In Vitro Neoplastic Transformation by Neutron Beams:Relative Biological Effectiveness and Dose Fractionation

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In vitro cell transformation assay has proved to be a powerful means of quantitating the neoplastic action of sparsely ionizing radiation and analyzing the relevant damage-repair and expression processes. With respect to particulate radiations, however, transformation data are rather limited. The oncogenic potential of neutrons has been studied most extensively, due to the ready availability of neutron sources as compared with sources of other radiations. Findings of this kind are undoubtedly needed to provide a basis for high LET radiotherapy and for radiation protection standards. Borek et al. have reported that low doses of 430 KeV neutrons induced neoplastic transformation of cultured golden hamster embryo cells with a relative biological effectiveness (RBE) of ca.8. Subsequent studies with mouse 10T1/2 cells have shown that (1) RBE values for transformation were larger for neutrons of low energy than high energy, and tended to be larger at low doses than high doses, and (2) with fission-spectrum nuetrons, transformation was significantly enhanced either at a low dose rate or by multiple fractions as compared to single equivalent total doses at a high dose rate.
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