Altered Fractionation Schedules in Radiotherapy of Head and Neck Cancer. A Review

Abstract

The authors review the main contributions of international literature to show the current status in clinical trials on unconventional fractionations of the dose in radiotherapy of head and neck cancers. Several clinical (but only a few randomized) trials have been conducted over the last 15 years using hyperfractionated (HF), accelerated (AF) or mixed (HF-AF) schedules. HF schedules have obtained promising results in terms of local control in comparison with conventional fractionation (CF) of the dose. Improvement in survival was also obtained by the random trials of Pinto and Sanchiz, whereas in EORTC trial no. 22791, the improvement in survival rate was only marginal. A significant increase in local control and, less frequently, in survival has been claimed in several studies using HF-AF. Such data still need to be confirmed by a random study, since EORTC trial 22811 showed superimposable results in comparison with CF. Selection of the most suitable cases for altered fractionation schemes is also being studied in ongoing trials of the EORTC (22851) and RTOG (90-03). As regards acute reactions during and after altered fractionation, they are more severe than after CF. Only pure HF with a dose intensity approximately comparable to CF seems to produce similar acute reactions. Several factors have been found to influence the severity of acute mucosal reactions: interfraction interval, overall treatment time, total dose, and field size. As regards late damage, genuine HF schemes seem to cause roughly equivalent late damage in comparison to CF, whereas high-dose intensity schedules have a higher rate of complications. Interfraction interval, overall treatment time, total dose, fraction size and field size can influence the risk of late sequelae. Before altered fractionations can be considered standard therapy, more data are needed, which should be provided by multicentric randomized trials, some of which are already in progress.