Magnetic Resonance Imaging of Tumor Physiology: Implications in Radiotherapy planning

Abstract

Many solid tumors exhibit hypoxic regions as well as possess high interstitial fluid pressure (IFP). While hypoxia in tumors limits the efficacy of radiation treatment, high IFP limits the efficacy of chemotherapy by inhibiting the accumulation of effective levels of chemotherapeutic drugs. Additionally, hypoxic cells in tumors are more reducing and may offer opportunities for bioreductive drugs or selective normal tissue radioprotectors which do not modify the tumor radioresponse and improve treatment outcome.
We have evaluated a variety of non-invasive techniques to monitor tumor oxygen status, tumor IFP and the tumor redox status in experimental animals bearing murine as well as human tumors. Using Electron Paramagnetic Resonance Imaging (EPRI), we have been able to non-invasively map tumor pO2 in three-dimensions with high spatial, temporal resolution with sensitivity to discriminate oxygen status differences of +/- 2 mm Hg. We have also used Overhauser enhanced Magnetic Resonance Imaging (OMRI) to map anatomically co-registered pO2 maps as well as tumor IFP. Using conventional MRI with nitroxyl radicals as T1-sensitive contrast agents which are metabolized selectively to diamagnetic form in tumors, the tumor redox-status was examined.
In my presentation, I will present results on some recent studies using these techniques to non-invasively examine tumor physiology.