62. Correlation between intratumoral pO₂ and local control in radiation therapy for cervical cancer

Yoshiyuki Suzuki^*, Takashi Nakano , Tatsuya Ohno , Atsuko Abe, Shinroku Morita , Yuzuru Niibe and Hirohiko Tsujii
(^*Department of Radiology and Radiation Oncology, Gunma University School of Medicine)

Keywords: hypoxic cells, radiation therapy, pO₂

Objective: The existence of hypoxic cells is well recognized as one of the major factors for resistance against radiation therapy and local failure. However, in a clinical situation, correlation between intratumoral pO₂ status and local control is a matter of controversy. Hence, we investigated this relationship for cervical cancer treated with radiation therapy.

Materials and Methods: This study involved 28 patients with squamous cell carcinoma of the uterine cervix who were treated with a combination of external and high dose rate intracavitary irradiation between 1995 and 1998. The pO₂ was measured by using a needle-type polarographic oxygen electrode and a pO₂-monitoring machine. The electrode was inserted 1 cm under the surface of the tumor before radiation therapy and at the 5th radiation therapy day or at 9 Gy (designated at The 5th Day).

Results: The mean intratumoral pO₂ before radiation therapy was 15.4±9.3 mmHg (range, 4.2-38.6 mmHg). The numbers of patients with O₂ =< 20 mmHg and > 20 mm Hg before radiation therapy were 22 and 6, respectively. The 3-year local control rates of patients with pO₂ =< 20 mmHg and > 20 mmHg were 65% and 100%, respectively, which meant no significant difference (p=0.19). At The 5th Day, the mean intratumoral pO₂ was 24.6± 11.7 mmHg (range, 7.2-66.4 mmHg), which was a significant increase compared to the pO₂ before radiation therapy (p=0.002). The numbers of patients with pO₂ =< 20 mmHg and > 20 mmHg at The 5th Day were 11 and 17, respectively. The 3-year local control rates of pO₂ =< 20 mmHg and > 20 mmHg at The 5th Day were 43% and 94%, respectively. The local control rate of the pO₂ =< 20 mmHg at The 5th Day was significantly lower than that of the pO₂ > 20 mmHg (p=0.016).

Conclusion: The increases in both intratumoral pO₂ at The 5th Day and the number of oxygenated tumors indicated that the reoxygenation phenomenon occurred within 1 week after initiation of radiation therapy. The significantly better local control for oxygenated tumors at The 5th Day indicated that reoxygenation by radiation had an important role in local control and an assessment of the intratumoral pO₂ status at The 5th Day was useful for predicting the local control in radiation therapy for cervical cancer.