The induction of ovarian tumors in BALB/c female mice exposed to graded doses of137 Cs gamma rays (49-392 rads) at rates of 1.75, 3.5, 7, 14, 28, 56, and 112 rads/day has been studied. The incidence of ovarian tumors was an increasing function of both total dose and dose rate or, stated in alternate terms, a decreasing function of exposure time. The incidence varied as the second power of the dose (2.0 ± 0.16), when exposure time was held constant, demonstrating that the dose-response curve for this cancer cannot be linear. The incidence was inversely related to the 0.69 power of the exposure time, and approximately one-third of this exposure time factor resulted from age-dependent loss of sensitivity. The remaining two-thirds of the overall exposure time factor is presently under study and is concluded to be the product of both intra- and intercellular recovery.

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