The effect of immobilisation on localisation error in the radiotherapy of head and neck cancer.

With the use of treatment verification films for the detection of localisation error (LE), a study was undertaken to determine the effect of change in position and immobilisation on LE in the radiotherapy of patients with head and neck cancer. For those patients not immobilised and treated in the lateral position, 28 errors were recorded in a review of 172 films, giving an error incidence of 16%. For patients immobilised by bite block and treated in the supine position, a total of four errors were recorded on review of 382 films, giving an error incidence of 1%. The reduction of LE from 16% to 1% by supine positioning and bite block immobilisation was significant with a P value of less than 0.001. The potential significance of LE in relation to CNS injury and tumour recurrence is discussed.