Impact of stereotactic interstitial radiation on brain capillary physiology.

rCBF, capillary permeability and vascular volume have been measured during the time course of interstitial stereotactic radiosurgery in normal and tumour-bearing dog brain. For rCBF measurement the stable Xenon-CT-technique with a modified Kety-Schmidt equation has been used, and for measurement of blood-to-brain transport of meglumine iothalamate the two-compartment CT-method as developed by Groothuis, which also reflects vascular volume. Anaplastic gliomas had been induced by intracerebral injection of avian sarcoma virus. Radiation sources have been 192-iridium and 198-gold. Both of the isotopes caused spherical blood-brain-barrier lesions with a more than 10-fold blood-to-brain transport increase. These effects occurred earlier and more pronounced with 192-iridium, but much longer lasting with 198-gold. Interstitial radiosurgery of the tumours led to a further increase of capillary permeability. Blood flow was significantly lowered not only within radionecrosis but also in the adjacent brain areas.