Tissue injury by microbeam irradiation depends on the stage of vascular maturation

Abstract

PurposeThe aim of this study is to explore the effects of Microbeam Radiation (MR) on vascular biology using the chick chorio‐allantoic membrane (CAM).MethodsCAMs were irradiated with multiple planar synchrotron X‐ray beams at doses between 100 and 300 Gy and were evaluated morphologically and in vivo at days 8 and 12.ResultsIn vivo monitoring and morphological investigations of day 8 CAM immature vasculature 6 hr after MR revealed a near total destruction of the capillary plexus within the beams’ width. Surprisingly, arteries and veins were not affected. Conversely, at day 12, only well defined lesions in the microvasculature (mature ones, covered by pericytes) were observed.After 300 Gy MR, TEM revealed enlargement of the interendothelial cell junctions which could explain the oedema, the microvessels along the beam path showed signs of disruption and apoptosis. The remaining vasculature recovered rapidly and CAM regained its normal thickness. Between 1 hr and 6 hr no additional morphological changes were observed.Conclusions The effects of MR are most likely mediated by capillary damage. The vascular toxicity of MR depends on the stage of capillary maturation: the immature vessels are much more vulnerable than the mature ones. The physiological effects of MR appear within a short time, the most important structural alterations being present between 15 and 60 minutes after irradiation.