Abstract

The presence of hypoxic cells is one of the major factors affecting resistance against radiation therapy. In the clinical setting, little information exists as to the relationship between intratumoral oxygen partial pressure (pO₂) and outcome. This study involved 30 consecutive patients with cervical cancer, who were treated with a combination of external and high–dose rate intracavitary irradiation. The pO₂ was measured before radiation therapy and at 9 Gy, using a needle-type polarographic oxygen electrode. The mean intratumoral pO₂ before radiation therapy was 17.3 ± 10.8 mm Hg. The 3-year local control rates of patients with pO₂≤ 20 mm Hg and pO₂ > 20 mm Hg before radiation therapy were 52% and 100%, respectively, representing a significant difference (P = 0.035). At 9 Gy, mean intratumoral pO₂ was 23.6 ± 9.1 mm Hg, a significant increase compared to the value before radiation therapy (P = 0.006). The 3-year local control rates of tumors with pO₂≤ 20 mm Hg and pO₂ > 20 mm Hg at 9 Gy were 35% and 93%, respectively, representing a significant difference (P = 0.001). The significantly better local control for oxygenated tumors at 9 Gy as well as before radiation therapy indicated that the oxygen effect and reoxygenation by radiation played an important role in local control in radiation therapy for cervical cancer.