Low-dose radiation carcinogenesis in mammals : A review of A Database of Cancer Induction by Low-Dose Radiation in Mammals: Initial Observations and comparison with some human data

The International Centre for Low-Dose Radiation Research (ICLDRR) has assembled, in a single database, all published results from experimental radiation carcinogenesis in mammals. The database contains experimental conditions and outcomes for about 87,000 exposed animals (̃ 60,000 cancers) and 40,000 controls (̃ 19,000 cancers). Experiments were conducted with all types of ionizing radiation, at doses starting at 10 mGy for gamma radiation, 40 mGy for X-rays, 2 mGy for beta radiation, 2 mGy for alpha radiation, and 5 mGy for neutrons. The data form 748 datasets, each providing a dose-response curve for a particular species, strain, sex, age at exposure exposed to a range of doses under specific exposure conditions. No cancers were observed in the control groups of about 30% of the datasets. When cancers were observed in control animals, no effect or an apparent reduction in cancer risk were observed in 40% of the neutron datasets, 50% of the X-rays datasets, 53% of the gamma datasets, and 61% of the alpha datasets. Apparent reductions in cancer rate, significant at up to 10 standard deviations were observed in mice exposed to 100 and 250 mGy of gamma radiation. It is confirmed that, in some experiments, exposed animals live considerably longer (up to 40%) than their controls. The frequency of lack of effect, protective effects or increased longevity in exposed animals challenges the general validity of the Linear No Threshold hypothesis (LNT). For comparison, clear beneficial effects observed in the US shipyard nuclear workers and anomalies in uranium mine dosimetry leading to overestimated radon risk are also examined.