Hypothermia is associated with reduced metabolism of tissues and especially reduced oxygen consumption by tumours. If the blood supply to a hypothermic tumour can be maintained then the hypoxic fraction of cells should be reduced and the radiation response increased. This hypothesis has been tested with radiation under hyperbaric oxygen and increased tumour response has been demonstrated.
Nias, Perry, Photiou, , , , , , (1988). Modulating the oxygen tension in tumours by hypothermia and hyperbaric oxygen. Journal of the Royal Society of Medicine, 1988 Nov;81(11):633-6. https://www.ncbi.nlm.nih.gov/pubmed/3210193