Enhanced normal tissue doses caused by tumour shrinkage during brachytherapy.

Published data concerning shrinkage rates of low-grade gliomas implanted with 125I seeds have been used to determine the likely influence of such shrinkage on normal tissue doses. It is demonstrated that a tumour volume shrinkage of 50% over 6 months can bring about a 30% increase in the dose delivered to tissues which shrink centripetally towards the implanted volume. The use of radionuclides with a half-life shorter than that of 125I would substantially reduce shrinkage-induced dose increments.