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 reports and articles. Results : Radiation-induced demise of endothelial cells is due to apoptosis. These cells are considered to be very radiosensitive. In vivo, however, the basal membrane might play a protective role. Early effects are characterized by swelling and shloughing of endothelial cells. Late effects are due to endothelial and smooth muscular cell proliferation. The underlying biologic mechanisms are little known. One hypothesis is the production of PDGF (platelet derived growth factor) and FGF (fibroblast growth factor) by endothelial cells. Perivascular fibrosis might occur because of the TGF-beta production by endothelial cells and/or macrophages. Occurrence of late complications is probably multifactorial. Individual susceptibility to harmful effects of ionizing radiation, other vascular risk factors, and non optimal use of radiation treatment might contribute to the occurrence of late vascular complications. Modern radiotherapy using new techniques as the intensity modulation radiation therapy (IMRT) and the reduction of radiation doses and size of radiation fields should permit a dramatic reduction of vascular complications in cancer patients. Conclusions : Ionizing radiation treatments can lead to serious late vascular complications. A better understanding of the underlying biologic processes and newer radiation techniques might lead to fewer late complications in the very near future.