RADIATION-INDUCED TRANSFORMATION OF SV40-IMMORTALIZED HUMAN THYROID EPITHELIAL-CELLS BY SINGLE EXPOSURE TO PLUTONIUM ALPHA-PARTICLES IN-VITRO

Human thyroid carcinomas have been induced following exposure of SV40- immortalized human thyroid epithelial cells In vitro to single doses ( 0.14 Gy to 1.57 Gy) of 3.26 MeV alpha-particles from a plutonium 238 s ource. Tumours were detected between 50 and 160 days following subcuta neous transplantation of the irradiated cells in athymic mice. No tumo urs were observed following transplantation of unirradiated cells. The relative biological effectiveness (RBE) of the alpha-particles, estim ated from cell survival curves, was 4.8 at 50% survival and 3.3 at 5% survival. A first estimate of the RBE at peak tumour induction was 3.8 . This system provides a means of studying the mechanisms of tumourige nesis in human thyroid epithelial cells induced by ionizing radiations , including tumours induced by single alpha particles such as from env ironmental natural radon and polonium and artificial plutonium and ame ricium, and those induced by beta-or Auger-emissions from particular i odine isotopes.