Fluctuations in pO2 in poorly and well-oxygenated spontaneous canine tumors before and during fractionated radiation therapy

Background and purpose: The spatial heterogeneity in oxygen tension (pO(2)) in tumor tissue has been studied extensively, whereas, the information about the temporal heterogeneity is sparse. The purpose of the present study was to search for pO(2) fluctuations in untreated and irradiated spontaneous canine tumors, and to investigate whether there is a relationship between overall tumor oxygenation status and pO(2) fluctuation pattern. Patients and methods: Six dogs scheduled for radiation therapy of head and neck cancer were included in the study. The primary tumors were irradiated with 18 fractions of 3 Gy. Eppendorf polarographic electrodes and OxyLite fluorescence probes were used to measure overall oxygenation status and pO(2) fluctuation pattern, respectively. Tissue pO(2) was recorded at three subsequent days prior to treatment, and immediately before radiation fraction 4, 7, and 10. Results: Overall oxygenation status differed substantially among the tumors. Radiation therapy had no consistent effect on overall oxygenation status. Fluctuations in pO(2) were detected in untreated as well as irradiated tumors, and independent of whether the tumors were poorly or well oxygenated. Conclusions: Fluctuations in pO(2) can occur in untreated and irradiated spontaneous canine tumors. There is no correlation between pO(2) fluctuation pattern and overall tumor oxygenation status. (c) 2005 Elsevier Ireland Ltd. All rights reserved.