Radiation hormesis hypothesis compared with LNT and linear model with threshold. In all 3 graphs, x-axes represent radiation dose and y-axes represent magnitude of health effect. Zero-equivalent point (ZEP) represents level of health effect in absence of radiation. The quadratic model of Figure 1 approximates threshold graph of this figure. A threshold model would imply no effects of radiation up to certain level, after which risk rises linearly with dose. The radiation hormesis model, in contrast, shows beneficial effect at low levels of exposure as it drops below ZEP.
Dr. Calabrese presents his (highly generalisable) findings about the nature of dose response in the low dose zone, discovering that longstanding "scientific" standards underlying regulatory rulings systematically ignore the true reaction pattern, thereby introducing massive bias. The key insight presented by Dr. Calabrese seems to me to consist in the fact that rather than following a linear pattern, dose responses are characterised by two phases such that at low doses they may act in a stimulating way, only to display inhibiting effects at higher doses - (hence the terms "biphase" or "hormetic"). Low doses of radiation for instance may stimulate healthy reactions in the human body, thus actually improving their well-being, while causing harm only at higher doses.