Divergence of opinion over the linear-quadratic model

In several recent papers, it has been suggested that the linear-quadratic (LQ) model may be of value for the solution of problems in clinical radiotherapy which involve changes in fractionation (Thames et al, 1983; Fowler, 1983, 1984; Dale, 1986a, b). I have been in correspondence with several radiobiologists and radiotherapists on this topic and it appears that there are quite sharp divergences of opinion. To initiate discussion, I would like to raise four questions. Under what circumstances might the absence of a time factor in simple LQ theory mislead the clinician? Recent reviews make it clear that time is still a vital factor in fractionation theory. For instance, Fowler (1984) says “The method described above is easy to use; requires the conscious choice of an α/β ratio for specific tissues; and conscious choice of new time corrections.” But in the same article there was a calculation which omitted time.