We examined the effect of
radiotherapy after hyperbaric
oxygen (HBO) breathing in experimental
tumors using a
tumor growth delay assay.
Tumor models used were SCCVII (radiobiological hypoxic fraction: approximately 10%) and 9L
tumors (containing less hypoxic cells) subcutaneously transplanted into C3H/He mice and Fisher 344 rats, respectively. Irradiation using X-rays was locally administered to the
tumors immediately after
decompression. HBO breathing enhanced the radiation response in SCCVII
tumors but not in 9L ones. In the next experiment using SCCVII
tumors, irradiation was administered 5, 15, 30, and 90 min after
decompression. A significant growth delay was seen in the treated animals within 30 min after HBO breathing, and the
tumor growth delay time was prolonged 1.61 times as long as that in
radiotherapy alone. We concluded that: (1)
radiotherapy after HBO breathing is effective for
tumors with hypoxic cells; and (2) the time lapse from
decompression to irradiation is an important factor in improving radiosensitivity.
Radiotherapy after HBO breathing can be used to enhance the efficacy of clinical treatments.