A PROPOSED FIGURE OF MERIT FOR THE ASSESSMENT OF UNSCHEDULED TREATMENT INTERRUPTIONS

There are, as yet, no standard radiobiological methods for devising co mpensation for unscheduled interruptions to fractionated radiotherapy. For the foreseeable future it is likely that the concept of biologica lly effective dose (BED) will play an important role in the intercompa rison of treatment regimes, and in the examination of the options avai lable for dealing with unscheduled treatment interruptions. However, c omparison of the BEDs associated with different treatment options does not provide an intuitively obvious indication of the magnitude of any associated differences in biological effect-an important consideratio n in the case of those treatments which are designed to deliver near-t olerance doses. This article reviews the implications which derive fro m this complication, and discusses the desirable properties of possibl e ''one-number'' treatment scoring systems which could utilize the BED s of both the tumour and the critical normal tissue. One possible form of such a scoring parameter is suggested, and applied to some clinica l examples. No special ''robustness'' is claimed for the proposed scor ing system, but the method nevertheless allows the ranking of treatmen t options such that the least satisfactory may be identified and rejec ted.