Measuring Tumor Oxygenation By Electron Paramagnetic Resonance Oximetry In Vivo

The efficacy of radiation therapy and combined therapies of tumors were found to depend considerably on the oxygenation of tumors. Therefore it is of great importance to measure the oxygen content in tumors before and during treatments and to modify, the oxygen level in tumors with respect to the therapy used. In this work we have applied a new approach for increasing tumor oxygenation in order to increase the efficacy of radiotherapy. For this purpose a vasodilator, benzyl nicotinate (BN) was applied dermally onto the skin of subcutaneously grown radiation-induced fibrosarcoma (RIF-1). Oxygen content in two subcutaneous tumor models during tumor growth and after application of benzyl nicotinate on RIF-1 tumor was measured by electron paramagnetic resonance spectroscopy (EPR) in vivo. It was found that oxygen content in tumors decreases with the time of tumor growth in all tumor types irrespective of initial vascularization of tumors. BN increases significantly oxygen content in tumors in first four days of repeated application, but it becomes inefficient after that. Maximal increase was observed between 20 and 30 min after application of the drug. We have concluded that dermal application of BN might improve the efficacy of radiotherapy. Optimal time for radiotherapy would be 30 min after application of BN for this type of tumors.