Patient position reproducibility in fractionated stereotactic radiotherapy: an update after changing dental impression material.

The reproducibility of patient positioning within the Gill-Thomas-Cosman relocatable stereotactic frame was re-evaluated following the substitution of a new, softer, dental impression material for the original hard acrylic compound. The average total displacement for a series of 10 patients was 1.1 mm (+/- 0.6 mm). Rotational discrepancies were small. This technique cannot deliver accurate repositioning in the absence of patient co-operation.