The biological isoeffect distributions are calculated on the basis of the physical isodose distributions. They consider parameters of biological relevance such as the dose per fraction and the overall treatment time. A clinical example is presented to illustrate the method. The technique presented in this paper only requires minimal modifications in the conventional computer programs for treatment planning and can be updated very easily. The calculation of biological isoeffect distributions is a simple technique to facilitate the transfer of new radiobiological and clinical findings on alpha/beta ratios, tolerance doses and repopulation kinetics, into treatment planning. However, before they can be introduced into clinical practice, more reliable radiobiological data on normal tissues and tumours are required.
