A calculator for fractionated doses

A method of constructing nomograms for the calculation of radiobiologically equivalent fractionated doses has been described by Burns (1965). The first stage in this procedure is the preparation of a master nomogram embodying the relationship Sf=(S1)f, where Sf is the cell-survival fraction resulting from a series of f equal doses, each of which produces a cell-survival fraction S1. This relationship is valid with the proviso that total recovery of non-lethally damaged cells takes place between exposures. The second stage is the construction of a working nomogram based on the particular cell-survival curve to be adopted. For this purpose the surviving fraction scales of the master nomogram are transformed into dose scales by inscribing the individual values of dose at the appropriate points of the S1 and Sf scales. Shuttleworth and Fowler (1966) pointed out that the presentation of a single nomogram based on a particular dose-response curve could be misleading. It is indeed apparent that fractionation calculations with differing applications, e.g., in connection with tumour response, skin reaction, or experimental materials, require the adoption of different dose-response curves, for each of which a separate working nomogram must be prepared. The point-by-point construction of the dose scales is tedious, and the following alternative procedure has been devised with the object of reducing the labour involved in the adoption of any desired dose-response curve.