Lauriston S. Taylor Lecture. Limitation and assessment in radiation protection

Protection against ionizing radiation can follow two fundamentally different approaches. In limitation, the maximum permissible dose equivalent is selected on the basis of worst-case assumptions on the shape of dose-effect curves and the influence of other factors (dose distribution, relative biologic effectiveness, etc.). This system has the restricted aim of ensuring that radiation exposure results in risks below stipulated levels. In assessment, the functional relation and the numeric values required for risk estimation are postulated. This permits statements of the absolute values of risks, not only for the maximum permissible dose equivalent but also for any lesser dose equivalents. The principal concept underlying the assessment system is that of incoherence: lack of interdependence between the effects of dose increments and lack of interdependence between the effects on the constituent cells and organs of the body. The notion of incoherence and the choices of numeric values of risks are subject to substantial doubts. They must nevertheless be adopted when risk estimation cannot be avoided.