Biological Effects of Radioactive Hot Particles on the Skin

Abstract

Exposure of the skin to β irradiation from discrete radioactive 'hot particles' represents a difficult problem for radiological protection. The skin reactions of concern which set the criteria for dose limitation, cannot be equated with those associated with more general radiation exposure of the skin. Only small volumes of skin are irradiated from a discrete hot particle and any resulting lesion depends on the energy of the β ray emissions. For high and intermediate β ray energies (≥0.9 MeV) the lesion of concern is acute dermal ulceration, while for low β ray energies (≤0.5 MeV) it is acute epidermal necrosis. The target cells, loss of which is responsible for these lesions are fibroblasts/endothelial cells and supra-basal epithelial cells, respectively, at depths in the skin of 100-150 μm or ∼50 μm in the skin, respectively. Although biological studies suggest that a dose limit should be linked to a specified range of β ray energies, practical considerations make a single dose limit, specified at a single depth, and averaged over a defined area a much more convenient approach. However, it must be emphasised that the biological differences make such an approach purely arbitrary. Based on this approach, a dose of Gy, measured at 70 μm depth and averaged over 1 cm 2 , would prevent the deterministic effects irrespective of the energy of the β ray emissions from a hot particle.