Absence of a dose-rate effect in the transformation of C3H 10T1/2 cells by α-particles

The findings of Hill et al. (1984) on the greatly enhanced
transformation frequencies at very low dose rates of fission
neutrons induced us to perform an analogous study with -particles
at comparable dose rates. Transformation frequencies were
determined with γ-rays at high dose rate (0·5 Gy/min), and with
-particles at high (0·2 Gy/min) and at low dose rates (0·83-2·5
mGy/min) in the C3H 10T1/2 cell system. α-particles were
substantially more effective than γ-rays, both for cell
inactivation and for neoplastic transformation at high and low dose
rates. The relative biological effectiveness (RBE) for cell
inactivation and for neoplastic transformation was of similar
magnitude, and ranged from about 3 at an -particle dose of 2 Gy to
values of the order of 10 at 0·25 Gy. In contrast to the
experiments of Hill et al. (1984) with fission neutrons, no
increased transformation frequencies were observed when the
-particle dose was protracted over several hours.