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Stochastic Risks from 'Hot-Particle' Skin Exposures

Some recent studies have renewed concerns regarding the carcinogenicity of 'hot particles'. These claim an enhanced induction of malignant transformation following non-uniform compared with uniform irradiation. Enhancement factors, however, vary widely between studies. Even fewer animal studies are available and these too show divergent results. Determination of possible 'hot particle' enhancement factors is critically dependent on both reliable dosimetry and biological protocols. Some of these experiments are flawed for one or both of these reasons. In this study internationally validated protocols for dosimetry and malignant transformation in vitro have been used. Uniform and non-uniform sources of 90 Sr/ 90 Y and 170 Tm β particles and 250 kV p X rays were used to measure the induced transformation frequency in C3H IOTA mouse fibroblasts. 'Hot particle' exposures were found not to be significantly different in their transforming ability (expressed as transformation frequency per surviving cell) than uniform irradiation, although moderate enhancement factors are possible. There are, however, suggestions of moderate enhancements for transformation frequency per cell at risk.