Oxygen remains one of the most potent sensitizers of mammalian cells yet studied and, most important, it is maximumly sensitizing at physiologic concentrations. There is very good evidence that solid tumors of both experimental animals and man contain hypoxic and viable cells. In experimental animals hyperbaric oxygen does result in improvement of radiation therapy even when the treatment is highly fractionated and protracted over periods of up to 3 to 4 1/2 weeks. This represents strong evidence that–at least in some human tumors–results of fractionated irradiation will be significantly improved by the addition of hyperbaric oxygen. At the same time it is admitted that results of clinical trials of hyperbaric oxygen and radiation therapy do not indicate any marked improvement by the addition of hyperbaric oxygen. However, the trials are early and based on small numbers; they may well show a modest but clinically important improvement as they mature. It is essential that the trials cover several tumor types. Hyperbaric oxygen may not be useful in radiotherapy for all tumors. Evidence from the tests of tourniquet hypoxia and radiotherapy indicate that, at least for osteosarcoma, the hypoxic cell per se may not be the dominant factor in deciding results of standard fractionated therapy.

Suit, , , , , , , , (1968). Application of radiobiologic principles to radiation therapy. Cancer, 1968 Oct;22(4):809-15. https://www.ncbi.nlm.nih.gov/pubmed/4951130