Reoxygenation is the phenomenon by which tumours with hypoxic regions become oxic again during radiotherapy treatment. Tumours under 1 mm in size are fully oxic, but tumours over this size develop regions of hypoxia.
Reoxygenation occurs through several proposed mechanisms:
- Reopening of temporarily occluded blood vessels occurs in the minutes following radiation exposure
- Reduced respiration of lethally damaged cells leads to increased oxygen supply to anoxic cells within minutes to hours of radiation
- Death of cells due to mitotic catastrophe occurs within hours of radiotherapy
- Cell death due to ischaemia occurs within hours of radiotherapy
- The resorption of dead cells leads to decreased distance from capillaries to tumour cells, improving their oxygen supply. This is the longest process, taking days.