ENHANCED TUMORIGENESIS BY SMALL, PROTRACTED DOSES OF DENSELY IONIZING RADIATION

<正>Starting with observations that were first published in 1982, a series of additional findings led to the discovery of an important property of cells in late G2/mitosis. In addition to being the most sensitive to killing, cells in this age-interval were also shown to be the most sensitive to radiation-induced neoplastic transformation. In this work. C3H mouse cells, designated 10T1/2, were irradiated with fission-spectrum neutrons and assayed in vitro via the endpoint focus formation on a monolayer of normal cells. From these observations, a biophysical model was developed to explain the anomalous finding that the frequency of transformation by low doses was enhanced when the exposure was protracted. In contrast to transformation by X- and y-rays where repair and kinetics during exposure play dominant roles, with radiations like reactor neutrons and x-particles repair has a minimal effect; only cell kinetics acts significantly to modify transformation due to protracted doses. In this report, the lack of