Effectiveness of Hyperbaric Oxygen During Fractionated Irradiation of a Transplanted Mouse Tumor

A study was made of the response of C3H/He mouse mammary tumors to 10 equal fractions of 137CS γ-rays given under air or high-pressure oxygen breathing (O2, 30 psi) conditions; O2, 30 psi also was given for the first or second half of treatment to determine the extent of the presence of hypoxic cells during each segment. Both latter forms of treatment produced tumor responses similar to those obtained when O2, 30 psi, was given for all 10 treatments, which indicated the presence of large numbers of hypoxic cells at all stages of irradiation. By a cell survival model it was deduced that the extent of transfer of cells from a hypoxic to an oxygenated status was greater during the second half of treatment than the first, under both airbreathing and O2, 30 psi, breathing conditions.