There are many clinical situations in which radiobiological considerations can be usefully applied and all clinicians should be aware of the potential benefits of developing a quantitative radiobiological approach to their practice. The concept of biologically effective dose (BED) in particular is useful for quantifying treatment expectations, but clinical oncologists should recognize that careful interpretation of modelling results is required before clinical decisions can be made and that there is a lack of reliable human parameters for application in some situations. Correct use of the BED concept will, in more complex treatment situations, sometimes involve the use of multiple parameters and BED calculations. Examples include: