In a randomized controlled clinical trial of hyperbaric oxygen in the radiotherapy of carcinoma of the bladder a total of 241 cases were contributed by four radiotherapy centres in the United Kingdom. In this trial where in each centre identical radiotherapy was employed for both oxygen and air cases, no benefit was shown with the use of hyperbaric oxygen.
Cade, McEwen, Dische, Saunders, Watson, Halnan, Wiernik, Perrins, (1978). Hyperbaric oxygen and radiotherapy: a Medical Research Council trial in carcinoma of the bladder. The British journal of radiology, 1978 Nov;51(611):876-8. https://www.ncbi.nlm.nih.gov/pubmed/361143