A theoretical investigation into post-operative, intracavitary beta therapy of high-grade glioblastomas using yttrium-90.

Beta therapy with yttrium-90 (90Y) has recently been introduced as a post-operative intra-cavitary treatment for malignant glioblastoma, a generally radioresistant tumour for which cure rates with conventional radiotherapy are usually very disappointing. This short theoretical study investigates the conditions under which 90Y treatment might be most effective and assesses the likely amounts of activity which must be infused in order to successfully cope with the low radiosensitivities which characterize such tumours. The radiobiological and physical analysis is investigated using the linear quadratic (LQ) model and a range of possible scenarios for the distribution and density of the tumour cells surrounding the surgically formed cavities are considered. The results suggest that, in the absence of diffusion of 90Y from the cavity, the activity typically required for 50% tumour cure is well over 40 mCi (1480 MBq), this being considerably more than the clinically determined activities which may be tolerated. Suggestions are provided for improving the versatility of the model.