Abstract
Radiation therapy is one of the main modalities to treat cancer/tumor. The response to radiation therapy, however, can be influenced by physiological and/or pathological conditions in the target tissues, especially by the low partial oxygen pressure and altered redox status in cancer/tumor tissues. Visualizing such cancer/tumor patho-physiological microenvironment would be a useful not only for planning radiotherapy but also to detect cancer/tumor in an earlier stage. Tumor hypoxia could be sensed by positron emission tomography (PET), electron paramagnetic resonance (EPR) oxygen mapping, and in vivo dynamic nuclear polarization (DNP) MRI. Tissue oxygenation could be visualized on a real-time basis by blood oxygen level dependent (BOLD) and/or tissue oxygen level dependent (TOLD) MRI signal. EPR imaging (EPRI) and/or T1-weighted MRI techniques can visualize tissue redox status non-invasively based on paramagnetic and diamagnetic conversions of nitroxyl radical contrast agent. 13C-DNP MRI can visualize glycometabolism of tumor/cancer tissues. Accurate co-registration of those multimodal images could make mechanisms of drug and/or relation of resulted biological effects clear. A multimodal instrument, such as PET-MRI, may have another possibility to link multiple functions. Functional imaging techniques individually developed to date have been converged on the concept of theranostics.
Highlights
Published: 14 March 2021Incidence of cancer/tumor is increased markedly with aging, and the prevalence among elder people is high
Free radical species and/or reactive oxygen species (ROS) induced by water radiolysis can reach a target molecule through chain reactions mediated by membrane lipids, or form stable oxidizing species such as like H2 O2
We describe detection and visualization of tumor/cancer microenvironments, especially hypoxia, and the factors influenced by the hypoxic environment
Summary
Incidence of cancer/tumor is increased markedly with aging, and the prevalence among elder people is high. Energy production in such low pO2 environment in the cancer/tumor tissue may induce glycolytic activity of cancer/tumor cells, causing a low pH environment as a result or lactate accumulation [20] Visualizing such microenvironmental characteristics in tumors would be a useful for planning radiotherapy and for early detection. Quantifying hypoxia and/or redox status in cancer/tumor tissue is an important objective for theranostic medical imaging working with radiotherapy [21,22]. Analysis of biological information using MRI, electron paramagnetic resonance imaging (EPRI), and PET with a specific contrast agent have been developed to detect tumor microenvironment for achieving theranostic radiation therapy. Recent developments of translational multimodal imaging techniques using MRI, EPRI, and PET were introduced
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