Abstract #1762

Martinive P, Feron O, Gallez B, Crokart N, Jordan B, Baudelet C, Cron G, Hotton J, Radermacher K, Gregoire V, Beghein N

We hypothesized that glucocorticoids may enhance tumor radiosensitivity by increasing tumor oxygenation via inhibition of mitochondrial respiration. EPR oximetry studies indicate an early increase in tumor oxygenation after administration of hydrocortisone, dexamethasone and prednisolone. At the time of maximal reoxygenation, the blood flow (monitored with DCE-MRI) was decreased, and oxygen consumption by tumor cells (measured using X-Band EPR) was decreased. We observed a longer regrowth delay when irradiation was combined with hydrocortisone compared with radiation alone. This effect is not due to a direct radiosensitization effect of hydrocortisone on tumor cells as evaluated by survival clonogenic assay.