.g. molybdenum, strontium, ruthenium, zirconium.
By measuring the time dependent concentrations of different isotopes of the same element in the biological samples, plasma clearance and urinary excretion can be evaluated, and therefrom biokinetic parameters can be derived. The dependence of the biokinetic parameters on the amount of material administered and of the form of administration is studied.
For all elements investigated so far, we found considerable deviations from the currently adopted ICRP biokinetic models and the calculated radiation doses. See below an example of a biokinetic model. The arrows represent the transfer rates between different organs.
The calculation of radiation dose from internally incorporated radionuclides was until recently based on MIRD-type
anthropomorphic phantoms which are mathematical phantoms describing the geometry of a reference body and its organs by simple equations. The voxel phantoms developed at GSF, which are based on CT scans of real persons,
are now used for internal dosimetry due to their undoubtedly greater realism.
Topics of research:
- Improvement and validation of biokinetic models of specified radiologically important elements (Sr, Ru, Zr, Mo) using tracer kinetic investiagtions on human volunteers.
- Investigations on factors influencing the biokinetik behaviour of radionuclides.
- Assessment of the internal radiation exposure based on revised dose models.
- Investigation of the influence of the individual variability of the human anatomical model on the SAF values and organ doses due to incorporated radionuclides.
- Calculation of new sets of internal dose coefficients, using the SAFs obtained with the adult voxel reference models for radiopharmaceuticals.
- Validated parameters as basis for setting legal limits.
Methods:
- Investigation of biokinetic data on healthy volunteers using stable isotopes by means of a double tracer technique
- Determination of the tracer concentrations in biological samples by mass spectrometry: thermal ionisation mass spectrometry (TIMS), inductively coupled plasma mass spectrometry (ICP-MS), and proton/neutron activation analysis (PAA/NAA)
- Determination of factors influencing the biokinetic parameters to modify the resulting radiation dose
- Development of improved dose models for humans
- Optimisation and validation of innovative methods for the analysis of incorporated radionuclides by TIMS and ICP-MS
Contact persons:
Dr. Uwe Oeh, phone: +49 89 3187-4247
Dr. Vera Höllriegl, phone: +49 89 3187-3219