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Doses from Radiation exposure
The Foundation Document on dosimetry provides a detailed discussion of ICRP dose quantities and their application in radiological protection in the asssessment and limitation of doses resulting from external and internal exposures. It explains the basis for and use of radiation weighting factors in the calculation of equivalent dose to organs and tissues and discusses the use of age- and gender- averaged tissue weighting factors, derived by Committee 1, in the calculation of effective dose. The document also discusses the relationship between these dose quantities and operational quantities used in dose monitoring and assessment. Doses calculated using ICRP methodology are single-valued, based on calculations for reference individuals, although in practice there is variation between individuals and uncertainties in the assumptions made in calculating dose. The document discusses sources of uncertainty and limitations on the use of ICRP dose quantities.
There are some changes to the recommended radiation weighting factors, wR, used in the calculation of equivalent dose. In particular a continuous energy function is to be given for neutrons (with some change in the function above 1 MeV from that given in Publication 92) and the wR for protons is to be reduced from 5 to 2. For low-LET x-rays and gamma rays as well as tritium, the wR will continue to be one and the values for alpha particles remains as 20.
Effective dose has been widely used in radiological protection and is a valuable quantity for demonstrating compliance with dose limits in relation to exposure to external radiation and intakes of radionuclides. It is not appropriate in all circumstances and guidance is given on where its use is not appropriate, for example in retrospective assessments of organ/tissue dose for epidemiological studies, in individual risk estimates after exposures above dose limits and especially after exposures to high radiation doses.
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