Improving measurements of personalised internal dose
Modern radiation protection and safety methods for individual monitoring involve the application of dynamic air concentration assessment in the working room air, sampling of human excreta and in-vivo monitoring. In comparison to other techniques, in-vivo monitoring displays increased possibilities of fast assessment of incorporated activity and high counting efficiency. Nevertheless, there are still some difficulties in interpreting measurements, such as the conversion of the number of pulses in spectrometry channels into retained activity. The so-called calibration procedure uses phantoms that do not take into consideration differences among subjects. Such differences include individual anatomy, specific size, shape, weight of organs as well as their placement in the body. Moreover, most of the radiotoxic incorporated radionuclides used, emit low-energy radiation that enhances absorption and scattering effects in the subject's body (organs). This makes specification of whole body (or organ) counting calibration coefficients for further calculations very hard to derive. Alternatively to reference phantoms, mathematical simulation such as Monte Carlo method can be adopted for fast and accurate calculations. One of the tools that is currently used in patient-specific dosimetry (targeted radiotherapy), the OEDIPE software was selected to be validated. This multi-platform graphic user interface employs individual subject tomograms to perform radiation transport calculations. The study involved two applications, one for the measurement of high-energy emitters in whole body counting and another one for the measurement of low energy actinides in the lung. The OEDIPE software tool provided results that were in good agreement with measurements in both cases. It was shown that allowing inclusion of individual anatomy of the subject may lead to up to two-fold and more correction factors for activity assessment. Due to its flexibility particularly for complex geometries, this outstanding tool may be used in other areas apart from in-vivo measurement. For instance, it may be applied in the study of contamination with mixed actinides and any other Monte Carlo simulation where a set of superimposed images results in complex geometry.