The use of radioisotopic techniques to demonstrate early and late vascular changes in irradiated tissues

The present investigations were aimed at evaluating the role of damage to the fine vasculature in radiation-induced changes in the skin, brain, and lung. The approach adopted was to study changes in functional parameters, using quantitative isotopic methods, with the intention of establishing changes in the magnitude of the response for doses above and below clinical tolerance. An isotopic clearance technique was used to measure dermal capillary blood flow with sup(99m)Tc in both normal and irradiated pig skin. Cephalic and cerebral blood flows in rats were assessed using two isotopic techniques, sup(99m)Tc dilution and iodoantipyrine (125I) extraction respectively. One lung base in the pig was X-irradiated with single doses of 810-1500 rad. This treatment volume closely mimics the clinical situation. Radiation-induced modifications in blood flow and ventilation were assessed from xenon-133 accumulation and washout curves. Modification in the functional vascularity of the three organs examined was transient as the irradiated tissues would appear to adapt to the reduction in vascularity or net function, either by contraction and atrophy of the tissue parenchyma (as in pig skin and lung) or by a compensatory vasodilatation (as in the rat brain). (author)