Late effects of the different dose-rates of gamma radiations in Sprague Dawley rats

Attempts have been made to investigate the influence of radiation dose and dose-rate based on a variety of biological end points. Analogous effects observed among different mammalian species have suggested that interdependency could exist between dose and dose-rate, although total dose used have been pretty high. The present work was undertaken to determine whether or not late effects produced by a given total dose of gamma radiation were significantly influenced by dose-rate difference. For this purpose, Sprague Dawley rats of 11–12 weeks age were irradiated with Co -60 gamma rays in three fractionated doses of 0.10 Gy or 0.40 Gy (cumulative dose 0.30 Gy or 1.20 Gy) given at an interval of one month with two different dose-rates (0.00368 Gy/min. and 0.0589 Gy/min). A sham-irradiated control group was maintained under the same conditions of food, water and temperature. A high percentage (61.29%) of mortality was noticed in the animals irradiated with the total dose (1.20 Gy) of higher dose-rate (0.0589 Gy/min). Incidence of tumours (mammary and ovarian) was very high in the animals exposed to 1.20 Gy at higher dose-rate. From the above observations, it is evident that the total dose delivered may have a bearing on the widely varied dose-rates of sparsely ionizing radiation used. Further, lower dose-rates have been found less effective than higher doserate of ionizing radiations in terms of inducing delayed effects.