Imaging of Hypoxia with PET-CT

For a number of tumors, including head and neck squamous cell carcinoma (HNSCC) and cervical carcinoma, radiotherapy (RT) may fail to achieve local control due to the presence of tumor hypoxia (pO₂ < 10 mmHg), which decreases the availability of the oxygen free radicals necessary to induce suficient DNA damage to cause cell death. The role of hypoxia in increasing tumor resistance to radiation therapy was first recognized a century ago, but it was not until 1953 that the crucial role of oxygen in radiation response was fully acknowledged and described as the oxygen enhancement effect. There is a great variability in the oxygen availability to cancer cells, and most human malignancies show microscopic hypoxic regions that are heterogeneously distributed within the tumor mass and may be located within an apparently well-vascularized lesion. Hypoxic cells are about 3 times more radioresistant than well-oxygenated cells and their presence in tumors contributes to failure of local control in RT. There is also evidence that hypoxia increases resistance to chemotherapy. This may be because hypoxia induces a decrease in proliferating cells, which constitute to target cell population of most chemotherapeutic drugs. Cells further away from a functional blood vessel may also receive a decreased concentration of drug.