Purpose: Tumor oxygenation is thought to influence the radiocurability of many malignancies. Advances in polarographic electrode technology have facilitated the in situ measurement of human tumor pO2. The optimal method of defining a "hypoxic" tumor is not known. Characterization of intra-tumor and intertumor pO2 heterogeneity could help with this process. This study was performed to evaluate pretreatment tumor oxygenation status and pO2 heterogeneity in patients with soft tissue sarcoma.
Methods and materials: Nine patients with soft tissue sarcomas underwent pretreatment pO2 measurements with the Eppendorf pO2 histograph. Two grossly distinct anatomic sites within each tumor were measured in all but one patient; these were localized under computerized tomography guidance to ensure that all measurements were obtained from tumor tissue. Multiple probe tracks were studied at each site. Measurements were performed in resting, awake patients.
Results: A total of 1588 pO2 readings was obtained (mean = 176/patient). Measurement path lengths ranged from 22-36 mm. The average hypoxic fraction (pO2 < 5 mm Hg) was 29% (range 0-76%). Arterial pO2 was positively correlated with mean and median tumor pO2. Tumor hypoxic fraction increased with increasing tumor volume. Linear pO2 profiles and frequency histograms provided similar estimates of the extent of hypoxia in individual tumors. Marked variation in oxygenation existed both within and between individual tumors. The intertumor variation was greater than the intratumor variation.
Conclusion: Radiobiologic hypoxia exists in human soft tissue sarcomas. The pO2 variation within individual tumors is less than the variation between tumors. Further study is necessary to identify the best parameter for defining tumor hypoxia and to discern the relationship between tumor pO2 and treatment outcome.