Tumor Induction and Life Shortening in BC3F 1 Female Mice at Low Doses of Fast Neutrons and X Rays

Abstract

Extension of previous investigations at this laboratory regarding life shortening and tumor induction in the mouse has provided more complete dose-response information in the low dose region of X rays and neutrons. A complete observation of survival and late pathology has been carried out on over 2000 BC3F1 female mice irradiated with single doses of 1.5 MeV neutrons (0.5, 1, 2, 4, 8, 16 cGy) and, for comparison, of X rays (4, 8, 16, 32, 64, 128, 256 cGy). Data analysis has shown that a significant life shortening is observable only for individual neutron doses not lower than 8 cGy. Nevertheless, assuming a linear nonthreshold form for the overall dose-effect relationships of both radiation qualities, an RBE value of 12.3 is obtained for the 1.5 MeV neutrons. The induction of solid tumors by neutrons becomes statistically significant at individual doses from 8 cGy and by X rays for doses larger than 1 Gy. Linear dependence on neutron dose appears adequate to interpret the data at low doses. A separate analysis of ovarian tumor induction substantiates the hypothesis of a threshold dose for the X rays, while this is not strictly needed to interpret the neutron data. A trend analysis conducted on the neoplasm incidence confirms the above findings. Death rates have been analyzed, and a general agreement between the shift to earlier times of these curves and tumor induction was found.

Relationship between oocyte apoptosis and ovarian tumours induced by high and low LET radiations in mice

“…The high incidence of liver and lung tumours influenced the life shortening of the neutron-exposed animals. These data were consistent with a previous report (Covelli et al 1988), in which the decrease of latency for the elicitation of solid tumours increased with dose. In case of the A-bomb survivors in Hiroshima, the estimated excess relative risk at 1 Sv for the cancer of ovary was highest at an exposed age of 0-9 years followed by over 40 years (Thompson 1994).…”

“…The relative biological effectiveness (RBE) for different radiations on oocyte killing (Straume et al 1987, Satow et al 1989 does not explain directly the efficiency of the development of ovarian stromal cell tumours (Ullrich et al 1977). The relationship between the ovarian tumour spectrum and radiation quality with regard to the age at exposure has not been described to date, although a low incidence of granulosa cell tumours following high linear energy transfer (LET)-radiation exposure at 4-6 weeks of age was reported (Covelli et al 1988). …”

Radiation‐induced lymphoid tumors and radiation lethality are inhibited by combined treatment with small doses of zinc aspartate and wr 2721

“…Models for experimental tumor induction by ionizing radiation are not entirely satisfactory because of their long duration, while often only a moderate rate of tumor development is achieved (Broerse et al, 1985;Coggle, 1988;Covelli et al, 1988;Fry, 1981;Mole, 1984;Twentyman et al, 1980;Ullrich, 1983). Little work has been directed towards the question of how radioproteetive agents influence radiation carcinogenesis in vivo.…”

The Dose-response Relationships for Tumor Induction after High-LET Radiation.

“…However , as previously observed for X rays, a threshold-model cannot be excluded to describe the dose-response relationship for neutrons. In fact, a linear relationship fits well the data (P=0.58) with a threshold-dose of 6 cGy (Covelli, et al 1988)').…”