Practical methods for compensating for missed treatment days in radiotherapy, with particular reference to head and neck schedules.

Unscheduled interruption of a radiotherapy treatment can lead to significant loss in local tumour control, particularly in tumours that repopulate rapidly. General guidelines for dealing with such treatment gaps have been issued by the Royal College of Radiologists and more specific advice on the use of compensation methods has been published previously [Hendry et al., Clin Oncol 1996;8:297-307; Slevin et al., Radiother Oncol 1992;24:215-220]. This article further elaborates on the practical application of these methods. It sets out the main considerations arising in the especially critical case of head and neck treatments and simple calculations are used to illustrate the approaches which may be adapted for particular situations. Radiobiological parameter values are suggested for use in the calculations, but these may require modification in the light of further research in this important area.