Radiation Protection Guidelines for the Limitation of Hot-Particle Skin Exposures: Dosimetric Aspects

摘要

We have shown that uncertainties which currently exist in the measurement and calculation of skin dose from well-characterised "test" hot particles, made in a research context, are at least 10-20%. In some cases, the uncertainties may be as large as a factor of 2. Hot-particle dose limits which are set on the basis of radiobiological studies are therefore subject to significant uncertainties in dosimetry as well as to uncertainties of determining threshold doses from poorly defined dose-response relationships at low doses. It is also important to realise that the measurement and calculation of doses from real hot particles encountered in routine, practical situations will be subject to much greater uncertainties. In contrast to stochastic effects, the probability of inducing deterministic effects, such as skin ulceration, rises steeply with dose. Uncertainties in dose measurements together with uncertainties in threshold doses therefore require that dose limits be set cautiously for deterministic effects. This has been the policy of the ICRP to date. The NCRP have, however, recently recommended a hot-particle skin dose limit which is several times higher than the ICRP value and which is commensurate with a significant probability of induction of acute epithelial necrosis. The NCRP recommendations have a number of caveats which, if implemented by legislators, would avoid the dose limits from being exceeded. In the special case of hot-particle exposures, it is clear that the uncertainties in dosimetry, the uncertainties in radiobiological data, and the lack of direct data for humans, would certainly support a need for caution. There is a need for legislators to cautiously interpret radiobiological data and to advocate hot-particle dose limits which err on the side of safety. Operators should aim to stay well below hot-particle dose limits unless they already contain a reasonable margin of safety to allow for the underlying dosimetric and radiobiological uncertainties.