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Different mechanisms of reoxygenation
1. Classic: preferential killing of well-oxygenated cells, and
the surviving hypoxic cells getting access to O
2
. Caveat: it
takes time for cells to physiologically die, even after
several divisions, and in human tumors this may take
several days.
2. Reoxygenation due to acute/cycling hypoxia. Based on
changes in perfusion (min-hours) and vascular
function/remodelling (hours-days).
3. Reoxygenation due to reduced energy metabolism.
Occurring rapidly and detectable by nitroimidazole PET or
IHC markers. Caveat: reoxygenated cells after irradiation
may be clonogenically dead (but they don’t know it yet).