Effects of hyperthermia, radiotherapy and thermoradiotherapy on tumor microvascular permeability.

Morphological changes in rabbit VX-2 tumor and its vascular permeability to ferritin following hyperthermia, radiotherapy and thermoradiotherapy were investigated by light and electron microscopy. Tumors treated by thermoradiotherapy successively showed a decrease in volume compared with those treated by hyperthermia or radiotherapy. Light microscopically, degenerative or necrotic changes progressed more widely in tumors treated by thermoradiotherapy than in those treated by hyperthermia or radiotherapy alone. When vascular permeability to ferritin was examined, an increase in tumor vascular permeability occurred at 1 day after hyperthermia or thermoradiotherapy, and at 3 days after radiotherapy. These results suggest that the early reaction of tumor microvasculature is a factor contributing to delayed cell death in tumors after thermoradiotherapy or hyperthermia.