Cerebrovascular response after interstitial irradiation.

To characterize the role of the cerebrovascular response in the development of brain injury after focal irradiation, 125I sources were implanted in frontal white matter of the brain of normal dogs; dose was 20 Gy, 7.5 mm from the source. Cerebral blood flow, vascular volume and mean transit time of blood were quantified in irradiated tissues relative to tissues in the contralateral hemisphere and analyzed with respect to previously determined volumetric measurements of damage and the blood-to-brain transfer constant. Blood flow and vascular volume within the radiation-induced focal lesion were maximally reduced 3 weeks after implant, when necrosis volume was maximal. By 6 weeks, vascular volume and mean transit time were increased, suggesting a strong neovascular response. In tissues surrounding the lesion, blood flow and vascular volume were reduced 1-4 weeks after irradiation and approached normal at 6 weeks; average mean transit time was not altered significantly. Alterations in blood flow and mean transit time were significantly related to edema volume and transfer constant, but alterations in vascular volume were not, suggesting that edema-induced vascular compression was not responsible for changes in blood flow. Reductions of radiation-induced permeability of the blood-brain barrier and/or edema might limit radiation-induced changes in blood flow and the extent of tissue injury.