Hypoxia and tumor metabolism in radiation oncology: targets visualized by positron emission tomography

Due to the amazing leap of technology in radiation oncology in the past few years, cancer treatment will become more individualized. Molecular imaging with PET contributed to this with its many tracers available, each of them visualizing a specific feature of a tumor and its microenvironment revealing the biological characteristics of cancer. Hypoxia is of interest as hypoxic tumor cells are associated with lower disease control because of an increased resistance to cytotoxic treatment. This is especially the case for radiotherapy. Treatment adaptations overcoming the negative effect of hypoxia have shown promising results. Several hypoxia tracers are available of which [18F]FMISO is studied most extensively, however other tracers are studied as well and the search for highly specific and reproducible PET tracers is still ongoing. Wide experience has been gained with the use of [18F]FDG PET as it is used on a routine basis for diagnosing and staging of cancer. Although not a specific marker for hypoxia, increased metabolic rate reflects increased proliferation and glycolysis indicating increased treatment resistance. Molecular imaging by means of PET creates an opportunity to provide personalized care, with optimal disease control, minimal toxicity and best cost-effectiveness.