The statement: any dose of ionizing radiation, however small, is detrimental could serve as the present paradigm of radiation protection. Adaptive response and other inconsistencies encountered when extrapolating radiation effects from high doses and high dose rates to low doses and low dose rates suggest that linear extrapolation from higher dose ranges on which ICRP bases its quantitative evaluations of risk and current recommendations on radiation protection may require review, as well as our perception of low dose, of the limits of the applicability of dose-related concepts such as RBE, quality factor, or the sieviert. An attempt is presented here at such a review, on the premises of the cellular track structure approach by Katz et al., reflecting the belief that conclusions drawn from quantitatively successful microdosimetric modelling of irradiated cellular cultures may be relevant to radiation protection.