Hepatomas in Mice: Incidence Increased after Gamma Irradiation at Low Dose Rates

Abstract

Irradiation of LAf₁ mice with gamma-rays (total doses of 618 to 1335 rad) at a rate of 1.45 rad per hour markedly increased the incidence of hepatomas and ovarian adenomas, compared with incidence of these tumors in mice irradiated with x-rays at 30 rad per minute. This was somewhat unexpected, since chromosome aberrations in the liver cells were less frequent after irradiation at the low dose rate. Other types of tumors were not increased by irradiation with gamma-rays at the low dose rate. It is suggested that indirect hormonal mechanisms may contribute to the production of the hepatomas as well as of the ovarian adenomas.