The importance of oxygen with low LET radiations has been established beyond any doubt in many different systems, both plant and animal. While some studies, especially head and neck tumors, are impressive, it has not been demonstrated unequivocally that radiation under hyperbaric conditions is superior to well fractionated, well conceived, conventional radiotherapy. Any resulting gain in survival from the addition of hyperbaric oxygen will be limited, especially with more advanced stages of disease. Well controlled studies, especially with earlier stage disease, are still necessary. It would be worthwhile to undertake such trials, especially with tumors of the head and neck constituting the most promising site of study, as others have noted, since even a 5% to 10% improvement in survival would mean many lives saved. Continued trials with hyperbaric oxygen, oxygen in other forms, neutrons and other particles, and radiation sensitizing drugs are all justified in an attempt to overcome the oxygen effect on human tumors.

Glassburn, Brady, Plenk, , , , , , (1977). Hyperbaric oxygen in radiation therapy. Cancer, 1977 Feb;39(2 Suppl):751-65. https://www.ncbi.nlm.nih.gov/pubmed/319896