Ionizing radiation and blood vessels.

Purpose : To study the biologic and clinical effects of ionizing radiation on blood vessels. Materials and Methods : Data extracted from experimental and clinical repor ts and articles. Results : Radiation-induced demise of endothelial cells is due to apoptosis . These cells are considered to be very radiosensitive. In vivo, however, t he basal membrane might play a protective role. Early effects are character ized by swelling and shloughing of endothelial cells. Late effects are due to endothelial and smooth muscular cell proliferation. The underlying biolo gic mechanisms are little known. One hypothesis is the production of PDGF ( platelet derived growth factor) and FGF (fibroblast growth factor) by endot helial cells. Perivascular fibrosis might occur because of the TGF-beta pro duction by endothelial cells and/or macrophages. Occurrence of late complic ations is probably multifactorial. Individual susceptibility to harmful eff ects of ionizing radiation, other vascular risk factors, and non optimal us e of radiation treatment might contribute to the occurrence of late vascula r complications. Modern radiotherapy using new techniques as the intensity modulation radiation therapy (IMRT) and the reduction of radiation doses an d size of radiation fields should permit a dramatic reduction of vascular c omplications in cancer patients. Conclusions : Ionizing radiation treatments can lead to serious late vascul ar complications. A better understanding of the underlying biologic process es and newer radiation techniques might lead to fewer late complications in the very near future.