On the basis of the review of radiobiological date, a formalism is developed for the analysis and prediction of iso-effect relations for tissue tolerance, which can be used as an alternative to the norminal standard dose(NSD) formaula of Ellis and its derived equations. An important feature of the described formalism is that directly based on radiobiological insights and it provides a more logical concept to account for the diversity of tissue responses. The NSD concept has subsequently been extended to the formalisms of timedose-fractionation(TDF) value. The authors deriveded TDF equation on the basis NSD of Ellis. TDF=0.07(NSD)-26.